Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 8 October 2018 doi:10.20944/preprints201810.0128.v1 Peer-reviewed version available at Molecules 2018, 23, 2834; doi:10.3390/molecules23112834 1 Heteroatom Substitution at Amide Nitrogen — Resonance Reduction and HERON 2 Reactions of Anomeric Amides 3 4 Stephen A. Glover and Adam A. Rosser 5 Department of Chemistry, 6 School of Science and Technology, 7 University of New England, Armidale, NSW 2351, Australia 8 Corresponding author, Email:
[email protected] 9 10 Abstract: This review describes how resonance in amides is greatly affected upon substitution 11 at nitrogen by two electronegative atoms. Nitrogen becomes strongly pyramidal and resonance 12 stabilisation, evaluated computationally, can be reduced to as little as 50% that of N,N- 13 dimethylacetamide. However, this occurs without significant twisting about the amide bond, 14 which is borne out both experimentally and theoretically. In certain configurations, reduced 15 resonance and pronounced anomeric effects between heteroatom substituents are instrumental 16 in driving the HERON (Heteroatom Rearrangement On Nitrogen)† reaction, in which the more 17 electronegative atom migrates from nitrogen to the carbonyl carbon in concert with heterolysis 18 of the amide bond, to generate acyl derivatives and heteroatom-substituted nitrenes. In other 19 cases the anomeric effect facilitates SN1 and SN2 reactivity at the amide nitrogen. 20 21 1. Introduction 22 Amides are prevalent in a range of molecules such as peptides, proteins, lactams and many 23 synthetic polymers [1]. Generically, they are composed of both a carbonyl and an amino 24 functional group, joined by a single bond between the carbon and nitrogen.