Cycloaddition of primary phosphines to divinyl sulfide

Primary phosphines reacted with divinyl sulfide under radical initiation conditions (AIBN, 65–70°C, reactant molar ratio 1:1) according to the addition-cyclization pattern to give 4-substituted 1,4-thiaphosphinanes which underwent almost quantitative oxidation with oxygen or elemental sulfur, yielding the corresponding 4-substituted 1,4-thiaphosphinane oxides (sulfides). The reaction of 4-(2-phenylethyl)-1,4-thiaphosphinane with methyl iodide afforded 4-methyl-4-(2-phenylethyl)-1,4-thiaphosphinanium iodide with high chemoselectivity.