Photocyclisation of enamides. Part 27. Total syntheses of (±)-yohimbine, (±)-alloyohimbine, and (±)-19,20-didehydroyohimbines

Abstract

Total syntheses of five indole alkaloids, (±)-yohimbine (10), (±)-alloyohimbine (11), and three (±)-19,20-didehydroyohimbines (15a, b, and c)(for the first time) were completed from a single common key intermediate (4)via a route involving the stereoselective isomerisation of the double bond of (4) followed by regioselective functionalisation of the enones (5a and b).