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The Use of Iron Carbonyl Complexes in Organic

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The Use of Iron Carbonyl Complexes in Organic THE USE OF IRON CARBONYL COMPLEXES IN ORGANIC SYNTHESIS a thesis presented by GARY DAVID ANNIS in partial fulfilment of the requirements for the award of the degree of DOCTOR OF PHILOSOPHY OF THE UNIVERSITY OF LONDON WHIFFEN LABORATORY CHEMISTRY DEPARTMENT IMPERIAL COLLEGE LONDON SW7 2AY. AUGUST/ 1979. 1. CONTENTS page ABSTRACT 3 ACKNOWLEDGEMENTS 5 INTRODUCTION 6 1. CARBONYL INSERTION REACTIONS 8 (a)Sodium Tetracarbonylferrates 8 (b)Sodium Hydridotetracarbonylferrates 13 (c)Lithium Acyl Iron Complexes 14 (d)Magnesium Acyl Iron Complexes 15 (e)Potassium Tetracarbonylferrates 16 (f)Miscellaneous Ferrates 17 CARBONYL INSERTION REACTIONS USING DICARBONYL- PENTAHAPTOCYCLOPENTADIENYL IRON COMPLEXES 20• CARBONYL INSERTION REACTIONS USING IRON CARBONYLS 25 (a)Reactions of Simple Vinyl Cyclopropanes with Iron Carbonyls 25 (b)The Reactions of More Complex Hydrocarbons with Iron Carbonyls 33 (c)Diene Complexes of Iron Carbonyls 38 (d)The Reaction of Hetero Systems with Iron Carbonyls 46 (e)Coupling of Olefins using Iron Carbonyls 52 2. RING FORMING REACTIONS USING IRON CARBONYLS 55 3. FUNCTIONAL GROUP REMOVAL AND REDUCTION USING IRON CARBONYLS 58 4. ISOMERISATION AND REARRANGEMENTS USING IRON CARBONYLS 61 2. page 5. OTHER METHODS OF C—C BOND FORMATION USING IRON CARBONYLS 62 6. FUNCTIONAL GROUP PROTECTION USING IRON CARBONYLS 64 7. ACTIVATION OF ALKENES USING IRON CARBONYLS 66 REFERENCES 67 RESULTS AND DISCUSSION 77 Preparation of Lactones from Ferrolactones 78 Mass Spectral and N.m.r. Data of the Ferrolactones 99 Mechanism of Formation of Ferrolactones 104 Mechanism of the Oxidation of Ferrolactones 106 Structure of Iron Carbonyl Complexes 110 Preparation of Lactams from Ferrolactams 115 Mechanism for Formation and Oxidation of Ferrolactams 122 Preparation of NH Lactams 123 Miscellaneous Chemistry 126 EXPERIMENTAL 130 REFERENCES 162 3. ABSTRACT A number of ferrolactones have been prepared by the irradiation of vinyl epoxides in the presence of iron pentacarbonyl. In this way, syn- and anti-tricarbonyl{l,1',2'-n-l-vinylcyclopentan-l-yl)-2-oxycarbonyl iron (3) and (4), E- and Z-tricarbonyl-(1,2,3-n-l-nonen-3-yl)-4-oxycarbonyl iron (21) and (22), tricarbonyl-(2,3,4-n-2,3-dimethyl-3-buten-2-yl)-1- oxycarbonyl iron (27), tricarbonyl-(1',2',3'-n-1-propenylcyclohexan-1'- yl)-1-oxycarbonyl iron (35), tricarbonyl-(2,3,4-n-3-cyclohexen-2-yl)- 1-oxycarbonyl iron (41), and 2-tricarbonyl-(2,3,4-n-2,3-(tetramethylene- 3 -buten-2-yl)-1-oxycarbonyl iron (54) were prepared from their respective epoxides. A previously unobserved structural isomerisation has been shown to exist by the separation of syn- (3) and anti- (4). Oxidation of ferrolactones with ceric ammonium nitrate has been shown to produce S- and 6-lactones. Thus, complexes (3), (4), (21), and (22), (27), (35), (41) and (54) have been converted to 1-vinyl-6-oxabicyclo- 3.2.0 - hept-7-one (6) and 2-oxabicyclo [4.4.0}dec-5-en-3-one (7), (7), trans- and cis-3-pentyl-4-vinyloxetan-2-one (23) and (24), 3-(isopropenyl)-3-methyloxetan- 2-one (28) and 3,6-dihydro-4,5-dimethyl-2-pyrone (29), cyclohexanespiro-4'- (3'--vinyloxetan-3'-one) (37), 7-oxabicyclo14.2.0] oct-2-en-8-one (44), and l 2-methylenecyclohexanespiro-4'-oxetan-2-one (56) and 5,6,7,8-tetrahydroisochro- man-3-one (55) respectively. Ferrolactones (3) and (4), (21) and (22), and (27) have been converted to their corresponding ferrolactams; tricarbonyl-(2',1,2-n-l-ethyl-l-cyclo- penten-l'-yl)-2'-benzylaminocarbonyl iron (80), E=tricarbonyl-(2,3,4-n-3-nonen- 2-yl)-benzylaminocarbonyl iron (83), and tricarbonyl-(2,3,4-n-2,3-dimethyl- 3-buten-2-yl)-l-benzylaminocarbonyl iron (77) by the zinc chloride catalysed addition of benzylamine. By analogy to the ferrolactones, the ferrolactams (80), (83), and (77) were converted to their respective lactam derivatives, 1-benzyl-3-(1'-cyclopent-. enyl)azetidinone (81), cis- and trans-l-benzyl-3-(1'-heptenyl)azetidino ne (84) and 1-benzyl-3-(isopropenyl)-3-methylazetidinone (79) and 1-benzyl-3,6-dihydro- 4,5'-dimethyl-2-pyridone (78) by oxidation with ceric ammonium nitrate in ethanol. V 4. The lactone (6) and 3-(1-pentenyl-oxetan-2-one (90) have been rearranged to 1-vinyl-3-oxabicyclo[2.2.1hept-2-one (89) and 3-methyl-l-oxa- bicyclo L3.3.O0 oct-3-en-2-one (91) respectively, by thermolysis in benzene in the presence of zinc chloride. 5. ACKNOWLEDGEMENTS I would like to thank Dr. S.V. Ley for his advice, guidance, encouragement, and friendship throughout the course of this work. I thank Mr. K.T. Jones and his staff for the microanalytical service, Mrs. Lee for the mass spectrometry service, and Mrs. Day and Mrs. I. Hamblin for their service at the stores. I would also like to thank my friends (they know who they are) in the laboratory for their help, cooperation, and friendship. Finally, I would like to thank the Science Research Council for a studentship for the period of this research. 