thiourea and 3-nitrobenzenesulfonic-acid

Cationic organic intermediates participate in a wide variety of useful synthetic transformations, but their high reactivity can render selectivity in competing pathways difficult to control. Here, we describe a strategy for inducing enantioselectivity in reactions of protio-iminium ions, wherein a chiral catalyst interacts with the highly reactive intermediate through a network of noncovalent interactions. This interaction leads to an attenuation of the reactivity of the iminium ion and allows high enantioselectivity in cycloadditions with electron-rich alkenes (the Povarov reaction). A detailed experimental and computational analysis of this catalyst system has revealed the precise nature of the catalyst-substrate interactions and the likely basis for enantioinduction.

Topics: Acids; Alkenes; Benzenesulfonates; Catalysis; Chemical Phenomena; Imines; Magnetic Resonance Spectroscopy; Protons; Stereoisomerism; Thiourea; Urea