A Synthetic Strategy for Polyfunctionalized Bicyclo[3.3.1]nonanes Based on a Tandem Three-Component [3+2] Cycloaddition of α-Cinnamoyl Ketene-S,S-acetals with Oxalyl Chloride

A simple and highly efficient three-component reaction of the readily available alpha-cinnamoyl ketene-S,S-acetals 1 with oxalyl chloride has been developed and the corresponding gamma-alkylidenebutenolides 2 were obtained stereospecifically in excellent yields under very mild conditions. On the basis of this reaction, a series of highly functionalized bicyclo[3.3.1]nonanes 3 were constructed in good to high yields in an atom-economic manner with good diastereoselectivity via a BF(3)center dot OEt(2)-mediated novel tandem double cyclization of gamma-alkylidenebutenolides 2 under very mild conditions.