Nucleophilic alkenes. III. Addition of 1,1-dialkoxyethenes to 1,4-naphthoquinones. The 1 : 2-process

Abstract

Anthraquinones have been synthesized by 1 : 2-addition of 1,1- dialkoxyethenes to 1,4-naphtho-quinones, prior bromination of the naphthoquinone being unnecessary. The reactions were markedly accelerated by polar solvents and there was orientational specificity in most cases. Addition to 5-hydroxy-1,4-naphthoquinones gave derivatives of 1,3,8-trihydroxyanthraquinone while 5-methoxy-1,4- naphthoquinone gave the 1,3,5-substitution pattern. 6-Hydroxy- and 6- alkoxy-naphthoquinones gave chiefly the 1,3,7-orientation, appropriate prior bromination being required to generate the 1,3,6-series. These orientations are interpreted in terms of initial nucleophilic attack of 1,1-dialkoxy-ethene at a quinonoid carbon. This also takes into account concurrent 1 : 1-addition processes.