Reduction benzo thiophenes

Benzo[ >]thiophene dianion (173) has been prepared by reduction of benzo[ >J thiophene with sodium metal at - 78°C in [2H8]THF. The H and 13C NMR spectra of the purple solution obtained prove that it is the dianion and not a radical anion. This is the first example of a sulfur-containing (4n)Tr polycyclic dianion. The dianion undergoes oxidation to benzo[ ]thiophene with oxygen (85CC1033). 

The 77 -bound benzo[/ ]thiophene and dibenzothiophene complexes of iridium undergo reduction to the corresponding 77-complexes by hydride reaction with 2 mol of Red-Al results in addition of two H to give the cyclohexadiene complexes (Scheme 78) <2000CCR63>. 

Benzo[ ]thiophene 1,1-dioxides could be also prepared by the following reductive methods (Scheme 4) [65-67]. 

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]. 

Several refractory thiophenes, that are often not reductively removable by conventional refining processes, can be oxidized under these conditions, e.g. benzo-thiophenes are oxidized to the corresponding sulfoxides and sulfones using ultrasonic and microwave irradiation, respectively, in the presence of NaI04-silica [129]. A noteworthy feature of the procedure is its applicability to long-chain fatty... 

Ionic hydrogenation has been referred to in CHEC-I <84CHEC-I(4)741>. Logically, this has to find a place in this section, since it represents reaction of a thiophenium ion with a hydride ion derived from triethylsilane. This has been reviewed <85HC(44/i)457>. Reduction of 5-hydroxy-benzo[ >]thiophene with triethylsilane in TEA has given the 2,3-dihydroderivative <91SC959>. 

Benzo[(>]thiophene dianion has been prepared by reduction of benzo[(>]thiophene with sodium metal at — 78 C in pHgjTHF. The H and C NMR spectra of the purple solution obtained prove... 

The validity of the Hammett relationship log K/Ko = pa- has been extensively investigated for five-membered heteroaromatic compounds and their benzo analogues. The ratio Pheterocycie/Pbenzene is closest to Unity for thiophene. Judged from work on the polarographic reduction of nitro compounds, the ability to transmit electronic effects is HC=CH = S < O < NH. 

Benzo[6]thiophene, 4-N-methylcarbamoyl-biological activity, 4, 913 Benzo[6]thiophene, 2-methyl-3-vinyl-cycloaddition reactions, 4, 795 Benzo[fc]thiophene, 2-( 1 -naphthyl)-synthesis, 4, 915 Benzo[6]thiophene, 2-nitro-reduction, 4, 815 synthesis, 4, 923 Benzo[6]thiophene, 3-nitro-cycloaddition reactions, 4, 789 Benzo[6]thiophene, 4-nitro-synthesis, 4, 923 Benzo[6]thiophene, 5-nitro-synthesis, 4, 923... 

The reaction of butadiene with the sulfone of 3-benzo[6]thiophene-carboxylic acid under Diels-Alder conditions gives the adduct (32). Catalytic reduction over platinum oxide removes the 2,3-double bond. 

Cagniant and Cagniant have reported that succinoylation of benzo[6]thiophene under Friedel-Crafts conditions yields a separable mixture of the y-ketobutyric acids 42a and 43a in a ratio of 9 1 (combined yield 85%). Huang-Minlon reduction of 42a to the butyric acid (90%) followed by cyclization of the derived acid chloride (90%) was reported to yield 4-keto-l,2,3,4-tetrahydrodibenzothiophene (44a) (69% overall). Likewise, acylation of benzo[6]thiophene with the ester chloride of succinic acid in carbon disulfide-aluminum chloride gave a separable mixture (80%) of the 2- and 3-y-ketobutyric esters. Two alternative... 

The 4a,9b double bond in 1,2,3,4-tetrahydrodibenzothiophene 5,5-dioxide (68) and similar compounds, is essentially nonaromatic and in this respect resembles the 2,3 bond in benzo[6]thiophene 1,1-dioxide. Catalytic reduction of 68 results in the formation of l,2,3,4,4a,9b-hexahydrodibenzothiophene 5,5-dioxide (92 /o). Subsequent reduction of the sulfone with LAH yields 1,2,3,4,4a,9b-hexahydrodibenzothiophene (69) as an oil (78 /o). Oxidation of 4-keto-l,2,3,4-tetrahydrodi-benzothiophene (44a) to its sulfone with peracetic acid (63 /o) followed by... 

Similar reduction of benzo[Z)]thiophene furnishes the 2,3-dihydro derivative and o-ethylthiophenol. ... 

Thienothiophenes, like thiophenes and benzo[h]thiophenes, easily undergo reductive desulfurization with Raney nickel. The method was fvst applied in this series by Challenger et to determine the structures of 2-acetylthieno[3,2-h]thiophene and 2-acetylthieno[2,3-hl-thiophene the former gave 2-octanone (229), and the latter 5-methyl-heptan-2-ol (230) [Eqs. (75) and (76)]. 

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. 

Reduction of 3-nitro-2-(a>-nitrovinyl)benzo[6]thiophene (42) with iron and acetic acid in ethanol gave 43.49,50... 

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