Morita-Baylis-Hillman reaction solvent effects

In a different study, based on the reaction rate data collected in aprotic solvents, the Morita-Baylis-Hillman reaction has been found to be second order in aldehyde and first order in DABCO and acrylate. On the basis of these data, a new mechanism has been proposed, involving a hemiacetal intermediate (110). The proposed mechanism is further supported by two different kinetic isotope effect experiments.145... 

The kinetics of the aza-Morita-Baylis-Hillman reaction have been studied for a range of imine substrates in various solvents, using triphenylphosphine as catalyst, and p-nitrophenol as a Brpnsted acid co-catalyst. The effects of varying the phosphineiphenol catalyst ratio on the rate indicate interdependence between them. This and the solvent effects support reversible protonation of zwitterionic intermediates within the mechanism. ip-NMR and quantum calculations also support such a route. 

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