Stereospecific synthesis of two epimeric 2-chlorodeoxy pentoses involving anomeric chlorine participation

Abstract

A simple procedure has been developed for the stereospecific synthesis of some 2-chloro-2-deoxy pentoses. Treatment of P-D-xylopyranosyl chloride 2,3,4-tri(ch1orosulfate) with aluminum chloride (> 1 mole equivalent) resulted in specific chloro-displacement of the C-2 chlorosulfate group via a mechanism involving anomeric chlorine migration, which occurred to the extent of almost 100%. The resultant crystalline 2-chloro-2-deoxy-a-D-lyxopyranosyl chloride 3,4-di(chlorosulfate) when treated with sodium iodide yielded crystalline 2-chloro-2-deoxy-D-lyxose. Similarly a-D-lyxpoyranosyl chloride 2,3,4-tri(chlorosulfate) yielded 2-chloro-2-deoxy-a-D-xylopyranosyl chloride 3,4-di(chlorosulfate) from which pure 2-chloro-2-deoxy-D-xylose was obtained by a modified procedure. The structures of these compounds have been confirmed and the mechanism is discussed.