Metal-free synthesis of 2-aminobenzoxazoles using hypervalent iodine reagent
作者:Yogesh S. Wagh、Neelam J. Tiwari、Bhalchandra M. Bhanage
DOI:10.1016/j.tetlet.2012.12.127
日期:2013.3
A facile, simple, mild, and metal-free protocol for the synthesis of 2-aminobenzoxazoles has been developed via C–H bond amination of benzoxazoles with amines through a ring-opening and subsequent ring-closure approach. The reaction was performed in two steps wherein nucleophilic addition of amines across benzoxazoles takes place in the absence of any reagent or catalyst under solvent-free condition
Merging the ring opening of benzoxazoles with secondary amines and an iron-catalyzed oxidative cyclization towards the environmentally friendly synthesis of 2-aminobenzoxazoles
作者:Daqian Xu、Wenfang Wang、Chengxia Miao、Qiaohong Zhang、Chungu Xia、Wei Sun
DOI:10.1039/c3gc41206g
日期:——
A facile and environmentally friendly method was developed through merging the ring opening of benzoxazoles with secondary amines and an iron-catalyzed oxidative cyclization towards the synthesis of 2-aminobenzoxazoles. In the oxidative cyclization step, with catalytic amounts of FeCl and aqueous H2O2 as a green oxidant, highly desirable 2-aminobenzoxazoles were isolated in excellent yields of up to 97%. A plausible radical process is proposed for the oxidative cyclization on the basis of mechanistic studies.
Visible-light-initiated photo-oxidative cyclization of phenolic amidines using CBr4 – A metal free approach to 2-aminobenzoxazoles
作者:Twinkle Keshari、Vishnu P. Srivastava、Lal Dhar S. Yadav
DOI:10.1039/c3ra46314a
日期:——
A mild and efficient one-pot operation for the amination of benzoxazoles has been achieved via ring opening of benzoxazoles followed by visible-light-mediated aerobic photo-oxidative cyclization of the resulting o-phenolic amidines using CBr4 as a mild oxidant. The protocol is economical and environmentally benign as it utilizes visible light and does not require any photosensitizers, additives, heating
Visible-Light-Triggered Oxidative C–H Aryloxylation of Phenolic Amidines; Photocatalytic Preparation of 2-Aminobenzoxazoles
作者:Vishnu Srivastava、Lal Yadav
DOI:10.1055/s-0033-1340150
日期:——
Visiblelight efficiently mediates an intramolecular cyclization reaction of o-hydroxy-N-aryl-N,N-dialkylformamidines (phenolic amidines) leading to 2-aminobenzoxazole derivatives in the presence of only 1 mol% tris(2,2′-bipyridine)ruthenium(II) as a photoredox catalyst along with air as terminal oxidant. The protocol involves oxidative functionalization of an amidinic C–H bond to a C–O bond and affords
The direct coupling of benzoxazoles and amines was realized by visible light irradiation and CuCl catalysis. Various aminated benzoxazoles were successfully synthesized under mild conditions with air as an oxidant.