Ground-State Distortion in N‑Acyl-tert-butyl-carbamates (Boc) and N‑Acyl-tosylamides (Ts): Twisted Amides of Relevance to Amide N–C Cross-Coupling

Amide N–C­(O) bonds are generally unreactive in cross-coupling reactions employing low-valent transition metals due to nN → π*CO resonance. Herein we demonstrate that N-acyl-tert-butyl-carbamates (Boc) and N-acyl-tosylamides (Ts), two classes of acyclic amides that have recently enabled the development of elusive amide bond N–C cross-coupling reactions with organometallic reagents, are intrinsically twisted around the N–C­(O) axis. The data have important implications for the design of new amide cross-coupling reactions with the N–C­(O) amide bond cleavage as a key step.