Thiophene-2-lead

Does the fact that thiophene reacts similarly to benzene mean that it is aromatic One way to tell is to calculate first and second hydrogenation energies of thiophene, leading to dihydrothiophene and tetrahydrothiophene, respectively. (The energy of hydrogen is provided at right.)... 

Beckmann rearrangement (SOClj/McjCO) of the oximes of 2-acetyl-thieno[2,3-6] and [3,2-6]thiophene leads to the formation of 2-acetamidothienothiophenes identical with those obtained by reductive acetylation (Hj/Ni/AcjO) of the 2-nitro compound. ... 

Thiadisilacyclopropanes result from the reaction of disilenes with sulphur and episul-phides. From the mechanistic standpoint, the reaction of RR,Si=SiRR/ is of great interest and the separation of the (E)- and (Z)-isomers (trans and cis) [R = 2,4,6-( -Pr)3C6H2, R = t-Bu] has led to the separate addition of sulphur to each. This occurs within a minute to give trans and ds-isomers, respectively, the latter with slightly different Si—S bond lengths60. Propylene sulphide reacted similarly, and the reaction of (i-Bu)2Si=Si(Bu-t)2 with thiophene leads to sulphur abstraction with the formation of the thiadisilacyclo-propane, with Si—S bonds of 217.1 pm, along with the l,2-disilacyclohexa-3,5-diene and 2,6-disilabicyclo[3.1.0]hex-3-ene (equation 29)61. 

Although the Birch reduction of thiophenes leads to ring cleavage (equation the corresponding... 

Intramolecular stepwise transfer of two hydrides to the bound thiophene leads to a thioallyl intennediate (B), characterized by NMR spectroscopy, in which the sulfur-containing ligand itself has come to formally occupy three coordination sites, this is of interest if a similar mechanism were to be invoked for a heterogeneous catalyst, since then a highly unsaturated site (3 CUS) would be required, assuming that hydrogen activation takes place elsewhere, or has taken place previously at the same site. 

The action of hot phosphoric acid on thiophene leads to a trimer its structure suggests that, in contrast with pyrrole (16.1.1.8), the electrophile involved in the first C-C bonding step is the a-protonated cation. 

Uncontrolled -oxidation of a thiophene leads to 5, 5 -dioxides that from thiophene itself has been isolated, but above -40 °C it dimerises giving eventual products depending on concentration, but with substituted thiophenes the dioxides can be isolated. Peracids or dimethyldioxirane can be used, but do not succeed if there are electron-withdrawing substituents. A solution of fluorine in water (hypofluorous... 

Oxidatively generated electrophilic malonyl radicals react regiospecifically with thiophene to form (2-thienyl)malonic ester <88H(27)2627>. Treatment of thiophene with cerium(IV) sulfate and an excess of dimethyl malonate in methanol at room temperature yields 2-thienylmalonic ester in 85% yield. In this case, the initially formed cr-radical is oxidized by the cerium(IV) sulfate. 2-Methylthiophene similarly gives the 5-malonyl-substituted product. Benzo[i]thiophene leads to the 2-malonyl-benzo[Z)]thiophene in 41% yield. Monosubstituted malonates could also be used in this reaction. Thiophene and 2-acetylthiophene react with triethyl methanetricarboxylate in the presence of Mn(III) to form the corresponding thienylmethane tricarboxylic esters. Yields are about 55% <91S567>. 

Position Y must be functionalized. Compared with methyl, a phenyl group or a thiophene leads to a broader spectrum, but also to phytotoxicity on cereals. In parallel, some activity on broadleaf weeds and a strong inhibition on cytosolic ACC are observed. 

Oxidation of a thiophene leads to a dioxide, which in the case of thiophene itself dimerises in low yield, but with substituted thiophenes can be isolated peracids or 2,2-dimethyloxirane, which improves yields from 2,5-disubstituted thiophenes, can be used. The 5,5-dioxides are no longer aromatic thiophenes and react as dienes in Diels-Alder reactions generally sulfur dioxide is extruded from the initial adduct, leading to further reaction" - eventual aromatisation in the example shown. ... 

Photochemistry of Thiophens.—Wynberg and co-workers have continued their investigations on the photochemistry of thiophens, and an excellent essay by Wynberg on the photochemistry and other aspects of thiophen chemistry has recently been published. The photoisomerizations of thiophens are also discussed in a detailed review article on the photoisomerization of five-membered heterocyclics. Irradiation of 2-methyl-, 2-benzyl-, 2-neopentyl-, and 2-t-butyl-thiophens leads to their irreversible transformation to the corresponding 3-substituted derivatives in 8— 27% yields. 2,5-Di-t-butylthiophen rearranges irreversibly to the 2,4-isomer, which is remarkably stable under the reaction conditions. Irradiation of 2,2 -bithienyl leads to 2,3 -bithienyl and a small amount of benzo[6]thio-phen. 2,3 -Bithienyl affords 3,3 -bithienyl and benzo[6]thiophen as major products. 5,5 -Dideuterio-2,2 -bithienyl gives 5,5 -dideuterio-2,3 -bithienyl... 

Synthesis.—Rearrangement of 2- and 3-(propargylthio)thiophen leads to 2-methylthieno[2,3-6]thiophen (183) and 2-methylthieno[3,2-Z>]thiophen (184). A number of mono- and di-methylthieno[2,3-6]thiophens and thieno[3,2-6]thiophens, such as (284)—(286), were prepared by condensation... 

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