Regioreversed nucleophilic substitution of 2-(allyloxy)benzothiazole by allylic Grignard reagents. A regioselective synthesis of 1,5-dienes

Abstract

2-(Allyloxy)benzothiazoles react with allylic organomagnesium compounds in the presence of copper bromide to give 1,5-dienes. The C–C coupling occurs almost exclusively in a head-to-tail fashion. Contrary to this the same electrophiles, when complexed with copper(I) bromide before the addition of the allylic Grignard reagents, give only 1,5-dienes derived from a head-to-head coupling process. The change in the selectivity is probably due to the co-ordinative effects of the substrates towards the organometallic species.