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N‐Ethynylation of Anilides Decreases the Double‐Bond Character of Amide Bond while Retaining trans ‐Conformation and Planarity
Author(s) -
Yamasaki Ryu,
Morita Kento,
Iizumi Hiromi,
Ito Ai,
Fukuda Kazuo,
Okamoto Iwao
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201901451
Subject(s) - acetanilide , amide , chemistry , planarity testing , peptide bond , substituent , double bond , stereochemistry , bond cleavage , crystallography , polymer chemistry , organic chemistry , catalysis , enzyme
Abstract Activated amide bonds have been attracting intense attention; however, most of the studied moieties have twisted amide character. To add a new strategy to activate amide bonds while maintaining its planarity, we envisioned the introduction of an alkynyl group on the amide nitrogen to disrupt amide resonance by n N→C sp conjugation. In this context, the conformations and properties of N ‐ethynyl‐substituted aromatic amides were investigated by DFT calculations, crystallography, and NMR spectroscopic analysis. In contrast to the cis conformational preference of N ‐ethyl‐ and vinyl‐substituted acetanilides, N ‐ethynyl‐substituted acetanilide favors the trans conformation in the crystal and in solution. It also has a decreased double bond character of the C(O)−N bond, without twisting of the amide. N ‐Ethynyl‐substituted acetanilides undergo selective C(O)−N bond or N−C(sp) bond cleavage reactions and have potential applications as activated amides for coupling reactions or easily cleavable tethers.