Electrophilic attack at sulfur

For the preparation of [l]benzothieno[3,2- ][l]benzofuran-10,10-dioxide 64, hydrogen peroxide in acetic acid, 3-chloroperoxybenzoic acid, and also the urea-hydrogen peroxide adduct with phthalic anhydride were employed. All three methods provided 64 in excellent yields (88-94%). Monitoring the course of the reaction showed the 

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Nucleophilic attack at sulfur is implicated in many reactions of 1,2,4-thiadiazoles generally, soft electrophiles attack at sulfur, cf. (150)— (151). -Butyllithium with 4,5-diphenyl-l,2,3-thiadiazole yields PhC = CPh, probably by initial nucleophilic attack at sulfur. 

Very few examples of electrophilic attack at sulfur(II) have been reported for these systems, with the exception of oxidation. Alkylation of the benzothiadiazine (88) with trimethyloxonium tetrafluoroborate gave a poor yield of the imino ether (89). The major product (90) resulted from alkylation at sulfur followed by hydrolytic ring opening of the resulting azasulfonium salt (79JCR(S)214). 

Sulfones and sulfonamides - the S+O class are similarly powerful directors,141 and do not suffer electrophilic attack at sulfur (though occasionally suffer nucleophilic attack on the aromatic ring)134143 but are less useful because of their more limited synthetic applications.144 143 Aryl J-butylsulfoxides are also powerful ortho-directors,145 but less hindered diaryl sulfoxides are susceptible to attack by organolithiums at sulfur146 (see section 3.3.3 for discussion of this sulfur-lithium exchange ). 

Saturated and Partially Saturated Rings Reactivity 4.29.7.7.1 Electrophilic attack at sulfur... 

The CS group can undergo a wide variety of reactions, including electrophilic attack at sulfur and nucleophilic attack at C, for example,... 

A problem with equation (11) is the separation of W(CO)sC8 from W(CO)e formed in side reactions, since these compounds have very similar properties. Coordinated C8 is reactive toward an electrophilic attack at sulfur and a nucleophihc attack at carbon (equations 12 and 13). The... 

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