Manifestation of Polar Reaction Pathways of 2,3-Dichloro-5,6-dicyano‑<i>p</i>‑benzoquinone

Abstract

Reactions of 2,3-dichloro-5,6-dicyano-<i>p</i>-benzoquinone (DDQ) with silyl enol ethers, silyl ketene acetals, allylsilanes, enamino esters, and diazomethanes have been studied in CH₃CN and CH₂Cl₂ solutions. The second-order rate constants for C attack at DDQ (log <i>k</i>_C) correlate linearly with the nucleophile-specific parameters <i>N</i> and <i>s</i>_N and are 2–5 orders of magnitude larger than expected for SET processes, which strongly supports the polar mechanism for C–C bond formation. The second-order rate constants for O attack agree well with the calculated rate constants for rate-determining single electron transfer (SET). As a radical clock experiment ruled out outer sphere electron transfer, an inner sphere electron transfer mechanism is suggested for O attack