Potassium tert‐Butoxide‐Catalyzed Selective Synthesis of 1,4‐Benzodioxepines via 7‐exo/7‐endo‐dig Cyclization of Alkynol: Experimental and DFT Study

Abstract A new method utilizing base catalysis is outlined for the synthesis of 1,4‐benzodioxepines, introducing a unique scaffold containing a seven‐membered ring heterocycle. The reaction proceeded under thermal conditions, with no waste was generated during the transformation, highlighting its remarkable atom efficiency and environmental friendliness. A straightforward metal‐free reaction condition utilizing 2‐propynyloxy benzyl alcohols as starting material and a catalytic amount of t‐ BuOK in mesitylene at 100 °C for 1 hour was employed for this intramolecular cyclization transformation, resulting in the formation of 1,4‐Benzodioxepines in good to excellent yields and high regio‐ and diastereo‐selectivity. The density functional theory (DFT) calculations yielded the relative internal energy (U), enthalpy (H), and Gibbs free energy (G) values for all possible products, aligning closely with our experimental data.