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

The first enantioselective total syntheses of the beta-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(N)2'-substitution of propargyl oxiranes 13/14 and the gold-catalyzed cycloisomerization of alpha-hydroxyallene 15, resulting in a highly efficient center-to-axis-to-center chirality transfer.