Norbornadiene As a Universal Substrate for Organic and Petrochemical Synthesis V.R

Eurasian ChemTech Journal 3 (2001) 73-90

Norbornadiene as a Universal Substrate for Organic and Petrochemical Synthesis V.R. Flid*, O.S. Manulik, D.V. Dmitriev, V.B. Kouznetsov, E.M. Evstigneeva, A.P. Belov, and A.A. Grigor’ev Lomonosov State Academy of Fine Chemical Technology, pr. Vernadskogo 86, Moscow, 117571 Russia

Abstract A wide range of rare polycyclic hydrocarbons can be obtained through catalytic processes involving norbornadiene (NBD). The problem of selectivity is crucial for such reactions. The feasibility of controlling selectivity and reaction rate has been shown for cyclic dimerization, co-dimerization, isomerization and allylation of NBD. Kinetic rules have been scrutinized. Consistent mechanisms have been proposed. Fac- tors affecting directions of the reactions and allowing us to obtain individual stereoisomers quantitatively, have been established. A series of novel unsaturated compounds has been synthesized; they incorporate a set of double bonds with different reactivity and can find an extremely wide range of applications.

Introduction possibilities, its utilization as a universal substrate is rather limited, since NBD-derivatives can form all The importance of NBD and its derivatives in vari- kinds of isomers: skeleton, regio, stereo, enantio ones. ous fields of human activity is growing. More and A resultant mixture of isomeric products is often dif- more new applications are being discovered for these ficult to separate and analyze, and the consumption compounds. Since they were first obtained less than of reagents may become excessive. All this restricts 50 years ago, these substances have been success- widespread use of NBD. fully utilized in medicine, agriculture, rocketry, syn- Metal-complex catalysis is very interesting and theses of polymers with unique properties, microelec- attractive for solving various problems connected with tronics, and as solar energy converters. The number selectivity [5]. By applying its tenets and methods to of patents concerned with synthesis and application reactions involving NBD and its derivatives, by scru- of NBD derivatives and norbornene-2 (NBN) had ex- tinizing mechanisms of reactions, we can control struc- ceeded 100 hundreds by the year 2000. Due to their ture and range of regio- and stereo isomers, synthe- unique structure, compounds with NBD and NBN- size new compounds of this type, and can make their moieties are achieving the leading positions in con- production sensible from technological and economi- temporary chemistry and chemical technology [1-3]. cal points of view. It should be strongly emphasized that NBD itself The present article bases on several research di- and some of its simplest derivatives are obtained from rections concerned with application of the above-men- chemicals, produced on a large scale during oil pro- tioned methods in some of the most promising pro- cessing [4]. They are cyclopenta-1,3-diene (CPD), cesses involving NBD. acetylene, alkenes, and alkadienes with various structures. Production of CPD can easily be combined with Experimental synthesis of other petrochemical products, for example ethylene. Today, a large proportion of CPD cannot All of the experimental techniques are described be duly utilized, so it is very important to search for in detail in the literature cited. Synthesis of signifi- new ways of its utilization. cant quantities of mentioned compounds by means of Even though NBD has extremely rich synthetic non-catalytic Diels-Alder reaction needs high pres- *corresponding authors. E-mail: [email protected] sure and temperature (autoclave etc.). As for cata-

 2001 al-Farabi Kazakh St.Nat. University 74 Norbornadiene as a Universal Substrate for Organic and Petrochemical Synthesis lytic methods of their synthesis under homogeneous absence of a sensitizer is low (Φ = 0.05). conditions, they take high-vacuum equipment and us- The characteristics of phototransformaiton of age of purified inert gases. All cited compounds were NBD into Q can be substantially improved through identified by means of: chromato-mass spectrometry introduction of substituents into the NBD molecule. with use of chemical ionization and electron blow as For instance, when both an electron donating and an well («Kratos MS-80» and «HP-5989B MS MG»); electron withdrawing moieties (Ñ6Í5 and ÑÎÑ6Í5 re- 1H, 13C and 31P NMR spectroscopy («Bruker WP- spectively) are simultaneously introduced into one of 250», «Bruker DPX-300», «Bruker MSL-200»); in- the double bonds, the limit of adsorption can be moved fra-red Fourier-transform spectroscopy («Bruker IFS- into the long-wave area up to 350 nm or, if the aryl 113V» supplied with chromatographic device «Karlo- substituent gets additionally modified, up to 400 nm, Elba Strumentation 4200»); gas-liquid chromatogra- with the quantum yield increasing up to 0.3÷0.6 [7]. phy («Khrom-5» with a range of capillary and pre- Further introduction of substituents into different parative columns). Structure of catalysts was inves- double bonds allows us to vary λ from 350 to 450, tigated by X-ray photoelectron spectroscopy («Riber with a quantum yield being up to 0.96; the best re- LAS-4000») and electron spin resonance spectros- sults were attained when electron-acceptor substitu- copy («Bruker ER-200»). ents were introduced into one of the double bonds, and electron-donor ones into the other. Results and discussion Compounds of the NBD-series with a similar structure are suitable for practical application, even though Valence isomerization of NBD they have shortcomings. The most serious of them are the decrease in the quantity of accumulated en- Valence isomerization of NBD into quadricyclane ergy per 1 g of compound (due to the increase in the (Q) has a considerable practical importance [6]. This molecular weight of substituted NBD) and complex- reaction draws attention, since it allows us to accu- ity of their synthesis. mulate solar energy through a cyclic process (reac- One more general drawback is side reactions with tion 1). NBD. Even though the yield of side products is neg- ligible from the conventional point of view (hundredths of one per cent per one working cycle), they accumu- hν late as the cycle NBD↔Q repeats over and over again. (1) This substantially deteriorates the performance of the NBD Q system. catalyst To increase the number of working cycles, NBD molecules can be covalently bound to a polymeric In this photoreaction, solar energy is accumulated matrix. For instance, application of polymethylacrylate due to the formation of a methastable structure incor- films increases the number of working cycles up to porating highly-strained moieties: one cyclobutane and 103-104, with λ and Ô remaining high [8]. two cyclopropane rings, which results in an unusu- Phototransformation of unsubstituted NBD into ally high thermal effect of the reverse dark reaction Q features a low quantum yield. This can be con- (110 kJ/mol). This system is also characterized by siderably increased through applying sensitizers. the following positive qualities: The best results were obtained for Cu (I) salts (Φ=0.2) and phenylketones (acetophenone, benzophe- (i) the direct photochemical reaction can be sensi- none Φ=0.5÷0.9). However, even these systems have tized; imperfections. First, they work only in the UV spec- (ii) the reverse reaction has a high activation barrier trum area. Second, Cu (I) complexes turn into Cu (its half-life period is 14 hours at 140°C), but (II) ones, which show no photoactivity. Third, ketones can be accelerated catalytically; chemically react with NBD to give photo-adducts. (iii) NBD and Q are liquids, which is convenient from All this prevent such stabilizers from practical appli- the technological point of view. cation. These obstacles may probably be overcome The process has some shortcomings, too: NBD through use of natural or artificial polyheterocyclic adsorbs in the short-wave area (up to 300 nm) and sensitizers such as porphyrins[9]. the quantum yield of the direct photoreaction in the A system for solar energy accumulation can only

