Regioselective synthesis of 2,4-disubstituted thiophenes

A highly regioselective route was established to 2-aryl-, 2-cyclohexyl-, and 2-(2-arylethyl)4-alkylthiophenes, which are potential candidates as liquid crystalline compounds of low viscosity. The key synthetic intermediates, 2-substituted-4-(chloromethyl)thiophenes 6, 14, and 20 were prepared respectively from the reactions of β, γ-epoxycarbonyl compounds 5, 13, and 19 with Lawesson's reagent in the presence of a catalytic amount of p -toluenesulfonic acid. The epoxycarbonyl compounds were obtained from the TiCl₄-mediated reactions of 2-(chloromethyl)-3-(trimethylsliyl)propene (10) with acid chlorides followed by epoxidation with m-chloroperoxybenzoic acid, or from prior epoxidation followed by oxidation with pyridinium dichromate of homoallylic alcohols 3. The homoallylic alcohols 3 were synthesized from the reactions of 2-(chloromethyl)-3-(trichlorosilyl)propene (2) with aldehydes in N, N-dimethylformamide. Copper (I) catalysed cross-coupling reactions of 2-substituted-4-(bromomethyl)thiophenes (which were prepared by transhalogenation of 2-substituted-4- (chloromethyl)thiophenes with NaBr in acetone) with Grignard reagents afforded 2,4-disubstituted thiophenes. Using this method, eleven 2,4-disubstituted thiophenes were synthesized and their potentials as liquid crystalline compound of low viscosity were examined. The synthesized 2-(4-cyanophenyl)-4-pentylthiophene was observed to have a lower melting point than the corresponding 2,5-disubstituted thiophene. This observation is consistent with the expectation from the basis of molecular linearity which can affect the viscosity and/or melting point of crystalline compounds.     

Electrophilic substitution reactions of metallabenzynes

The electrophilic substitution reactions of metallabenzynes Os(≡CC(R)═C(CH(3))C(R)═CH)Cl(2)(PPh(3))(2) (R = SiMe(3), H) were studied. These metallabenzynes react with electrophilic reagents, including Br(2), NO(2)BF(4), NOBF(4), HCl/H(2)O(2), and AlCl(3)/H(2)O(2) to afford the corresponding bromination, nitration, nitrosation, and chlorination products. The reactions usually occur at the C2 and C4 positions of the metallacycle. These observations support the notion that metallabenzynes exhibit aromatic properties.     

Electrophilic substitution reactions of dipyrroheptane

Dipyrroheptanes have been reacted with a number of electrophiles, including aryldiazonium salts, acyl chlorides and isocyanates to give selectively the mono- or disubstituted derivatives. The bis(trichloroacetyl) dipyrroheptane can be used for the synthesis of amide and ester derivatives.     

Electrophilic substitution reactions of 2-furylcyclopropanes

2-Furylcyclopropanes undergo typical electrophilic substitution reactions. In acetylation and Vilsmeier formylation, the substituent enters the 5 position of the furan ring without involvement of the three-membered ring; this may serve as a convenient method for the synthesis of 2-formyl- and 2-acetyl-5-cyclopropylfurans.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1591–1593, December, 1972.     

Increased efficiency in cross-metathesis reactions of sterically hindered olefins

Efficiency in olefin cross-metathesis reactions is affected upon reducing the steric bulk of N-heterocyclic carbene ligands of ruthenium-based catalysts. For the formation of disubstituted olefins containing one or more allylic substituents, the catalyst bearing N-tolyl groups is more efficient than the corresponding N-mesityl catalyst. In contrast, the formation of trisubstituted olefins is more efficient using the N-mesityl-containing catalyst. A hypothesis to explain this dichotomy is described.     

Rapid consecutive three-component coupling-Fiesselmann synthesis of luminescent 2,4-disubstituted thiophenes and oligothiophenes

(Hetero)aroyl chlorides, alkynes, and ethyl 2-mercapto acetate can be reacted in a consecutive three-component synthesis to give 2,4-disubstituted thiophene 5-carboxylates in good to excellent yields. In the sense of a pseudo-five-component reaction highly blue luminescent symmetrical terthiophenes and a quinquethiophene can be synthesized in excellent yield.     

Synthesis and some reactions of sterically hindered 3-imidazoline 3-oxides

Sterically hindered 3-imidazoline 3-oxides were obtained by condensation of -amino oximes with ketones. It is shown that the reaction of these compounds with electrophilic agents takes place at both the nitrone grouping and the amino group. The oxidation of the products makes it possible to obtain stable nitroxyl radicals.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 103–109, January, 1979.     

