[1,4]-SPh shift cyclisations or [1,2]-SPh-cyclisations as alternative cascade sequences for stereocontrolled synthesis of substituted tetrahydrofurans

Treatment of 4-phenylsulfanyl-1,5,7-triols with TsCl in pyridine gives subs tituted tetrahydrofurans by [1,4]-SPh participation via a five membered sul fonium salt and then capture by a tethered nucleophile. Acid catalysed rear rangement gives other THFs by [1,2]-SPh migration and cyclisations.