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[Prof. Seung Hwan Cho]ZnMe2-Mediated, Direct Alkylation of Electron Deficient N-Heteroarenes with 1,1-Diborylalkanes: Scope and Mechanism

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ZnMe2-Mediated, Direct Alkylation of Electron Deficient N-Heteroarenes with 1,1-Diborylalkanes: Scope and Mechanism

Woohyun Jo, Seung-yeol Baek, Chiwon Hwang, Joon Heo, Mu-Hyun Baik and Seung Hwan Cho

 The regioselective, direct alkylation of electron-deficient N-heteroarenes is, in principle, a powerful and efficient way of accessing alkylated N-heteroarenes that are important core structures of many biologically active compounds and pharmaceutical agents. Herein, we report a ZnMe2-promoted, direct C2- or C4-selective primary and secondary alkylation of pyridines and quinolines using 1,1-diborylalkanes as alkylation sources. While substituted pyridines and quinolines exclusively afford C2-alkylated products, simple pyridine delivers C4-alkylated pyridine with excellent regioselectivity. The reaction scope is remarkably broad, and a range of C2- or C4-alkylated electron-deficient N-heteroarenes are obtained in good yields. Experimental and computational mechanistic studies implicate that ZnMe2 serves not only as an activator of 1,1-diborylalkanes to generate (α-borylalkyl)methylalkoxy zincate, which acts as a Lewis acid to bind to the nitrogen atom of the heterocycles and controls the regioselectivity, but also as an oxidant for rearomatizing the dihydro-N-heteroarene intermediates to release the product.   https://pubs.acs.org/doi/10.1021/jacs.0c06827

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