Bifunctional primary amine-thiourea-TfOH (BPAT center dot TfOH) as a chiral phase-transfer catalyst: the asymmetric synthesis of dihydropyrimidines

An enantioselective Biginelli reaction has been developed by using a bifunctional primary amine-thiourea-TfOH (BPAT center dot TfOH) as a chiral phase-transfer catalyst and t-BuNH(2)center dot TFA as an additive in saturated brine at room temperature. The corresponding dihydropyrimidines were obtained in moderate-to-good yields with up to 99% ee under mild conditions. A plausible transition state has been proposed to explain the origin of the activation and the asymmetric induction.