A stereochemical test for ether-oxygen participation and oxonium ion formation in the acetolysis of 3-tetrahydropyranyl brosylate

Optically active tetrahydropyran-3-ol was obtained by the horse liver alcohol dehydrogenase (HLADH)-catalysed reduction of tetrahydropyran-3-one, and the corresponding brosylate was prepared. Acetolysis of the optically active brosylate gave racemic 3-tetrahydropyranyl acetate as well as varying amounts of racemic tetrahydropyran-3-ol. Within experimental error, the polarimetric rate of acetolysis was the same as the previously measured titrimetric rate. The results provide no support for the intermediacy of a bicyclic oxonium ion in the acetolysis of 3-tetrahydropyranyl brosylate.