2019
DOI: 10.1002/chem.201902242
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Room‐Temperature, Metal‐Free, and One‐Pot Preparation of 2H‐Indazoles through a Mills Reaction and Cyclization Sequence

Abstract: The Mills reaction and cyclizationo fr eadily available 2-aminobenzyla lcohols and nitrosobenzenes using thionyl bromidep rovided 2H-indazoles in up to 88 %y ields. In the metal-free process, acetic acid played a crucial role for the both Mills reactiona nd cyclization. A brominated 2H-indazole could also be obtained through the one-pot sequence.Indazoles are au seful class of N-heteroaromatic compounds because they are crucial structural motifs of various biologically active compounds, [1] particularly,b ioi… Show more

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Cited by 19 publications
(7 citation statements)
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“…Oxygen may play additional roles in the catalytic mechanism, such as the formation of nitroso or nitro intermediates, but no oxygenated side products were observed. Amine and nitroso compounds are known to thermally react to form azo compounds. , To examine this possibility, reactions with equal mixtures of aniline and nitrosobenzene or nitrobenzene respectively were performed as shown in Figure and discussed in detail in the SI. The reactions containing oxygenated starting materials resulted in product distributions that were quite different from the product distributions obtained from reactions containing only aryl amine starting material.…”
Section: Resultsmentioning
confidence: 99%
“…Oxygen may play additional roles in the catalytic mechanism, such as the formation of nitroso or nitro intermediates, but no oxygenated side products were observed. Amine and nitroso compounds are known to thermally react to form azo compounds. , To examine this possibility, reactions with equal mixtures of aniline and nitrosobenzene or nitrobenzene respectively were performed as shown in Figure and discussed in detail in the SI. The reactions containing oxygenated starting materials resulted in product distributions that were quite different from the product distributions obtained from reactions containing only aryl amine starting material.…”
Section: Resultsmentioning
confidence: 99%
“…According to the mechanism, acetic acid plays a significant role in the cyclization process (Scheme 44). 83 Jiao and Shao et al established 1,3-dihydro-2 H -indazoles by the [4 + 1] cycloaddition of aza- ortho -quinonemethides with N -tosyloxycarbamates at room temperature. Under basic conditions, azo- ortho -quinonemethides are formed first, followed by a nucleophilic nitrogen anion formed by the deprotonation of a N1 synthon.…”
Section: Transition Metal (Tm) Free Methodsmentioning
confidence: 99%
“…2 H ‐indazole derivatives 1 a – 1 k were synthesized according to literature procedures [6b] . Acetic acid (50 mL), 2‐aminophenyl alcohols (10 mmol) and nitrosobenzenes (20 mmol) prepared from oxidation of anilines by potassiumperoxomonosulfate (OXONE) were added into a 100 mL flask.…”
Section: Methodsmentioning
confidence: 99%