Dibenzothiophene 5-oxide, reaction with

The usual range of reactions has been recorded for the aldehydes of dibenzothiophene. Oxidation yields the corresponding acid, - reduction with LAH the corresponding alcohol, reduction under Huang-Minlon conditions the corresponding methyl compound, and two examples of the Cannizarro reaction have been described. ... 

Several standard electrophilic reactions have been carried out on dibenzothiophene <85JHC215>. Nitration with cone. HNO3 and glacial acetic acid leads to a mixture (40% each) of 2-nitro-dibenzothiophene and dibenzothiophene-5-oxide. Nitration of the latter (fuming nitric acid and cone, sulfuric acid) gives 3-nitrodibenzothiophene-5-oxide, which could be deoxygenated to 3-nitrodibenzothiophene by 48% hydrobromic acid and glacial acetic acid. 

Oxidation. The reagent (1) easily oxidizes secondary alcohols to ketones, and l,2-dihydroxy-4-hutylbenzene to the quinone derivative. Phs and dibenzothiophene are oxidized in room temperature reactions with CSOSO2OF. ... 

Dibenzothiophene was P-functionalized via metallation, reaction with PhaPCl and oxidation. Both the mono- and the diphosphinoyl produets... 

Oxidation of thiophene with Fenton-like reagents produces 2-hydroxythiophene of which the 2(570 One isomer is the most stable (Eq. 1) <96JCR(S)242>. In contrast, methyltrioxorhenium (Vn) catalyzed hydrogen peroxide oxidation of thiophene and its derivatives forms first the sulfoxide and ultimately the sulfone derivatives <96107211>. Anodic oxidation of aminated dibenzothiophene produces stable radical cation salts <96BSF597>. Reduction of dihalothiophene at carbon cathodes produces the first example of an electrochemical halogen dance reaction (Eq. 2) <96JOC8074>. 

Oxidation of dibenzothiophene with <-butylhydroperoxide proceeded slowly and it was only possible to measure reaction rates in the concentration range 0.3-0.6 mole/liter in acetic acid at 60°. The reaction did not proceed beyond the sulfoxide stage and 21a was obtained in 35% yield,... 

Low-temperature chlorination of dibenzothiophene with elemental chlorine produces a chlorine adduct at the sulfur atom which is readily decomposed to dibenzothiophene 5-oxide. However, nuclear chlorination of dibenzothiophene has still not been studied. 2-Chlorodibenzo-thiophene has been prepared by the Sandmeyer reaction on 2-amino-dibenzothiophene and this route has now been extended to give... 

An unsuccessful attempt to repeat this reaction was made by Bird however, he was able to show that dibenzothiophene 5-oxide did, in fact, react with either thionyl chloride or phosphorus oxychloride to yield 2-chlorodibenzothiophene in good yield. Since all methods of nitration of dibenzothiophene yield a mixture of 2-nitrodibenzothio-phene and dibenzothiophene 5-oxide, which have identical melting points, it was concluded that the earlier workers had in fact been working with the sulfoxide and not the nitro compound. The reaction was rationalized as being a deoxygenative halogenation of a heterocyclic 5-oxide akin to the Meisenheimer reaction of A-oxides, which already had precedents in the sulfoxide field. Unfortunately the 2-chlorodibenzothiophene prepared by this route is contaminated with 2,8-dichlorodibenzothiophene which cannot be removed by crystallization. The best method of preparation of this compound is therefore via a Sandmeyer reaction on 2-aminodibenzothiophene. ... 

Dibenzothiophene 5-oxide is sufficiently nucleophilic to be alkylated at the oxygen atom by alkyl halides in the presence of silver perchlorate (96). Such compounds were found to be readily hydrolyzed back to the sulfoxide. The reaction of 96 with amines is discussed in Section VI, E, 3. 

The synthesis of the four monocarboxylic acids of dibenzothiophene has been recorded in the previous review. However, several modified preparations have since been described. Ethyl 1-dibenzothiophene-carboxylate has been synthesized from 2-allylbenzo[6]thiophene (Section IV,B, 1) hydrolysis afforded the 1-acid (57% overall). In a similar manner, 3-methyl-1-dibenzothiophenecarboxylic acid was obtained from the appropriately substituted allyl compound. This method is now the preferred way of introducing a carbon-containing substituent into the 1-position of dibenzothiophene. 2-Dibenzothiophenecarboxylic acid has been prepared by oxidation of the corresponding aldehyde or by sodium hypoiodite oxidation of the corresponding acetyl compound. Reaction of 2-acetyldibenzothiophene with anhydrous pyridine and iodine yields the acetyl pyridinium salt (132) (92%), hydrolysis of which yields the 2-acid (85%). The same sequence has been carried out on 2-acetyldibenzothiophene 5,5-dioxide. The most efficient method of preparing the 2-acid is via carbonation of 2-lithio-... 

Disulfides were shown to be intermediates in the iodine oxidation of 1,3-butadiene-l-thiols and related compounds to form thiophenes (56JOC39). Several simple disulfides were converted to thiophene derivatives under these same conditions (64JOC2372). For example, bis(2-biphenyl) disulfide (13) produced dibenzothiophene (14) in 64% yield when heated with iodine in ethylene glycol for one hour. Treatment of (13) in benzene with aluminum bromide gave (14) in 76% theoretical yield, with an equivalent amount of the thiol, 2-biphenylthiol (62JOC4111). Thus the iodine reagent is more efficient, since it oxidizes the mercaptan, formed by the Friedel-Crafts reaction of disulfide on the adjacent aromatic ring, to disulfide for further reaction, and also serves as a catalyst for the initial reaction. 

The electrochemical oxidation of 2,5-diaryl-1,4-dithiins (50) has been studied using various voltametric techniques and all compounds were found to undergo quasi-reversible one-electron transfers to the radical cations and dications.126 The first formal redox potential and the lifetime of the radical cation were found to decrease with increasing electron donation from the aryl ring. The major products were the 2,2 -dimers, which result via reaction of two radical cations for which rate constants are given. Dibenzothiophene radical cations reacted with tetranitromethane under... 

Diels-Alder reactions of N-substituted benzo[4,5]thieno[2,3-c]pyrroles 149 [27] and benzo[4,5]furo[2,3-c]pyrroles 150 [26] with Af-phenylmaleimide and DMAD gave the corresponding exo cycloadducts 151-153 (Scheme 28). Oxidative extrusion of the nitrogen bridge in cycloadducts 152 and 153 via intermediates 154, 155 afforded derivatives of dibenzothiophene 156 [27] and diben-zofuran 157 [26],... 

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