Eurasian ChemTech Journal 3 (2001) 73-90 V.R.Flid et al. 75 be created if the product of the photoreaction is chemi- with a high energy content. They can be used as com- cally stable. The high energy barrier for the thermal ponents of high-density jet fuel. Their specific com- transition NBD→Q results from orbital symmetry rule bustion heats and densities are extremely high (up to for [2σ+2σ]–addition. This barrier can be made lower 11000 kcal/l and 1.1 g/cm3 respectively). To com- through using compounds of transition metal as cata- pound high-quality products of these dimers, synthetic lysts. methods are required allowing us to obtain pure sub- Of these substances, flat-square cobalt (II) com- stances. Even though this reaction seems to be very plexes are the most promising. They are more active simple, it can yield a wide range of isomers (Fig. 1). than compounds of other metals under both heteroge- neous and homogenous conditions. Besides, no side reactions occur when Co (II) compounds are used. However, under isomerization conditions, many of Co (II) complexes oxidize easily into Co (III), which in turn leads to formation of NBD dimers and trimers. 1 2 3 From this point of view, Co(II) porphyrin complexes are considered the best nowadays. When covalently bonded to a polymeric support or applied to inorganic carriers (activated carbon, alumina), they can easily be regenerated and are suitable for practical use. The global ecological problem imposes stricter 4 5 6 requirements on chemical production processes. Hence photochemical methods can play an important role, since they are able to provide a means to absorb solar energy and utilize it in chemical transformations. Light is a kind of an inertialess chemical reagent creating 7 8 9 10 no wastes. However, photochemical processes only have minor importance now, chiefly because some complicated technical problems have not been solved yet. All the above-described is completely correct for the NBD-Q system. Its practical significance is obvi- 11 12 13 14 ous. NBD-based pilot power units have already been being developed in several countries. CH3 However, economical obstacles hinder the widespread use of heat energy emitted through the chemical transformation of Q into NBD. At the moment 15 16 17 heat (as water steam) generated though this process Fig. 1. NBD-dimers. Possible structures. is 50 to 100 times more expensive than that obtained through conventional methods. The mentioned sys- NBD can participate in various cycle-formation tems need further improvements: the number of work- reactions. Products of its cyclodimerization can be ing cycles should be increased up to 104 and higher, categorized into 4 groups. The first three groups cor- the quantum yield and conversion of NBD per cycle respond to different types of cycloaddition: [2π+2π], should be increased, and the cost of synthesis of NBD [2π+4π] and [4π+4π]. The fourth group includes prod- with required spectral characteristics must be reduced. ucts of subsequent skeletal isomerization of dimers However, the creation of portable units may be sen- incorporating a strained cyclopropane moiety. sible even now: they can be used in sunny regions Dimers 1 to 6 of the group I are products of located far away from other energy sources, or for [2π+2π]-cycloaddition. They are pentacyclic com- space satellites. pounds incorporating two double bounds and a cyclobutane moiety. Of this group, only trans-dimers Catalytic homodimerization of NBD were separated: exo-trans-exo- (1), endo-trans-endo- (2) and exo-trans-endo- (3) pentacyclo[8.2.1.1.4,7.02,9. Norbornadiene dimers are strained hydrocarbons 03,8]-tetradeca-5,11-dienes. Cis-isomers have not been

