THEORETICAL-STUDY OF PERICYCLIC-REACTIONS OF NITROSOETHYLENE AND (THIONITROSO)ETHYLENE

Structure and reactivity of the title compounds 1 were examined by ab initio methods at the post Hartree-Fock level of theory. Both compound s are expected to undergo electrocyclic ring closure to 4H-1,2-oxazete (4O) and 4H-1,2-thiazete (4S), respectively. The alternative electroc yclic reaction affording 2H-azirine 1-oxide (3O) and 2H-azirine 1-thio xide (3S) is definitely less favoured. (Thionitroso)ethylene (1S) is m ore reactive than the oxygen-containing congener. The same holds for t he cycloaddition reaction with ethylene. [4 + 2] Hetero Diels-Alder re actions furnishing 4H-1,2-oxazine (5O) or 4H-1,2-thiazine (5S) are fav oured over the [3 + 2] cycloaddition reactions providing 2H-pyrrole 1- oxide (20) and 2H-pyrrole 1-thioxide (2S). The results of RMP2/6-31G calculations and results obtained at lower levels of theory (RHF, PM3) are compared and discussed with respect to the experimental material available. Some additional single-point calculations at the computatio nally more demanding QCISD/6-31G level confirmed conclusions drawn fr om RMP2 calculations. Some test calculations also showed that the theo retical results are less affected by consideration of the temperature by statistic thermodynamics and by inclusion of solvent effects by a s elf-consistent reaction-field method.