Chemistry of Sulfur Analogue of Trimethylenemethane

Abstract

Thioxyallyl which is a sulfur analogue of trimethylenemethane is thought to be an intermediate of cyclopropanethione-allene episulfide tautomeric system. However, there has been few studies for characterization of this system.
The MCSCF (multiconfigration self-consiste nt-field) studies of thioxyallyl intermediate showed that ¹B₁ state is more stable than ¹A₁ state, and is the lowest singlet state. This result suggests a striking contrast to the lowest ¹A₁ state of oxyallyl. Flash vacuum pyrolysis and thermolysis of both tetramethylallene episulfide [5] and 3, 3, 5, 5-tetram ethyl1-pyrazoline-4-thione [6] gave 2, 4-dimethyl-1, 3-pentadiene-3-thiol [7] via thioxyallyl intermediate [8]. Thermolysis of allene episulfide [5] is of first-order in unimolecular C-S bond cleavage of [7]. Solvent effects also appear on first-order rate co nstants and activation parameters, which may be due to the dipole moment of thioxyallyl intermediate [8]. Thermal reaction of allene episulfide [5] with carbonyl compounds gave 1, 3oxathiolane derivatives and pentadienethiol [7], whereas oxathiolane did not from in the reaction of 1-pyrazolinei-4-thione [6]. These results show that oxathiolane derivatives may be formed in direct reaction of allene episulfide [5], not via thioxyallyl intermediate. Reaction of diphenylcyclopropenethione [15] and 1, 3-diphenylisobenzofuran gave benzbthiophene derivative [19] via formation of cyclopropanethione [16] and its ring opening to thioxyallyl intermediate.
These resu lts suggest that thioxyallyl intermediate is a polarized biradical species, and is accordingly different from zwitterionic oxyallyl one.