Synthesis of diethyl alkoxymethylphosphonates via Lewis acid promoted regiospecific cleavage of alkoxy-4-chlorophenoxymethanes

Abstract

Alkoxy-4-chlorophenoxymethanes, readily prepared from 1-chloro-4-chloromethoxybenzene and sodium alkoxide, generate alkoxymethyltriethoxyphosphonium ions in a regiospecific reaction with triethyl phosphite and titanium tetrachloride or boron trifluoride. Precise reaction conditions are necessary since the phosphonium ions can undergo disproportionation. Subsequent addition of water gives diethyl alkoxymethylphosphonates; if disproportionation has been permitted these contain 4-chlorophenyl ethyl alkoxymethylphosphonates. Under the preferred conditions (titanium tetrachloride, –78 °C, 15 min, dichloromethane) yields of ca. 80% of diethyl alkoxymethylphosphonates have been obtained from primary, secondary, tertiary, and allylic alcohols.