Dibenzo thiophene complexes

Pathway III of Fig. 26 has been demonstrated for thiophene and benzo-thiophene with Ir complexes (4) and for all thiophenes, including dibenzo-thiophene, with Rh complexes (94, 95). These oxidative additions appear to be influenced by substituents present on the carbon atoms adjacent to the sulfur atom. Insertion between sulfur and the unsubstituted carbon is highly preferred. For 2-methylthiophene the exclusive product is the 1-5 bond insertion product, whereas for 3-methylthiophene, no preference for insertion was observed (1-2 and 1-5 bond insertion products were equal). In competitive studies, thiophene was found to be about twice as reactive as 2,5-dimethylthiophene. This behavior is similar to that observed for relative reaction rates of substituted thiophenes observed with conventional HDS catalysts. Thus steric limitations can occur, even with monomeric, homogeneous catalysts. 

TABLE 2.4. Known Ti complexes of the benzo- and dibenzo-thiophenes. 

Sulfur-containing compounds These may be thiols, sulfides, thiophenes, benzo- and dibenzo-thiophenes, and more complex structures. Solvent extraction reduces measured sulfur levels and therefore the content of sulfur compounds in solvent refined lubes in solvent refined lubes, oxidation studies show that there appears to be an optimum level for sulfur compounds. Lube hydrocracking generally will reduce sulfur to about 10 ppm or less in the base stocks. The 4,6-di-alkyl... 

Complexation of dibenzo-18-crown-6 ether with 3,6-dimethylthieno[3,2-Z)] thiophene-2,5-dione 293 (77JCS(P2)1327), homolytic aromatic silylation of 2-cyanothieno[2,3-Z)]- and -[3,2-Z ]thiophenes (79G395), addition of silyl radicals to 3,6-dimethylthieno[3,2-Z)]thiophene-2,5-dione and 5-benzylidene-3,6-dimethylthie-no[3,2-Z)]thiophen-2-one (86JA4993) and the conformational behaviour of the dithieno[3,2-Z 2, 3 -< -thiophene-2,6-dicarbaldehyde radical anions (78JCS(P2)212) were studied by ESR spectroscopy. 

A review entitled thiophenes from Viktor Meyer to Poly (thiophene) some reactions and synthesis was published in a special issue of Phosphorus, Sulfur and the related elements (13PS287). Over 80 reaction schemes are presented outlining important discoveries in the chemistry of thiophenes. Another review generalized published data on the reactions of 4-(2-R-aryl)-1,2,3-thia- and selenadiazoles (13RJOC479). Special emphasis on the use of these selenadiazole for the synthesis of 1-benzothiophenes, 1-benzosele-ophenes, and their more complex derivatives was presented. A recent review on recent advances in the use of the Wfllgerodt-Kindler reaction in thiophene syntheses appeared this year (13CSV7870). Extensive reviews on selenium and tellurium chemistry from small molecules to biomolecules and materials (B-13M001) as well as data on the synthesis, reactions, crystal structures, and spectral characteristics of benzo[b]tellurophene, dibenzo[b,d]... 

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