asymmetric conjugate addition of t-butyl nitroacetate to o-quinone methides : synthesis of optically active a-nitro-b , b-diaryl-propionates †

1 1a 83 1/1 95/95 2 1b 76 1/1 96/96 3 1c 68 1/1 95/95 4 1d 69 1/1 95/96 5 1e 61 1/1 85/84 o-Quinone methides (o-QMs) are valuable intermediates for organic synthesis. Although most o-QMs are unstable and inseparable, applications of o-QMs in organic synthesis have been developed. In recent years, great progress has been made in asymmetric reactions with o-QMs. A number of organocatalytic transformations with o-QMs have also been explored. Han and co-workers reported the quinine-catalyzed asymmetric cycloannulation of o-QMs with malononitrile. Zhou and coworkers reported asymmetric addition of thiols and malononitrile to o-QMs with bifunctional organocatalysis. Fochi, Bernardi and co-workers developed chiral squamide-catalyzed asymmetric addition of Meldrum's acid, malononitrile and 1,3dicarbonyl compounds to o-QMs. Sun, Rueping, Schneider, Shi, List and co-workers reported a series of asymmetric reactions of o-QMs with chiral Brønsted acid catalysts. Ye and coworkers developed asymmetric reactions of o-QMs catalyzed by chiral nitrogen heterocyclic carbenes. Very recently, Scheidt and co-workers reviewed the related progresses of organocatalytic reactions of in situ generated o-QMs. In recent years, we have developed organocatalytic asymmetric conjugate addition of nitroacetates to b,g-unsaturated-aketoesters. To expand the application of nitroacetates in organocatalytic transformations, we are interesting in the asymmetric conjugate addition of nitroacetates to o-QMs. The reaction can provide optically active a-nitro-b,b-diaryl-propionates, which are useful intermediates for the synthesis of chiral drugs and natural products. In this paper, we report an organocatalytic conjugate addition of t-butyl nitroacetate to in situ generated