Catalytic Asymmetric Addition of Meldrum’s Acid, Malononitrile, and 1,3-Dicarbonyls to<i>ortho</i>-Quinone Methides Generated In Situ Under Basic Conditions
unstable ortho‐quinone methides (o‐QMs) in catalyticasymmetric 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 basicconditions for transiently generating o‐QMs in catalyticasymmetric processes is unprecedented
An efficient bifunctional squaramide-catalyzed Michael addition/cyclization reaction of o-quinone methidesgenerated in situ from 2-(1-tosylalkyl)phenols with active methylene compounds bearing a cyano group has been realized to synthesize chiral 2-amino-4H-chromenes with excellent enantioselectivities and broad substrate scope.
enantioselective synthesis of 2-amino-4H-chromenes via the cascade rhodium-catalysed conjugate addition/hetero Thorpe–Ziegler reaction is reported. Moderate to good yields (up to 98%) and high enantioselectivities (up to 92% ee) were obtained with a chiral diene-coordinated rhodium complex as the catalyst. This protocol remedies the methodological deficiency in the asymmetricsynthesis of 4-aryl 2-amino-4H-chromenes