Synthesis of vinca alakaloids and realated compounds 98. Oxidation with dimethyldioxirane of compounds containing the aspidospermane and quebrachamine ring system. A simple synthesis of (7S,20S)‐(+)‐rhazidigenine and (2R,7S,20S)‐(+)‐rhazidine

The oxidation of (‐)‐tabersonine (1) with dimethyldioxirane (DMD) in neutral and acidic medium gave 16‐hydroxytabersonine‐N‐oxide (3) and the didehydrovincamine isomers 4 and 5, respectively. (+)‐14,15‐Didehydro‐quebrachamine (7) furnished the hydroxyindolenine 9, and the pentacyclic derivative 11. (+)‐Quebrachamine (8) and DMD in neutral medium gave (7S,20S)‐(+)‐rhazidigenine (12) which was converted to (2R,7S,20S)‐(+)‐rhazidine (13b) with hydrochloric acid.