Abstract
We have been investigating the proline catalyzed Mannich-type reaction of cyclic imines and found that the reaction of 3,4-dihydro-beta-carboline with acetone or 3-ethyl-3-buten-2-one catalyzed by proline afforded corresponding 1-substituted-3,4-dihydro-beta-carboline in a high yield with a high enantioselectivity. As an application of this method to the synthesis of natural products, total syntheses of dihydrocorynantheine, isorhynchophylline and deserpidine were investigated, and formal total syntheses of dihydrocorynantheine and isorhynchophylline were achieved. Our synthetic feature of deserpidine is that C ring is formed prior to construction of the D and E rings, and the synthesis is now under investigation using optically active 1-acetonyl-3,4-dihydro-beta-carboline obtained by the present method.
