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Heteroatom Substitution at Amide Nitrogen—Resonance Reduction and HERON Reactions of Anomeric Amides

Department of Chemistry, School of Science and Technology, University of New England, Armidale, NSW 2351, Australia
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Molecules 2018, 23(11), 2834; https://doi.org/10.3390/molecules23112834
Received: 6 October 2018 / Revised: 23 October 2018 / Accepted: 24 October 2018 / Published: 31 October 2018
(This article belongs to the Special Issue Amide Bond Activation)
This review describes how resonance in amides is greatly affected upon substitution at nitrogen by two electronegative atoms. Nitrogen becomes strongly pyramidal and resonance stabilisation, evaluated computationally, can be reduced to as little as 50% that of N,N-dimethylacetamide. However, this occurs without significant twisting about the amide bond, which is borne out both experimentally and theoretically. In certain configurations, reduced resonance and pronounced anomeric effects between heteroatom substituents are instrumental in driving the HERON (Heteroatom Rearrangement On Nitrogen) reaction, in which the more electronegative atom migrates from nitrogen to the carbonyl carbon in concert with heterolysis of the amide bond, to generate acyl derivatives and heteroatom-substituted nitrenes. In other cases the anomeric effect facilitates SN1 and SN2 reactivity at the amide nitrogen. View Full-Text
Keywords: amide resonance; anomeric effect; HERON reaction; pyramidal amides; physical organic chemistry; reaction mechanism amide resonance; anomeric effect; HERON reaction; pyramidal amides; physical organic chemistry; reaction mechanism
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MDPI and ACS Style

Glover, S.A.; Rosser, A.A. Heteroatom Substitution at Amide Nitrogen—Resonance Reduction and HERON Reactions of Anomeric Amides. Molecules 2018, 23, 2834.

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