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.