Eurasian ChemTech Journal 3 (2001) 73-90 76 Norbornadiene as a Universal Substrate for Organic and Petrochemical Synthesis described in literature. They probably cannot be and THF are more favorable for the reaction than formed due to spatial difficulties. toluene, methanol or acetonitrile [10]. Dimers 7-10 (group II) are products of [2π+4π]- Cluster complex 18 proved to be a highly active cycloaddition: hexacyclic compounds containing one catalyst. It [2π+2π]-dimerizes NBD into 1 almost double bond and a nortricyclyl moiety: endo-endo- quantitatively at 60°C in benzene [11]. (7), exo-exo- (8), exo-endo- (9) and endo-exo-(10) hexacyclo-[9.2.1.02,10.03,7.04,9.06,8.]tetradec-12-enes. Me Me Saturated heptacyclic dimers 11-14 (group III) As results from [4π+4π]-cycloaddition. Of these compounds, «Binor-S» (11) possesses the most interest- (CO)4Fe Fe(CO)2NO ing properties. 18 Dimers of group IV (15-17) obtained in the presence of [Rh(PPh3)3Cl] are probably derivatives of 9. It is interesting, that the character of cycloaddi- We can suppose that they appear due to incorpora- tion can be changed completely through adding an tion of the Rh(I) complex in the cyclopropane ring of equimolar quantity of BF3·OEt2: in CH2Cl2, the only the nortricyclyl moiety 9 with a subsequent transfer product is [4π+4π]-isomer 11 (Binor-S). When two- of a hydrogen atom from the bridge carbon. component systems like Fe(acac)3–AlEt3 are used, a Catalysts are necessary for NBD cyclodimeriza- mixture of dimers 1, 3, 7 è 9 is usually formed [12]. tion to take place. They are usually complexes of Ni, The content of isomers depends on the solvent type Co, Fe and Rh in lower oxidation states. Some ex- and how the catalyst was synthesized [13-14]. amples of utilization of Cr, Ti, Pd and Ir compounds The yield of hexacyclic dimers can be increased were reported. The type of the central atom substan- through adding phosphine ligands to this catalytic tially influence the direction of cyclodimerization of system, and substituting reducer AlEt2Cl for AlEt3. NBD, i.e. the structural selectivity of the process. When a chelate bis-(diphenylphosphino)ethane Iron-containing catalytic systems can act in a num- (diphos) is used, the yield of 9 increases up to 80- ber of different ways. Various kinds of cycloaddition 90%. In the presence of triphenylphosphine the ma- can be realized through varying ligands, reducing jor product is dimer 7 [15]. agents, and reaction conditions. [2π+4π]-cycloaddition is also the major reaction For example, iron carbonyl complexes Fe(CO)5, route in the presence of other ferruginous systems: Fe2(CO)9, Fe3(CO)12 catalyze all routes of NBD FeCl3 – (i-Pr)MgCl, FeCl3 – AlR3, FeCl3 – Na, cyclodimerization and give rise to a mixture of prod- Fe(C8H8)2 etc. ucts, chiefly isomers 1, 8 and 9. These systems generally manifest a high activity, If several nitrosyl ligands are substituted for car- yield and turnover. Their shortcomings are low selec- bonyls, the activity and selectivity of ferruginous cata- tivity to individual isomers and non-repeatability of lysts can be enhanced. For instance, when results. Fe(CO)2(NO)2 is used, dimerization only proceeds Cobalt systems resemble iron catalysts in a num- through the [2π+2π]-direction to give dimers 1 and ber of ways. NBD cyclodimerization can go through 3. The unsaturated complex Fe(NO)2 formed in situ [2π+2π]-, [2π+4π]- and [4π+4π]-directions in their via a reaction of nitrosylferrates with NBD or its presence. dimers, is probable the key intermediate through which Binuclear carbonyl complex Cî2(CO)8 augmented

NBD dimers are formed. with PPh3 leads NBD dimerization through the That the moiety Fe(NO)2 is catalytically active is [2π+2π]-route. Pentacyclic isomers 1 and 3 are indirectly confirmed by a series of electrochemical formed. Their ratio is 10 to 1. experiments where a range of nitrosyl iron salts were The selectivity of nitrosyl Co complexes is lower reduced. Catalysts generated this way yield dimers 1 than that of analogous ferruginous catalysts. Even and 3 only, independent of the structure and type of though Ño(CO)3NO is isoelectronic with Fe(CO)2(NO)2, the initial complex. NBD cyclodimerization in its presence gives not only The type of reducing agent almost does not affect 1, but also a mixture of hexacyclic hydrocarbons. Iso- the yield of dimers and the selectivity of the process. mer 1, however, can be synthesized with a selectivity

However, when powdered zinc is used, the conver- up to 98% when complexes Co(NO)2Cl or Co(NO)2Br sion of NBD depends on the type of solvent. Acetone promoted with AgBF4 or NaBPh4 are used [16].

Eurasian ChemTech Journal 3 (2001) 73-90 V.R.Flid et al. 77

A series of catalysts like M[Co(CO)4]n (M = Zn, activity. For example, the system Co(acac)2–AlEt3 Cd, Hg) can stereospecifically dimerize NBD into yields the following mix of dimers: 1 – 62%, 3 – 29%, Binor-S (11) with a yield of 95% [17]. These com- hexacyclic dimers 9%. The direction of this reaction pounds only manifest their catalytic activity in the can be changed through adding phosphines. When presence of Lewis acids (BF3, SbF3, AlBr3, BF3·OR2) PPh3 is used, Binor-S forms rather selectively. If as co-catalysts with a ratio of 1 to 8. Lewis bases diphos is substituted for PPh3, hexacyclic dimer 8 is (pyridine, triethylamine) favor formation penta- and generated almost quantitatively. This system has a hexacyclic dimers [17]. unique feature: it catalyzes not only NBD dimeriza- Acetylacetonate Co systems reduced by organo- tion, but also its co-dimerization with NBN. The yield aluminum compounds demonstrate a high catalytic of the co-dimer is 42%.

Co(acac) -AlEt Cl-Diphos + 3 2 (2)

Rhodium complexes probably manifest the most ried out for the following initial compounds: Ni(1,5- 3 versatile synthetic possibilities as compared with other C8H12)2, Ni(CH2=CHCN)2, Ni(CO)4, Ni(η -C3H5)2, 5 catalysts of NBD cyclodimerization. They can cata- Ni(η -C5H5)2, and a catalytic system obtained through lyze all the above-described types of cycloaddition diffusing metal nickel on a frozen NBD-matrix under and also give new dimers 15-17. vacuum. Nickel catalysts are the best for [2π+2π]-cycload- NBD cyclodimerization was found to begin with dition. The ratio of isomers depends on the type of an induction period, the length whereof depends on ligands in nickel complex, temperature, solvent and the complex type and temperature. The reason for other conditions [18]. this phenomenon is that the NBD-nickel catalyst forms To discover general features and individual pecu- through substituting initial ligands, and this process liarities of nickel catalysts, kinetic studies were car- is different for each system (3-5) [19].

