The stereochemistry of the reaction of phosphonous and phosphinous halides with 1,3-dienes

Abstract

Buta-1,3-diene reacts with dimethylphosphinous chloride (Me₂PCl) to give the crystalline phosphonium salt 1,1-dimethylphosphol-3-en chloride. 1,1,2,5-Tetramethylphosphol-3-en chloride is formed stereospecifically by the reaction of trans,trans-hexa-2,4-diene with dimethylphosphinous chloride; ¹H n.m.r. studies on the phosphol-3-en and on the derived 3,4-dibromophospholan established the stereochemistry. trans,trans-Hexa-2,4-diene also reacts stereospecifically with methylphosphonous dichloride (MePCl₂). The reaction of the initial adduct with water and sulphur dioxide has been examined. The mechanism of the reaction of phosphonous and phosphinous halides with 1,3-dienes is discussed in the light of the stereochemical observations.