Electrophilic Reactivities of Azodicarboxylates

The kinetics of the reactions of the azodicarboxylates 1 with the enamines 2 have been studied in CH3CN at 20 degrees C. The reactions follow a second-order rate law and can be described by the linear free energy relationship log k(2)(20 degrees C)=s(N-+-E) (E=electrophilicity parameter, N=nucleophilicity parameter, and s=nucleophile-specific slope parameter). With E parameters from -12.2 to -8.9, the electrophilic reactivities of 1 turned out to be comparable to those of alpha,beta-unsaturated iminium ions, amino-substituted benzhydrylium ions, and ordinary Michael acceptors. While the E parameters of the azodicarboxylates 1 determined in this work also hold for their reactions with triarylphosphines, they cannot be used for estimating rate constants for their reactions with amines. Comparison of experimental and calculated rate constants for cycloadditions and ene reactions of azodicarboxylates provides information on the concertedness of these reactions.