NBD NBD NBD ..... (3) NiLn NiLn-1(NBD) + L NiLn-2(NBD)2 + 2L (3)

NiL2 + 2 NBD → Ni(NBD)2 + L–L (4)

NiL2 + 4 NBD → Ni(NBD)2 + [NBD +L – H] + [NBD + L + Í] (5)

Direction (3) is characteristic of complexes with Ni complexes with different number of NBD ligands ligands stable in the free state: Ni(CO)4, Ni(1,5- exist simultaneously in the reaction mass) are de-

Ñ8Í12)2 and Ni(CH2=CHCN)2. The second direction scribed by the following kinetic equations: takes place for compounds containing unstable moi- W = k ·C ·C 2 eties. They can decompose through ligand coupling 1 1 Ni NBD

(4) or intramolecular disproportionation (5). W3 = k3 ·CNi ·CNBD Intermediates Ni(NBD)n were separated at differ- W = k ·C ·C ent stages of the catalytic process with various initial 8 8 Ni NBD, nickel compounds. The molar ratio of NBD to Ni where k1, k3, è k8 are observed cyclodimerization rate proved to be 2.07 (±0.03) in all these cases, which constants. testifies that one the same catalyst forms in situ in all Even though these equations retain the same form the systems: it is an equilibrium mix of complexes for different solvents, the type of medium influences

Ni(NBD)2 and Ni(NBD)3 at a ratio of 12÷14 to 1. the ratio of products and the general rate of the pro- Kinetic studies showed that the formation rate of cess. It should be emphasized, that dimers 1, 3 and 8 dimers 1, 3 and 8 (with taking into consideration that have different kinetic orders with respect to NBD,

Eurasian ChemTech Journal 3 (2001) 73-90 78 Norbornadiene as a Universal Substrate for Organic and Petrochemical Synthesis which is quite unusual for concurrent formation of NBD molecules coordinated in the complex. The pro- isomers with a similar structure. portion of dimer 1 is growing with an increase in the

Observed rate constants k1, k3, and k8 are in a sat- conical angle of phosphine. isfactory agreement with the Arrhenius equation. Ac- The catalytic action mechanism of nickel com- tivation parameters are presented in Table 1. plexes was scrutinized. Phosphine nickel complexes where at least two An NBD molecule can be either a η2- or a η4- places are blocked with ligands are not active in NBD coordinated ligand. A bidentate coordination of NBD cyclodimerization. When the ratio of PR3 to Ni is is thermodynamically more favorable than a equimolar, dimers 1, 3 and 8 are formed in accor- monodentate one. The difference between these two dance with a common kinetic equation, which is right states equals to the homoconjugation energy of double for various phosphines: bonds (about 8.0 kJ/mol), which can contribute to the stability of the resultant complex. Kinetic data W = k obs ⋅ C ⋅ C i i Ni NBD testify that three different π-complexes of Ni and NBD The mutual ratio of resulting cyclodimers of NBD are formed (19-21); there is an equilibrium between depends on the steric characteristics of the phosphine, them (Fig. 2) [20]. which probably influence the mutual orientation of When considering the stereochemistry of cycload-

NBD Ni Ni

Ni(NBD)1

NBD NBD Ni Ni Ni

19 20 21

Fig. 2. Mechanism of NBD catalytic cyclodimerization.

Eurasian ChemTech Journal 3 (2001) 73-90 V.R.Flid et al. 79

Table 1 Activation parameters of NBD cyclodimerizaton Avctiraytion ene g Pxree paonen ti,l factor Avctinahtion e t,alpy ⋅ PcrodutStolv en -1⋅ -1 Entropy, J/(mo l K) Eact, kJ/mol M c kJ/mol 1*) nn-4nonane 333± 1, ⋅102 330±4 -209±2 TFH 404± 5 1, ⋅103 401±5 -187±1 3 nn-anenon 760± 7 5, ⋅107 608±7 -97±1 T6HF 511± 7, ⋅103 409±6 -171±2 8 nn-anonen5525± 1, ⋅104 562±5 -168±1 *) dimension of preexponential factor is c-1 dition, we must take into account not only the coordination type of an NBD molecule on a nickel atom (monodentate or chelate), but also its exo/endo-orientation. When an NBD is coordinated monodentately, its exo-coordination is preferable from both sterical and thermodynamic points of view. A stereochemical analysis of various possible orientations of NBD- moieties in complex Ni(NBD)4 testifies that four NBD ligands can only be exo-coordinated there. A dimer molecule is formed already in the intermediate π-complex, and the NBD-nickel system is a matrix prede- termining the structure of the product. Oxidative addition of coordinated NBD molecules to the Ni center results in the creation of metallocyclic intermediates. Decomposition of the latter is the limiting stage. Monodentate NBD-molecules remaining in the coordination sphere after the complex has de- Fig.3. Ratio of dimers 1 and 3 vs. temperature and NBD composed transform into chelate ligands and stabi- concentration; a – n-nonane, b – THF lize Ni(0). The results of our studies of the kinetics and the creasing, the relative amount of exo-trans-endo iso- mechanism of the process allow us to forecast the mer is increasing; its yield reaches 95% at 100°C and behavior of the system in various conditions. For ex- an NBD concentration of 0.5 mol/l. Virtually any re- amples, if one coordination vacancy is blocked on the quired ratio of 1 and 3 can be achieved through vary-

Ni atom (the ratio of PR3 to Ni = 1:1), kinetic regu- ing these parameters. larities of the process change. Use of phosphines with The process rate decreases in the presence of phos- large conical angles is favorable for the more com- phines. Besides, the selectivity cannot any longer be pact exo-coordination of NBD molecules and, conse- controlled through NBD concentration in phosphine- quently, results in an increased content of dimer 1. containing systems [21]. The difference in kinetic orders with respect to NBD in the above equations testifies that the forma- Co-dimerization of NBD with unsaturated com- tion rate of isomer 1 depends on NBD concentration pounds. more strongly than that of isomer 3. Analysis of the activation parameters of the process indicates that the Co-dimerization with NBD is a very versatile and yield of exo-trans-endo isomer 3 is growing dramati- prospective way of synthesizing polycyclic com- cally as temperature is increasing (Fig.3). pounds. It often is an alternative to diene syntheses Isomer 1 is formed quantitatively in the tempera- based on cyclopentadiene. Sometimes co-dimeriza- ture range from 10 to 30°C in non-polar media at tion is preferable. NBD concentrations above 3 mol/l. As reaction tem- The range of substrates suitable for catalytic co- perature is growing and NBD concentration is de- dimerization with NBD is rather narrow. It is obvi-

