Epoxides and episulphides

A truly vast literature has accumulated on the polymerization of the epoxides and episulphides. This is probably the result of their far reaching commercial importance and of their high reactivity and the multiplicity of possible reaction pathways. The investigation of their polymerization appears to continue at an almost frantic pace still today. New catalyst 

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Clearly, more research needs to be done. For instance, there is a real need for more detailed product studies. The initial products with oxygen and sulphur atoms are the epoxides and episulphides. With selenium and tellurium the cyclic adducts are apparently only transient, so there is no accumulation of initial product to serve as a measure of the reaction rate. Callear and Tyerman [123] measure the selenium—olefin reaction rate by photometric methods, in which the appearance of bands attributed to an alkyl selenide are observed. These products are not stable, and decay according to... 

These sulphur analogs of the 1,2-epoxides are variously known by the names thiiranes, thiacyclopropanes, alkylene sulphides, and episulphides. They are known to polymerize by the three catalytic mechanisms discussed for the oxygen compounds. Thus the same divisions are possible. For a discussion of some of the mechanistic aspects of these polymerizations as compared to epoxides, the reader is referred to a recent paper by Vandenberg [35]. 

The thiiran groups of thia-tris-a-homobenzenes (37) and (38) are formed from the tris(oxiran) (36) via isothiouronium salts. Interconversion of epoxides into episulphides has also been reported in the carbohydrate series. ... 

Some of the more important monomers whose ring opening polymerisations have been induced by stable cation salts include, 1,4-epoxides, notably tetra-hydrofuran (20,112,113), 1,2-epoxides (114), 1,3-episulphides (thietans) (33,53), 1,2-episulphides (thiiranes) (53), azetidines (115,116), aziridines (117), the cyclic formals, 1,3-dioxolan (23,54, 118-120), and 1,3-dioxepan (118,119), trioxane (121,122) and more recently lactones (123). Aldehydes (124) may also be included since these molecules can be regarded as the smallest possible oxygen hetero-... 

Coordination polymerisation of heterocyclic monomers comprises polymerisation and copolymerisation processes of such monomers as oxacyclic monomers, especially epoxides [2,61-71], thiacyclic monomers like episulphides [72-76], azacyclic monomers [77,78] and phosphacyclic monomers [79]. Monomers with an exocyclic oxygen atom, such as cyclic esters like lactones [80-90] and lactide [90-92], cyclic acid anhydrides [93-98], cyclic carbonates [99,100] and related monomers, belong to oxacyclic monomers undergoing coordination polymerisation or copolymerisation. 

Epimer A diastereomer having the opposite configuration at only one chiral centre Episulphide The sulphur equivalent of an epoxide, which is also called a thiirane. Episulphone A three-membered ring that contains two carbons and an S02 group. 

A new thiophen synthesis is based on deprotonation and cyclization of the resultant carbanion (65) of a keten dimethylthioacetal. Other applications of cr-(phenylthio)- or cr-(alkylthio)-alkyl-lithiums include preparations of disparlure (the sex pheromone of the gypsy moth) and other chiral epoxides,of an anti-peptic-ulcer diterpene from Croton sublyratus, of carbene-thiometal chelates through reaction with fCr(CO)gl or fW(CO)jl, of olefins via )ff-hydroxy-sulphides, and of Michael adducts of enones. In other work, the chiral solvent l,4-dimethylamino-2,3-dimethoxybutane is employed in enantioselective addition reactions of cr-thio-carbanions with ketones and Michael acceptors. a,P -Elimination of cr-thio-carbanions such as (66) provides a useful synthesis of olefins, and a 2-(lithiomethylthio)-A -oxazoline (67) has been used to prepare a C-labelled thiiran for a microwave study of the valence tautomerism of allene episulphide. ... 

Several new methods for the preparation of olefins by deoxygenation of epoxides or desulphurization of episulphides have been reported. Mono-, di-, tri-, and tetra-substituted epoxides yield olefins (75—97%) when treated with lithium in refluxing THF (16— 98 h). Aliphatic epoxides give olefins with retention of stereochemistry, but JB-stilbene was produced from each isomer of the corresponding epoxide. Episulphides are reduced to olefins with better than 99% retention of configuration and in yields of 50—80% by 2-alkyl-oxaziridines. °... 

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