Golden opportunities in natural product synthesis: first total synthesis of (–)-isocyclocapitelline and (–)-isochrysotricine by gold-catalyzed allene cycloisomerization

Abstract

The first enantioselective total syntheses of the β-carboline alkaloids (–)-isochrysotricine (1) and (–)-isocyclocapitelline (2) are reported which confirm the absolute configuration of these natural products. Key steps are the copper-mediated S_N2′-substitution of propargyl oxiranes13/14 and the gold-catalyzed cycloisomerization of α-hydroxyallene 15, resulting in a highly efficient center-to-axis-to-center chirality transfer.