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

Abstract

A structural, spectroscopic and computational study of a series of oximes was undertaken to investigate how geometric and structural changes relevant to the reaction coordinate for the Beckmann reaction (normal Beckmann) and Beckmann fragmentation (abnormal Beckmann) manifest in the ground state. X-ray structures of a range of oximes derived from dihydrolevoglucosan (CyreneTM; which undergoes the abnormal Beckmann reaction), in which the oxygen substituent was systematically varied were determined. As the electron demand of the OR group increased, the major structural changes included lengthening of the N-OR bond distance, and a decrease in the magnitude of the C2=N-O bond angle, consistent with the changes seen for cyclohexanone oximes, which undergo the normal Beckmann reaction. However, unique to the Cyrene oximes, an increase in the length of the fissile C1-C2 bond was observed, which correlated with an increase in the 13C-13C 1-bond coupling constants as the electron demand of the OR substituent increased. Computational studies of Cyrene and cyclohexanone oximes using Natural Bond Orbital analysis support an electronic structure involving n(O) → σ*C1-C2 and σC1-C2 → σ*N-O orbital interactions.

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Publication details

The article was received on 10 Oct 2017, accepted on 13 Nov 2017 and first published on 14 Nov 2017


Article type: Paper
DOI: 10.1039/C7OB02499A
Citation: Org. Biomol. Chem., 2017, Accepted Manuscript
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    Structure-reactivity correlations of the abnormal Beckmann reaction of dihydrolevoglucosenone oxime

    A. Alhifthi, B. L. Harris, L. Goerigk, J. White and S. J. Williams, Org. Biomol. Chem., 2017, Accepted Manuscript , DOI: 10.1039/C7OB02499A

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