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.
An asymmetric catalytic epoxidation of alpha-branched, alpha,beta-unsaturated aldehydes is presented. A highly synergistic combination of a primary cinchona-based amine and a chiral phosphoric acid was found to promote the reaction with excellent enantiocontrol for alpha-monosubstituted and alpha,beta-disubstituted enals.
The Lewis acid-catalyzed ring-opening of methyl 1-nitrocyclopropanecarboxylates with amine nucleophiles is described. The reaction proceeds at room temperature and with complete preservation of the enantiomeric purity from the electrophilic center of the cyclopropane to the acyclic product. The methodology was applied in an enantioselective synthesis of the dual serotonin/norepinephrine reuptake inhibitor (3R)-3-(1 H-indol-1-yl)- N-methyl-3-phenylpropan-1-amine.
It's amine business: A readily available cinchona‐derived primary amine is an effective catalyst for the direct asymmetric α benzoyloxylation of cyclic ketones (see scheme; Bz=benzoyl). This efficient and highly enantioselective method uses inexpensive benzoyl peroxide as the oxygen source and stoichiometric amounts of the ketone, and expands the current set of methodologies to directly access valuable protected 2‐hydroxyketone derivatives.
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