Formation of ethyl 1,5-dideoxy-5-ethylthio-1-mercapto-α- and -β-L-arabinofuranosides by an intramolecular displacement of 5-O-toluene-p-sulphonyl-L-arabinose diethyl dithioacetal

Abstract

On heating an aqueous acetone solution of 5-O-toluene-p-sulphony-L-arabinose diethyl dithioacetal in the presence of an acid acceptor two anomeric ethyl 1,5-dideoxy-5-ethylthio-1-mercapto-α- and -β-L-arabinofuranosides were formed, the structures of which have been confirmed by conversion into, and synthesis of the β-anomer from, the known 5-deoxy-5-ethylthio-L-arabinose diethyl dithioacetal. We suggest that the reaction proceeds via an intramolecular displacement leading to an intermediate cyclic sulphonium ion.