Eurasian ChemTech Journal 3 (2001) 73-90 80 Norbornadiene as a Universal Substrate for Organic and Petrochemical Synthesis ously stipulated by the peculiarities of complex-form- special-purpose rubbers. ing by NBD and the second substrate on a metal atom. All the above-mentioned confirms that such com- To form a mixed hetero-substrate complex, the sec- pounds can be used as semiproducts in medicine, ond co-monomer and NBD must have comparable microelectronics, perfumery etc. The range of appli- abilities to coordinate on the metal atom. Ankynes, a cation of NBD co-dimerization-based processes is lim- range of alkenes with highly-reactive double bonds, ited for some reasons. They are possible homodimer- and some oxygen- and nitrogen-containing compounds ization of NBD or the second substrate; formation of are suitable for this process. Co-dimerization of NBD side products through consecutive cycloaddition to with unsaturated compounds results in products of both the double bonds of NBD; formation of isomers [2π+2π] and [2π+4π]–cycloaddition; each direction of all kinds: skeletal, spatial (exo/endo, cis/trans, of such a reaction can give a range of spatial and enantio) ones. Hence it is extremely important to de- optical isomers. velop highly active and selective catalytic systems for [2π+2π]-cycloadducts retain an intra-cyclic the aforementioned processes. norbornene double bound. They can be used for fur- In the presence of Ni(0)-catalysts, alkenes with ther transformations, for example in methathesis electron withdrawing substituents usually react with oligomerizaitoin or polymerization. When NBD co- NBD to give [2π+4π]-adducts. However, strained alk- dimerize with some dienes or alkynes, the resulting enes like methylenecyclopropane (MCP) react with product has several double bonds with different reac- NBD to yield [2π+2π]-cycloadducts with chiefly tivity, which is rather attractive for manufacturing of endo-structure (reaction 6).

Ni(COD)2 + 2PPh3 H (6) + o H C6H6, 25 C, 48 h, 60 % 22

Such a spatial structure of 22 is mostly predeter- tion of NBD and MCP through use of chiral phos- mined by the combination of ligands in the key inter- phine ligands were not successful. Substitution of mediate 23 where NBD is bonded to nickel as an endo- Pd(0) for Ni(0) results in formation of [3π+2π]- chelate ligand. cycloadducts [22]. Even though unsaturated NBD-derivatives usually react with alkenes with acceptor substituents to give [2π+4π]-cycloadducts, sometimes we can observe [2π+2π]-cycloaddition with a high regio- and even Ni stereo-selectivity. These reactions usually proceed through the unsubstituted double bound of NBD, and L substituents in locations 2 and 3 can favor one direction of the reaction or the other, exo- or endo-. 23 Electron-acceptor substituents promotes exo-cycloaddition, while donor-substituents shift the reac- Attempts to perform enantioselective cycloaddition toward endo-adducts (reactions 21-23): O E E O Ni(COD)2 + 2PPh3 + N Ph o E toluene, 110 C, 16 h, 49 % E NPh (7) O O CN Ni(COD)2 + 2PPh3 CN (8) + 1,2-dichloroethane, MeO MeO 21 h, 52 % endo : exo = 4 : 1

Eurasian ChemTech Journal 3 (2001) 73-90 V.R.Flid et al. 81

O MeO Ni(COD)2 + 2PL3 O + N Ph MeO 1,2-dichloroethane, NPh (9) O O 80 oC, 21 h

L = PPh3: 69% (5:1) L = P(OPh)3: 34% (12:1) Stereoselectivity to the endo-isomer in reaction (9) ence of transition metals, and their stereoselectivity increases if a phosphite is substituted for a phosphine changes, too. For example, if the thermal process ligand. mostly gives endo-adducts, a catalyst promotes for- Unsubstituted NBD usually reacts to give [2π+4π]- mation of exo-cyclic compounds [23-24] (reaction 10 adducts. These reactions proceed far easier in the pres- and Table 2):

Ni(COD)2, PPh3, + 1,2-dichloroethane (10) A A 24 Table 2 Effect of the type of acceptor (A) and temperature of the yield of co-dimer 24 and stereoselectivity. ¹ ACTdemperature, ° Yiel 2244,o% exo/end 1eC0OM 899120 : 2OC0H 28513 : 3NC082814 :

4 SO2Ph 250 711 : 5* S0OPh 237119 : ∗ P(OPh)3 was used instead of PPh3.

The indicated regularities, however, do not imides of maleic acid (reactions 11, 12 and Table work for cyclic dienophiles: enones, lactones and 3):

Ni(COD)2 : PPh3 = 1:2, 1,2-dichloroethane + O O 80 oÑ, 18 h H H (11) N O O N Ph 78% Ph

Ni(COD)2 : PPh3 = 1:2 + 80 oC O H H (12) X 78 % X O 25 Table 3 Product type vs. substituent type X

XOCH2 CH2CH2 Yield 2255,8% 56532

Eurasian ChemTech Journal 3 (2001) 73-90 82 Norbornadiene as a Universal Substrate for Organic and Petrochemical Synthesis

Interesting regularities concerned with regio- dition rules vary considerably for NBD molecules and stereo-selectivity of cycloaddition were estab- with different substituents in location 2 (reactions lished for reactions of unsymmetrical NBDs. Ad- 13–15):

MeOOC MeOOC Ni(COD)2 : PPh3 = 1:2 + 1,2-dichloroethane, 80 oÑ (13) CN CN 94% para-26 exo : endo = 2.3 :1

Ni(COD)2 : PPh3 = 1:2 o + 1,2-dichloroethane, 80 Ñ OMe (14) COMe CÎÌå OMe 54% ortho-27

SiMe3 Ni(COD)2 : PPh3 = 1:2 SiMe3 o (15) + 1,2-dichloroethane, 80 Ñ (15) CN CN 47 % meta-28

Para-cycloadduct 26 is the major product for elec- influences the regio-selectivity of the process. An ex- tron-acceptor substituents, ortho-isomer 27 is for elec- tremely high exo-selectivity of cycloaddition is char- tron-donor ones, while a CN-moiety promotes for- acteristic of such reactions, independent of the type mation of metha-isomer 28. So, the type of the sub- of the substituent. However, syn/anti-isomerism be- stituent in diene and dienophile can affect the selec- comes possible in this case. The yield of anti-isomer tivity of [2π+4π]-cycloaddition. is growing with an increase in the electronegativity A substituent in position 7 in the NBD-ring also of substituent 7 [25] (reaction 16 and Table 4):

