Isomerism of semicarbazones of 6-hydroxy-4,7-dimethoxy- and 6-hydroxy-4-methoxy-benzofuran-5-yl methyl ketone and derivatives

Abstract

6-Hydroxy-4,7-dimethoxy- and 6-hydroxy-4-methoxy-benzofuran-5-yl methyl ketone (khellinone and visnagin-one) semicarbazones can be obtained in either of two isomeric forms, depending of their mode of preparation. No syn–anti-isomerism could be detected, but the isomers obtained under acidic conditions were shown to be cyclic tautomers of the normal semicarbazones. This followed from n.m.r. experiments and from the results of van Slyke nitrogen determinations.