3,4-dibromo thiophene

H- 1-Benzothiin, 3-bromo-4-hydroxy-3,4-dihydro-dehydration, 3, 908 2//-1-Benzothiin, 3,4-dibromo-thiophene synthesis from, 4, 902 277-1-Benzothiin, 3,4-dihydro-acylation, 3, 908 sulfilimines from, 3, 905 277-1-Benzothiin, 4-ethoxy-reactions... 

Magnesium, Copper, and Tin. 3-Substituted 4-aryl-2,5-dibromo-thiophens give dimagnesium compounds, when the Grignard reagent is prepared by the entrainment method (simultaneous reaction with... 

I.r. Spectra and Dipole Moments.—Complete sets of harmonic symmetry force constants have been developed for several heterocyclics, including thiophen. The calculations were based on observed vibrational frequencies from the literature. Calculated frequencies for [ H4]thiophen, [2,5- H2]thiophen, and [3,4- Ha]thiopheu are given. The i.r. (3650— 50cm ) and Raman spectra of 2-chloro- and 2-bromo-thiophen, 2,5-dimethyl-, 2,5-dichloro-, and 2,5-dibromo-thiophen, in the liquid state, have been interpreted. The spectroscopic thermodynamic functions have been calculated and the values for 298 K have been reported. The... 

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>. 

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