Synthesis of Aristotelia‐type alkaloids. Part VII. Syntheses of (±)‐sorelline, (±)‐serratenone, and (±)‐aristotelin‐19‐one

Abstract

AbstractThe imine obtained by condensing indole‐protected 2‐(indol‐3‐yl)acetaldehyde (5) with the terpinylamine derivative (±)‐4 was cyclized in 51% yield to the 19‐substituted hobartine derivative (±)‐20 upon exposure to anhydrous HCOOH. This pivotal intermediate was further elaborated into the indole alkaloids (±)‐serratenone ((±)‐22) and (±)‐sorelline ((±)‐29). In the course of these investigations, a novel rearrangement was uncovered; a Lewis acid‐catalyzed 1,3‐migration of an arylsulfonyl group from the indole N‐atom into the benzene ring. The discovery that synthetic (±)‐aristotelin‐19‐one ((±)‐34) has decidedly different spectroscopic properties than aristolasicone, a metabolite for which the structure has been recently proposed, led to a revision of the structure of the latter.