Reactions of 2-(α-Haloalkyl)thiiranes with nucleophilic reagents: V. Reactions of 2-(α-Chloroalkyl)thiiranes with organolithium compounds

Abstract

2-(α-Haloalkyl)thiiranes reacted with methyl-, butyl-, and phenyllithium to give the corresponding allyl sulfides. The reactions of diastereoisomeric erythro-and threo-2-(1-chloroethyl)thiiranes with phenyllithium were stereospecific, and they afforded (E)-and (Z)-1-phenylsulfanylbut-2-enes, respectively. 3-Chloromethyl-2,2-dimethylthiirane and phenyllithium gave rise to a mixture of 3-methyl-3-phenylsulfanylbut-1-ene and 3-methyl-1-phenylsulfanylbut-2-ene. The reactions of 2-chloromethylthiiranes with phenyllithium and methyllithium in the presence of a catalytic amount of copper(I) iodide (10 mol %) led to the formation of substituted thiiranes as the major products. Mechanisms of the observed transformations are discussed. * For communication IV, see [1]. † Deceased.Unlike oxiranes, reactions of alkylthiiranes with organometallic compounds involve desulfurization or polymerization processes rather than opening of the three-membered ring [2][3][4]. Presumably, desulfurization occurs through intermediate formation of ate complexes and is stereospecific; furthermore, this reaction may be regarded as a method for the preparation of alkenes [2]. On the other hand, there are published data indicating that 2-(chloromethyl)thiirane (Ia) is capable of giving rise to monomeric products of formal chlorine replacement in reactions with organolithium reagents; however, these products have quite specific nature [5, 6] (Scheme 1). Unfortunately, these two examples represent all available information on such reactions which could underlie a convenient procedure for the synthesis of substituted thiiranes. Therefore, in the present work we examined reactions of the simplest organolithium compounds with some 2-(α-haloalkyl)thiiranes in diethyl ether.We found that phenyllithium and butyllithium reacted with 2-(chloromethyl)thiirane (Ia) at a fairly high rate on moderate cooling. Methyllithium was inert up to 0°C, but it did react with compound Ia in the presence of DABCO. Quite surprisingly and contrary to published data, as low-molecular products of these transformations we identified the corresponding allyl sulfides IIa-IIc (Scheme 2). 2-(Bromomethyl)thiirane (Ib) (which is less convenient to handle with) reacted with phenyllithium to give sulfide IIc in a considerably better yield.