Internal acetylenes, synthesis

Synthesis of internal acetylenes from vinylic tellurides... 

Intermolecular dimerization has also been effected by a comparable protocol.24-26 Treatment of triethylborane with silver nitrate and sodium hydroxide in water at 25°C led to the rapid evolution of M-butane (72%), ethylene (9%), and ethane (9%). Reaction of two different alkylboranes led to statistical mixtures of dimerized and cross-coupled products. Furthermore, this strategy has been used successfully in the synthesis of olefins from dihydroborated internal acetylenes,27 and in polymerizations of bifunctional organoboron compounds.28... 

A typical example of such reactions of 1-alkynyltrialkylborates is demonstrated in the synthesis of internal acetylenes. When 1-alkynyltrialkylborates (18), readily prepared from lithium acetylides and trialkylboranes, are treated with iodine, the corresponding internal alkynes are obtained in almost quantitative yields (Eq. 39)... 

Terminal Acetylene with sp -carbon Halides 5.3.5.1 Synthesis of internal acetylenes... 

Roesch, K. R., Larock, R. C. Synthesis of isoindolo[2,1-a]indoles by the palladium-catalyzed annulation of internal acetylenes. J. Org. 

Synthesis of internal acetylenes Into a CHCI3 solution (5 mL) of vinylic telluride (2 mmol) was added an aqueous sodium hypochlorite solution (5-8 equiv) at 25°C, and the mixture was stirred for 30 min. The products were extracted with CHCI3, and the extract was dried over MgS04, concentrated and heated gradually in a Kiigelrohr distillation apparatus up to 250°C in vacuo, giving rise to the corresponding internal acetylenes. 

Pyrroles 531 are formed from the chromium complex 529 and alkynes 530 (R = H, Me or Ph = Me, Ph or NEt2). The dicobaltoctacarbonyl-catalysed reaction of cyanotrimethylsilane with a variety of acetylenes R C=CR (R R = alkyl or Ph) furnishes pyrroles 532, in which the bulkier of the two substituents of unsymmetrical internal acetylenes appears at the position marked with an asterisk . An indole synthesis from o-iodo-aniline and alkynes R C=CR (R R =alkyl or Ph) in the presence of palladium(II) acetate, triphenylphosphine, lithium chloride and potassium carbonate has been described (equation 56). In the case of unsymmetrical alkynes, the bulkier substituent tends to be in position 2 of the indole. ... 

Ogura and co-workers ° reported a general synthesis of 4,5-disubstituted-2-methyloxazoles 190 from attempted amidotellurinylation of internal acetylenes (Scheme 1.50). Normally, terminal acetylenes undergo an F-stereoselective... 

The motives underlying the original synthesis of 3 were based on the observation that certain tungstacyclobutadienes react with internal acetylenes to give (substituted) cyclopentadienyl complexes.Consequently, alkynyl-substituted organometallics were deemed to be appropriate for use in the syntheses of heterobimetallic complexes. To this end, the alkynyl-substituted (ii -C5Me4CH2CH2C CEt)Rh(CO)2 (4), was synthesized via reaction of [RhCl(CO)2l2 with 3 (Scheme III). Subsequent treatment with... 

A conjugated terminal acetylene is an important intermediate in organic synthesis. The reaction of acetylene gas with organic halides preferentially gives only internal acetylenes because of the higher reactivity of monosubstituted acetylenes than that of acetylene gas. 

The mercuric-ion-catalyzed hydration of terminal acetylenes has been a significant method for synthesis of methyl ketones. The reaction can also be used with internal acetylenes if they are symmetrical. Unsymmetrical alkynes would be... 

Xiao, Y, Chung, T.-S., Guan, H.M. and Guiver, M.D. 2007. Synthesis, cross-linking and carbonization of co-polyimides containing internal acetylene units for gas separation. J. Memb. Sci. 302 254-264. 

This tactic has been adopted for the construction of a wide range of internal acetylenes and could also be employed for the synthesis of 1,3-diynes from chloroaUcynes, which often fail under the Cadiot-Chodkiewicz conditions [329]. 

Carbonyl compounds are an important class among organic molecules. Literature records several methods for their synthesis. However, there are very few methods to convert carbon-carbon unsaturation to carbonyl compounds. Hydroboration of acetylenes, followed by oxidation provides a novel method for carbonyl synthesis. It has been noted that regioselectivities achieved in the monohydroboration of internal acetylenes with thexylborane [1], disiamylbo-rane [1], dicyclohexylborane [1], and catecholborane [2] are similar to, but less pronounced than, that realized by 9-BBN [3]. The B-alkenyl-9-BBN derivatives undergo oxidation to the corresponding ketones or aldehydes under aprotic conditions with trimethylamine N-oxide [4, 5] or under protic conditions by inverse addition to buffered hydrogen peroxide [3]. The inverse addition, i.e., the slow addition of the B-alkenyl-9-BBN in THF to the buffered H O, suppresses the otherwise undesirable protonolysis reaction and favors the oxidation pathway to the desired aldehyde or ketone. 

Terminal acetylenes can be alkylated to give chain-lengthened internal acetylenes in good yield, either by the rapid addition of trialkylalanes in the presence of nickel(ii) catalysts or by electrochemical addition of organoboranes. Hydroalumination may be used in a convenient conversion of terminal olefins into the corresponding acetylenes. An improved procedure for the synthesis of cyclo-octyne from cyclo-octene by a bromination-dehydrobromination sequence has been reported. ... 

Konno T, Chae J, Tanaka T, Ishihara T, Yamanaka H. A sequential highly stereoselective hydroboration and Suzuki-Miyaura cross-coupling reaction of fluoroalkylated internal acetylenes a practical one-pot synthesis of fluoroalkylated trisubstituted alkenes. Chem. Commun. 2004 690-691. 

Internationally renowned authors, among them K. C. Nicolaou, H. Iwamura, R. H. Grubbs and H. Hopf, present the full potential of acetylene chemistry, from organic synthesis through materials science to bioorganic chemistry. 

Ebdon and coworkers22 "232 have reported telechelic synthesis by a process that involves copolymerizing butadiene or acetylene derivatives to form polymers with internal unsaturation. Ozonolysis of these polymers yields di-end functional polymers. The a,o>dicarboxy1ic acid telechelic was prepared from poly(S-s tot-B) (Scheme 7.19). Precautions were necessary to stop degradation of the PS chains during ozonolysis. 28 The presence of pendant carboxylic acid groups, formed by ozonolysis of 1,2-diene units, was not reported. 

The reaction of chiral six-membered cyclic nitronates with internal and terminal acetylenes was used with advantage in the synthesis of enantiomerically pure fused substituted aziridines containing several stereocenters (96) (Scheme... 

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