Abstract
Benzimidazoles are important N-heteroaromatic compounds with various biological activities and pharmacological applications. Herein, we present the first iron-catalyzed selective synthesis of 1,2-disubstituted benzimidazoles via acceptorless dehydrogenative coupling of primary alcohols with aromatic diamines. The tricarbonyl (η4-cyclopentadienone) iron complex catalyzed dehydrogenative cyclization, releasing water and hydrogen gas as by-products. The earth abundance and low toxicity of iron metal enable the provision of an eco-friendly and efficient catalytic method for the synthesis of benzimidazoles.
Highlights
Benzimidazoles, which have been found in pharmaceuticals and natural products, are important N-heteroaromatic structural motifs because of their biological activities (Bansal and Silakari, 2012; Chandrika et al, 2016; Suk et al, 2019)
We explored the feasibility of benzimidazole formation between 1,2-diaminobenzene 1a and benzyl alcohol 2a using standard Knölker complex cat
Various kinds of bases were screened in the reaction system, and tBuOK was found to be a more effective base than KOH and K2CO3 for the formation of 1,2-disubstituted benzimidazoles 3a
Summary
Benzimidazoles, which have been found in pharmaceuticals and natural products, are important N-heteroaromatic structural motifs because of their biological activities (Bansal and Silakari, 2012; Chandrika et al, 2016; Suk et al, 2019). 1,2-disubstituted benzimidazoles show various biological activities, such as anticancer (Zimmermann et al, 2013, 2014) antibacterial (Bandyopadhyay et al, 2011; Göker et al, 2016), antiallergic (Nakano et al, 2000), and anti-HIV (Morningstar et al, 2007) traits along with cannabinoid-1 (CB1) and cannabinoid-2 (CB2) receptors (Watson et al, 2011; Nanda et al, 2014). Based on their attractive biological profiles, the synthesis of 1,2-disubstituted benzimidazoles has gained the interest of synthetic chemists. Another approach is the classic cyclocondensation of (iii) N-alkyl-N-acyl-1,2-diaminobenzene (Smith and Krchnák, 1999; Takeuchi et al, 2000) or (iv) N-alkyl-1,2-diaminobenzene with aldehyde (Smith and Krchnák, 1999; Özden et al, 2005)
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