Conversion of shikonin angelate into [2,2-dimethyl-1-(2-methylcrotonoyloxy)cyclobutyl]-5,8-dihydroxy-1,4-naphthoquinone; a novel cyclisation of a 4-methylpent-3-enyl side chain in a natural quinone

Abstract

During isolation of 5,8-dihydroxy-2-(4-methylpent-3-enyl)-1,4-naphthoquinone and shikonin angelate, the side chain of the latter cyclised to give an unusual four-membered ring system. The identification of this product and some of its reactions are described.