Using cinchona alkaloid-derived primary amines as catalysts and aqueous hydrogen peroxide as the oxidant, we have developed highly enantioselective Weitz-Scheffer-type epoxidation and hydroperoxidation reactions of α,β-unsaturated carbonyl compounds (up to 99.5:0.5 er). In this article, we present our full studies on this family of reactions, employing acyclic enones, 5-15-membered cyclic enones, and α-branched enals as substrates. In addition to an expanded scope, synthetic applications of the products are presented. We also report detailed mechanistic investigations of the catalytic intermediates, structure-activity relationships of the cinchona amine catalyst, and rationalization of the absolute stereoselectivity by NMR spectroscopic studies and DFT calculations.
A convergent,
catalytic asymmetric formal [4 + 2] annulation for
the synthesis of dihydroquinolones has been developed. Carboxylic
acids can be employed as precursors to NHC enolates through an in
situ activation strategy. Simultaneous generation of a reactive aza-o-quinone methide under the basic conditions employed for
NHC generation leads to a dual activation approach.
116 years after the discovery of the Knoevenagel condensation, the first catalytic asymmetric variant has been developed. Dynamic kinetic resolution in the reaction of α‐branched aldehydes with malonates in the presence of a newly designed and readily available modified cinchona amine catalyst gives the corresponding alkylidene malonates in high enantioselectivity (see scheme).
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