Abstract
The syntheses of a series of CpW(CO) 2 (π-γ-lactonyl) complexes bearing a tethered aldehyde are described. These π-allyl complexes are prepared as either syn- or anti-stereoisomers. Treatment of these dicarbonyl complexes with NOBF 4 and NaI in CH 3 CN effects an intramolecular allylation of the tethered aidehyde, yielding bicyclic α-methylene butyrolactones comprising a homoallylic alcohol. Both syn- and anti-isomers of tungsten-π-allyl compounds produce the same α-methylene butyrolactones. The cyclizations proceed with high diastereoselectivities to give only the cis-fused bicyclic γ-lactones. The preference for cis-fused stereoselection can be rationalized based on a tricyclic transition state mechanism.