Synthesis of Benzazoles by Hydrogen-Transfer Catalysis

Abstract

Transition-metal-catalyzed hydrogen-transfer reactions have been used for the conversion of alcohols into benzimidazoles and aldehydes into benzoxazoles and benzothiazoles.

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“…Synthesis of 2-(para-tolyl) benzothiazole by transition metal-Ir-catalyzed hydrogen-transfer reactions of 4-methylbenzaldehyde with 2-aminothiophenol have suggested by Blacker and colleagues (Scheme 10, Method 5) 17 .…”

Sonicated Assisted Synthesis of Benzimidazoles, Benzoxazoles and Benzothiazoles in Aqueous Media

“…The reaction mixture was sonicated at room temperature (25 0 c) for the appropriate time ( Table 2, entries [26][27][28][29][30][31], and the progress of reaction was monitored by TLC. After completion of reaction, the mixture was extracted with ethyl acetate (2×10mL).…”

“…These heterocycles can be prepared by condensing carboxylic acid 12 , acid chloride 13,14 , orthoester [15][16][17] , esters 18 and aldehydes [19][20][21][22][23][24] with o-phenylenediamine, o-aminophenols and o-aminothaiophenols, dehydration of o-acylaminophenols 25 , reaction of o-quinones with amines 26 and Beckmann rearrangement of o-acylphenoloximes 27 . The most common method of synthesis of these heterocycles includes condensation of o-phenylenediamine, o-aminophenol or o-aminothiophenol with suitable aldehyde [28][29][30][31][32] . Most of these procedure have their own advantages and disadvantages, thus there is still a need to search better ecofriendly procedure.…”

Diphosphorus Tetraiodide (P2I4): An Efficient Catalyst for Synthesis of 2-Aryl-1,3-benzazoles via Cyclocondensation of o-Amino/Mercaptan/Hydroxy Anilines with Aryl Acids

“…Alternatively, benzimidazoles have also been synthesized using transition-metal catalyzed amination followed by condensation [16] and cyclization of o-nitroaniline derivatives with aryl isothiocyanates [17]. Recently, substituted alcohols have been used for the synthesis of benzimidazoles and benzothiazoles, however, the use of oxidative steps in case of aldehydes or alcohols affect the overall economy of the reaction [18]. Also, benzoxazoles have been obtained by reacting o-hydroxyphenyl ketoximes with PCl5 or P2O5 and reaction of 2-aminophenols with allenic and acetylenic nitriles [19,20].…”