Electrophilic additions to acetylenes. Part I. Addition of some alkyl chlorides to phenylacetylene

Abstract

The addition of t-butyl, benzyl, and diphenylmethyl chlorides to phenylacetylene in dichloromethane with a Lewis acid as catalyst afford high yields of the 1 : 1 addition products, mainly of the (E)-configuration, corresponding to predominant anti-addition. Products with (E)-configuration also result predominantly from the addition of hydrogen chloride to 3,3-dimethyl-1-phenylbutyne, 1,3-diphenylpropyne, and 1,3,3-triphenylpropyne under the same reaction conditions; this corresponds to predominant syn-addition. The structure and the configuration of the addition products are assigned by independent synthesis and by ¹H n.m.r. spectroscopy. The results are discussed in terms of the intermediacy of linear vinyl cations, which are preferentially attacked by the nucleophile Cl^– from the less hindered side.