Reexamination of the traditional Baylis–Hillman reaction

Alternative energy input: mechanochemical, microwave and ultrasound-assisted organic synthesis

Microwave, ultrasound, sunlight and mechanochemical mixing can be used to augment conventional laboratory techniques. By applying these alternative means of activation, a number of chemical transformations have been achieved thereby improving many existing protocols with superior results when compared to reactions performed under traditional conditions. The purpose of this critical review is to highlight the advances in this general area by presenting such newer applications in organic synthesis (175 references).

Computational investigation on the mechanism and the stereoselectivity of Morita-Baylis-Hillman reaction and the effect of the bifunctional catalyst N-methylprolinol

The mechanism of the Morita-Baylis-Hillman (MBH) reaction between formaldehyde and methyl vinyl ketone (MVK) catalyzed by N-methylprolinol was investigated using density functional theory (DFT) method. The overall reaction includes two steps: C-C bond formation and hydrogen migration. In the presence of water, the hydrogen migration occurs via a six-membered ring transition state and the corresponding energy barrier decreases dramatically, and therefore the RDS is the C-C bond formation step. The calculations indicate that the C-C bond formation step controls the stereochemistry of the reaction. In this step, the hydrogen bonding induces the direction of the attack of enamine to aldehyde from the -OH group side of N-methylprolinol. The energy-favored transition states are mainly stabilized by hydrogen bonding, while the chirality of the products is affected by the hydrogen bonding and the steric hindrance. The calculations correctly reproduce the major product in (R)-configuration, which is consistent with the experimental observation.

The Baylis–Hillman approach to quinoline derivatives

Baylis-Hillman reactions of 2-nitrobenzaldehydes with various activated alkenes afford adducts that undergo reductive cyclisation to quinoline derivatives. The chemo- and regioselectivity of cyclisation appears to be influenced by the choice of both the substrate and the reagent system, and competing reactions have been observed.