Benzo thiophenes sulfur derivatives

The benzo[fc]thiophene sulfoxides, such as (142), generated from the parent benzo-thiophene on the H202-TFA-mediated oxidation, undergoes Michael-type nucleophilic addition of oxygen and sulfur nucleophiles in acidic media to produce 3-substituted benzo[fc]thiophenes (143). This method provides an easy two-step functionalization of 2-acylbenzo[fc]thiophene derivatives. ... 

Incidentally, a 1,3-cycloaddition of benzyne to thiophene has been postulated (81CC124) to account for the small, but reproducible amount of benzo[ >]thiophene formed in this reaction (Scheme 79). Reactive alkynes have been successfully used as dienophiles to cycloadd with thiophenes benzene derivatives are obtained after extrusion of sulfur from the adduct (Scheme 80) (72TL605, 72TL1909, 73CB674). 

The cycloaddition of a variety of sulfur heterocycles to alkenes has also been reported. Dibromomaleic anhydride undergoes [ 2 + 2] cycloaddition to thiophen295 and to benzo[b]thiophen.296 The photoaddition of benzo-[(>]thiophen 1,1-dioxides to alkenes also affords cyclobutane derivatives.297 Of particular interest is the addition of 3-acetoxybenzo[6]thiophen (350) to cyclohexene to give the adduct (351), which on treatment with base, undergoes a retro-aldol ring opening to benzo[6]thiepinone (352).298 A mixture of stereoisomeric cyclobutane derivatives were obtained on irradiation of 2,6-diphenyl-4//-thiopyran-4-one 1,1-dioxide in cyclohexene.299 The [ 2 + 2] cycloaddition of sulfolen to maleic anhydride and to maleimide has been reported.300... 

Metal chelates are preser t in the complexes of Schiff bases of amino-(X = NR2), hydroxy- (X = O), and mercapto- (X = S) derivatives of monoheteroaromatic five-membered systems, azoles, and azines. A few publications on the complexes of azomethines of the monoheteroaromatic five-membered systems have appeared only recently. The X-ray structural study of copper(II) bis(2-N-n-octyliminomethyl)benzo[ 7]thio-phene-3-olate) 199 (04ZNK1696) is interesting in the sense that its square-planar structure is complemented by an extended octahedral one due to the intermolecular contacts of the thiophene sulfur with the copper site. Among the azole complexes, azomethine derivatives of p3Tazole (Equation (32)) prevail (05RCR193). There are several types of coordination units (N,N-, N,0-, N,S-, N,Se-) created by variation of the donor sites X in position 5 of the pyrazole ring. When X = O, S, Se, tautomer b is realized, whereas when X = NR, tautomer a predominates (Equation (32)). However, irrespective of the type of tautomer, in the chelates the coordination units have practically equalized bonds. 

The orf/zo-alkenylarylzinc reagent obtained by the migratory arylzincation serves as a precursor to benzo[ijchalcogenophenes such as benzo[fe]thiophenes and benzo[h]selenophenes (Scheme 10.9) [28]. Treatment of the zinc intermediate with sulfur powder in the presence of Cul allows one-pot synthesis of a benzo[h]thiophene derivative (route A). Alternatively, the zinc intermediate is quenched with iodine to give ortho-alkenylaryl iodide, which is then subjected to copper-catalyzed reaction with sulfur or selenium powder to furnish the corresponding benzo[i]thiophene or benzo[(i]selenophene derivative (route B). Collectively, these approaches allow for expedient synthesis of functionalized benzo[h]thiophenes and benzo[()]selenophenes, many of which are difficult to... 

Smirnov-Zamkov et al. have shown that sulfur dioxide and hydrogen bromide react with alkynes with phenylacetylene derivatives, such as the sulfonamide (42), a benzo[b]thiophene (43) is formed.50 The mixture of sulfur dioxide and hydrogen bromide appears to behave like thionyl bromide, cf. thionyl chloride (see Section V,B). 

Concerning the transformation of substituents, a special note should be made on a series of ring-closure reactions carried out on the side chain of some [l,2,4]triazolo[4,3-r]benzo[l,2,3]triazines published by Moustafa <2001SC97>. The results are summarized in Scheme 18. This scheme shows that by transformation of the R group attached to the sulfur atom of derivative 97 a fairly large set of cyclic products - involving thiazolidone 97a, [l,2,4]triazole 97b, coumarone and its imine 97c and 97d, respectively, benzoxazylpyrane, 97e, thiophene 97f, and cyclopenta- or cyclohexa-fused protected pyrone 97g substituents - have been obtained. 

In 1967 Cava and Pollack obtained derivatives of the fourth, so-called nonclassical , thienothiophene— thieno[3,4-c]thiophene (4), a condensed heterocycle with formdly tetracovalent sulfur (42)j. The reaction of 3,4-bischloromethyl-2,5-dimethylthiophene (141) with sodium sulfide afforded 4,6-dimethyl-lif,3ff-thieno[3,4-c]thiophene (142) periodate oxidation of 142 gave die corresponding sulfoxide (143) in 91% yield. Attempts to convert the sulfoxide (143) into the thieno-[3,4-c]thiophene by the method used for S3mthesizing benzo[c]-thiophene led only to polymer. However, 24% of adduct 144 and 10% of 145 were obtained by refluxing sulfoxide (143) with N-phenylmaleimide in acetic anhydride, indicating that the thieno[3,4-c]-thiophene was formed as an intermediate. 

The first successful Diels-Alder addition of thiophene appears to have been with tetrafluorobenzyne (66CC143). The adduct apparently loses sulfur, resulting in the isolation of the tetrafluoronaphthalene in 40% yield (Scheme 78). Other thiophene derivatives (69T25) and fluorinated benzynes <71JCS(C)604) have been similarly reacted. Subsequently it was found (80H 14)647) that unsubstituted benzyne, generated from diphenyliodonium-2-carboxylate, could be trapped with thiophene to form naphthalene in 33% yield. The earlier failure to add thiophene to benzyne generated by other methods must have been due to intervention of side reactions. Thiophyne also has been similarly trapped to yield benzo[A]thiophene (see Section 3.14.2.2). 

Benzo[6]thiophene 1,1-dioxides have been made by cyclization procedures (Section 3.15.3.1.7). Homologs of acetophenone cyclize on treatment with chlorosulfonic acid to give 2-substituted 3-chlorobenzo[6]thiophene 1,1-dioxides (equation 86). Similarly 1,1-diaryl-1-propenes in concentrated sulfuric acid gave 2-methyl-3-arylbenzo[6]thiophene 1,1-dioxides (65JOC2840). Friedel-Crafts cyclization of l,l-diphenylethylene-2-sulfonyl chloride gave 3-phenylbenzo[6]thiophene 1,1-dioxide (equation 87) (59JA2000). Treatment of various biphenyl derivatives with fuming sulfuric acid forms the dibenzothiophene 5,5-dioxides (Section 3.15.3.1.7). 

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