A novel dimerization mode of a cyclic ketene imine.

The strained seven-membered cyclic ketene imine 9, obtained by cycloaddition of thiocarbonyl ylide 6 with 2,3-bis(trifluoromethyl)fumaronitrile (7), underwent base-catalyzed dimerization at room temperature on treatment with KCN in acetonitrile or with proton sponge in acetonitrile or CDCl(3). Two diastereoisomeric dimers, (6SR,3'RS)-13 and (6SR,3'SR)-13, were formed in 1:1 ratio in high yield. X-ray analysis revealed a deep-seated structural change which is unrelated to known dimerization pathways of ketene imines.

A computational study of the cycloaddition of thiobenzophenone S-methylide to thiobenzophenone.

The cycloaddition of thiobenzophenone S-methylide to thiobenzophenone, an experimentally well-known reaction, was studied, using (U)HF/3-21G* for finding stationary points and (U)B3LYP/6-31G*//(U)HF/3-21G* single-point calculations for energies. Some optimizations were performed by (U)B3LYP/ 6-31G* to check the reliability of the calculations. The comparison of the concerted pathways and stepwise reactions via C,C-biradicals and C,S-zwitterions showed that the formation of a tetraphenyl-substituted C,C-biradical and its ring closure to 4,4,5,5-tetraphenyl-1,3-dithiolane constitutes the energetically most probable pathway of product formation, despite the fact that the regioisomeric 2,2,4,4-tetraphenyl-substituted product is more favorable by 17 kcal mol(-1).

1,3-dithiolanes from cycloadditions of alicyclic and aliphatic thiocarbonyl ylides with thiones: regioselectivity.

The regiochemistry of 1,3-dithiolanes obtained from thiocarbonyl ylides 9 and thiones 10 shows a striking dependence on substituents. Previously and newly performed experiments indicate that sterically hindered cycloalkanethione S-methylides and dialkylthioketone S-methylides react with alicyclic and aliphatic thiones to give the 2,2,4,4-tetrasubstituted 1,3-dithiolanes 11 exclusively. Aryl groups in one or both reactants lead to a preference for, or even complete formation of, 4,4,5,5-tetrasubstituted 1,3-dithiolanes 12.

Thioformaldehyde S-methylide and thioacetone S-methylide: an ab initio MO study of structure and cycloaddition reactivity.

The mechanisms of cycloaddition of thioformaldehyde S-methylide and thioacetone S-methylide, as models for an alkyl-substituted ylide, to thioformaldehyde and thioacetone, as well as to ethene as a model for a C=C double bond have been studied by ab initio calculations. Restricted and unrestricted B3LYP/6-31G* calculations were performed for the geometries of ground states, transition structures, and intermediates. Although basis sets with more polarization functions were tested, the 6-31G* basis set was applied throughout.

1,3-Dipolar Activity in Cycloadditions of an Aliphatic Sulfine(,)(1).

2,2,4,4-Tetramethyl-3-thioxocyclobutanone S-oxide (4) combines with diaryl thioketones at room temperature furnishing spiro-1,2,4-oxadithiolanes 6 in equilibrium reactions. Compound 6a was oxidized to the cis-S,S-dioxide 9, the structure of which was established by X-ray analysis. These are the first unequivocal 1,3-cycloadditions of thione S-oxides (sulfines) which possess an allyl anion type MO; cycloadditions to the C=S bond of sulfines as dipolarophile and dienophile had been described before.