A novel asymmetric vinylogous tin-Pummerer rearrangement.

A new type of vinylogous tin-Pummerer rearrangement reaction was observed when benzyl tin derivatives containing a sulfinyl group at the ortho position were allowed to react with acyl chlorides or TFAA. The reaction is thought to proceed by nucleophilic attack of the leaving carboxylate at the gamma-position of the conjugated thionium ion. The enantioselectivity (ee) of the reaction can reach values as high as 98%. The observed stereoselectivity is related to the nature of the solvent, the temperature employed, and the stability of the migrating carboxylate anion. [reaction--see text]