Total Synthesis of (±)-Lycojaponicumin D and Lycodoline-Type Lycopodium Alkaloids

摘要

Lycopodium alkaloids with structural diversity and biological significance have been stimulating an increasing interest in the synthetic and medicinal communities, in which inspiration and exploration of their related biogenetic relationship generally constitute one of the major concerns. Driven by the plausible biogenetic entry to lycojaponicumin D as the first member of Lycopodium alkaloids having a structurally unusual C3-C13-linked scaffold, a new connection with lycodoline has been proposed and discovered on the basis of the design of an unprecedented bioinspired tandem fragmentation/Mannich reaction. Initiated by expeditious assembly of bridgehead hetero- functionalization in the [3.3.1] bicyclic system of lycodoline, a novel tandem palladium-mediated oxidative dehydrogenation/hetero-Michael reaction has been developed for the strain-driven formation of the C-heteroatom bond, leading to a new approach to conformationally rigid bridgehead heteroquaternary carbons. The present unified strategy provides a scenario for the divergent total syntheses of nine natural Lycopodium alkaloids and four unnatural C12 epimers, wherein (±)-lycojaponicumin D and six lycodoline-type alkaloids have been synthetically achieved for the first time.