Nucleophilic substitution in benzylic thiophosphinyl and thiophosphonyl chlorides: the contribution of elimination–addition pathways with methylenethioxophosphorane (thiophosphene) intermediates

Abstract

For the reactions of ArCH₂P(S)(Ph)Cl and ArCH₂P(S)(NMe₂)Cl with Et₂NH, changing ArCH₂ from benzyl to 4-nitrobenzyl increases the rates of substitution by factors of 80 and > 10³, respectively, and reduces markedly the ability to discriminate between competing Et₂NH and Me₂NH nucleophiles. With Et₂ND, the nitrobenzyl substrates give products that contain deuterium in the benzylic methylene group. These observations point to substitution by elimination–addition, with a three-coordinate methylenethioxophosphorane (thiophosphene) intermediate, for the nitrobenzyl compounds.