Preparation of sulfines by alkylidenation of sulfur dioxide using α-silyl carbanions

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.

Bis(trimethylsilyl)methanesulfonyl and tris(trimethylsilyl)methanesulfonyl chlorides and their reactions by way of sulfenes

Bis(trimethylsilyl)methanesulfonyl and tris(trimethylsilyl)methanesulfonyl chlorides (2c and 2d, respectively), have been prepared for the first time. Reactions of 2d with nucleophiles give products evidently derived from bis(trimethylsilyl)sulfene (1c). Reaction of 2c with piperidine gives the same piperidide as that from 2d, presumably via 1c formed by dehydrochlorination of 2c, whereas water and fluoride ion yield products consistent with their formation via trimethylsilylsulfene (1b) formed from 2c by attack at silicon with loss of the trimethylsilyl and chloro groups. No evidence for any enhanced stability in 1c was found.Key words: sulfonyl chlorides, sulfenes, silylsulfonyl chlorides, silylsulfenes, desilylation.