Donthireddy SNR, Siddique M, Rit A. N-Heterocyclic Carbene-Supported Nickel-Catalyzed Selective (Un)Symmetrical N-Alkylation of Aromatic Diamines with Alcohols.
J Org Chem 2023;
88:1135-1146. [PMID:
36603160 DOI:
10.1021/acs.joc.2c02639]
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Abstract
The "borrowing hydrogen" (BH) approach for the N-alkylation of phenylenediamines using alcohols as coupling partners is highly challenging due to the selectivity issue of the generated products. Furthermore, the development of base-metal systems that can potentially substitute precious metals with competitive activity is a major challenge in BH catalysis. We present herein an efficient protocol for the N,N'-di-alkylation of aromatic diamines using an in situ-generated Ni-NHC complex from NiCl2 and the ligand L1, which gave access to a wide range of N,N'-di-alkylated orthophenylene diamines (rather than the generally observed benzimidazole derivatives), meta- and para-phenylene diamines along with 2,6-diamino pyridine derivatives in good to excellent yields. Moreover, the catalyst system was also successful in the derivatization of a clinically important drug molecule, Dapsone. Notably, the present protocol could be applied effectively to synthesize unsymmetrically substituted N,N'-di-alkylated diamines via sequential alkylation and is the first report in the base-metal system to the best of our knowledge. Diverse control experiments including the deuterium incorporation studies suggest that the present protocol proceeds via a BH sequence.
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