Acyclic stereoselection. 19. Total synthesis of (±)-ristosamine and (±)-megalosamine.

Abstract

(±)-Ristosamine ( 1) has been synthesized in seven straightforward operations from ketone 5 and O-benzyllactaldehyde. The key step is a stereoselective aldol addition reaction in which diastereomeric aldols 7 and 8 are produced in a ratio of 78:22. A simple modification of the synthesis provides (±)-megalosamine ( 4.