Hindawi Publishing Corporation Journal of Chemistry Volume 2014, Article ID 163074, 47 pages http://dx.doi.org/10.1155/2014/163074 Review Article Synthesis and Reactions of Five-Membered Heterocycles Using Phase Transfer Catalyst (PTC) Techniques Ahmed M. El-Sayed,1 Omyma A. Abd Allah,1 Ahmed M. M. El-Saghier,1 and Shaaban K. Mohamed2,3 1 Department of Chemistry, Faculty of Science, Sohag University, Sohag 82524, Egypt 2 Chemistry and Environmental Division, Manchester Metropolitan University, Manchester M1 5GD, UK 3 Chemistry Department, Faculty of Science, Minia University, El-Minia 61519, Egypt Correspondence should be addressed to Omyma A. Abd Allah; [email protected] Received 1 May 2013; Revised 15 September 2013; Accepted 28 October 2013; Published 25 February 2014 Academic Editor: Jorge F. Fernandez-Sanchez Copyright © 2014 Ahmed M. El-Sayed et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Phase transfer catalysts (PTCs) have been widely used for the synthesis of organic compounds particularly in both liquid-liquid and solid-liquid heterogeneous reaction mixtures. They are known to accelerate reaction rates by facilitating formation of interphase transfer of species and making reactions between reagents in two immiscible phases possible. Application of PTC instead of traditional technologies for industrial processes of organic synthesis provides substantial benefits for the environment. On the basis of numerous reports it is evident that phase-transfer catalysis is the most efficient way for generation and reactions of many active intermediates. In this review we report various uses of PTC in syntheses and reactions of five-membered heterocycles compounds and their multifused rings. 1. Introduction (1) elimination of organic solvents, Organic synthesis is an essential way to get chemical prod- (2) elimination of dangerous, inconvenient, and expen- ucts having practical applications such as pharmaceuti- sive reagents such as NaH and NaNH2, cals, plant protection agents, dyes, photographic sensitizers, (3) increasing the reactivity and selectivity of the active and monomers. Transformations of starting materials into species, desired final products usually require number of chemi- cal operations in which additional reagents, catalysts, and (4) improving the yield and purity of products to the solvents are employed. Thus, during any synthetic method, optimum records, besides the desired products, many waste materials are (5) simplifying the whole synthetic process and making produced because transformations of reactants into products it safer and objective, are neither quantitative nor selective processes. This waste (6) reducing industrial wastes and overall costs and sav- could be regenerated, destroyed, or disposed. This will lead ing energy which gives a positive impact on economic to consuming much energy and creating heavy burden on and environmental interests, the environment. Therefore it is of a great importance to develop and use synthetic methodologies that minimize (7) accelerating and performing mimic reactions in an or eliminate such problems. One of the most common efficient mode. and efficient methodologies that fulfill this requirement is employing phase-transfer catalyses techniques [1–4]. The 1.1. Fundamentals of Phase Transfer Catalysis (PTC). First most significant advantages of use of PTCs in industrial phase transfer catalysis was discovered by Jarrouse and Hebd applications are [5] in 1951 when they observed that the quaternary ammonium 2 Journal of Chemistry OH OCH2Ph Cl PhCH2NEt3Cl + (1) NaOH CN CN PhCH2NEt3Cl + C2H5Cl C2H5 NaOH (2) Figure 1 − + PhCH2CN + NaOH PhCHCN Na + H2O org. int aq. − + + − − + PhCHCN Na + QX PhCHCN Q + NaX int org. org. aq. − + Ph + − PhCHCN Q + R-X CHC N + QX org. org. R org. org. Figure 2 NC NH2 ClCH2R N R Ph 2a–c PhNH-CH = C(CN)2 R: a = CO2Et, b = CONH2, c = COPh NC NH BrCH(COOEt)2 CO2Et N CO2Et Ph 3 Figure 3 CN PTC ArNHCOCH2Cl + CH2(CN)2 O NH N 2 Ar 45 6 Figure 4 salt and benzyltriethylammonium chloride accelerated two- 1.2. Mechanism of Phase-Transfer Catalysis. All phase- phasereactionofbenzylchloridewithcyclohexanol(Figure 1; transfer catalyzed reactions involve at least two steps: (1)) and the two-phase alkylation reaction of phenylacetoni- trile with benzyl chloride or ethyl chloride [6](Figure 1; (2)). (1) transfer of one reagent from its ground phase into the In addition, numerous publications and patents [7–12] second phase as an intermediate, have been reported during the period of 1950–1965. PTCs (2)reactionofthetransferredreagentwiththenon- techniques have been further developed by Makosza et al. for transferred reagent, for example, the alkylation of