AN EFFICIENT APPROACH TOWARD PYRROLIDINYLLACTONE SYSTEM CHARACTERISTIC OF THE STEMONA ALKALOIDS - LEWIS-ACID CATALYZED STEREOSELECTIVE REACTION OF N-BENZYLOXYCARBONYL-2-METHOXYPYRROLIDINE WITH 3-METHYL-2-TRIMETHYLSILYLOXYFURAN
Pyrrolidinyllactone system 7, common partial structure presented in most Stemona alkaloids, was stereoselectively prepared by two-step sequence: i) syn-selective condensation of N-benzyloxycarbonyl-2-methoxypyrrolidine (8) with 3-methyl-2-trimethylsilyloxyfuran (9) catalyzed by Lewis acids: ii) diastereoselective hydrogenation of the product 10 (NaBH4, NiCl2/MeOH).