3-Methyl-2- thiophene, formation

Oxidation of thiophene and its derivatives was studied using hydrogen peroxide (H2O2), t-butyl-hydroperoxide and Ti-Beta redox molecular sieve as selective oxidation catalysts. A new reaction pathway was discovered and investigated using C-13 NMR, GC, GC-MS, HPLC, ion chromatography, and XANES. The thiophene oxidized to thiophene-sesquioxide [3a,4,7,7a-tetrahydro-4,7-epithiobenzo[b]-thiophene 1,1.8-trioxide] and the sesquioxide oxidized mostly to sulfate. 2-Methyl-thiophene and 2,5 dimethylthiophene also oxidized to sulfate and sulfone products. The Benzothiophene oxidation product was sulfone. This proposed new reaction pathway is different from prior literature, which reported the formation of thiophene 1,1-dioxide (sulfone ) as a stable oxidation product... 

On heating the sulfonium ylide 464 (R = H) the isomeric bis(methoxycarbonyl)methyl-thiophene 465 is formed. Thermolysis of the ylide 464 (R = Cl) yields the thienofuran 466. When heated in the presence of copper or rhodium catalysts, 464 (R = Cl) undergoes cleavage of the carbonsulfur bond resulting in the formation of carbenoid intermediates which can trapped with activated aromatic substrates or alkenes to yield the corresponding arylmalonates or cyclopropanes, respectively. 

The related reaction of [Os3(CO)io(NCMe)2] with 2-methylthiophene " results in the formation of [Os3(/i-H)( /-C4H2MeS)(CO)io] (21b, 22b) proton NMR indicates that this thienyl cluster also exists as exo (major) and endo (minor) isomers. The thienyl compounds that are formed with thiophene and 2-methyl-thiophene can be compared with the reported furyl complex [Os3(jU-H)(//-C4H30)(CO)io], which is formed in a similar way from furan. " -" ... 

Lithiation of 3-methylthiophene and subsequent addition of an electrophile, in this case methyl iodide, produces a mixture of products at the C2 or C5 positions, with the 2,4-disubstituted thiophene predominating. However, a strong electron-withdrawing or sterically hindered C5-substituent will direct the formation of the C5 methylated thiophene to the more sterieally favorable position. ... 

A two-phase thermochromic behavior, as in PDDT and poly(3-methyl-4-octyloxythiophene), is related to the formation of delocalized conformational defects upon heating. These defects are possible due to the presence of sterically demanding substituents between each consecutive repeating unit [330]. In the solid state at room temperature, PDDT and poly(3-octyloxy-4-methyl-thiophene) have a coplanar conformation for the main chain. Heating (25 to 150°C) increases the repulsive intrachain steric interactions and introduces some conformational disorder in the side groups, forcing the polymer backbone to adopt a nonplanar conformation [331, 332]. Temperature dependent UV/vis absorption measurements of fluorinated PTs, e.g., poly(3 -perfluorohexyl-2,2 5, 2"-terthiophene), poly[3-(pentadecafluorooctyloxy)-4-methylthiophene] and poly[3-(tridecafluorononyl)thiophene], show a blue shift of the maximum... 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

Complexes 79 show several types of chemical reactions (87CCR229). Nucleophilic addition may proceed at the C2 and S atoms. In excess potassium cyanide, 79 (R = R = R" = R = H) forms mainly the allyl sulfide complex 82 (R = H, Nu = CN) (84JA2901). The reaction of sodium methylate, phenyl-, and 2-thienyllithium with 79 (R = R = r" = R = H) follows the same route. The fragment consisting of three coplanar carbon atoms is described as the allyl system over which the Tr-electron density is delocalized. The sulfur atom may participate in delocalization to some extent. Complex 82 (R = H, Nu = CN) may be proto-nated by hydrochloric acid to yield the product where the 2-cyanothiophene has been converted into 2,3-dihydro-2-cyanothiophene. The initial thiophene complex 79 (R = R = r" = R = H) reacts reversibly with tri-n-butylphosphine followed by the formation of 82 [R = H, Nu = P(n-Bu)3]. Less basic phosphines, such as methyldiphenylphosphine, add with much greater difficulty. The reaction of 79 (r2 = r3 = r4 = r5 = h) with the hydride anion [BH4, HFe(CO)4, HW(CO)J] followed by the formation of 82 (R = Nu, H) has also been studied in detail. When the hydride anion originates from HFe(CO)4, the process is complicated by the formation of side products 83 and 84. The 2-methylthiophene complex 79... 

Interaction of the iron metal atoms with thiophenes (thiophene, 2-methyl-, and 2,5-dimethylthiophene) in the vapor phase at 77 K with subsequent heating in a carbon monoxide atmosphere also leads to the formation of ferrole 83 [76JOM(l 18)37, 77CJC3509]. The iron cyclopentadienyl ring is planar and all the bonds have multiple character. 

The [2 + 2] photodimerization of a, j8-unsaturated sulfones is correctly viewed as a photoreaction of alkenes, rather than the sulfone group, and this aspect has been reviewed recently by Reid, as part of a wider survey of the photoreaction of O- and S-heterocycles. The topic continues to attract considerable interest and a few recent examples, as well as some synthetic applications, will be discussed here. Much of the photodimerization work has been carried out on the benzo[fc]thiophene (thianaphthene) 1,1-dioxide system. For example. Porter and coworkers have shown that both 3-carboxybenzo[i]thiophene 1,1-dioxide (65) and its methyl ester give only the head-to-head (hth), anti dimer (66) on irradiation in ethanol. In a rather unusual finding for such systems, the same dimer was obtained on thermal dimerization of 65. Similar findings for a much wider variety of 3-substituted benzo[fi]thiophene 1,1-dioxides have been reported more recently by Geneste and coworkers . In the 2-substituted analogs, the hth dimer is accompanied by some of the head-to-tail (htt), anti dimer. The formation of the major dimer appears to proceed by way of an excited triplet and the regiochemistry observed is in accord with frontier MO theory. 

The authors confirmed the formation of vinyl Ru-complex 21 by the reaction of [Cp Ru(SBu-t)]2 with methyl propiolate (Eq. 7.15). To my knowledge, this is the first observation of the insertion of an alkyne into the M-S bond within a catalytically active metal complex. In 2000, Gabriele et al. reported the Pd-catalyzed cycloisomerization of (Z)-2-en-4-yne-l-thiol affording a thiophene derivative 22 (Eq. 7.16) [26]. 

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