Intramolecular Addition of 2-(Trimethylsilyl)methyl-substituted Alkyl Cations to Double Bonds–Synthesis of Bicyclo[3.3.0]octane Derivatives^†‡

The title reaction, a transformation that theoretically should be difficult, has been successfully carried out. The exploitation of two “β effects” was crucial: β-silicon stabilizes the intermediate allyl cation and two geminal methyl groups in the β position control the course of the reaction. An example is the transformation of 1 into 2, which is converted into 3 under acid catalysis.