2-Methylbenzo thiophene, reaction

Under these strong acid conditions, products from other rearrangements and acid cleavage reactions are sometimes found. For example, a mixture of 5-r-butyl-3-methyl-benzo[6]thiophene (the expected product), 6-(-butyI-3-methylbenzo[ >]thiophene and 3-methylbenzo[6 ]thiophene was obtained on cyclization of p-t- butylphenylthioacetone with phosphorus pentoxide. During the cyclization of phenyl phenacyl sulfide to give a mixture of 2- and/or 3-phenylbenzo[6]thiophenes, small amounts of diphenyl disulfide and 5-phenylthio-3-phenylbenzo[6]thiophene were also formed (70AHC(ll)t77). 

The first example of a [2 + 4] cycloaddition of a thiophene 1-oxide seems to be the formation of a 1 1 mixture of the syn and anti isomers of 3-(2,4,6-trimethylphenyl)-8b-methylbenzo[6]thieno[2,3-mesitonitrile oxide with 3-methyIbenzo[6]thiophene 1-oxide (Scheme 190) (79TL4845). The cycloaddition seems to be regioselective. 

There are several examples of this approach to thiophenes. The reaction of thiophenol with acetylene in the vapor phase at 600-650 °C gave benzo[h]thiophene in 71% yield. p-Toluenethiol affords 5-methylbenzo[h ]thiophene in 54% yield under the same conditions (54HC(7)l). The best example of this type of synthesis was the reaction of 3-mercaptocy-clohexanones (235) with glyoxal to form the thiophenes (236), which was the subject of a patent (70USP3511854). The reaction proceeds smoothly under reflux conditions, using ah inert solvent, such as benzene or toluene, which will azeotrope with water, and a protic acid catalyst. A solution of (235) in the solvent is added to 40% aqueous glyoxal solution containing some acid. After reflux the thiophene (236) can be isolated in 70-90% yield. 

Halobenzo[6]thiophenes are readily obtained from the corresponding 2-benzo[6]thienyllithium by the reactions described in Section VII. 2-Iodo-3-methylbenzo[6]thiophene is obtained by treatment of the 2-acetoxymercury compound with iodine.496... 

Bromomethylbenzo[6]thiophenes are readily obtained in high yields by treatment of the corresponding methyl compound with. V-bromosuccinimide in the presence of benzoyl peroxide.91,105,298 343,4i3,447,487,489-492,517,518 Applied to 3-methylbenzo[6]thiophene, this procedure affords 2-bromo-3-methylbenzo[6]thiophene (12%), in addition to the required product the yield of nuclear substituted product rises to 78% when peroxides are excluded.487 When 3,5-dimethylbenzo[6]thiophene is treated with W-bromosuccinimide, the 3-methyl group is preferentially brominated,489 but in the cases of other 5-alkyl-3-methylbenzo[6]thiophenes inseparable mixtures of products are formed.292 The above reaction has also been applied to... 

Additional examples of syntheses of polycyclic triazoles continue to be reported. 2-(2 -Hydroxyphenyl)benzotriazole (84) is prepared in >90% yield from azointermediate (83) by reaction with Raney nickel and DMSO, DMS or thiophene [95JAP07228577]. 2-Methylbenzo-triazole (85) is cyclized under acidic conditions and subsequently converted into the chloro analog (86) by treatment with POCl3 [95FES47],... 

UV irradiation of 2,5-diphenyloxadiazole (43) together with benzo[6]thiophene (42) yields an oxadiazepine (44) as the initial and major product, along with the 3-substituted benzo[6]thiophenes (45a) and (45b). These latter products are also obtained on photolysis of the oxadiazepine (Scheme 6). Prolonged irradiation gives products (45) and what is formally a trans [2 + 2] cycloadduct (46). This cycloadduct is also formed from oxadiazole (43) and benzo[6 jthiophene on irradiation with benzophenone as a sensitizer and the reaction presumably involves the triplet state of the oxadiazole. Somewhat similar photoreactions have been observed between oxadiazole (43) and methylbenzo[f ]thiophenes, indazoles, furan and indene (77BCJ3281). 

Bordwell et a/.354 358 have made an extensive study of the rearrangement reactions brought about by nucleophilic attack on a range of substituted halogenobenzo[b]thiophene-1,1-dioxides. 3-Chloromethyl- and 2-bromo-3-methylbenzo[b]thiophene-l,1-dioxide each give the same product with piperidine, the structure of which (Ref. 2, p. 358) has now been amended to 84 (R1 = R2 = H). With piperidine, 2-bromo-3-ethyl- and 2-ethyl-3-bromo-benzo[/>]thiophene-l,1-dioxides give amines 82a and 82b, respectively.354... 

Hydroxybenzo[b]thiophene is conveniently obtained by the dehydrogenation of ketone 68.292 4-, 5-, and 6-Methoxy-3-methylbenzo[f>]thiophene-2-carboxylic acids are obtained from the appropriate j3-aryl-a-mercaptoacrylic acid (Ref. 2, p. 233) by cyclization with chlorine477 the reaction is cleaner than with iodine, but some ring chlorination may also occur.247 The methoxy... 

A 5-(methylthio)-6-(C30H61)-benzo[b]thiophene-4,7-quinone has been isolated from cultures of an extremely thermophilic and acidophilic microorganism.502 In connection with the structure determination of this natural product, 5-bromo-6-methylbenzo[6]thiophene-4,7-quinone was treated with MeS, to give mainly the 5-SMe derivative. Unexpectedly, a minor product from this reaction was the 5-SMe, 6-CH2SMe compound, formed by both nuclear and side-chain methylthiolation.503... 

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