Y Y Y Y Y Ni(COD)2 : PPh3 = 1:2 1,2-dichloroethane, 25 oÑ (16) + + + + (16) COMe MeOC COMe MeOC COMe 29 30 31 32

Table 4 Selectivity of reaction (16) vs. type of substituent Y in position 7 of the NBD ring. ¹ Y%Yield, 2229:30:31:32 aoantinti : ssynyn e exoxo : eendond 1 nn-3hexyl 84480:58:1,6:0, 422:5 98: 2hP482554:45:0,8:0, 515:4 99: 3lC062781:28:0,8:0, 712:2 99: 4hO7COP 90800:20:0: 800:2 100:

5 O-t-C4H9 905 955:5:0: 905: 100:

Eurasian ChemTech Journal 3 (2001) 73-90 V.R.Flid et al. 83

Changes in reaction temperature or substitution tuted NBDs carried out in the basis STO-3G,[26-27] of phosphite for phosphine influence selectivity of A bimetallic system capable of catalyzing reac- such cycloadditions weakly. tion between CO2 and NBD under mild conditions These data agree completely with the results of was synthesized from bis-π-allyl nickel and cationic quantum-chemical ab initio calculations of 7 substi- π-allyl palladium complexes [31].

cat. + CO2 NBD-dimers

O O

As a result of the reaction, isomeric pentacyclic examples of [2π+2π]-cycloaddition. Some iron and lactones form. cobalt compounds also induce [2π+2π]-addition with Acetylenes usually add to NBD through the a low yield; only exo-adducts form in the latter case [2π+4π]-route [29] (reaction 17). There are only rare (reaction 18):

Ph Ni(CN)2(PPh3)2 + PhC CPh (17) o 120 C, 59 % Ph

Y Co(acac)2 + dppe + Et2AlCl Y + (18) Y C H , 80 oC Y n-Bu n-Bu 6 6 OMe

Y = , SiMe3 OMe

Low-valence ruthenium complexes also catalyze and NBD [30] (reaction 19): [2π+2π]-cycloaddition of various acetylenes to NBD

Cp*RuCl(COD) R1 + R R (19) 1 2 o 100 C R2

The type of substituents affects the reaction rate Table 5 considerably (Table 5) Effect of the substituent type in alkyne on regularities It should be emphasized that [2π+2π]-cycloaddi- of reaction (19) tion of alkenes to NBD yields endo-adducts chiefly, R1 R2 T%ime, hours Yield, while reactions with acetylenes result in exo-adducts only. CeOOMe C4OOM 273 [2π+4π]-Cycloaddition is more characteristic of Mee C4OOM 278 NBD in reactions with alkynes. Phh P0132 2 In such systems even non-activated alkynes react

Eurasian ChemTech Journal 3 (2001) 73-90 84 Norbornadiene as a Universal Substrate for Organic and Petrochemical Synthesis easier than alkenes with electron-acceptor substituents (reaction 20):

Co(acac)3 : Et2AlCl = 1:4 + 1 2 R R dppe, C H , 20-60 oC 6 6 (20) R , R = H, Ar, Alk, (CH ) OR 1 2 2 n 50-100 % R1 R2 29

First publications have appeared recently tuted NBDs is low (50÷70%), the enantioselec- where enantio-selective cyclocodimerization of tivity reaches 85÷90%. NBD and alkynes is described. The system Very interesting examples of intramolecular cy-

Co(acac)2 – Et2AlCl with chiral diphosphines cloaddition with the participation of 2-alkenyl-sub- was used as a catalyst. The regioselectivity of stituted NBD with various lengths of the hydrocar- these processes with the participation of substi- bon bridge were described [28] (reaction 21):

[2π+2π+2π] + (21) R R R 30 31

The aklyne moiety has two possible ways of place at any bridge length. The last characteristics attachig to NBD. However, only direction 30 takes influences the yield of 32 (reaction 22):

Yield R n1==n2 Co(acac) : Et AlCl = 1 : 4, 3 2 o H8746 dppe, C H , 25 C 6 6 (22) M9e 634 ( )n R ( )n SiMe3 683 4 R P0h 7- 32

Formation of 8-membered cycles was also de- An example of this type of cyclization is co-dimer- scribed for reactions of NBD with conjugated dienes. ization of NBD and 1,3-butadiene in the presence of Metal complexes play the major role in these processes. iron complexes [32] (reaction 23):

Fe(acac)3 + Et2AlCl + + NBD-dimers (25 %) (23) (23) + o C6H6, 80 C, 3 h 33(25 %) 34 (12 %)

In addition to [4+2+2]-cycloaddition, [2π+4π]-cy- ferent structures. clization also proceeds to give 34 during this reac- If a cobalt catalyst (CoCl2-diphos) is substituted tion, and so does formation of NBD dimers with dif- for ferruginous one in similar conditions, the yield of

Eurasian ChemTech Journal 3 (2001) 73-90 V.R.Flid et al. 85

33 increases up to 68 %, and product 34 virtually zene is used, NBD can dimerize not only with 1,3- ceases forming [33]. butadiene, but with its derivatives as well [34] (re-

When system Co(acac)3-dppe-Et2AllCl in ben- action 24):

R1 = R2 = H 89% Co(acac)3, dppe, Et2AlCl R + 1 R1 = H, R2 = CH3 40% (24) o R = CH , R = H 38% R C6H6, 35-50 C 1 3 2 1 R2 (25 %) R2 35

Lautens and his colleagues performed this re- the ligand. The best results were obtained for R- action enantioselectively recently [35]. Co(acac)2 diphenylphosphinepropane (R-Propos), where the or Co(acac)3 can be used for the initial cobalt com- selectivity to ee-isomer exceeded 70% (reaction 25 pound, and a chiral diphosphine can be applied as and Table 6):

* Co(acac)2, R-prophos, Et2AlCl * * + * * * (25) o R C6H6, 25 C R Table 6 Effect of the phosphine type on the reaction yield and stereoselectivity in reaction 25. R%y%ield, ee,

