Enantioselective Oxidative (4+3) Cycloadditions between Allenamides and Furans through Bifunctional Hydrogen-Bonding/Ion-Pairing Interactions.

Abstract

BINOL-based N-trifluoromethanesulfonyl phosphoramides catalyze the enantioselective (4+3) cycloaddition between furans and oxyallyl cations, the latter being generated in situ by oxidation of allenamides. The chiral organic phosphoramide counteranion is proposed to engage in the activation of the oxyallyl cation intermediate through cooperative hydrogen-bonding and ion-pairing interactions, enabling an efficient chirality transfer that provide the final adducts with high diastereo- and enantioselectivities. Remarkably, the reaction shows a wide substrate scope that includes a variety of substituted allenamides and furans.