Grant S. Buchanan, John B. Feltenberger and Richard P. Hsung Pages 363 - 401 ( 39 )
An aza-[3 + 3] annulation or formal cycloaddition strategy for constructing complex heterocycles, chiefly alkaloids, is reviewed here. This annulation involves a Knoevenagel-type condensation of α,β-unsaturated iminium salts with vinylogous amides or urethanes followed by a 6π-electron electrocyclic ring-closure. Both the inter- and intramolecular aza-annulation pathways illustrated here constitute a stepwise formal [3 + 3] cycloaddition in which two -bonds are formed in addition to a new stereogenic center adjacent to the heteroatom. This review describes our total synthesis efforts in the last ten years to unequivocally demonstrate that this aza-[3 + 3] annulation can serve as a powerful approach and a unified strategy in alkaloid synthesis.
Alkaloid synthesis, Aza-[3 + 3] annulation, Formal cycloaddition, Heterocycle, A unified synthetic strategy
Division of Pharmaceutical Sciences and Department of Chemistry, University of Wisconsin, Madison, WI 53705, USA.