1,3-Dihydrobenzo thiophene 2,2-dioxide

During thermal dimerization of thiophene dioxides, one molecule functions as the 2ir-component and the other as the 477-component (B-67MI31401, 70AHC(11)177>. The initially formed dimer (513) eliminates a molecule of S02 to form the dihydrobenzo[6]thiophene (514) when R is chlorine, aromatization occurs by loss of HC1. Pyrolysis of benzo[6]thio-phene 1,1-dioxide at 185-200 °C similarly leads to (515). 

Benzo[fr]thiophene 1,1-dioxide and its derivatives are reduced to the corresponding 2,3-dihydro derivatives by catalytic hydrogenation in good yields (Scheme 94). In this reduction, the sulfonyl moiety remains unchanged [13,189, 238, 239]. However, reduction of benzo[ ]thiophene 1,1-dioxide with LiAlH4 affords deoxygenated 2,3-dihydrobenzo[ ]thiophene in 79% yield [233]. Benzo[fr]thiophene 1,1-dioxide was also reduced to the 2,3-dihydro derivative by an electrochemical method (Scheme 95) [240]. 

During investigation of the synthesis of benzocyclobutane 193, Cava and coworkers118 found that o-quinodimethane 192, generated in the pyrolysis of 1,3-dihydrobenzo[c]thiophene 2,2-dioxide (191), can be trapped by Af-phenylmaleimide to give N-phenyl-1,2,3,4-tetrahydronaphthalene 2,3-dicarboimide (194) (equation 125). 

Charlton121 has recently reported the asymmetric induction in the reaction of dimethyl fumarate and l,3-dihydrobenzo[c]thiophene 2,2-dioxide (198) containing a chiral a-alkoxy group at the 2-position (equation 128). A diastereomeric excess of 2.8 1 of 199 to 200 is achieved by using 198 derived from optically active a-methylbenzyl alcohol. 

The synthetic utility of o-quinodimethane generated by cheletropic elimination of S02 has been amply demonstrated by Oppolzer and Nicolaou, who have conducted an intramolecular cycloaddition coupled with the alkylation of 1,3-dihydrobenzo[c]thiophene 2,2-dioxide122. When 1,3-dihydro-l-(4-pentenyl)benzo[c]thiophene 2,2-dioxide (201) prepared from 1,3-dihydrobenzo[c]thiophene 2,2-dioxide and 4-pentenyl bromide is heated in di-n-butyl... 

For benzo[Z ]thiophene the heterocycle is rather more resistant to ring opening and oxidation with hydrogen peroxide in acetic acid at 95 C, for example, gives the 1,1-dioxide (Scheme 7.22) reduction with either sodium and ethanol or triethylsilane in trifluoroacetic acid affords 2,3-dihydrobenzo[Z)]thiophene. Electrophiles give mainly 3-substituted benzo[Z ]thiophenes, although these products are often accompanied by smaller amounts of the 2-isomers. 

The mass spectra of 2-phenyl-, 3-phenyl-, and 3-methyl-2-phenyl-benzo[6]thiophene have been discussed, and tentative structural assignments of the main fragment ions have been made.121 The mass spectra of benzo[6]thiophene-l, 1-dioxide and its 2,3-dihydro derivative have been examined in detail.121> 127 The partial mass spectrum of 2,3-dihydrobenzo[6]thiophene has been recorded.124... 

The cis and trans isomers of ethyl-2,3-dihydrobenzo[i>]thiophen-2,3-ylene acetate (30)228 and cis -and fr]thiophene 27 have been synthesized. Addition of chlorine to the 5,6-double bond of 31 affords a mixture of cis- and[Pg.206]

Bergmann and Meyer264 cyclized the 1,1-diarylpropenes (55 R = H or Cl) to the corresponding benzo[6]thiophene-1,1 -dioxides (56 R = H or Cl) using sulfuric acid. 3-Phenylbenzo[6]thiophene-l,l-dioxide is obtained by cyclization of the trans isomer of 57 under Friedel-Crafts conditions.265-266 Similar cyclization of 58 (R = H 267 or CH2CH2Ph268) affords the corresponding 2,3-dihydrobenzo[6]thio-phene-1,1-dioxide. Thioindoxy 1-1,1-dioxide (60) is obtained in 81%... 

