Reaction of ketene and [dimethyl(phenyl)silyl]ketene with the aminoxyl radical TEMPO: preparative, kinetic, and theoretical studies of unreactive ketenes

Abstract

Ketenes CH2=C=O (1) and PhMe2SiCH=C=O (12) react with tetramethylpiperidinyloxyl (TEMPO, TO•) forming the products RCH(OT)CO2T resulting from addition of one TEMPO radical to the carbonyl carbon and a second to the resulting radical. The rate constants estimated for TEMPO addition are the lowest so far determined for addition to ketenes, and together with previous results give a qualitative correlation of log k2(TEMPO) = 1.20 log k(H2O) –4.45, r = 0.94 for the rate constants for hydration and for TEMPO reaction of the same ketenes. Computations using DFT methods for the reactions of CH2=C=O (1) and H3SiCH=C=O with aminoxyl radicals are in agreement with the observed relative reactivities and selectivities.