Copper(I)-Catalyzed Enantioselective α-Alkylation of 2-Acylimidazoles.

Abstract

Catalytic asymmetric α-alkylation of simple carboxylic acid derivatives is a challenging issue due to the difficulties in achieving high catalytic efficiency and controlling the enantioselectivity. Herein, by using a copper(I)-(R)-DTBM-SEGPHOS complex as a catalyst and 2-acylimidazoles as pronucleophiles, a general method for the catalytic asymmetric α-alkylation of simple carboxylic acid derivatives is accomplished. Various alkyl electrophiles, including allyl bromides, benzyl bromides, propargyl bromide, and unactivated alkyl sulfonates, serve as efficient alkylation reagents. The reaction enjoys the advantages of an easy reaction protocol, good functional group tolerance, and high enantioselectivity. 2,4,6-Trimethylphenol is found as an effective additive to increase yields. Preliminary 1H NMR experiments indicate the precoordination of 2-acylimidazoles to a copper(I) catalyst, which might acidify the α-hydrogens of 2-acylimidazoles and allow facile generation of stabilized copper(I) enolates. Finally, the synthetic utility of the present method is demonstrated by the asymmetric formal synthesis of AZD2716, a potent secreted phospholipase A2 inhibitor.