Benzo dithiophenes

In recent work, the eleetron-rich units, alkylthienyl-substituted benzo-dithiophenes (BDTT), are aetively utilized to construct D-A1-A2 terpolymers... 

Gas-phase photoelectron spectroscopy (PES) has been used in conjunction with theoretical calculations to investigate the hole-vibrational and electron-vibrational couplings in fused benzodithiophenes. The first ionization energies of benzojl,2- 5,4- ]dithiophene 21 and benzo[l,2-A4,5- ]dithiophene 22 were found to be to be 7.585 and 7.573eV, respectively <2006CEJ2073>. 

The methylene protons in cyclopentadithiophenes absorb at 5 = 6.36-6.52 ppm <1996CHEC-II(7)841>, and subsequent studies have shown that the methylene protons in 4-substituted cyclopentadithiophenes absorb at slightly higher b values <1999SM(102)1000, 2002OL4535>. In a-substituted benzo[2,T7 3,4-7 ]dithiophene-4,5-diones 28, the methylene protons absorb around b = 7.32-7.68 ppm <2003SM(135)85>. 

Benzo[l,2-A4,5- ]dithiophene 22 undergoes photochemical [2n+2n] cycloaddition with electron-deficient buta-diynes on irradiation at 300 nm to produce photoadducts in low yields. The reaction with dimethyl acetylenedicar-boxylate proceeds directly to produce the secondary photoadduct 56 (Equation 6) <2003JOC8258>. 

Benzo[l,2- 4,3-7 ]dithiophene 59 undergoes monoformylation using the Vilsmeier reagent in toluene (Equation 8) <2000CC1139, 2001CM3906>. 

An intramolecular Friedel-Crafts approach has also been employed to synthesize l,3,5,7-tetramethyl-4,8-dihydro-benzo[l,2-f 4,5-f ]dithiophene-4,8-dione <20030L1883>. 

The isomeric benzo[l,2-A4,3- ]dithiophene-4,5-quinone is prepared in reasonable yields by a one-step Friedel-Crafts reaction of 3,3 -bithienyl with oxalyl chloride in refluxing 1,2-dichloroethane over 7-10 days (Equation 85) <2001JA11899>. 

A similar analysis has been done91 on CT-complexation of the series benzene, benzothiophene, benzo[l,2-b, 4,3-b ]dithiophene ([3]SBS), and the homologs [5]SBSBS and [7]SBSBSBS with TCNQ as the acceptor. Beside association constants, also AH- and AS-values were determined by measurements at different temperatures (Table 21). It is striking that the gradual increase of the association constant in the series is interrupted at [5]SBSBS the next member has even a lower value. 

Research Focus Synthesis of poly(4,8-didodecyl-2,6-bis-(3-methyl-thiophen-2-yl)-benzo[l,2-b 4,5-b ]dithiophene) derivatives for use as semiconductors in... 

A CNDO study on benzo[l,2-c 4,5-c ]dithiophene predicted that it would be more polar than thieno[3,4-c]thiophene, and that excess electron density would be distributed at the bridgehead carbon atoms. A singlet ground state was also predicted <75ACR139>. The heats of atomization, charge densities, and resonance energies of a series of benzodithiophenes were calculated <80T27il>. A [c] fusion led to less resonance stabilization of a system than a [b] fusion. 

Ab initio calculations, using a 4-31G basis set, have been used to predict intramolecular interactions of sulfur lone-pair electrons in two benzo[c rf ]dithiophenes <87CL257>. On some cyclo-octatetraenes with fused hetero rings these calculations suggested an increase in the length of the fused bond (91JOC5426). 

Benzo[l,2-6 4,5-6 ]dithiophene undergoes metallation at the 2-position, allowing formylation with dimethylformamide <83MAC627>, and treatment of a benzo[l,2-6 4,3-6 ]dipyrrole (26a) with LITMP and excess methyl chloroformate afforded a 2-carboxylic ester (26b) <87H(25)70i>. 

The synthesis of the benzo[l, 2-b 4,5-6 ]difuran (56) is a variation of a common approach involving base-catalyzed cyclizations <87CA(106)176085>. Other variations formed 2-nitrobenzodifurans by cyclization of o-nitromethoxy aldehydes <87CA(107)211476>. The acidity of the 5-methyl protons in the bismethylthio dialdehyde (57a) allowed base-catalyzed cyclization to the benzo[2,l-6 3,4-6 ]dithiophene (58) <91BSB1>. 

The acid-catalyzed cyclization of appropriate aryloxyketones formed benzo[l,2-6 5,4-6 ]difuran and benzo[ 1,2-6 4,5-6 ]difuran (63BSF1003). Another variation involved the cyclization of an aryl thioacetal to a benzo[l,2-6 4,5-6 ]dithiophene <86CB3198>. In investigations of the synthesis of a unit of the CC-1065 skeleton (see Section 7.21.12), a carbene derived from the azo-compound (59) constructed the cyclopropano-fused benzodipyrrole (60) by simultaneous formation of the heterocyclic ring and the cyclopropane ring <83TL4773>. 

Electron impact mass spectrometry of 2,2 -dibromo-3,3 -dithienyl gave a radical cation of benzo[2,l-6 3,4-6 ]dithiophene <90JHCI867>. 

A similar mercaptoacetate addition reaction to 5-acyl-4,7-dioxo-4,7-dihydrobenzo[i]thiophene-2-carboxylates followed by cyclization and oxidation to give benzo[ 1,2-6 5,4-ft ]dithiophene-4,8-dione derivatives 29 has been shown <03H1689>. Nitrogen bridged heterocycles, 3-(benzylthio)thieno[3,4-6]indolizine derivatives 30 have been synthesized and intramolecular arene-arene interactions within these compounds were reported <03CPB75>. The arene-arene interaction leads to significant shifts in the proton NMR signals and red shifts in the absorption maxima. 

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