A DFT Perspective on Diels-Alder Organocatalysts Based on Substituted Phosphoramides

Abstract

Phosphoramides are an interesting alternative to the thiourea motif that has long been used in organocatalysis. In the R1N(H)-P(O)(R3)-N(H)R2 formulation, phosphoramides give the advantage of having a third variable substituent, R3, compared to the two available in thioureas, and the possibility of introducing chirality with an asymmetric phosphorous center. In this work, we present a systematic computational study on the catalytic properties of these underexplored compounds. These studies show the catalytic potential of a series of substituted phosphoramides in Diels-Alder reactions, including the asymmetric [4+2] cycloaddition of pro-chiral substrates. The nature of the phosphorous-bound R3 substituent has a significant impact both on catalytic activity and enantioselectivity. Remarkably, several of the phosphoramides studied are predicted to be more active than the Schreiner’s thiourea organocatalyst.