Transition Metal-Free One-Pot Synthesis of Fused 1,4-Thiazepin-5(4H)‑ones and Theoretical Study of the S–N Type Smiles Rearrangement Process

A series of 1,4-thiazepin-5­(4H)-one derivatives were synthesized via a transition metal-free one-pot Smiles rearrangement process at room temperature. Regioselective seven-membered heterocycles were constructed in good to excellent yields. To gain an in-depth understanding of the S–N type Smiles rearrangement mechanism, a theoretical study was also performed by quantum chemistry calculations.