A Formal [3 + 3] Cycloaddition Approach to Natural-Product Synthesis

摘要

A formal [3 + 3] Cycloaddition strategy for constructing complex heterocycles is reviewed here.This formal Cycloaddition involves condensation of alpha,beta-unsaturated iminium salts with 1,3-dicarbonyl equivalents.These reactions consist of a Knoevenagel-type condensation followed by a reversible 671-electron electrocyclic ring-closure.They constitute a step-wise formal [3 + 3] Cycloaddition protocol with the net result being the formation of two sigma-bonds in addition to a new stereocenter adjacent to the heteroatom.This review describes in some detail,but not comprehensively,some precedents,problems,solutions,and stereochemical mechanistic issues,and focuses on applications of this formal Cycloaddition strategy in natural product synthesis.