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Structure–reactivity correlations of the abnormal Beckmann reaction of dihydrolevoglucosenone oxime

Structure–reactivity correlations of the abnormal Beckmann reaction of dihydrolevoglucosenone oxime Ketoximes undergo rearrangement reactions involving cleavage of the carbon–carbon bond adjacent to the imino carbon.1 These reactions include the Beckmann rearrangement (‘normal’ Beckmann reaction),2–4 leading to amides, and the Beckmann fragmentation (‘abnormal’ Beckmann reaction),5,6 leading to nitriles. The normal Beckman reaction involves the generation of an incipient carbocation at the carbon atom located anti to the oxime oxygen, which is intercepted by migration to nitrogen to afford a nitrilium ion intermediate, which is subsequently hydrolyzed to yield an amide (Fig. 1). The abnormal Beckmann reaction occurs in cases where the adjacent carbon can stabilize positive charge; a carbocation intermediate is formed that undergoes heterolytic fragmentation of the carbon–carbon bond anti to the leaving group to yield a nitrile.7–12 The initiating step of both the normal and abnormal Beckmann reactions involve the departure of an oxygen leaving group from nitrogen, with the propensity of a substrate to undergo one or the other transformation dictated by the nature of the anti substituent.13 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Organic & Biomolecular Chemistry Royal Society of Chemistry

Structure–reactivity correlations of the abnormal Beckmann reaction of dihydrolevoglucosenone oxime

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Royal Society of Chemistry
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Abstract

Ketoximes undergo rearrangement reactions involving cleavage of the carbon–carbon bond adjacent to the imino carbon.1 These reactions include the Beckmann rearrangement (‘normal’ Beckmann reaction),2–4 leading to amides, and the Beckmann fragmentation (‘abnormal’ Beckmann reaction),5,6 leading to nitriles. The normal Beckman reaction involves the generation of an incipient carbocation at the carbon atom located anti to the oxime oxygen, which is intercepted by migration to nitrogen to afford a nitrilium ion intermediate, which is subsequently hydrolyzed to yield an amide (Fig. 1). The abnormal Beckmann reaction occurs in cases where the adjacent carbon can stabilize positive charge; a carbocation intermediate is formed that undergoes heterolytic fragmentation of the carbon–carbon bond anti to the leaving group to yield a nitrile.7–12 The initiating step of both the normal and abnormal Beckmann reactions involve the departure of an oxygen leaving group from nitrogen, with the propensity of a substrate to undergo one or the other transformation dictated by the nature of the anti substituent.13

Journal

Organic & Biomolecular ChemistryRoyal Society of Chemistry

Published: Dec 6, 2017

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