Abstract
A highly efficient method for parallel synthesis of a diversity of 1,2-disubstituted benzimidazoles from N-substituted phenylenediamines and aldehydes has been developed by using 10 mol% HfCl4 on activated carbon (HfCl4/C) as the catalyst. The newly reported HfCl4/C catalyst not only mediated fast and clean formation of benzimidazoles but also could be easily removed from the reaction solution and reused up to eight times. Scanning electron microscope (SEM) and thermal desorption studies showed that activated carbon could reversibly adsorb and release Hf(IV) in ethanol upon cooling and heating, thereby serving as a thermal-controlled solid support.
Highlights
As one of the most important heterocyclic scaffolds, 1,2-disubstituted benzimidazole has been extensively employed in the development of novel pharmaceutical agents and functional materials [1,2,3].In contemporary drug discovery, a huge number of benzimidazole derivatives have been synthesized and utilized as anti-infective, anti-inflammatory, antihypertensive, antitumor, antiallergic, antidiabetic, analgesic, and proton pump inhibitory agents [4,5,6,7].In our previous research, we found that the synthesis of 2-aminovinyl benzimidazoles represented a huge challenge to the commonly known synthetic methods for benzimidazoles
We found that the synthesis of 2-aminovinyl benzimidazoles represented a huge challenge to the commonly known synthetic methods for benzimidazoles
The formation of the colored intermediates was much slower without a catalyst. These results indicated that HfCl4 promoted the formation of both imine and benzimidazoline intermediates, which is similar to the catalytic mechanism of Hf(IV) on the formation of fluorinated benzimidazolines elucidated by NMR tracing data [27]
Summary
As one of the most important heterocyclic scaffolds, 1,2-disubstituted benzimidazole has been extensively employed in the development of novel pharmaceutical agents and functional materials [1,2,3].In contemporary drug discovery, a huge number of benzimidazole derivatives have been synthesized and utilized as anti-infective, anti-inflammatory, antihypertensive, antitumor, antiallergic, antidiabetic, analgesic, and proton pump inhibitory agents [4,5,6,7].In our previous research, we found that the synthesis of 2-aminovinyl benzimidazoles represented a huge challenge to the commonly known synthetic methods for benzimidazoles. As one of the most important heterocyclic scaffolds, 1,2-disubstituted benzimidazole has been extensively employed in the development of novel pharmaceutical agents and functional materials [1,2,3]. A huge number of benzimidazole derivatives have been synthesized and utilized as anti-infective, anti-inflammatory, antihypertensive, antitumor, antiallergic, antidiabetic, analgesic, and proton pump inhibitory agents [4,5,6,7]. We found that the synthesis of 2-aminovinyl benzimidazoles represented a huge challenge to the commonly known synthetic methods for benzimidazoles. None of these methods afforded the desired 2-aminovinyl benzimidazoles, because the conjugation of electron-donating aniline significantly lowered electropositivity of the carbonyl in 3-aminoacroleins. We found that the non-toxic and inexpensive Group
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