THE ENANTIOSELECTIVE SYNTHESIS OF (-)-PHYSOSTIGMINE VIA CHIRAL SULFOXIDES

The total synthesis of naturally occurring (-)-physostigmine is described. The key element for the asymmetric induction is the chirality transfer from optically active 2-(alkylsulfinyl)indoles to indoline butyrolactones bearing two chiral centers. Novel features of this synthesis involve the use of a new class of sulfoxylating agents, N-(alkylsulfinyl)oxazolidinones, to prepare the starting indolyl sulfoxides and the correlation of the size of the alkyl group on the sulfoxide with the degree of asymmetric induction. The overall synthesis requires a dozen steps from commercially available 5-(benzyloxy)indole.