Synthetic approach to (±)-vincamine via cleavage of an α-diketone monothioacetal. Alternative synthesis of (±)-eburnamine, (±)-isoeburnamine, and (±)-eburnamenine

Abstract

The half ester (8) prepared from cleavage of 2-(1,3-dithian-2-yl)-4-ethoxycarbonyl-4-ethylcyclohexanone (7) has been converted into (±)-eburnamine (20), (±)-isoeburnamine (21), and (±)-eburnamenine (22) by a stereospecific reaction sequence proceeding via the dithian intermediate (16). However an attempted conversion of (16) into (±)-vincamine (6) was unsuccessful.