6. INTRODUCTION Iron carbonyls are the least toxic and inexpensive transition metal carbonyls available to the organic chemist. This goes some way in ex- plaining the enormous interest shown in the reactions of these species over the past few years. Three of these carbonyls, iron pentacarbonyl 1 (1), diiron nonacarbonyl (2) and the triiron dodecacarbonyl (3) have found extensive applications in organic synthesis. o `° -coo 0C—Fei—"CO `CO oc/Ī f-e4ō CO co co (1) (3) Elemental iron has 8 electrons in its valence shell (3d6, 4s2). By coordinating to the equivalent of five 2-electron donors, it can achieve the electronic configuration of the next inert gas, Krypton (3d10, 4s2, 4p6). This is the electronic configuration adopted by iron in all its stable complexes, and the iron is said to be coordinatively saturated. Removal of a 2-electron donor leaves 16 electrons in the valence shell, and the species is said to be coordinatively unsaturated. Transitory •reaction intermediates commonly have this configuration. Iron tetra- carbonyl, the simplest of these species can be generated by thermolysis -.or photolysis of iron pentacarbonyl=(1), and the thermolysis of diiron a - noncarbonyl (2) and triiron dodecacarbonyl (3). It reacts with a great variety of organic compounds including olefins, dienes, a,6-unsaturated carbonyl compounds, vinyl cyclopropanes, strained cyclopropanes and vinyl epoxides forming pi or sigma bonds to complete its valence shell. 7. Further ligands may be replacedin this manner to generate highly functionalised complexes. Saturatively coordinated complexes can also react with ligands, either in ligand substitution reactions or in reactions where the adding ligand forces a carbonyl ligand to insert into an iron sigma bond. Because of the property of iron tetracarbonyl to form complexes with electron rich systems, iron carbonyl complexes are finding an increasing number of applications in organic synthesis.3 Many products formed from iron carbonyl complexes are difficult to make efficiently by other methods. This review will deal with carbonyl insertion reactions of iron complexes in detail. However, in order to demonstrate the potential of iron complexes in synthesis, examples of other important reactions will be highlighted in later sections. 8. I. CARBONYL INSERTION REACTIONS CARBONYL INSERTION REACTIONS USING IRON CARBONYL ANIONS (a) Sodium Tetracarbonylferrates Disodium tetracarbonylferrate is a nucleophilic reagent which sub- stitutes alkyl halides/tosylates or acyl halides to give two different types of complex, both of which have been characterised.2 The reactions of these complexes are summarised in Figure 1. FIGURE 1 RH Na t Fe (CO)4 RC HO ,,,...00I1 H+ Fri 0 R'X OC OC — e CO CO \ fL L (CO or P73) \X21 ROH XZlROFi~ 02 i rho r 02/ HZO ROR RCO H R cod 2 X = Halogen , R'= R= Alkyl In this way, disodium tetracarbonylferrate can transform alkyl halides/ tosylates and acyl halides to aldehydes4, ketones5'6, acids?, esters7 and amides 7'8 (Figure 2). Of particular importance is the fact that the reagent shows a high selectivity for halides in the presence of other 9. functional groups. FIGURE 2 1/. a CHO 81% 2/. H+ 02Et 1/. a Br 2Z EtI 11 Ts 21. MeI • 79% 99% Optical yield 1/.a NC NC 2/ C F COCQ 715 11. Fe(C0)2- 2tEtI 81 % 1/. a Br 02H Cl 21. IH~ Ōl O-2 2 84% 1/. Fe(C0) 2/. I2I McOH ~Br 1/ 0 NMe2 2/. I2/ Me2NH Na2Fe(CO)4 / CO 80 % The reagent is also useful for the preparation of polyfluorinated ketones which are difficult to make by conventional methods.6 Br 1/..a Cl 2/ C7F,sCOQCt 10. There is only one example of an amide being prepared from the additi- on of an amine to an acyl complex, although a more general method has been reported, in which the acyl complex is added to an alkyl or aryl nitro compound.9 The nitro group is spontaneously reduced to the correct oxi- dation state during the course of the reaction. H0 Me CO Fe(CO)4 Na + t NO2 --~ - Me CO NH~ As disodium tetracarbonylferrate is toxic, has a basicity equivalent to the hydroxide anion, and is spontaneously flammable in air, its syn- thetic use is limited. Initial substrate choice is also limited to prima- ry halides and secondary tosylates, as competing elimination reactions and steric hindrance are important considerations. Allylic halides produce 1,3-diene complexes by elimination of hydrogen bromide. Migratory insertion fails for alkyl groups with adjacent electronegative groups. For the second substitution reaction substrates are limited to a primary halide, usually (but not always) the iodide. Acyl iron complexes can also be generated by addition of an anion to iron pentacarbonyl.
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