Treatment of 3,4-dichlorosulfolane with ammonia affords 3a, 7a-dihydrobenzo[6]thiophene-1,1 -dioxide (107) as the major product, together with 113.379 380 3,4-Dibromosulfolane behaves analogously on treatment with pyridine.373,378... 

On being heated in an inert solvent (e.g., tetralin) at 180°-200°, benzo[6]thiophene-1,1-dioxide affords 6a, 1 la-dihydrobenzo[6]naph-tho[l,2-d]thiophene-7,7-dioxide (347a) through formation of the intermediate adduct 349, which readily loses sulfur dioxide.377,479, 729,730 kinetics of this self-condensation in various solvents have been studied recently.730 The product (347a) may be aromatized with palladium-charcoal,377-479 or by treating its dibromide with base,729 to give the sulfone (348a) of benzo[6]naphtho[l,2-d]thiophene, which... 

Dihydrobenzo[6]thiophene-l, 1-dioxide is metallated by ethyl-magnesium bromide in the 2-position to give the Grignard compound (355). Its 2-methyl,740-742 2-bromo,718or 2-ethoxycarbonyl215 derivative may be prepared by treating 355 with methyl iodide, bromine, or ethyl chloroformate, respectively. 2-(Ethoxycarbonyl)thioindoxyl-1,1-dioxide may be methylated in the 2-position by successive treatment with sodium ethoxide and methyl iodide.215... 

With chlorine or bromine, 3a,7a-dihydrobenzo[6]thiophene-l,l-dioxide (107) affords unidentified tetrahalogeno derivatives.750 Elimination of hydrogen chloride from 2,3-dichloro-2,3-dihydro-benzo[6]thiophene-l,1-dioxide occurs on treatment with pyridine to give 2-chlorobenzo[6]thiophene-1,1-dioxide.473... 

Dehydrogenation of 6-amino-2,3-dihydrobenzo[6]thiophene-l,l-dioxide with stannous chloride dihydrate is reported to afford 6-aminobenzo[6]thiophene-1,1-dioxide.475 It is noteworthy that 2-methyl-2,3-dihydrobenzo[6]thiophene-l,1-dioxide undergoes ring opening with potassium fer -butoxide to give a quantitative yield of 2-propenylbenzenesulfinic acid.279... 

Wolff-Kishner reduction of thioindoxyl-1,1-dioxide gives 2,3-dihydrobenzo[6]thiophene-1,1 -dioxide.543 754... 

With thiophenol in the presence of zinc chloride and hydrochloric acid, thioindoxyl-1,1-dioxide and related compounds give 3-phenyl-thiobenzo[6]thiophene-l, 1-dioxides, which afford the corresponding 2,3-dihydrobenzo[6]thiophene-l,1-dioxide on reduction with zinc and sodium hydroxide.756... 

The methylene group of thioindoxyl-1,1-dioxide condenses with aromatic aldehydes 271,753,756,757 and cyclopentanone.451 2-Aryl-idene-2,3-dihydrobenzo[6]thiophen-3-one-l, 1-dioxides give adducts... 

Cyclizations can occur with heteroatoms present in the tether as long as the groups are not strongly nucleophilic. Decomposition of a-diazo- 3-arylmethanesulfonyl esters (173) resulted in the formation of 1,3-dihydrobenzo[c]thiophene 2,2-dioxides (174 equation 38),143 which are valuable precursors to o-quinodimethanes. Reaction with /V-aryldiazoamides (175) has been shown to be a useful method for preparing 2(3//)-indolinones (176 equation 39),22a while reaction of a-diazo-(3-keto esters (177) has been developed as a process to synthesize 3-acetylbenzofiiran-2(3//)-ones (178 equation 40).144... 

Since hydrobenzo[c]thiophenes are often used as intermediates for the preparation of benzo[c]thiophene and its derivatives, it is convenient to review the chemistry of these compounds first. Hydro-benzo[c]thiophene 2-oxides and 2,2-dioxides are reviewed in Section VI and l,3-dihydrobenzo[c]thiophen-I-one and l,3-dihydrobenzo[c]-thiophen-l,3-dione are covered in Section VII. 

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