A new approach to the utilization of highly reactive and unstable ortho-quinone methides (o-QMs) in catalytic asymmetric settings is presented. The enantioselective reactions are catalysed by bifunctional organocatalysts, and the o-QM intermediates are formed in situ from 2-sulfonylalkyl phenols through base-promoted elimination of sulfinic acid. The use of mild Brønsted basic conditions for transiently generating o-QMs in catalytic asymmetric processes is unprecedented, and allows engaging productively in the reactions nucleophiles such as Meldrum's acid, malononitrile and 1,3-dicarbonyls. The catalytic transformations give new and general entries to 3,4-dihydrocoumarins, 4H-chromenes and xanthenones. These frameworks are recurring structures in natural product and medicinal chemistry, as testified by the formal syntheses of (R)-tolterodine and (S)-4-methoxydalbergione from the catalytic adducts.
Catalytic Asymmetric Addition of Meldrum's Acid, Malononitrile, and 1,3-Dicarbonyls to ortho-Quinone Methides Generated in situ under Basic Conditions. -A new approach to the utilization of highly reactive and unstable ortho-quinone methides (o-QM) in catalytic asymmetric settings is presented. The enantioselective reactions are catalyzed by bifunctional organocatalysts, and the o-QM intermediates are formed in situ from 2-sulfonylalkyl phenols through base-promoted elimination of sulfinic acid. The use of mild Broensted basic conditions for transiently generating o-QMs in catalytic asymmetric processes is unprecedented, and allows for engaging nucleophiles like Meldrum's acid, malononitrile and 1,3-dicarbonyls. The catalytic transformations give new and general entries to 3,4-dihydrocoumarins, 4H-chromenes and xanthenones. -(CARUANA, L.; MONDATORI, M.; CORTI, V.; MORALES, S.; MAZZANTI, A.; FOCHI, M.; BERNARDI*, L.; Chem. -Eur. J. 21 (2015) 16, 6037-6041, http://dx.
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