Flash vacuum thermolysis of 4H-3,1-benzoxathiin-4-thione: UV-photoelectron spectroscopy characterization and quantum chemistry studies
Résumé
The mechanism of the reaction of 4H-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 4H-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. © 2008 Verlag Helvetica Chimica Acta AG.