Thiophen 2,5-dibromo

Benzo[6]thiophene, 4,7-dialkoxy-synthesis, 4, 930 Benzo[6]thiophene, 2,3-dialkyl-synthesis, 4, 877-878 Benzo[6]thiophene, 3 -(dialkylamino)-synthesis, 4, 925 Benzo[c]thiophene, 1,3-diaryl-oxidative ring opening, 4, 768 Benzo[6]thiophene, 2,3-dibromo-reactions, 4, 830... 

Recent gas chromatographic analysis showed that about 9% of 2,3-dibromo-and 2% of 2,4-dibromothiophene is formed in the dibromination of thiophene. Sice, J. Am. Chem. Soc. 75, 3697 (1953). 

In the reactions of 2,5-disubstituted thiophenes elimination of an a-substituent occurs to a much greater extent than in the benzene series. The Friedel-Crafts acetylation of 5-bromo-2-ethylthiophene in the presence of SnCE gives 2-ethyl-5-acetyIthiophene. Elimination of an a-bromine occurs also in the chloromethylation of 2,5-di-bromothiophene, leading to a mixture of 2-bromo-5-chloromethyIthio-phene and 2,5-dibromo-3-chloromethyIthiophene. Bromine atoms at both the and -position are exchanged for chlorine in the... 

In contrast to 6-azidobenzo[/)]thiophene, which yields only benzo[i]thiophen-6-amine (9 %) and JVh,Ar(1-diethylbenzo[/)]thiopheiie-6,7-diamine (25 % bp 175-177 C/0.7 Torr), 6-azido-2,3-dibromobcnzojhjthiophene (1 a, R = R2 = Br) on irradiation in diethylamine in the presence of pyrene, a triplet nitrene quenching agent, yields a mixture of 2,3-dibromo-./V6,./V6-diethyl-benzo[5]thiophene-6,7-diamine (2a, R1 = R2 = Br 13%) and the 8W-thieno[2,3-r]azepine 3a.14<1 Likewise, methyl 6-azidobenzo[6]thiophene-2-carboxylate (lb, R1 = C02Me R2 = H) yields the thienoazepine ester 3b.147... 

The bromination behavior of isomeric thienothiophenes (53-55) has been studied in detail. Both the [2,3-b] (53) and the [3,2-h](54) isomers reacted with one equivalent of NBS in acetic acid to give an a-monobrominated product, with some evidence of 2,5-dibromo species also being formed. With 2 mol of NBS these latter products were formed in good yield three molar equivalents led to 2,3,5-tribromothieno-[2,3-h]-and -[3,2-6]-thiophenes (Scheme 28). The monobromo compounds can also be prepared from lithium derivatives quenched with bromine [76AHC( 19) 123]. Apparently the [2,3-c]isomer (55) also reacted initially in the 2-position. 

The direct Suzuki coupling of 2,6-dibromo-DTT 97 with (4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yIIS - -hexy 1-2,2 -hi thiophene 150 and (4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)-9,9-dimethyl-fluorene 152 gave... 

An improved synthesis of dithieno[3,2-A2, 3 -<7]thiophene 15a has been achieved from 2,3-dibromothiophene 304 (Scheme 57). Lithiation of 2,3-dibromothiophene 304 using -butyllithium followed by oxidative coupling with cupric chloride provided 3,3 -dibromo-2,2 -bithiophene 305 in 79% yield. Treatment of 305 with 2 equiv of -butyllithium in ether at —78 °C under nitrogen for 40 min and then adding benzenesulfonic acid thioanhydride and leaving the reaction mixture to reach room temperature afforded dithieno[3,2-A2, 3 -<7]thiophene 15a in 70% yield <2002TL1553>. 

Treatment of the benzo[6]thiophene derivative (82) with perchloric acid yields 2,4-diphenyldibenzothiophene. Reaction of 2,3-dibromo-... 

The heterocyclic 2,5-dilithio-3,4-di-(f-butyl)thiophene (78) could be generated by Nakayama and coworkers, starting from the corresponding 2,5-dibromo compound 77. The bromide-lithium exchange reaction was effected using two equivalents of... 

