2.1.3- Benzothiadiazole 4.7- dibromo

Bromination of (1) leads to the tetrabromide which, when treated with base, forms 4,7-dibromo-2,1,3-benzothiadiazole <70RCR923>. It was subsequently demonstrated that the 4,6-dibromo (20%) and a trace of the 4,5-dibromo derivatives are also produced in this reaction <70JHC629>. In the presence of iron, bromination of a melt of (1) yields almost exclusively the 4,7-dibromo derivative even when equimolar quantities of bromine are used. As in the chlorination of (1), the process under these conditions cannot be limited to monosubstitution <70RCR923>. Monobromination and subsequent dibromination can be achieved, however, when the reaction is carried out by dropwise addition of bromine to (1) in 47% hydrobromic acid at 130°C <70JHC629>. 

The mildness of the Sonogashira coupling conditions allows for the functionalization of otherwise sensitive substrates too. The dibromo derivative of 2,1,3-benzothiadiazole was reacted with different pyridylacetylenes to give the expected fluorescent products (8.28.). The intermediate mono-coupled product was also isolated in each case, although in varying yield.37... 

Electron-donating substituents at the C-4 atom direct the incoming nitro group to the position 5 or 7 however, the amount of 7-nitro isomer is higher than that of 4-nitro isomer [222-234], The direction of the nitration of di- and tri-substituted 2,1,3-benzothiadiazoles is determined by the position and electron nature of substituents [223, 227, 229, 230, 232, 235-239], Ipso-nitration of 4,7-dibromo-2,l,3-benzothiadiazole to form 4-bromo-7-nitroderivative has been reported [235],... 

The mass spectral characteristics of 4,7-dibromo-5,6-dinitro-2,l,3-benzothiadiazoles and 4-bromo-5-nitro-6,7-(2, l, 3 -oxadiazole)-2,l,3-benzothiadiazole have been considered [1361],... 

The polymer 12c can be prepared with the similar method to Example 10 (eqn (14.15)). The mixture containing monomer 32 (0.1154g, 0.1463mmol), 4,7-dibromo-2,l,3-benzothiadiazole (0.409g, 0.1393 mmol), AsPhs (16% mol) and Pd2(dba)3 (4% mol) in 1.2mL of degassed chlorobenzene was heated by microwaves at 120 °C for 5 min, 150°C for 5 min and finally 180 °C for 2h. After cooling to room temperature, the precipitate was collected with 0.45 pm nylon filter in cold methanol (100 mL) and washed in a Soxhlet apparatus with acetone, hexanes and then chloroform. The chloroform fraction was condensed and then poured in methanol. After filtration through 0.45 pm nylon filter, the polymer 12c was obtained in 73% yield. The and Mw/M of polymer 12c were 12 400 and 1.7, respectively. 

To a solution of 4,7-dibromo-2,l,3-benzothiadiazole (73.5 mg, 0.25 mmol) in a mixture of water (3 mL) and toluene (6 mL), potassium carbonate (828 mg, 6 mmol) and monomer 9a (182 mg, 0.25 mmol) are added. The mixture is degassed for 30 min and Pd(PPh3)4 (5 pmol) is added. The resulting mixture is heated at 85 °C for 20 h and then poured into a large amount of acetone. The precipitate is filtered, washed with methanol and acetone and then dried under vacuum to afford 9b as a bright yellow powder. Yield 65%. 

Example 22 Suzuki Cross-coupling Polymerization of 2,7-Dibromo-4,4,9,9-tet-raalkyl-4,9-digerma-4,9-dihydro-s-indaceno l,2- 5,6- )ditiIiophene (dibromo-digermaindacenodithiophene) (42) with 2,l 3-Benzothiadiazole-4,7-bis(boronic Acid Pinacol Ester) (43) to give P44-PGeTPTBT ... 

The Ar-H functionalization approach has also been used in the preparation of polymers. For instance, a diketopyrrolopyrrole-based polymer was prepared via a palladium-catalyzed direct C-H (hetero)arylation reaction between a di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-l,4-dione and 4,7-dibromo-2,l,3-benzothiadiazole (eq31). The reaction was conducted using palladium acetate as the catalyst and pivalic acid as an additive. A survey of different phosphines demonstrated that molecular weights of the same order and similar polydispersity indexes (PDI) were obtained using tri-terf-butylphosphonium and tri-ferf-cyclohexyl tetrafluoroborate. ... 

Bo et al. reported the synthesis of a series of D-A alternating conjugated polymers P24-31 with 5,6-bis(octyloxy)benzothiadiazole as the acceptor unit by Suzuki polyeondensation of dibromo monomers and 5,6-bis(octyloxy)benzo-thiadiazole based diboronic acid pinacol ester. P24) with a of 102 kg mol and a PDI of 1.66, gave a PCE of 5.08% in devices with P24 PC7iBM as the active... 

A number of useful replacement reactions in the 2,1,3-benzothiadiazole series involve the production and reactions of their nitriles. 4,7-Dicyano-2,l,3-benzothiadiazole is of particular interest because of its potent herbicidal and defoliating activity. It is produced by the action of a pyridine-copper(n) cyanide complex on the readily available 4,7-dibromo-compound. Other nitriles of this series are similarly obtained. A second method, of more limited applicability, is the Sandmeyer reaction, which, in the present instance, gives improved results when the amino-2,1,3-benzothiadiazoles are diazotized with nitrosyl-sulphuric acid. The nitriles are convertible by conventional methods into other functional derivatives. Successive coupling with diazotized aniline, and... 

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