I. LEWIS BASE-CATALYZED ALDOL REACTION IN THE TOTAL SYNTHESIS OF ERYTHRONOLIDE B; II. EFFORTS TOWARDS THE TOTAL SYNTHESIS OF AMPHIDINOLIDE H

Lewis base (trimethylsilylquinine and trimethylsilylquinidine) catalyzed acyl halide-aldehyde cyclocondensation (AAC) reactions have been developed to prepare synthetically important bispropionate units previously by the Nelson group. A new Lewis base-catalyzed diastereoselective Mukaiyama aldol reaction has extended this bispropionate unit preparation methodology to all-syn bispropionates which widely occurred in polypropionate natural products. By using phenoxides as Lewis base catalysts, enol silanes were activated and underwent a Felkin attack on an aldehyde through an antiperiplanar transition state to generate all-syn bispropionate product in high yields and excellent diastereoselectivities.All-syn bispropionate prepared from the Lewis base-catalyzed diastereoselective Mukaiyama aldol reaction has been untilized in natural product synthesis of erythronolide B establishing ¡°syn,syn,syn¡± stereochemical relationships from C2-C5.Studies towards the total synthesis of the cytotoxic marine macrolide amphidinolide H have been disclosed. By exploiting AAC methodology, several key stereochemical relationships present in major fragments 198 and 199 were established. A highly enantioselective synthesis of methyl ketone 200 was realized from commercially available (S)-(−)-glycidol. Iodide 198 was coupled with boronic ester 199 via an efficient Suzuki reaction to form a C7-C20 fragment.