Thienyl lithium

Thienyliodomium salts (e.g., 28, 29) can be made by direct oxidation of thiophene with iodine in either the +5 or the +3 oxidation states (58JA4279), or by iodination of thienyl-lithium species (77JHC281 80CS(15)135). Such compounds are, however, of limited use only for the synthesis of halogenated thiophenes (Scheme 11). 

Lithiation of benzo[6]thiophene occurs exclusively at position 2, leading to good yields of 2-substituted products. 2-Methoxybenzo[6]thiophene is reported to be lithiated at position 3 this is the only known direct lithiation at the /3-position (70AHC(11)177). Competitive metallation of benzo[6]thiophene and N-methylindole affords only 2-benzo[6]thienyl-lithium. 

The reaction of thienyl- and benzo[6]thienyl-lithium with DMF to generate aldehydes is well known (790R(26)1, 70AHC(11)177). The use of a,a,a-trifluoro-A,A-dimethylacetamide... 

Reaction of 2-benzo[6]thienyllithium (and its 7-methyl derivative 90) with aldehydes 486,5fl4, 620 or ketones 467 483 affords a secondary or tertiary alcohol, respectively. Treatment of 2-benzo[6]thienyl-lithium with acetyl chloride gives mainly l,l-di(2-benzo[6]thienyl)-ethylene.132 Side-chain alcohols in positions other than the 2-position are most easily prepared by reaction of the appropriate benzo[6]-thienylmagnesium halide with aldehydes 460,471 or ketones,186,3o9, 349, 4 7,466,479,498 or foy reaction of a benzo[fe]thiophene aldehyde, ketone, or ester with an alkylmagnesium halide.358,427 465 The preparation of alcohols from 2- and 3-benzo[6]thienylmethyl-magnesium chloride485,528 is discussed in Section VI, D, 4. 

A first-generation carbosilane dendrimer consisting of 16 thiophene rings could be isolated in 19% yield, albeit together with various by-products in comparable amounts [85]. The synthetic building block methyl tris(2-thienyl)silyl ether was first prepared from tetramethoxysilane and an excess of thienyl-lithium (Fig. 4.44). 

Bis[2-thienyl Tellurium1 To a stirred solution of 10.6 mmol of 2-thienyl lithium in diethyl ether at 20° are added 0.50 g (5.3 mmol) of 2,5-dihydrotellurophene dichloride and the mixture is heated under reflux for 0.5 h. The cooled solution is poured into 50 ml of saturated aqueous ammonium chloride solution. The organic phase is separated and the aqueous phase is extracted with 50 ml of diethyl ether. The combined organic phases are washed with water, dried with anhydrous calcium chloride, filtered, and the solvent is evaporated yield 0.46 g (79%) m.p. 50°. 

Butyl 2-thienyl tellurium and butyl 3-thienyl tellurium were converted by butyl lithium to the corresponding thienyl lithium derivatives3. 

Organometallic Derivatives of Monocyclic Thiophens - Lithium. Numerous a-substituted thiophens have been prepared via metallation of thiophens with organolithium derivatives. Thus 2-thienyl-lithium has been allowed to react with tetraisopropylthiuram disulphide to give 5-(2-thienyl) A(,A -di-isopropyl-dithiocarbamate in quantitative yield. ° Through the reaction of 2-thienyl-lithium with tellurium in THF, the tellurolate was obtained, which was converted into various products. The reaction of 2-thienyl-lithium with 1,1-dichloro-2,2-difluoroethene has been developed into a very useful method for... 

The reactions of 2- and of 3-thienyl-lithium with pyridazine are dependent upon the solvent and the temperature that is used. Thus, using THF as cosolvent, at low temperatures, the 4-position of pyridazine is attacked, leading (after hydrolysis and oxidation) to 4 2-thienyl)- and 4-(3-thienyl)-pyridazine. If ether is used as the solvent, at 0°C, 3-(2-thienyl)- and 3-(3-thienyl)-pyridazines were obtained after oxidation. The structures of the initially formed dihydro-derivatives were studied to some extent. The reaction of... 

The reaction of 3-thienyl-lithium, prepared by halogen-metal exchange of 3-bromothiophens, has been used for the synthesis of many geminal 3,3-dithienyl derivatives of pharmacological interest. Thus the reactions with ethyl 3-bromopropionate, ethyl cyclopropylcarboxylate, and (90) were used for the synthesis of (91), (92), and (93), respectively. The reaction of 3-thienyl-lithium with quinoxaline has been used for the preparation of... 

The halogen-metal exchange between 4-iodo-2-methoxythiophen and butyl-lithium, followed by reaction with dimethyl disulphide, carbon dioxide, or DMF, was used for the synthesis of various 4-substituted 2-methoxythio-phens. In connection with work on optically active 3-(cyclohexenyl)-thiophens, substituted 3-thienyl-lithium derivatives were allowed to react with cyclohexanones and cyclohexenones. The reaction of 3,4-dibromothiophen with two equivalents of butyl-Hthium and sulphur, followed by CS2, was used for the synthesis of (96), an intermediate for the synthesis of the organic metals (97). ... 

The synthetic usefulness of the ring-opening reaction of 3-thienyl-lithium derivatives has been further demonstrated. It was found that 2-(trimethylsilyl)-... 

By the addition of 2- and 3-thienyl-lithium to quinoxaline, mono- and dithienyl-substituted quinoxalines have been prepared and their lithiation and self-addition further investigated. From 1,5-diketones containing thienyl and furyl substituents, pyrylium and thiopyrylium salts such as (212) have been prepared.N.m.r. spectra of compounds related to (212) have been investigated. 1,5-Diketones were also used for the synthesis of... 

Although no pK values of allenic sulfides RCH=C=CHSR/ are known, other experimental data indicate the basicity of the lithiated compounds RCH=C=C(Li)SR/ to be somewhat lower than that of 2-thienyllithium. Competition experiments with butyl bromide in THF or in a THF-HMPT mixture showed the metallated allenic sulfide to be much more reactive than 2-thienyl-lithium [9]. This difference might be due to the higher polarisability of the allenyl system. 

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