Reactions with sulfur electrophiles

Thioglycosides can be activated for gfycosylation reactions with sulfur electrophiles, e.g., with dimethyl(methylthio)sulfonium triflate or with methanesulfenyi bromide and silver(l +) to form reactive sulfonium intermediates (F. Dasgupta, 1988). 

Reaction with Sulfur Electrophiles. Bisa2iridine compounds can be prepared from sulfur dichloride, thionyl chloride, or sulfuryl chloride... 

Reaction with Sulfur Electrophiles. Bisazitidine compounds can be prepared from sulfur dichloride, thionyl chloride, or sulfuryl chloride and ethyleneimine (288). The products are, respectively, l,T-thiobisaziridine [2881-79-0] (X = S), l,T-dithiobisaziridine [1623-84-3] (X = S—S),... 

An example of proton sponge reaction with sulfur electrophiles is known. The interaction of compound 1 with alkanesulfenyl chlorides led to a series of 4-alkylsulfenyl derivatives 190202. The proton sponge 1 can participate in an azo-coupling reaction, also proceeding at position 456. 

Beside these free radical reactions of sulfur dioxide, its electrophilic reactions generating sulfinates with organometallic compounds453,454 or sulfinic acids with arenes under Friedel-Crafts conditions455 are well known. To complete these three-component syntheses, the sulfinates prepared first are transformed to sulfones by reactions with appropriate electrophiles, discussed earlier in this chapter, i.e. equation 82. 

The higher homologue of 3-sulfolene, 2,7-dihydrothiepin-l,1-dioxide could be similarly metallated at low temperatures. Reaction with reactive electrophiles followed by extrusion of sulfur dioxide led [549] to the corresponding hexatriene derivatives, as in the stereoselective synthesis of (Z,E)-l,3,5-decatriene (considered as an undecatriene in the publication) shown here. 

Zirconium-benzyne complexes have been used rather extensively in organic synthesis.8 45 For this purpose, one particularly important characteristic of zirconium-aryne complexes is that olefin insertion into the Zr—C bond occurs stereospecifically. Thus, when generated in situ, the zirconium-benzyne complex (45) reacts with cyclic alkenes to give exclusively the cis-zirconaindanes (46), which upon treatment with electrophiles provide access to a variety of m-difunctionalized cycloalkanes (47-49) (Scheme 5).46 For example, carbonylation of intermediate 46 affords tricyclic ketone 49, reaction with sulfur dichloride gives thiophene 48, and reaction of 46 with tert-butylisocyanide followed by I2 gives 47 via 50 and, presumably, intermediate 51 [Eq. (12)]. 

Two of the reactions that are used in the industrial preparation of detergents are electrophilic aromatic substitution reactions. First, a large hydrocarbon group is attached to a benzene ring by a Friedel-Crafts alkylation reaction employing tetrapropene as the source of the carbocation electrophile. The resulting alkylbenzene is then sulfonated by reaction with sulfuric acid. Deprotonation of the sulfonic acid with sodium hydroxide produces the detergent. 

Direct nitration of compounds (20) and (22) are straightforward reactions, with preferential electrophilic substitution occurring at C-3. The nitration proceeded in yields of approximately 50% using a mixed nitric/sulfuric acid system <70JHC373>. 

Phenylenediamine is readily converted by HN02 into 1,2,3-benzotriazole 438 and by SOCl2 into 2,1,3-benzothia-diazole 439. Best synthetic methods for the preparation of 1,2,3-benzotriazoles are summarized in the related section of CHEC-III most important procedures are based on the reactions of substituted 0-pheny-lenediamines with nitrous acid or nitrites as illustrated by Scheme 227 <2006JME4762>. Likewise, the annulated thiadiazoles are commonly synthesized by the reaction of sulfur electrophiles with appropriate 1,2-diamines (e.g., Scheme 228) <1999JA10281, 2004BML5045, CHEC-III(5.09.9.2)550>. 

Allyltin bonds are among the most reactive carbon-tin bonds and they undergo reactions with mild electrophiles, e.g. aldehydes (equation 47). Protonolysis of allyltin bonds proceeds with y-regioselectivity and anti stereoselectivity. Sulfur dioxide cleavages, however, occur with y-regioselectivity and... 

CH2BU or p-MeCjH4]. The reaction is considered to be charge controlled and to proceed via electrophilic attack by Sg on the carbyne carbon (178). An additional complex (267, M = W, E = S, L = CO, R = Me) can be obtained from [W=CMe(Cp)(CO)2] and cyclohexenesulfide (179). With the osmium complex 268 (R = /7-tolyl), however, reaction with sulfur does not proceed beyond the t/ -thioacyl complex (269, E = S or Se). Seleno-and telluroacyl complexes result from analogous reactions (180). 

Scheme 2.135 Reaction of Me3SiCF3 with sulfur electrophiles [87-89],...

The procedure has also been applied to halobenzoic acids.3 Thus p-bromo-benzoic acid (6) was converted into the corresponding 2-oxazoline (7) as usual, and then into the Grignard derivative (8). This is, in effect, an aryl Grignard reagent with a protected carboxyl function. Reaction with an electrophile, for example benzonitrile, gives (9). The final step is hydrolysis. If carried out in 5-7% ethanolic sulfuric acid, the ester (10b) is obtained if carried out in an aqueous medium, the free acid (10a) is obtained. 

Finally in this category, the efficient synthesis of 3,4-dimethoxythiophene from 2,3-dimethoxy-l,3-butadiene on reaction with sulfur dichloride is notable it was easily transformed into EDOT (31.6.6.1). Here the sulfur source is electrophilic in character. 

The industrial synthesis of thiophene is based on butane and its reaction with sulfur or carbon disulfide. In comparison with benzene, thiophene can be more easily substituted electrophilically in the 2- or 5- position this reaction is used to produce a wide range of pharmaceutical products. An example of this is the antihistamine thenalidine, which is obtained from thiophene by chloromethylation to 2-thienylmethyl chloride followed by reaction with 4-anilino-l-methylpiperidine. 

The asymmetric a-sulfenylation of ketones is a particularly challenging reaction, as demonstrated by the poor success reported in the stereoselective variants via classical enolate/azaenolate reaction with an electrophilic sulfur reagent [71]. An umpolung approach has been devised by Coltart and co-workers [72] to effect the first asymmetric a-sulfenylation of ketones with arene thiols. Nitroso alkene derivatives, in i/tM-generated under basic conditions from a-chloro oximes, reacted with arene thiols in the presence of cinchona thiourea 27, which promoted the conjugate addition of thiophenol (Scheme 14.25). The chiral nonracemic a-sulfenylated oximes were directly hydrolyzed by IBX to ketones in high yield and good enantioselectivity. 

In 1971, the first s5 thesis of 242 used transmetallation of 3-bromothiophene (5) then reaction with the electrophilic sulfur source (PhS02)2S. The resulting 3, 3 -dithienyl sulfide (248) was a,a -dilithiated and the carbon-carlxMi bmid made by oxidation with CuCl2 [95] (Scheme 60). 

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