Electrophilic Attack on Sulfur

The acid-catalyzed additions of bromide and chloride ion to thiiranes occurs readily, with halide preferentially but not exclusively attacking the most substituted carbon atom of the thiirane. The reaction of 1-substituted thiiranes with acetyl chloride shows a slight preference for halide attack at the less substituted carbon atom (80MI50601). For further discussion of electrophilic catalysis of halide ion attack see Section 5.06.3.3.2. The reaction of halogens with thiiranes involves electrophilic attack on sulfur (Section 5.06.3.3.6) followed by nucleophilic attack of halide ion on carbon. 

Electrophilic Attack on Sulfur. 2.5 Nucleophilic Attack on Ring Atoms... 

Electrophilic Attack on Sulfur or Carbon 1.05.8.3.1 Episulfonium ions... 

Electrophilic Attack on Sulfur 2.10.2.5.1 Formation of thiophenium ions... 

As shown in Table 1.1, oxaziridine (29b) is a superior reagent for sulfide oxidation, compared to (28b). Values of ee up to 95% were obtained. The two chlorines of (29b) are crucial for the enantioselection (see entries 1, 2 and 5, 6 in Table 1.1). Chiral oxaziridines are now commercially available. A mechanism has been proposed for the electrophilic attack on sulfur. In the present case preferred transition states I and II were postulated. Rl and Rs are large and small groups, respectively. The steric influence seems to be of major importance, presumably because of a molecular cleft defined by a chlorine atom and the phenylsulfonyl... 

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