Highly enantioselective organocatalytic Biginelli reaction.
A series of binol- and H8-binol-based phosphoric acids have for the first time been evaluated for their ability to catalyze Biginelli reactions of aldehydes, thiourea or urea, and beta-keto esters. A new chiral phosphoric acid, derived from 3,3'-diphenyl-H8-binol, exhibited superior catalytic activity and enantioselectivity compared to its structural analogues, affording high enantioselectivities ranging from 85 to 97% ee with a wide scope of substrates. A metal-free preparation of optically active monastrol was achieved on the basis of the current process.
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