Can Acyl Transfer Occur by a Concerted Mechanism? Direct Evidence from Heavy-Atom Isotope Effects
Journal of the American Chemical Society
Nucleophilic acyl-transfer reactions most often occur by way of a two-step mechanism with a tetrahedral intermediate, described in the IUPAC system1 as AN + DN. Acyl halides can react through an acylium ion intermediate by an SN1 (DN + AN) mechanism.2 There has been interest in the question of whether ester acyl transfers can proceed by a concerted SN2 (ANDN) pathway.3 On the basis of structure-reactivity studies, Williams et al. proposed that the reaction of phenoxide anions with p-nitrophenyl acetate proceeds by such a concerted pathway,4a and they proposed a theory predicting when ester acyl transfers will be concerted and when they will go by the limiting stepwise mechanisms.5 These conclusions have been challenged.6 Recently, theoretical arguments have been presented in support of a concerted mechanism in reactions of aryl acetates with phenoxide anions.7
A. C. Hengge. “Can Acyl Transfer Occur by a Concerted Mechanism? Direct Evidence from Heavy Atom Isotope Effects.” J. Am. Chem. Soc.1992, 114, 6575-6576.