Synthesis and Characterization of Novel Quinone Methides: Reference Electrophiles for the Construction of Nucleophilicity Scales

Novel synthetic routes to the aryl-substituted quinone methides 3a-f have been developed, and a previously reported Mannich approach has been used for the syntheses of the acceptor substituted quinone methides 2e-g. The second-order rate constants for the reactions of R4 and 2e-g with the carbanions 9a-h were determined photometrically in DMSO. With Equation (1), log k(2) = s (N + E), and the known nucleophilicity parameters N and s for the carbanions 9a-h, it was possible to calculate the electrophilicity parameters E for these quinone methides. With E parameters between -12 and -17, these readily accessible quinone methides are recommended as reference electrophiles for the construction of nucleophilicity scales. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)