Azoles vinylation

Abbreviations aapy, 2-acetamidopyridine Aik, alkyl AN, acetoniuile Ar, aryl Bu, butyl cod, 1,5-cyclooctadiene COE, cyclooctene COT, cyclooctatetraene Cp, cyclopentadienyl Cp , penta-methylcyclopentadienyl Cy, cyclohexyl DME, 1,2-dimethoxyethane DME, dimethylformamide DMSO, dimethyl sulfoxide dmpe, dimethylphosphinoethane dppe, diphenylphosphinoethane dppm, diphenylphosphinomethane dppp, diphenylphosphinopropane Et, ethyl Ec, feirocenyl ind, inda-zolyl Me, methyl Mes, mesitylene nb, norbomene orbicyclo[2.2.1]heptene nbd, 2,5-norbomadiene OTf, uiflate Ph, phenyl PPN, bis(triphenylphosphoranylidene)ammonium Pi , propyl py, pyridine pz, pyrazolate pz, substituted pyi azolate pz , 3,5-dimethylpyrazolate quin, quinolin-8-olate solv, solvent tfb, teti afluorobenzobaiTelene THE, tetrahydrofuran THT, tetrahydrothiophene tmeda, teti amethylethylenediamine Tol, tolyl Tp, HB(C3H3N2)3 Tp , HB(3,5-Me2C3HN2)3 Tp, substituted hydrotiis(pyrazol-l-yl)borate Ts, tosyl tz, 1,2,4-triazolate Vin, vinyl. 

H-Pyr azoles readily undergo photochemically induced elimination of nitrogen to yield the corresponding cyclopropenes, often by way of detectable vinyl diazo intermediates. l-Aryl-3-methyl-2-phenyl-l-diazobut-2-enes have, in fact, been prepared in this way from the appropriate pyrazoles.345 The vinyl diazo compounds 416, obtained by irradiation of the 3//-pyrazoles 417, were further converted to cyclopropenes 418 via vinylmethylene intermediates 419 by irradiation at 10°C.346 1-Acylcyclopropenes have been... 

Another very instructive case concerns the alleged initiation of a cationic polymerisation by a charge-transfer complex formed by the compound chloranil (2,3,5,6-tetrachloroquinone) with the monomer N-vinyl-carb-azole. It was shown (Natsuume et al., 1969 1970) that this compound is not an initiator, but that the polymerisations were caused by a hydrolysis product, 2-hydroxy-3,5,6-trichloroquinone, which is a strong acid. One has learnt from this finding to be extremely suspicious of any claims for charge-transfer catalysis and to test one s suspicions by appropriate experiments involving progressive purification of the putative catalyst. 

Thiazoles, vinyl-radical polymerization, 6, 278 Thiazole-5-sulfonic acid, 2-amino-synthesis, 6, 255-256 Thiazole-2-sulfonic acids reactions, 5, 104 6, 291 Thiazole-5-sulfonic acids synthesis, 6, 255 Thiazole-5-thione, 2-phenyl-tautomerism, 6, 249 Thiazolethiones reactivity, 6, 250 Thi azole-2-thiones reactions, 5, 102 tautomerism, 5, 367 Thiazolidine, 2-alkyl-occurrence, 6, 327 Thiazolidine, 2-arylimino-X-ray analysis, 6, 238 Thiazolidine, 4-imino-mesoionic didehydro derivative nomenclature, 1, 34 nomenclature, 1, 34... 

The N-vinyl-azole class, in which the 1-N atom of the azole is directly bonded to an sp2-hybridized carbon of a substituted olefin, belongs to the relatively recently synthesized subgroup of bioactive azoles. Compounds of this nature can be obtained by condensation of aldehydes with triazolyl-pinacolone resulting in a mixture of the E and Z isomers of the corresponding a, f3 -unsaturated ketones. Borohy-dride reduction easily converts these ketones into the corresponding alcohols (9)(Figure 16). 

Katritzky, A. R. Li, J. Malhotra, N. N-Vinyl, N-allyl, N-propenyl and N-propargylbenzotri-azoles reactions of their lithium derivatives. Liebigs Ann. Chem. 1992, 843—853. 

V-Alky I groups in neutral azoles can rearrange thermally to carbon. For example, 2-alkylimidazoles can be prepared in this way in a reaction that is irreversible, uncatalyzed, intramolecular and does not involve radicals. A-Vinyl and A-alkyl groups in imidazoles also rearrange thermally to the 2- and 4-ring positions. 

