- Photocatalyzed Triplet Sensitization of Oximes Using Visible Light Provides a Route to Nonclassical Beckmann Rearrangement Products
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Oximes are valuable synthetic intermediates for the preparation of a variety of functional groups. To date, the stereoselective synthesis of oximes remains a major challenge, as most current synthetic methods either provide mixtures of E and Z isomers or furnish the thermodynamically preferred E isomer. Herein we report a mild and general method to achieve Z isomers of aryl oximes by photoisomerization of oximes via visible-light-mediated energy transfer (EnT) catalysis. Facile access to (Z)-oximes provides opportunities to achieve regio- and chemoselectivity complementary to those of widely used transformations employing oxime starting materials. We show an enhanced one-pot protocol for photocatalyzed oxime isomerization and subsequent Beckmann rearrangement that enables novel reactivity with alkyl groups migrating preferentially over aryl groups, reversing the regioselectivity of the traditional Beckmann reaction. Chemodivergent N- or O- cyclizations of alkenyl oximes are also demonstrated, leading to nitrones or cyclic oxime ethers, respectively.
- Zhang, Xiao,Rovis, Tomislav
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supporting information
p. 21211 - 21217
(2021/12/27)
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- Methyl ketone oxime esters as nucleophilic coupling partners in Pd-catalyzed C-H alkylation and application in the synthesis of isoquinolines
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Methyl ketone oxime esters have been found to be excellent coupling partners for C(sp2)-C(sp3) bond formation via Pd-catalyzed aromatic C-H activation. This transformation forms the basis of an approach to regioselectively synthesize substituted isoquinolines via coupling with aryloxime esters. Our mechanistic studies suggested that the reaction proceeded through Pd(II)-catalyzed aromatic C-H activation, tautomerization, and a 1,3-shift of the palladacycle-ligated methyl ketone oxime ester to enable the C-C bond formation by reductive elimination, and intramolecular condensation of an imido-Pd(II) intermediate to form the heterocycle. The aryloxime group not only was used as a directing group for Pd-catalyzed aromatic C-H activation but also functioned as an internal oxidant to allow the reaction to be redox-neutral. Our study illuminated the scope and limitations of this C-H alkylation process, which may serve as the point of departure for developing other C-H functionalization reactions using oxime esters and potentially other carbonyl derivatives as the nucleophilic coupling partners.
- Zhang, Zhi-Wei,Lin, Aijun,Yang, Jiong
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p. 7041 - 7050
(2014/08/18)
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- Direct carbohydroximoylation of aromatics with primary nitroalkanes in triflic acid (TFSA)
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Primary nitroalkanes react with aromatics in triflic acid to yield arylated oximes at 70-80°C.
- Coustard, Jean-Marie,Jacquesy, Jean-Claude,Violeau, Bruno
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p. 8085 - 8086
(2007/10/02)
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