Phase ethynylation

Alkynes react with haloethenes [38] to yield but-l-en-3-ynes (55-80%), when the reaction is catalysed by Cu(I) and Pd(0) in the presence of a quaternary ammonium salt. The formation of pent-l-en-4-ynes, obtained from the Cu(I)-catalysed reaction of equimolar amounts of alk-l-ynes and allyl halides, has greater applicability and versatility when conducted in the presence of a phase-transfer catalyst [39, 40] although, under strongly basic conditions, 5-arylpent-l-en-4-ynes isomerize. Symmetrical 1,3-diynes are produced by the catalysed dimerization of terminal alkynes in the presence of Pd(0) and a catalytic amount of allyl bromide [41]. No reaction occurs in the absence of the allyl bromide, and an increased amount of the bromide also significantly reduces the yield of the diyne with concomitant formation of an endiyene. The reaction probably involves the initial allylation of the ethnyl carbanion and subsequent displacement of the allyl group by a second ethynyl carbanion on the Pd(0) complex. 

Capillary gas chromatography is conducted with a cross-linked phenyl methyl silicone stationary phase (5%, 25 m x 0.2 mm x 0.5 pm film thickness, injector temp. 225°C, detector temp. 250°C, column temp. 40-200°C, 15°C/min after 1 min initial time). (Z)-2-Bromo-5-(trimethylsilyl)-2-penten-4-ynoic acid ethyl ester is observed to have a retention time of 14.0 min. GC data for bis(trimethylsilyl)butadiyne is as follows retention time 10.0 min, response factor (GC area produced relative to an equimolar quantity of (Z)-2-bromo-5-(trimethylsilyl)-2-penten-4-ynoic acid ethyl ester) 1.29. For (E)-2-[(trimethylsilyl)ethynyl]-5-(trimethylsilyl)-2-penten-4-ynoic acid ethyl ester the retention time is 17.0 min, the response factor 1.19. 

Four diastereomers of 2-ethynyl-7a-hydroxy-3a,7-dimethyl-4,6-diphe-nylperhydropyrrolo[3,2-c]pyridine (58B) were recently isolated (92KGS-903). It was established by means of H-NOESY and C-NMR spectroscopy that the stereochemical differences in the structures of the diastereomers involve cis and transfusion of the rings and different configurations at C(2). In solution and in the gas phase, the corresponding ring-chain equilibrium 58A 58B was detected, with two open-chain epimers (different configurations at C—NH2). 

The bromination with alkali hypobromite in aqueous solution gives good results with (hetero)arylacetylenes, enynes (RCH=CHOCH) and diynes (RC=CC=CH) all acetylenes that are more acidic than those acetylenes in the aliphadc or cycloaliphatic series with an isolated triple bond. For the conjugated systems the hypobromite method is superior to the reaction of metallated acetylenes with bromine. Various acetylenic alcohols are also brominated smoothly, which can be explained in part by their better solubility in water. Since in the case of primary and secondary ethynyl alcohols, oxidation of the alcohol can occur, the use of an excess of hypobromite should be avoided. The best procedure is drop wise additon of a small shot measure of hypobromite ro a mixture of alcohol and water. If the bromoalkynes to be prepared are not too volatile, small amounts of THF or dioxane may be added to effect a better solubility of the alkyne in the aqueous phase. Addition of a co-solvent may also be desired when the starting compound is a solid (e.g. ethynylcyclohexanol). 

Bromination of 1-alkynes with N-bromosuccinimide in the presence of catalytic amounts of silver nitrate, was used first for the bromination of 17-ethynyl steroids.7 Similarly, N-iodosuccinimide led to 17-iodoethynyl steroids, lodination of propiolates in this way has not been studied. A recent method of preparation of 1-iodoalk-l-ynes under phase-transfer conditions involves molecular iodine and copper(l) iodide as catalyst, in the presence of potassium or sodium carbonate as a base. Ethyl 3-iodopropiolate was prepared by this route in 80% yield.8... 

Following the idea of the first approach, monomers with the l,4-bis[(3 -flu-oro-4 -n-alkoxyphenyl)-ethynyl]benzene mesogens were laterally linked via a CH2-spacer to norbornene, XX-n (n= 1-12). The low molecular mesogens with n>6 showed a k-S -Sc-n-i phase sequence, whereas the norbornene monomers XX-n exhibited only a monotropic or enantiotropic nematic mesophase, respectively [72]. 

Tor has reported a versatile method for the site-specific incorporation of polypyridine Ru and Os complexes into DNA oligonucleotides using solid-phase phosphoramidite chemistry. Nucleoside phosphoramidites containing a [(bpy)2M(3-ethynyl-l,10-phenanthroline)] " metal center covalently attached to... 

Dichloroprop-l-yne does not generate chloro(ethynyl)carbene, but instead gives (chlorovinylidene)carbene, under the conditions of phase-transfer catalysis. The (chlorovinylid-ene)carbene undergoes addition to alkenes with the formation of (chlorovinylidene)cyclo-propanes. ... 

The relatively low thermal stability of the acetylene precursors inspired the search for a more stable, masked ethynyl group that can be quantitatively converted into acetylenes in the gas phase of the pyrolysis apparatus. Presently, the state of the art consists in the substitution of ethynyl groups by chloroethenyl substituents [54b -f, 55,56]). The latter show a higher thermal stability and are conveniently available from acetyl derivatives by reaction with PC15 or from tri-methylsilyl (TMS)-substituted acetylenes by treatment with hydrochloric acid in glacial acetic acid (see Scheme 8). 

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