In comparison to the popular pathway involving proton-transfer via a
four-centred cyclic transition state structure, the recently proposed overall lower
energy pathway involving proton-transfer via a seven-centred cyclic transition
state structure followed by Hofmann elimination for the Me<sub>3</sub>N-catalyzed
Morita-Baylis-Hillman reaction is applicable to the DABCO-catalyzed reaction equally
well. This finding clearly establishes that the zwitterion at the bridge-head
in DABCO is well tolerated. Also, the activation free energy of the
rate-limiting aldol reaction under DABCO-catalysis is lower than that under Me<sub>3</sub>N-catalysis,
suggesting that DABCO is likely a better catalyst to achieve faster conversion.
