Cyclopropyl compounds as chemical building blocks: Total syntheses of the alkaloids (-)-colchicine, imerubrine and grandirubrine

Abstract

Fully regio-controlled total syntheses of the title alkaloids (1), (13) and (14) have been developed. In each case, the key step involved acid- or thermally-promoted ring-expansion of the appropriate σ-homo-o-benzoquinone or σ-homo-o-benzoquinone monoacetal to generate the troponoid ring associated with the target compounds.