Structure and Additive-free Transamidation of Planar N-Cyano Amides.

Although transamidation of amides generally requires metals, additives, or harsh conditions, we present here a facile transamidation of N-cyano amides with various amines at ambient temperature without any additive. N-cyano amides preferred the trans conformation and have a reduced double bond character revealed by crystal analysis. The DFT study indicates that the transamidation reaction proceeds through the direct attack of amine on the amide carbonyl since the LUMO (or LUMO+1) is located at the carbonyl moiety.

N-Ethynylation of Anilides Decreases the Double-Bond Character of Amide Bond while Retaining trans-Conformation and Planarity.

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 nN→Csp 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.