Iron-Catalyzed Cyclization of Nitrones with Geminal-Substituted Vinyl Acetates: A Direct [4 + 2] Assembly Strategy Leading to 2,4-Disubstituted Quinolines
作者:Mingbing Zhong、Song Sun、Jiang Cheng、Ying Shao
DOI:10.1021/acs.joc.6b01910
日期:2016.11.18
An iron-catalyzed intermolecular [4 + 2] cyclization of arylnitrones with geminal-substituted vinyl acetates was developed for the synthesis of 2,4-disubstituted quinolines in moderate to good yields with good functional group compatibilities. Preliminary mechanistic studies suggest a plausible iron-catalyzed C–H activation process under external-oxidant-free conditions.
Organocatalytic Asymmetric 1,3-Dipolar Cycloaddition of Nitrones to Nitroolefins
作者:Ying-Chun Chen、Wei Du、Yan-Kai Liu、Lei Yue
DOI:10.1055/s-0028-1087300
日期:2008.12
The asymmetric1,3-dipolarcycloaddition of nitrones to nitroolefins was investigated by employing novel thiourea-containing organocatalysts. This transformation exhibited excellent diastereoselectivities (generally >99:1 dr) and moderate to high enantioselectivities (up to 88% ee). A 2,3-diaminopropanol derivative with three contiguous chiral centers was efficiently prepared from one cycloaddition
Synthesis of 3-Alkylbenzoxazolones from <i>N</i>-Alkyl-<i>N</i>-arylhydroxylamines by Contiguous <i>O</i>-Trichloroacetylation, Trichloroacetoxy <i>ortho</i>-Shift, and Cyclization Sequence
作者:Ram N. Ram、Vineet Kumar Soni
DOI:10.1021/jo401985h
日期:2013.12.6
Benzoxazolone pharmacophore is present in clinical pharmaceuticals, drug candidates, and many compounds having a wide spectrum of biological activities. The methods available for the synthesis of benzoxazolones have limited diversity due to problems in accessibility and air-sensitivity of diversely substituted o-aminophenols from which they are generally prepared by cyclocarbonylation with phosgene or its equivalents. The present paper describes a mild method for the synthesis of 3-alkylbenzoxazolones from easily accessible and air-stable nitroarenes. Nitroarenes were converted to N-alkyl-N-arylhydroxylamines in two steps involving partial reduction to arylhydroxylamines followed by selective N-alkylation. Treatment of N-alkyl-N-arylhydroxylamines with trichloroacetyl chloride and triethylamine afforded 3-alkylbenzoxazolones generally in good yields through an uninterrupted three-step sequence involving O-trichloroacetylation, N -> C-ortho trichloroacetoxy shift, and cyclization in a single pot at ambient temperatures. The present method is mild, wide in scope, economical, and regioselective. Many sensitive groups like alkyl and aryl esters, amide, cyano, and the carbon-carbon double bond survive the reaction.
Synthese von 4-Alkoxy- und 3-nitrosubstituierten Isoxazolidinen durch katalysierte 1,3-dipolare Cycloadditionsreaktionen von Nitronen mit Vinylethern und Nitroolefinen
作者:Michael Meske
DOI:10.1002/prac.19973390175
日期:——
1,3-Dipolar cycloadditions of the C-phenyl-N-alkylnitrones 1,3 and the C,N-diphenylnitrone (2) with vinyl ethers 5,6 are strongly catalyzed by chiral oxazaborolidines derived from N-arylsulfonyl substituted L-alpha-amino acids valine and tert-butyl leucine and BH3 . THF complex at -22 degrees C to room temperature to give predominantly the 3,5-trans-substituted 5-alkoxy-isoxazolidines 8b - 12b, but with moderate enantioselectivity. Thermal cycloaddition afforded predominantly the 3,5-cis-substituted 5-alkoxy-isoxazolidines 8a - 12a. The cycloaddition of (E)-1-ethyl-2-nitroethene (7) afforded a mixture of cis- and trans-substituted 4-nitro-isoxazolidines 13. The ratio depends on reaction temperature and catalyst. Mild ring cleavage after quarternization of 5-ethoxy-2-methyl-isoxazolidines (8) yields the corresponding beta-amino-esters 27, 28.
The simplest phenylnitrones and their conversion into isoxazolidine derivatives