Flash Vacuum Thermolysis of 4 H ‐3,1‐Benzoxathiin‐4‐thione: UV‐Photoelectron Spectroscopy Characterization and Quantum Chemistry Studies

The mechanism of the reaction of 4 H ‐3,1‐benzoxathiin‐4‐thione ( 3 ) under flash vacuum thermolysis conditions has been studied by UV‐photoelectron spectra. It was shown that in the first step of the reaction at 400° 3 underwent the Schönberg–Newman–Kwart rearrangement to give 4 H ‐1,3‐benzodithiin‐4‐one ( 6 ). Increasing of the temperature to 650° resulted in the elimination of thioformaldehyde and the formation of benzothiet‐2‐one ( 1 ). Subsequent elevation of the temperature prompted presumably the ring opening of 1 to (6‐thioxocyclohexa‐2,4‐dien‐1‐ylidene)methanone ( 7 ) (at 680°), which at 700° eliminated CO and underwent a Wolff ‐type ring contraction to give (cyclopenta‐2,4‐dien‐1‐ylidene)methanethione ( 2 ). UV‐Photoelectron spectra were recorded at different steps of the reaction and analyzed considering the theoretical evaluation of ionization potentials.