CH3 626 7

(CH2)8CH3 440 7

CH2CH2CH=C(CH3)2 499 7

(CH2)3OAc 532 7

CH2Si(CH3)3 419 7

The first example of intramolecular cycloaddition however (reaction 26): was described; the yield of the adduct was not high,

Co-cat, Et2AlCl, dppe (26) o C6H6, 25 C R H Co(acac)2: 40% Co(acac)2: 32%

All examples of such addition were described for a very restricted number of catalytic systems with a

Eurasian ChemTech Journal 3 (2001) 73-90 86 Norbornadiene as a Universal Substrate for Organic and Petrochemical Synthesis rather low yield of [4π+2π+2π]-adducts. In addition NBD-derivatives is a promising way to obtain com- to them, NBD dimers and products of polymerization pounds with unique structures. It was first described form. by M. Catellani and G. Chiusoli in 1979 [36]. This The codimerization processes involving NBD have method was substantially developed in studies by [37- a range of qualitative analogies. Intramolecular type 39]. A series of NBD-derivatives incorporating two of co-dimer formation implies formation of hetero- or more double bonds with different reactivity can be ligand π-complexes of nickel; the ability of the sub- obtained in one technological stage through this reac- strate to co-coordinate has to be between that of the tion. The various reactivity of the double bonds is mono- and bidentated NBD molecule. One must know rather valuable when these compound are used as co- these regularities to obtain individual products with a monomers for special-purpose synthetic rubbers. high yield and selectivity. Allylic esters of organic acids are the source of allyl moieties. The most unusual feature of this reac- Catalytic allylation of NBD. tion is the character of addition, which can be not only linear (the conventional type), but cyclic as well, Catalytic allylation of the strained double bond in or even proceed with breaking a C-C bond.

+ + + [Ni] 36 38 + 37 (27) OAc + +

39 40 41

Catalytic system – Ni(acac)2–AlEt3–P(OR)3 is very able to attain a high conversion of reagents due to active and sufficiently selective when used to obtain decomposition of the catalytic system in the last case. exo-methylenecyclobutane derivatives. Sterical fea- The shares of individual isomers among the oli- tures of substrates incorporating exo-substituents in gomeric products depend of temperature, the type positions 5 and 6 with respect to the intracyclic double and structure of the organophosphous ligand. At bond do not exert a substantial effect on the rate of 25°C, major products are methylenecyclobutane de- cycloaddition. Quite the opposite, the reactions slows rivatives. down considerably in the case of endo-substituents. The structure of substituents in location 7 of the The structure of allylating agent (allylic ester) is not NBD molecule exerts little influence on co-oligomer- decisive. For example, you can use not only ization catalysts. However, substituents in positions allylacetate (AA), but allylpropoinate, allylbenzoate 2 and 3 of the NBD-moiety can block this reaction and allylformate as well. However, you will not be route (reaction 28)

R R R [Ni] OAc + + (28) 43 44

Catalytic allylation of NBD and NBD derivatives The kinetics and mechanism of the process were is an extremely complicated multiparameter process, scrutinized through a complex of physical and chemi- which proceeds unconventionally. Different factors cal methods for catalytic system Ni(C3H5)2(P(O- affect its rate, yield, turnover, and selectivity. iC3H7)3)n. Its results indicate that there are equilib-

Eurasian ChemTech Journal 3 (2001) 73-90 V.R.Flid et al. 87 rium stages like: Analysis of the kinetic data let us assert that individual products 45-47 form due to the presence of NiLn NiLn-1 + L (29) nickel complexes with different number of phosphite Complexes with different number of phosphite ligands in the catalytic system (Fig. 5). ligands were detected through 31P NMR in model systems and in conditions of a catalytic process. Phos- phite gets re-esterified by acetic acid, one of the reac- n = 1 tion products. This leads to the formation of a mix of phosphonates and deactivates the catalytic system. n = 2 That NBD molecules can coordinate in the complex (ÀÀ) Ni (NBD) in different ways makes the process more complicated, and so does the successive allylation of two double Ln n = 3 bonds (Fig. 4).

Fig. 5. Possible routes of the intermediates destruction.

The experimental data allow us to propose a mechanism of catalytic allylation of NBD (Fig. 6). In

accordance with it, complexes all NiLnOAc dominate in the reaction media. An NBD molecule co-ordinates on a nickel atom, which induces η3-η1-isomerization of the allyl ligand, and then inserts into the η1-allyl- metal bond. Then, depending on «n», cyclization proceeds in one route or another. It finishes with a β- hydride transfer, formation of products and regenera-

tion of NiLn (a quick oxidative addition of an

allylacetate molecule to NiLn from solution). When n Fig. 4. Changes in concentrations of NBD, products of = 1, NBD coordinates chelately in the complex, which its allylation, and in the ratio P/Ni during a kinetic ex- gives rise to product 47 that has a nortricyclene struc- periment. ture.

n = 1 AcONi + LnNi NiLn NiLn Ln OAc n = 2, 3 OAc OAc

NiLn n = 3 OAc Í LnNi n = 2 H

Í H LnNi OAc NiLn OAc OAc

47 NiLn 45 46 OAc Í NiL NiL NiLn + AcOH n + AcOH n + AcOH Fig. 6. Catalytic allylation of NBD with allylacetate.

Eurasian ChemTech Journal 3 (2001) 73-90 88 Norbornadiene as a Universal Substrate for Organic and Petrochemical Synthesis

Hydrid transfer is probably the limiting step of of a β-carbon, which was confirmed through using the process. This step proceeds with the participation model system C3D5OCOCD3 – NBD (Fig. 7).

