RETRODIENIC REACTIONS .24. APPLICATION OF PHOTOELECTRON-SPECTROSCOPY TO MOLECULAR-PROPERTIES .41. FLASH VACUUM THERMOLYSIS OF 2,3-DIHYDRO-1,4-OXATHIIN - SYNTHESIS, PHOTOELECTRONIC SPECTROSCOPY, AND DIENOPHILIC REACTIVITY OF THIOXOETHANAL

Thioxoethanal has been generated in the gas phase by flash vacuum thermolysis of 2,3-dihydro-l,4-oxathiin. Its characterization was performed by chemical trapping and photoelectron spectroscopy (PES). The PE Hel-Hell study led to the conclusion that thiooxethanal was obtained, with ethylene, as the only thermolysis product at 720°C. At higher temperatures, a cleavage into methanethial and carbon monoxide was observed. The results from this PE study, as well as MNDO calculations, indicate a very weak interaction between the formyl and thioformyl moieties of the molecule through the er C-C bond. The HOMO sulfur lone pair is only slightly stabilized by the inductive effect of the carbonyl group. These conclusions account for the observed dienophilic reactivity of thioxoethanal. © 1990, American Chemical Society. All rights reserved.