the purpose of obtaining more efficient and pure yield13 [ – phenylacetonitrile with alkyl halide using aqueous 16]. NaOH as a base and tetrabutylammonium halide Journal of Chemistry 3 K2CO3 solid surface Ph NH CN CN Y NH2 Q Ph-N PhN CN HX + CN CN XCH2Y QX HX Organic layer Y Y NQ PhN Ph-N CN CN CN Y Q PhN CN CN Scheme 1 (QX) as a catalyst can be formulated as shown in the PTC mixture of dioxan/K2CO3/(TBAB). Replacing Figure 2. of ethyl ethoxymethylenecyanoacetate 8b with 8a gave ethyl[3-amino-4-ethoxy-carbonyl-1-phenyl-5-thioxo-2,5-di- The concept of phase-transfer catalysis is not limited to hydro-2-pyrrolidene]cyanoacetate 9b and 10 under the same anion transfer but is much more general, so that, in principle, experimental conditions [19](Figure 5). one could also transfer cations, free radicals, or whole Moreover, the reaction of ethyl cyanoacetate 11 with molecule. Phase transfer catalysis is classified as liquid-liquid, phenyl isothiocyante 7 and ethoxymethylenemalononitrile liquid-solid, liquid-gas, solid-gas, or solid-solid systems. 8a or ethyl ethoxymethylenecyanoacetate 8b in1:1:1molar ratio under same PTC experimental conditions afforded 2. Application of Phase Transfer Catalysis the corresponding pyrrole derivatives 12a, b,and13 [19] in Synthesis of Five-Membered Ring of (Figure 6). Heterocyclic Compounds Reaction of methyl 2,5-dibromopentanoate 14 with tri- chloroacetamide 15 under solid-liquid technique (CH3CN/ 2.1. Synthesis of Five-Membered Ring Heterocycles Con- K2CO3/TEBACl) yielded methyl N-trichloroacetyl-2-pyr- taining One Heteroatom. Treatment of anilinomethylene- rolidine carboxylate 16 [20](Figure 7). malononitrile 1 with ethyl chloroacetate, chloroaceta-mide, Substituted pyrrolidines 19 were synthesized via the phenacyl chloride, or diethyl bromomalonate in 1 : 1 : 1 1,3-dipolar cycloaddition reaction between imino esters 17 molar ratio (dioxan/K2CO3/tetrabutylammonium bromide (TBAB)) afforded the corresponding substituted pyrroles 2a– (derived from alanine and glycine with alkanes) and alkyl c and 3,respectively[17](Figure 3). acrylate 18 in a mixture of THF or toluene, KOH, and TBACl [21](Figure 8). The catalytic cycle which explains the reaction pathway can be simplified as in Scheme 1. 1,4-Di(malononitrilemethyleneamino)benzene 20 was A simple and convenient synthesis of 2-amino-1-aryl-5- allowed to react with ethyl chloroacetate, chloroacetamide, oxo-4,5-dihydro-1H-pyrrole-3-carbonitriles 6 was achieved phenacyl chloride, or diethyl bromomalonate in 1 : 2 by reaction of N-aryl-2-chloroacetamide 4 and malononitrile molar ratios under solid-liquid PTC technique to give the 5 under solid-liquid PTC condition (CH3CN/K2CO3/18- corresponding 1,4-bi(1-pyrrolyl) benzene derivatives 21a–c crown-6) at room temperature [18](Figure 4). and 22 [17](Figure 9). 3-Amino-4-ethoxycarbonyl-1-phenyl-5-thioxo-2,5-dihy- Pyrrolidine derivatives 24 were obtained with thiophenes dro-2-pyrrolidene malononitrile 9a was prepared via reac- 25 from the reaction of diethyl cyanomalonate 23 with phenyl tion of malononitrile 5,phenylisothiocyanate7, and ethox- isothiocyanate 7 and chloroacetonitrile or chloroacetamide ymethylenemalononitrile 8a in 1:1:1 molar ratio under using the PTC of (DMF/K2CO3/TBAB) [22](Figure 10). 4 Journal of Chemistry NC CN NC CN PTC CH2(CN)2 + PhNCS 57 S NH PhN SH Ph NC NC NH PTC NH2 2 + CN EtOCH = C(CN) X CN S N PhN S X CN Ph 10 8a, b 9a, b X: a = CN, b =COOEt Figure 5 EtOOC CN PTC EtOOC CN CNCH2COOEt + PhNCS S NH PhN SH 11 7 Ph EtOCH=C(CN)(COOEt) PTC PTC EtOCH=C(CN)2 8b 8a EtOOC NH EtOOC NH 2 2 EtOOC NH2 + CN CN CN PhN S N S S N COOEt COOEt Ph Ph CN Hydrolysis 12b 12a H2O/K2CO3 −PhNH2 EtOOC NH2 CN O S COOEt 13 Figure 6 PTC Br(CH ) CH(Br)COOCH + Cl CCONH COOCH 2 3 3 3 2 N 3 14 15 COCCl3 16 Figure 7 One-potreactionofmalononitrile5,carbondisulphide, CS2 and ethyl chloroacetate under the same experimental and chloroacetamide in 1 : 1 : 1 molar ratio under solid- conditions gave the corresponding thiophene derivative 27 liquid PT catalysis (benzene/K2CO3/TBAB) has furnished [23](Figure 11). 3-amino-2-carboxyamido-4-cyano-5-mercaptothiophene 26 Different thiophene compounds (24 and 28–30)prepared [23](Figure 11). Also, treatment of malononitrile 5 with from reaction of diethyl cyanomalonate 23 with carbon Journal of Chemistry 5 R R O + − N COOR + − R N X COOR N COOR + 4 R4N X R1 N R H 1 KOH KOH 17 18 19 R1 O Figure 8 R R H2N NH2 2ClCH2R N N NC NC CN NC HN NH CN 21a–c PTC R = CO Et, CONH , COPh 20 CN 2 2 CO Et EtO C EtO2C 2 2 CO2Et HN NH 2BrCH(CO2Et)2 N N NC CN 22 Figure 9 Et O Et O Et O CN CN O O Et O O Et O O Et + PhNCS PTC NC O PhN O PhNH O H SH SH PTC XCH2Y X Z X Z EtO2C EtO2C + S Y N PhN S Y Ph 25 24a–c X =