1- benzothiophene-2-, lithium

Dibenzothiophenecarboxaldehyde has not been reported but should be readily formed from 1-bromodibenzothiophene via the lithium exchange route as described above. Likewise a better route to 4-dibenzo-thiophenecarboxaldehyde may be via the readily formed 4-lithiodi-benzothiophene (Section VI,H, 1). 

Reductions of five-membered cyclic sulfones with lithium aluminum hydride were run in refluxing ether and of other sulfones in refluxing ethyl butyl ether (92°) (yields 12-92%). Benzothiophene-1,1-dioxide was reduced at the double bond as well, giving 2,3-dihydrobenzothiophene in 79% yield after 18 hours of refluxing in ether [687],... 

Bis[benzo-1 -thiophen-2-yltelluro]methane5 In a 250 ml, nitrogen-flushed flask fitted with a stirrer are placed 2.1 g (15.7 mmol) of benzothiophene and 50 ml of tetrahydrofuran. 6.5 ml (15 mmol) of n-butyl lithium solution are added to the stirred benzothiophene solution at 20°, stirring is continued for 1 h, and then 1.9 g (14.9 mmol) of tellurium are added. The mixture is stirred until all the tellurium has been consumed (1 h), then 40 ml of dry dichloromethane are added to the stirred mixture and stirring at 20° is continued overnight. The mixture is poured into 200 ml of water, the organic layer is separated, the aqueous layer is extracted with further dichloromethane, and the combined dichloromethane solutions arc dried with anhydrous calcium chloride, filtered, and evaporated. The residue is recrystallized from acetonitrile yield 2.7 g (68%) m.p. 127°. 

Hydrodesulfnrisation of benzothiophenes is conveniently achieved using Raney nickel. Reduction of the hetero-rings of both benzofuran and benzothiophene giving 2,3-dihydro derivatives, notably with retention of the snlfur in the latter case, can be achieved using triethylsilane in acidic solution, or with hydrogen over colloidal rhodium. Reductive cleavage of benzofuran to 2-hydroxystyrene is caused by lithium with 4,4 -di-f-butylbiphenyl (DTBB). ... 

Variations on the theme include the use of gold(I) chloride to transform orf/to-alkynylphenylthio-silanes into 3-trialkylsilyl-benzothiophenes, ° carbonylative closures to produce 3-aroyl-benzofurans, ° and cyclisation with hot lithium chloride. ... 

Thieno[2,3- >][l]benzothiophens (293), including the parent compound, were prepared from substituted 2-benzo[Z>]thiophenthiols, obtained from the corresponding lithium derivative followed by condensation with chloroacetaldehyde diethylacetal, chloroacetone, or 3-chlorobutan-2-one, and finally cyclization with hot polyphosphoric acid. For the synthesis of thieno[3,2-6][l]benzothiophens (294), the necessary thiol was... 

DFT computations showed that the intramolecular addition of the aryllithium generated from 425 occurs on the central carbon atom of the allenic moiety to yield the intermediate 427 from which lithium ethoxide is eliminated to furnish the benzofuran product 426. Both cyclization processes were found to pass through low-lying transition states, as it would be expected for fast reactions at low temperatures [123]. Further explorations on the anti selectivity in the intramolecular carbolithi-ation by DFT computations revealed additional details regarding the mechanism of this carbocyclization and led the authors to conclude that such a transformation is controlled by the appropriate molecular editing [123]. The synthesis of functionalized heterocycles can be relatively easy to achieve by intramolecular carbometallation reactions. For example, Kunz and Knochel [124] recently reported the preparation of benzothiophene scaffolds 429 by copper-catalyzed carbomagnesiation ofalkynyl thioethers 428 (Scheme 10.148). 

Benzo[6]thiophen is cleaved by lithium dimethylamide to the salt (249). The photochemical cycloaddition of 2,5-diphenyl-l,3,4-oxadiazole (250) to 3-methylbenzothiophen yields compound (251), but in the presence of iodine the addition is reversed, yielding compound (252). Benzothiophen 55-dioxide... 

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