D D D D C3D5OCOCD3+ C7H8 D D H D H + AcOH -Ni L H D n D NiLn M=137 D OAc 46

D D D D ... + AcOD D - Ni - OAc Ni Ln D DD M=136 D Ln 45 Fig. 7 A mechanism fragment for catalytic allylation of NBD with allylacetate in model system C3D5OCOCD3 – NBD

Molecular weights of products 46 and 45 are dif- 350 g/(l·hour) at 80°C and a L/Ni ratio of 3. The prod- ferent. This confirms that hydrogen can be torn from uct 46 forms with a selectivity of 95% and an output either the NBD-ring, or the allyl moiety. of 220 g/(l·hour) at 25°C and a P/Ni ratio of 2. Acetic acid destabilizes the catalytic system. This The product 47 can be obtained with a selectivity is why the number of catalyst turnovers does not ex- up to 70% at a L/Ni ratio equal to and a temperature ceed 150-200 in a static reactor. of 50 to 70°C. The lifetime of the catalyst and the number of its A very interesting situation exists when a double turnovers can be increased up to 2000 through use of excess of allylacetate over NBD is used. Second- zeolites adsorbing acetic acid selectively. ary allylation of norbornene-type compounds 45 Applying the regularities found, we can obtain and 46 yields a wide range of isomeric products product 45 with a yield up to 85% and an output of (reaction 30).

49 50 + 48 2 OAc

51 52 53

Structures and proportions of double allylation Conclusion products depends on conditions (the temperature and P/Ni ratio). Allylation of a double bound in NBD is Synthetic possibilities of NBD and its derivatives several times faster than the second stage, so the ki- are extremely versatile. However, this positive factor netic curves depicting accumulation of products 45 gives rise to problems caused by simultaneous real- and 46 have pronounced maximums (Fig. 8). ization of several reactions in a single system. Large- Hence NBD allylation has a general character. It scale use of NBD is substantially limited through dif- can be used as a promising method for obtaining rare ficulties connected with separation and analysis of polycyclic hydrocarbons. isomeric products, problems of sensible utilization of

Eurasian ChemTech Journal 3 (2001) 73-90 V.R.Flid et al. 89

3. Schrauzer G.N. On Transition Metal-Catalyzed Reactions of Norbornadiene and the Concept of π-Complex Multicenter Processes. Advances in Catalysis and related Subjects.,N.-Y.,London, Academic Press, 1968, 9, p.373-396. 4. Smagin V.M., Ioffe F.E., Grigoriev A.A. Chemi- cal Industry (Khemicheskaya Promyshlennost, rus.), 1983, No.4, p.198-201 5. Jemilev U.M., Podpodko N.R., Kozova E.V. Metal-complex catalysis in organic synthesis. (rus.) M., Khimia, 1999, 648 pp. 6. Bren B.A., Dubonosov A.D., Minkin V.I., Fig. 8. Kinetic curves of catalytic allylation of NBD with Chernoivanov V.A. Uspekhi Khimii (rus.), 1991, allylacetate. 1 – compound 45, 2 – compound 46, 3 – issue 60, p. 913-948. compound 47, 4 – sum of NBD double allylation prod- 7. Franceschi F., Floriani C. Inorganic Chemistry; ucts. A static reactor, 40°Ñ; allylacetate:NBD = 2:1; con- 1999, 38, No.7, p.1520-1522. centration of Ni(C3H5)2=0.05 mol/l, initial ratio L/Ni=3; 8. Nishikudo T. Macromolecules, 1998, 31, No.9, m-xylene. p.2789-2796. 9. Flid V.R., Aranson M.V., Kozyrev A.N. Journal reagents and insufficient catalyst activity. Metal-com- of general chemistry (rus.). 1992. V.62, issue 11. plex catalysts provide unique opportunities for ob- p.2636-2637. taining various polycyclic hydrocarbons. Use of these 10. Ballivet D., Billard C., Tkatchenko I. Inorg. complexes is the most promising way of developing Chim. Acta, 1977, 25, p.L58. this synthetic direction. Transition metals possess the 11. Langenbach H.J., Keller E., Vahrenkamp H. J. basic ability to influence selectivity to any degree; Organometal. Chem., 1979, 171, p.259. however, a thorough information about the mecha- 12. Scharf H.D., Weisgerber G., Höver H. Tetrahe- nism of their action is necessary to implement these dron Lett., 1967, N43, p.4227. possibilities. Unfortunately, relevant data are badly 13. BRD patent 1239304 (1967); Ñ.À., 1967, 67, scarce in literature. 53780. To find a decent place for NBD among principal 14. US Patent 3377398, 1968; U.S.C1 260-266. substrates in organic and petrochemical synthesis we 15. US Patent 4094917 (1978); Ñ.À., 1978, 89, need deeply understand the basis of NBD-involving Ð197060. processes, which in turn requires us to use a complex 16. Ballivet D., Tkatchenko I. J. Mol. Catal., 1975, of various physical and chemical methods and syn- p.319. thetic techniques, as well as scrutinize the kinetic regu- 17. Schrauzer G. N., Bastian B.N., Fosselius G.A. larities in the relevant systems. J. Amer. Chem. Soc., 1966, 88, p.4890. 18. US Patent N 3329732 (1967); Cl 260-666; C.A., Acknowledgements 1967, 67, 90467. 19. Flid V.R., Manulik O.S., Grigor,ev A.A., Belov This work was financially supported by Russian A.P. Kinetics and Catalysis, 1998, 39, ¹1, p. Foundation for Fundamental Research, Grants ¹ 99- 51-55 03-32151, 01-03-06059, 01-03-06060. 20. Flid V.R., Manulik O.S., Grigor,ev A.A., Belov A.P. Kinetics and Catalysis, 2000, 41, ¹5, p. References 597-603 21. Flid V.R., Kuznetsov V.B., Grigor,ev A.A., Belov 1. Feldblum V.Sh. Synthesis and application of A.P. Kinetics and Catalysis, 2000, 41, ¹5, p. unsaturated cyclic hydrocarbons. (rus.) Moscow, 604-611 Khimia, 1982, p. 207. 22. Binger P., Schuchardt U. Angew. Chem., 1977, 2. Bolshakov G.F. Chemistry and technology of 89, N4, p.254-255. components of liquid rocket fuel. (rus.) Leningrad, 23. Lucchi O.D., Licini G., Pasquato L., Senta M. Khimia, 1983, 248 pp. Tetrahedron Lett., 1988, 29, p.831.

Eurasian ChemTech Journal 3 (2001) 73-90 90 Norbornadiene as a Universal Substrate for Organic and Petrochemical Synthesis

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