Organophosphorus compounds. X. A new synthesis of 1,2,3,4-tetrahydrophosphinolines

Abstract

A new synthesis of the 1,2,3,4-tetrahydrophosphinoline ring is described. Reaction of 3-phenyl- propylphosphonous dichloride with zinc chloride at 170º followed by hydrolysis with hot concentrated hydrochloric acid, then oxidation with bromine, gave 91% of 1-hydroxy-1,2,3,4-tetrahydrophosphinoline 1-oxide (20b). Under conditions where oxidation was incomplete, 1,2,3,4-tetrahydrophosphinoline 1-oxide was isolated. On a small scale the reaction of 3-phenylpropylphosphonous dichloride with a catalytic amount of aluminium chloride at 220º gave 60% of l-chloro- 1,2,3,4-tetrahydrophosphinoline (18). Treatment of (20b) with thionyl chloride gave 1-chloro-1,2,3,4-tetrahydrophosphinoline 1-oxide which, upon reaction with the appropriate Grignard reagent, afforded 1-ethyl or 1-phenyl-1,2,3,4- tetrahydrophosphinoline 1-oxide. 1-Ethyl-1,2,3,4-tetrahydrophosphinoline 1-oxide was reduced with trichlorosilane to the phosphine, which upon reaction with sulphur yielded the corresponding phosphine sulphide. The methyl and ethyl esters of (20b) are described.