Chemistry of sulfines. Part III: Further investigations on the preparation

Synthesis of Sterically Encumbered Thiourea S-Oxides through Direct Thiourea Oxidation

Thiourea S-oxides can be viewed as formal analogs of the currently unknown diamino-substituted Criegee intermediates (urea O-oxides). However, the preparation of such S-oxides is rather challenging, and the direct oxidation of thioureas typically only leads to formation of desulfurized products. Employing the accurate revDSD-PBEP86-D4 double hybrid density functional, it was found that the peracid mediated oxidation of thiourea S-oxides exhibits a lower reaction barrier than the oxidation of the corresponding thiourea itself in contrast to most other ordinary thioketones. The undesired overoxidation reactivity, which is associated with strong π-donation from the thiourea's nitrogen atoms, can be partially suppressed by introduction of bulky substituents and the utilization of protic solvents. In this regard, we managed to prepare two sterically encumbered thiourea S-oxides in isolated yields of 35-40 %. The S-oxides are stable in the solid state and in alcoholic solutions at room temperature for extended periods of time, but swiftly decompose in aprotic solvents by disproportionation. A dimesityl-substituted thiourea S-oxide complexed with residual mCBA could be characterized by means of X-ray crystallography, confirming the importance of hydrogen bonding in the stabilization of the amino-substituted C=S⁺ -O^- moiety.

Synthesis of Functionalized Chiral Imidazole Derivatives Based on a Bornane Skeleton Bearing a Sterically Crowded Spirocyclic Substituent at the C-3 Position

10-Imidazolylbornane-2-one bearing a sterically crowded spirocyclic substituent at the C-3 position was prepared from d-camphor through the procedure involving the formation of 10-bromobornane-2-thiones or 10-iodobornane-2-thiones and the subsequent conversion into the corresponding 10-imidazolylbornane-2-thiones followed by an efficient oxidative S-O exchange via thione S-oxides.

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.

Reactions with thiaxanthen-9-ol: new thiaxanthene derivatives with molluscicidal and nematocidal activity

Thiaxanthen-9-ol (1) was condensed with nitriles 2a-e to yield the thiaxanthen-9-yl-acetonitriles 3a-e. With the thiols 7a-d, 1 yielded the thioethers 8a-d.