New homologation of 2-hydroxy and 2-mercapto benzylic alcohols

Abstract

The reaction of benzo-1,3-dioxanes or benzo-1,3-oxathianes 1 [easily prepared from 2-hydroxy or 2-mercapto benzylic alcohols ( 3 or 4, respectively) and carbonyl compounds] with an excess of lithium and a catalytic amount of DTBB (4.5 mol %) in THF at room temperature or −78°C leads, after hydrolysis with water, to the corresponding homobenzylic alcohols 2. Cyclisation of compounds 2 under acidic (85% H 3PO 4) or neutral (Ph 3P/DIAD) conditions affords the expected heterocycles 5.