In:
Beilstein Journal of Organic Chemistry, Beilstein Institut, Vol. 12 ( 2016-11-15), p. 2390-2401
Abstract:
Reactions of β-azolyl enamines and nitrile oxides were studied by both experimental and theoretical methods. ( E )-β-(4-Nitroimidazol-5-yl), (5-nitroimidazol-4-yl) and isoxazol-5-yl enamines smoothly react regioselectively at room temperature in dioxane solution with aryl, pyridyl, and cyclohexylhydroxamoyl chlorides without a catalyst or a base to form 4-azolylisoxazoles as the only products in good yields. The intermediate 4,5-dihydroisoxazolines were isolated as trans isomers during the reaction of ( E )-β-imidazol-4-yl enamines with aryl and cyclohexylhydroxamoyl chlorides. Stepwise and concerted pathways for the reaction of β-azolyl enamines with hydroxamoyl chlorides were considered and studied at the B3LYP/Def2-TZVP level of theory combined with D3BJ dispersion correction. The reactions of benzonitrile oxide with both E - and Z -imidazolyl enamines have been shown to proceed stereoselectively to form trans- and cis -isoxazolines, respectively. The preference of E -isomers over Z -isomers, driven by the higher stability of the former, apparently controls the stereoselectivity of the investigated cycloaddition reaction with benzonitrilе oxide. Based on the reactivity of azolyl enamines towards hydroxamoyl chlorides, a novel, effective catalyst-free method was elaborated to prepare 4-azolyl-5-substituted isoxazoles that are otherwise difficult to obtain.
Type of Medium:
Online Resource
ISSN:
1860-5397
Language:
English
Publisher:
Beilstein Institut
Publication Date:
2016
detail.hit.zdb_id:
2192461-2
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