Stereoselective organocatalytic sulfa-Michael reactions of aryl substituted α,β-unsaturated N-acyl pyrazoles

The asymmetric Michael addition of aryl thiols and thioacetic acid to challenging beta- or alpha,beta-aryl substituted alpha,beta-unsaturated N-acyl pyrazoles catalysed by bifunctional organocatalysts has been investigated. The corresponding sulfide derivatives are obtained under mild and simple conditions, using readily available amine-thioureas or squaramides with good to high stereocontrol (up to 89/11 dr and 98% ee). The protocols complement the few pre-existing methods reported for the asymmetric access to beta-thio-derivatives of alpha,beta-unsaturated esters or their ester equivalents.