Zwanenburg and Wynberg also proposed another route to the thienothiophene (112). 2,5-Dibromo-3,4-bisbromomethylthiophene (116) was cyclized with sodium sulfide to give 4,6-dibromo-l f,3/f-thieno[3,4-c]thiophene (117) in 60% yield 117 was then reduced to thienothiophene (112). l,3,7,9-Tetrabromo-4i/,67f,10.H, 12ff-dithieno-[3,4 C 3, 4 -/i][l,6]dithiecin (118) (18%) was also formed during the ring closure. Oxidation of thienothiophene (117) followed by reduction by zinc in acetic acid gave l/f,3H-thieno[3,4-c]thiophene 2,2-dioxide (119). ... 

Biedermann and Jacobson, who first prepared thieno[2,3-6]-thiophene (1) in 1886, characterized it as a 2,3,4,5-tetrabromo derivative with m.p. 172°. Later Capelle reported the isolation of a dibromo derivative of thienothiophene 1 with m.p. 122.5°, which was shown by Challenger and Harrison to be 2,3,5-tribromothieno[2,3-6]thiophene (m.p. 123°-124°). Capelle also obtained a tetrabromide, m.p. 223°, by bromination of the product of reaction of acetylene with sulfur. The tetrabromide seems to be identical with that prepared from the product of reaction of methane, acetylene, and hydrogen sulfide, m.p. 229°-230°, and is evidently 2,3,5,6-tetrabromothieno[3,2-6j-thiophene. ... 

IR spectroscopy has shown that thienothiophenes 1 and 2 are brominated with iV-bromosuccinimide to furnish dibromo along with monobromo derivatives. An unpurified bromination product of thienothiophene 1 contained 8% of the initial thienothiophene 1,83% of 2-bromothieno[2,3-fe]thiophene, and 9% of 2,5-dibromothieno[2,3-fc]-thiophene 15% of the initial thienothiophene 2, 70% of 2-bromothieno-[3,2-6]thiophene and 15% of 2,5-dibromothieno[3,2-6]thiophene were detected on bromination of thienothiophene 2. ... 

Treatment of 2,3,5-tribromothieno[3,2-h]thiophene with n-butyl-lithium followed by hydrolysis produced 74% yield of 2,6-dibromo-thieno[3,2-h]thiophene, and treatment with zinc dust in glacial acetic acid formed 3-bromothieno[3,2-h]thiophene, containing unsubstituted thienothiophene 2 and the 2,6- bromo comixiund as impurities. Pure 3-bromothieno[3,2-fi]thiophene was isolated using preparative gaa-liquid chromatography. 2,3,5-Tribromothieno[2,3-6]thiophene similarly afforded 3-bromothieno[2,3-h]thiophene. 

Similarly 4,6-dibromo-l/f,3H-thieno[3,4-clthiophcne (117) affords 90% of the 2,2-dioxide (219) the last can be debrominated to IHtiH-thieno[3,4-c]thiophene-2,2-dioxide (119) with zinc in acetic acid [Eq. (72)1. 

The related polythiophene 64 has been produced in 63% yield by a Stille coupling from 2-(tributylstannyl)-3,4-(ethylenedioxy)thiophene and 2,6-dibromo-4f/-cyclopenta[2,l- 3,4- ]dithiophen-4-one catalyzed by PdCl2(PPh3)2 or Pd(PPh3)4 in refluxing toluene <2004CM3667>. 

Treatment of 2-methoxy-5-methylthiophene with NBS gave a 4 1 mixture of 3- and 4-bromo products, with some 3,4-dibromination also evident. The dibromination became more significant when 2 mol of NBS were used. Similarly 2-methoxythiophene gave the 3,5-dibromo derivative (84BAU1447). Bromination of 2-(2 -thienyl)-thiophenes (21) and 2-(3 -thienyl)-thiophenes gave the 5- and 2-bromo products in high yield [79CS157 91H(32)1805]. With four molar equivalents of bromine in acetic acid the tetrabromo derivative (22) was obtained in 97% yield. Reduction removed the 5,5 -bromines preferentially [91H(32)1805] (Scheme 9). This... 

The electrochemical conversion of 2,5-dibromo-3-substituted thiophenes to the corresponding thienylzinc species has been achieved by a similar method in an undivided cell fitted with a zinc sacrificial anode using catalytic amounts of NiBr2(bpy) as the catalyst43. The overall reaction giving (11) and (12) is presented in equation 35. The results are reported in Table 3. 

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