Sulfenate ions, intermediates

Hydrolysis of 2,2,2-trifluoroethanesulfonyl chloride has been found to proceed via intermediate sulfene (CF3CH=S02) formed by iilcB reaction. At pH 1.8-5.0 the (ElcB) mechanism applies, whereby water and hydroxide ion act, respectively, as the carbanion-forming base at low and high pH extremes. The ( lcB)rev reaction applies in dilute acid and is accompanied by the expected H-D exchange of substrate protons when D2O is used as solvent. 

Sulfenes when generated in the presence of tricarbonyl partners give rise to 1,3,4-dioxathiane S,S-dioxides <82AP(315)57>. Typically, the treatment of propane-2-sulfonyl chloride (305) with tri-ethylamine in the presence of 1,2,3-indanetrione (307) gives initially the )S-sultone (308) that arises by cycloaddition of the intermediate sulfene (306). Thereafter, attack by chloride ion on (308) furnishes the jS-chlorosulfonate (309). At the same time, further cycloaddition occurs with excess of (307) to generate the doubly spirocyclic 1,3,4-dioxathiane dioxide (310) (Scheme 46). 

The reaction of acylsilanes with a-sulfinyl carbanions proceeds through the initial formation of an a-silyl alkoxide intermediates (5), followed by the cationotropic migration of silyl group to oxyanion and the elimination of sulfenate ion, to afford the corresponding silyl enol ethers (Scheme 3). ... 

In attempts to improve the yields of problematic glycosylation reactions, it has become clear that the mechanism is much more complex than Scheme 3.5 suggests. In essence, the oxycarbenium ion(V) is susceptible to attack by nucleophiles other than the glycosyl acceptor (Scheme 3.6). Two intermediates for which there is experimental evidence are glycosyl triflates(VII)17 and glycosyl sulfenates(IX).18... 

When the sulfenate ROSR is one where R SO- is the anion of a particularly acidic sulfenic acid and R+ is an easily formed carbonium ion, then isomerization to the sulfoxide by a mechanism involving an [R+ OSR l ion pair intermediate becomes possible. Braverman and Svendi (1974) found that on being heated in hexane solution / -methoxybenzyl trichloromethane-sulfenate [25] isomerized rather readily to the corresponding sulfoxide (93). 

A sulfenate ester analogous to but with methyl Instead of chlorine Is formed on MCPBA oxidation of the corresponding methallyl thlocarbamate this patent report ( ) does not mention any Intermediates or speculate on the mechanism of the reaction. Formation of the sulfenate ester Is conveniently monitored not only by IR and NMR but also by CI-MS, In the latter case because In contrast to the sulfoxides (7, 9) the sulfenates are sufficiently stable to exhibit a strong molecular Ion (7 ). 

The preceding section dealt primarily with the evidence that demonstrated sulfenes to be intermediates in these processes and also, where the evidence warranted it, with the mechanism of the sulfene formation. A continual point of concern is whether or not the reaction is really proceeding by way of the sulfene or not. In this section we shall attempt to find what circumstances of substrate, base and (where different) nucleophile tend to lead to the elimination-addition (sulfene) reaction, and which to some other process, notably the direct displacement reaction. Sometimes, indeed, it takes only a rather small change in conditions to alter the mechanism completely. For example, it has been noted above that azide ion reacts with a-disulfones or sulfonyl chlorides by the direct displacement49. This is also seen in the reaction of methanesulfonyl chloride with aqueous sodium azide when the... 

The chlorination of trimethylsilylmethyl sulfides with NCS and trifluoroacetic acid affords the product of chlorodesilation in high yield.3 The degradation of carboxylic acids to ketones can be achieved by a-sulfenation followed by reaction with NCS in the presence of NaHC03 (eq 6). The 5 -chlorosulfonium ion intermediate undergoes a decarboxylative Pummerer-like rearrangement to afford the ketone upon hydrolysis. a-Phenylthio esters... 

---