Novel bifunctional thiourea–ammonium salt catalysts derived from amino acids: application to highly enantio- and diastereoselective aza-Henry reaction

The development of new efficient and easily accessible catalysts has been one of the focuses in asymmetric phase-transfer catalysis. In this paper, a novel class of chiral bifunctional thiourea–ammonium phase-transfer catalysts were synthesized from commercially available α-amino acids. The structural modularity of these catalysts permits facile tunings to achieve optimum results, which was demonstrated in catalyzing the aza-Henry reaction with excellent enantioselectivities (up to 99.5% ee) and diastereoselectivities (up to >25:1 dr).