Abstract
The tungsten-η <sup>3</sup> -2-substituted pentadienyl complexes WC <sub>5</sub> H <sub>5</sub> (CO) <sub>2</sub> (syn-η <sup>3</sup> -R-C <sub>5</sub> H <sub>6</sub> ) (R = COOMe; CMe=CH <sub>2</sub> ) undergo BF <sub>3</sub> -catalysed stereoselective carbon-carbon bond formation with aldehydes to afford isolable s-trans-diene cations which after hydrolysis produces tungsten-η <sup>3</sup> -allyl-1,3-diols; utilization of the diols for stereoselective synthesis of α-methylene-γ-butyrolactones, furanone skeletons, have been reported in good yields (> 80%).