Synthetic studies towards naturally occurring γ-( Z )/( E )-alkylidenebutenolides through bimetallic cascade cyclization and an adventitious photoisomerization method.

A general and flexible visible light-induced photoisomerization method of γ-( Z )-alkylidenebutenolides to their corresponding E -components was reported in this article. Initially, a series of naturally occurring enantiopure γ-( Z )-alkylidenebutenolides was synthesized by employing a "Pd-Cu" bimetallic cascade cyclization protocol. In the later part, the synthesized γ-( Z )-alkylidenebutenolides were photoisomerized in the presence of a triplet photosensitizer to γ-( E )-alkylidenebutenolides in reasonably acceptable yields. Total synthesis of goniobutenolides, hygrophorones, ramariolide D, melodorinols/acetyl-melodorinols, versicolactones, and phomopsolidones was achieved by employing the developed methods.