Dithiophenes

Structures of naturally occurring dithiophenes with their Chemical Abstracts registry numbers are listed arbitrarily in Tables 1-7 according to their substitution patterns. 

The distribution of naturally occurring dithiophenes is detailed in Table 8, in which the genera are listed in alphabetical order. All genera 

Note the compound proposed to be 46 was subsequently proved to be 7 instead 36,12, 40). 

commutatus E. cornigerus E. dahuricus E. exaltus E. horridus E. humilis E. niveus E. persicus E. vitro 

sphaerocephalus E. spinosissimus E. strigosus E. viscosus Eclipta E. alba E. erecta 

---

Borepino[3,2-6 6,7-6 ]dithiophene, 4-methyl- H NMR, 1, 636 Borepinodithiophenes theoretical methods, 1, 633 Borepins... 

Similar results have been reported for 4,8-dihydrobenzo[l,2-c.- 4,5-c ]dithiophene-4-one (74JOC2239). In line with expectations, only the keto form of this compound was detected. 

Fraction 4 (P.E./CHjClj, 1 1) was a bright red solution the T1 NMR spectrum of which indicated a mixture of two acetylenic constituents (A and B) which were separated by preparative TLC on 1 mm silica gel plates. The red band (A), when left in soln for 15 hr at r.t., lost its color. The Tl NMR spectrum of the decolored soln was identical with the spectrum of compound B. Comparison of the physical data (1H NMR and MS) of the two compounds with the spectral data reported for the dithiophene (A) (10) and the thiophene (B)... 

A copper-mediated cyclization of metallated thiophenes has been utilized to prepare polycyclic thiophenes and thiophene cyclophanes. Treatment of dibromide 106 in succession with M-butyllithium (halogen-metal exchange), zinc chloride (transmetallation), and copper chloride gave 7//-cyclopcnta[ 1,2-fc 4,3-6 dithiophene (107) <00H(52)761>. This conversion has also been achieved using a palladium-mediated cyclization performed in the presence of hexamethylditin . Copper-mediated cyclizations have also been applied to the syntheses of cyclopenta[2,l-6 3,4-A ]dithiophen-4-one (108) (three steps from 73) <00S1253> and cyclophane 109 <00CC2329>. 

Novel C2-symmetric thiophene-containing ligands have recently been prepared and utilized in asymmetric synthesis. Dithiophene 158 was utilized as a ligand in the asymmetric reduction of p-ketoesters (prostereogenic carbonyl) and acrylic acids (carbon-carbon double bond) <00JOC2043>. Dibenzo[b]thiophene 159 was utilized as a ligand in enantioselective Heck reactions of 2-pyrrolines <00SL1470>. 

More activated substrates such as thiophene, produce a mixture of a,a -dithiophene mono-, di-, tri-, tetra-, and polysulfides. When both a-positions of thiophene are taken by methyl groups, a and a fused tricyclic product... 

Mas-Torrent M, Durkut M, Fladley P, Ribas X, Rovira C (2004) High mobility of dithiophene-tetrathiafulvalene single-crystal organic field effect transistors. J Am Chem Soc 126 984-985... 

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>. 

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>. 

Iodo-7-methylbenzo[l,2-/ 4,3- ]dithiophene 65 undergoes nucleophilic substitution on reaction with copper cyanide in DMF to produce the nitrile derivative 66 (Equation 10) <1997TL457>. 

The methyl substituent of 2-methyl-4,8-dihydrobenzo[l,2- 5,4-. ]dithiophene-4,8-dione 118 undergoes a number of synthetic transformations (Scheme 8), and is therefore a key intermediate for the preparation of a range of anthraquinone derivatives <1999BMC1025>. Thus, oxidation of 118 with chromium trioxide in acetic anhydride at low temperatures affords the diacetate intermediate 119 which is hydrolyzed with dilute sulfuric acid to yield the aldehyde 120. Direct oxidation of 118 to the carboxylic acid 121 proceeded in very low yield however, it can be produced efficiently by oxidation of aldehyde 120 using silver nitrate in dioxane. Reduction of aldehyde 120 with sodium borohydride in methanol gives a 90% yield of 2-hydroxymethyl derivative 122 which reacts with acetyl chloride or thionyl chloride to produce the 2-acetoxymethyl- and 2-chloromethyl-4,8-dihydrobenzo[l,2-A5,4-3 ]-dithiophene-4,8-diones 123 and 124, respectively. 

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>. 

---