Stereocontrolled Synthesis of Functionalized Bicyclic α-Methylene Butyrolactones via Tungsten-Mediated Intramolecular Allylation of Aldehydes

[[abstract]]The syntheses of a series of CpW(CO)(2)(pi-gamma-lactonyl) complexes bearing a tethered aldehyde are described. These pi-allyl complexes are prepared as either syn- or anti-stereoisomers. Treatment of these dicarbonyl complexes with NOBF4 and NaI in CH3CN effects an intramolecular allylation of the tethered aldehyde, yielding bicyclic alpha-methylene butyrolactones comprising a homoallylic alcohol. Both syn- and anti-isomers of tungsten-pi-allyl compounds produce the same alpha-methylene butyrolactones. The cyclizations proceed with high diastereoselectivities to give only the cis-fused bicyclic gamma-lactones. The preference for cis-fused stereoselection can be rationalized based on a tricyclic transition state mechanism.[[fileno]]2010327010093[[department]]化學