The application of vinamidinium salts to the synthesis of 2,4-disubstituted thiophenes

The synthesis of 2,4-disubstituted thiophenes by the condensation of symmetrical vinamidinium salts with methyl thioglycolate has been accomplished for the first time. Simple experimental conditions were used to prepare seven different methyl 4-aryl-2-thiophenecarboxylates, three of which are new compounds.     

Electrophilic substitution reactions of 3-acetylamino-5-methoxybenzofuran

The formylation, aminomethylation, azo coupling, and bromination reactions of 3-acetylamino-5-methoxybenzofuran have been investigated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 179–181, February, 1987.     

Electrophilic substitution reactions of acylated 2-aminoindole derivatives

The bromination, nitration, and acylation reactions of various acyl derivatives belonging to the 2-aminoindole series of compounds have been investigated. It has been found that substitution occurs both at the -carbon atom as well as at the 5- and 6-positions of the benzene ring. The ratio of reaction products depends upon the nature of the electrophile as well as on the degree of substitution of the 2-aminoindole.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 941–945, July, 1985.     

Electrophilic substitution reactions of alkylated 2-aminoindole derivatives

Bromination, nitration, and acylation of 1-methyl-2-dimethylaminoindole under mild conditions proceed to give the 3-substituted reaction products. In acidic media, in which the parent indole exists in the form of an amidinium cation, substitution occurs in the 5-position of the benzene ring. Aminoindoles, which are capable of existing only in the iminoindoline or aminoindolenine forms, always give products derived from substitution at the para position relative to the nitrogen atom, regardless of the reaction conditions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 946–951, July, 1985.     

Pyrrolopyrimidines. 1. Electrophilic substitution reactions of 1,3-dimethylpyrrolo[3,2-d]pyrimidine-2,4-dione

The reactions of halogenation, aminomethylation, acylation, and azo coupling in 1,3-dimethylpyrrolo[3,2-d]pyrimidine-2,4 dione proced at position 7, whereas nitration in acetic acid is directed primarily to position 6. In a num of cases, products of substitution of both hydrogen atoms in the pyrrole ring have been synthesized.Communication 11 from series Purines, pyrimidines, and condensed systems based on these compounds. For Communication 10, see [1].Rostov State University, Rostov-na-Donu 344104. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1242–1248, September, 1994. Original article submitted September 6, 1994.     

Reaction of sterically hindered o-benzoquinones with diazomethane

Conclusions In contrast to certain o-benzoquinones, the sterically hindered o-quinones react with CH₂N₂ both at the oxygen atoms to give cyclic ethers, and at the C=C and C=O bonds of the quinoid ring; the predominant direction of the reaction depends on the ratio of the reactants.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2360–2362, October, 1981.     

Modification of PET with sterically hindered diols

Poly(ethylene terephthalate) was modified by incorporating bis(hydroxyethyl) tetrasubstituted terephthalates (methyl, chlorine, and bromine) as a third component in the mole ratios of 2–50% (based on dimethyl terephthalate) which resulted in random copolyesters. The presence of steric hindrance imparted additional chain rigidity to the copolymer structure, as shown by increased glass transition temperature (T_g). The effectiveness of the steric groups for conferring rigidity to the copolymer structure was CH₃ > Cl?Br. The copolyesters which contained halogen substituents showed substantial enhancement in flame retardency compared with PET.     

Electrophilic aromatic substitution reactions of 1,2-dihydro-1,2-azaborines

The aromatic boron-nitrogen heterocycle 1,2-dihydro-1,2-azaborine undergoes classical electrophilic substitution. These reactions allow easy functionalization to provide a variety of 3- and 5-substituted derivatives. [reaction: see text].     

Arylation of nitromethane with sterically hindered aryl halides

Efficient conditions for Pd-catalyzed cross-coupling of sterically hindered aryl halides with nitromethane were developed to give corresponding aryl nitromethanes. The opportunity to carry out the reaction of polynitromethylation under these conditions was demonstrated, as well as to use the obtained products in the synthesis of bisnitrile oxides.

     

Reaction of sterically hindered gem-dialkylcyclohexadienones with acid agents

Conclusions A study was made of the reactions of six sterically hindered gem-dialkylcyclohexadienones with hydrogen chloride, aluminum bromide, acetic acid, and solutions of sulfuric acid in acetic acid and in acetic anhydride.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 178–180, January, 1972.