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Short Paper | Regular issue | Vol 92, No. 5, 2016, pp.944-953
Published online, 30th March, 2016
DOI: 10.3987/COM-16-13434
Facile Synthesis of Chiral Benzimidazolium Salts and the Application in Asymmetric Catalytic Borylation

Jie Zhou, Xiaohui Liu, and Zhihua Sun*

*College of Chemistry and Chemical Engineering, Shanghai University of Engineering Science, 333 Longteng Rd., Songjiang, Shanghai, 201620, China

Abstract

A synthetic method towards chiral benzimidazolium salts is developed. The stereocenter is introduced by direct aromatic substitution of 2-fluoronitrobenzene with optically pure amines. After nitro group reduction, selective arylation of the primary amine is achieved via copper catalyzed Chan-Lam coupling reaction. Finally, cyclization of the diamine with HC(OMe)3 afforded the desired chiral benzimidazolium salts. In situ generated benzimidazole carbenes show potential application for asymmetric catalytic borylation of α,β-unsaturated esters, providing up to 85% ee value with a catalyst loading of only 0.5 mol%.