A new efficient C-carbothioation of pyrroles with carbon disulfide in the KOH/DMSO system (Section 3.02.2.3.7) paves the way to richly functionalized C-vinyl pyrroles (Section 3.02.4.8) and further to a variety of pyrrole-azole assemblies and fused pyrrolic systems. 

Using the same base system a new expedient method of vinylation of azoles including carbazole was developed. In its traditional version, the reaction is carried out under pressure of about 15 atm and at a temperature as high as 180 °C. The yield of purified iV-vinylcarbazole does not exceed 75%. In the superbase promoted vinylation of carbazole, no pressure is required and the optimal temperature is within 90-95 °C, that is, half as much as in the classic version. The yield of iV-vinylcarbazole is near to quantitative and its purity exceeds 99% (Equation 41) <2002COR1121, 2003MI27>. 

Vinylation of various azoles (pyrrole, indole, carbazole, and their derivatives) with vinyl bromides catalyzed by palladium/phosphine complexes results in the A -vinylazoles in 30-99% yields (Equation 49) <20020L623>. This reaction with cis- and /ra r-P-bromostyrenes is stereospecific giving the respective products with full retention of configuration. 

The original procedure involved the coupling of aryl bromides with secondary amines. However, since then the scope has been expanded to include substrates such as aryl iodides, chlorides, fluorides, triflates, tosylates, nonaflates, iodonium salts, and even boronic acids. While the reaction has not been extensively utilized with vinyl or alkynyl substrates, it can be performed with various heteroaryl halides. Similarly, numerous types of nitrogen-containing coupling partners, including primary amines, imines, various azoles, lactams, and simple amides, can now be used in this reaction. 

Thermolysis of 2-azido cinnamates containing oriho-vinyl, -styryl, -allyl, and cycloalkenyl substituents led generally to mixtures of products, including isoquinolines, azepines, indoles, fused aziridines and cyclopropanes, arising from the decomposition of the intermediate dihydrotri-azole cycloadducts or azirines89. 

Recently, interest has been rekindled in the use of the vinyl group as a blocking agent which can be cleaved by ozonolysis [60, 61]. Critical assessment of the variety of blocking groups employed in azole lithiations has appeared elsewhere, and will not be discussed in detail here [24-26, 62]. 

A study of the intermolecular vinylation of azoles (pyrrole, carbazole, and indoles) and phenothiazines was published by I. P. Beletskaya and co-workers.116 This vinylation is catalyzed by Pd(f-Bu)3P and utilizes the lithium amide of various azoles. Various vinyl bromides efficiently undergo the cross-coupling with full retention of their configuration (E or Z). 

For example, the excessive addition of sensitizer can result in crystallization of the sensitizer. Some sensitizers, even when present in low concentrations can result in over-sensitization of the composition, in that the photocurrent generated upon exposure will persist comparatively long after the illumination ceases. As an alternative to the sensitization by additives, intramolecular charge transfer complexes have been proposed, where the electron donor and electron acceptor functions are located along a common vinyl backbone. Examples are nitrated vinyl polymers of poly-(acenaphthylene), poly(9-vinylcarbazole) and poly(l-vinylnaphthalene), copolymers from 3,6-diphenyl-vinylcarbazoleand 3,6-dinitro-9-vinylcarb-azole. ° and copolymers from NVK and iV-vinylphthahntide. ... 

M. Baibarac, P. Gomez-Romero, M. Lira-Cantu, N. Casan-Pastor, N. Mestres, and S. Lefrant. Electrosynthesis of the poly(V-vinyl carb-azole)/carbon nanotubes composite for applications in the supercapacitors field. Eur Polym. J., 42(10) 2302-2312, October 2006. 

Vinylation of azoles is also possible. The vinylation of indole with cis- -bromostyrene proceeded with retention of configuration to afford 59 in high yield using P(t-Bu)3 as a ligand [50],... 

C.i.d. Heck Reaction. 7r-Deflcient chloropyrazines can be Heck-coupled into 1,3-azoles (Scheme 50). It will be recalled that the same methodology was used to couple into the TT-excessive furan, thiophene, and pyrrole heterocycles and their benzo derivatives (vide supra). The Heck reaction in oxazole and thiazole proceeds in a regiospeciflc manner. The new carbon-carbon bond is formed in the 5-position 117 next to the ether heteroatom as commonly observed in vinyl ethers and strongly favored in furan and thiophene. In benzoxazole and benzothiazole the only vacant position is between the two heteroatoms, and the Heck coupling results in substitution into the 2-position 118. " ... 

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