Asymmetric synthesis of tetrahydrofurans and tetrahydropyrans with competitive [1,2]-phenylsulfanyl (PhS) migration (II): synthesis of protected tetrahydropyrans

Enantiomerically enriched triols were treated with trimethylorthoacetate an d pyridinium toluene p-sulfonate to give a mixture of unrearranged THF and rearranged THP; treatment of the product mixture with toluene p-sulfonic ac id equilibrated the mixture to the THP.