Enantioselective Conversion of Primary Alcohols to α-<i>exo</i>-Methylene γ-Butyrolactones via Iridium-Catalyzed C–C Bond-Forming Transfer Hydrogenation: 2-(Alkoxycarbonyl)allylation
作者:T. Patrick Montgomery、Abbas Hassan、Boyoung Y. Park、Michael J. Krische
DOI:10.1021/ja303839h
日期:2012.7.11
Upon exposure of acrylic ester 1 to alcohols 2a-i in the presence of a cyclometalated iridium catalyst modified by (-)-TMBTP, catalytic C-C coupling occurs, providing enantiomerically enriched 5-substituted α-exo-methylene γ-butyrolactones 3a-i. Bromination of the methylene butyrolactone products followed by zinc-mediated reductive aldehyde addition provides the disubstituted α-exo-methylene γ-butyrolactones
obtained via a two-step sequence consisting of a highly enantioselective chromium-catalyzed carbonyl 2-(alkoxycarbonyl)allylation and lactonization. A variety of functional groups are compatible under the mild reaction conditions. The synthetic utility of this methodology was demonstrated by two short derivatization transformations and the enantioselective synthesis of (+)-methylenolactocin.