Stereoselective synthesis of (3R*,3aS*,7aS*)-3-aryloctahydroindol-2-ones using radical cyclisation: a formal synthesis of (±)-pancracine

Abstract

The Bu₃SnH- or (TMS)₃SiH-mediated 5-endo-trig radical cyclisation of the N-(cyclohex-1-enyl)acetamide 10 gives a mixture of the cis-fused (3R*,3aS*,7aS*)- and trans-fused (3R*,3aS*,7aR*)-3-aryloctahydroindol-2-ones 11a and 11b, whereas the 5-exo-trig radical cyclisation of the N-(cyclohex-2-enyl)acetamide 17 proceeds in a stereoselective manner to give only 11a. The latter method has been applied to the synthesis of the 5,11-methanomorphanthridine derivative 30, a key intermediate for the synthesis of (±)-pancracine 1.