MAP-based multifunctional organocatalysts for asymmetric aza- and generic Morita–Baylis–Hillman reactions

MAP-based trifunctional organocatalysts, containing a phosphine Lewis base, amino Brønsted base, and phenol or N-tosyl Brønsted acid, have demonstrated highly proficient catalysis of asymmetric aza-MBH reactions with an acid additive. The phosphine nucleophile (Lewis base) initiates the aza-MBH reaction by addition to an activated alkene (e.g. MVK). The Brønsted base, activated by the acid additive, in conjunction with the Brønsted acid, promotes the subsequent aldol and proton-transfer elimination steps by H-bonding interactions to provide high rate and enantioselectivity. However, the reaction scope of this catalysis is limited to aza-MBH and not amenable to generic MBH reactions. In order to improve the proficiency and expand the substrate scope, new Brønsted acid motifs, such as substituted phenol, N-tosyl and pyrrole groups, were incorporated into the MAP-structure for testing in aza-MBH and generic MBH reactions. Change of Brønsted acidity in the phenol- and N-tosyl-containing catalysts did not improve on catalytic proficiency while pyrrole-containing catalysts provided the improvement in enantioselectivity in generic MBH reactions.