A GENERAL-SYNTHESIS OF CHROMENES

A general synthesis of chromenes, involving zinc promoted allyation of 2-hydroxyphenacyl derivatives followed by acid catalyzed cyclisation and dehydration is described. Several structurally different allylic b romides have been successfully employed. The synthesis is conveniently carried out without isolation of the intermediate benzyl alcohol deri vative, and usually good overall yields are obtained. Salicyl aldehyde was successfully employed as a substrate, but precocene was not forme d from 4,5-dimethoxysalicylaldehyde.