Alkynes example: alkyne

Monocyclic Aliphatic Hydrocarbons. Monocyclic aliphatic hydrocarbons (with no side chains) are named by prefixing cyclo- to the name of the corresponding open-chain hydrocarbon having the same number of carbon atoms as the ring. Radicals are formed as with the alkanes, alkenes, and alkynes. Examples ... 

Examples of alkylation, dealkylation, homologation, isomerization, and transposition are found in Sections 1,17,33, and so on, lying close to a diagonal of the index. These sections correspond to such topics as the preparation of alkynes from alkynes carboxylic acids from carboxylic acids and... 

Quaternary ammonium salts aid the transfer of the hypophosphite anion in the palladium-catalysed reduction of, for example, alkynes to alkenes, nitroarenes to aminoarenes, and in the hydrogenolysis of tetrazolyl aryl ethers to phenols [12-14], It has been demonstrated that the hydrogenolysis is ineffective when preformed tetra-n-butylammonium hypophosphite is employed in a dry homogenous organic solvent [13, 14], For optimum hydrogen transfer, the concentration of hypophosphite relative to the substrate must be controlled at a low level and this is most effectively accomplished with a two-phase system. 

The hydrogenation step is stereospecific and transfers hydrogen in the suprafacial manner. For example, alkynes are converted to m-alkenes ... 

Nucleophiles with high tendency to migrate preferentially undergo the tandem MCR reaction, providing a useful route for the synthesis of substituted 1-alkynes. Examples of the MCR reaction with little or no tendency to compete with the MCI pathway are summarized in Eq. (113) Nu = thiocyanate [200,201], thiotosylate [202], thiolate [203], phosphorodithioate [204], tosylate [205], car-boxylate [206], phosphate [206], lithium diphenylamine [207], and halide [171]. It appears likely that, because of the electron-deficient nature of the carbenic... 

Finally, epoxides can serve as useful substrates for cycloaddition strategies. For example, alkynes react with epoxides in the presence of gallium trichloride through tandem ring opening and cyclization to give naphthalene derivatives (e.g. 106). This protocol, which generally... 

Further transformations of such zirconacycles are possible before the organic product is removed from the metal center. Buchwald followed the insertion of an alkyne into a zirconaaziridine with the insertion of CO to obtain substituted pyrroles (in a single pot at ambient temperature) in moderate to good yields. A diverse array of substituents can be introduced by varying the amine and alkyne examples are shown in Table 4. The reaction is tolerant not only of various alkyls and aryls, but also of thiophenyl, furyl, and pyrrole substituents, and can create 2,2 -bipyrroles (see Table 4). It does, however, require high CO pressure (as much as 1,500 psi can be necessary) [56]. 

The ease of reduction is 1-alkynes > disubstituted alkynes > 1-alkenes, indicating that selective semihydrogenation of triple bonds can be achieved in molecules containing double bonds. For example, nonconjugated enynes can be hydrogenated regio-and stereospecifically in high yields. 

The catalytic conversion of alkynes with CO2 represents the sole example until now of a homogeneous catalytic reaction which yields C-C bond formation with CO2 and selective formation of eyclooligomers using a eheap 3d-metal complex catalyst. The variation of alkyne substituents allows the synthesis of a wide range of 2-pyrones (mono- and disubstituted alkynes and alkynes with functional groups such as -OR and -OOR [18]). 

Simultaneous introduchon of both sulfur and selenium functions into carbon-carbon unsaturated compounds via a radical mechanism is also demonstrated by selenosulfonahori [149] and selenothiocarboxylatiorl [150] (Scheme 15.70). In these addihon reactions, attack of sulfur-centered radicals at the terminal position of alkenes and the subsequent Sh2 reaction on the selenium lead to the formahon of anti-Markovnikov adducts regioselechvely. The selenosulfonahon can be apphed to a variety of unsaturated compounds, for example alkynes, allenes, and vinylcyclopropanes, and combination with the selenoxide syn-elimination procedure... 

In one example alkyne 96 is activated by hydrozirconation. The zirconium is in the terminal position 99. The two Cp rings are quite big and so it is usual for the zirconium to add preferentially to the less hindered end of the triple (or double) bond. This is the regioselective aspect of the reaction and not what concerns us here. Transmetallation to the organolithium and again with Cu(I) gives the cuprate and this cuprate does a conjugate addition to the double bond of an enone that looks suspiciously Robinson annelation-derived.13 Before we move on, notice that the double bond has a trans geometry - we shall come back to this. 

One of the early group 6 (VIB) metal-alkyne examples, W(CO)(3-hexyne)3, was prepared by Tate and Augl in the early 1960s according to (312, 313). 

In its reactions, coordinated cyclobutadiene exhibits aromatic character, undergoing electrophilic substitution, e.g. Friedel-Crafts acylation. A S5mthetic apphcation of (r " -C4H4)Fe(CO)3 in organic chemistry is as a stable source of cyclobutadiene oxidation releases the ligand making it available for reaction with, for example, alkynes as in scheme 23.117. 

There are only a few naturally occurring alkynes. Examples include capillin, which has fungicidal activity, and ichthyothereol, a convulsant used by the Amazon Indians for poisoned arrowheads. A class of naturally occurring compounds called enediynes has been found to have powerful antibiotic and anticancer properties. These compounds all have a nine- or ten-membered ring that contains two triple bonds separated by a double bond. Some enediynes are currently in clinical trials. 

It is useful to explore this analogy between known alkyne systems and potential benzyne ones. For example, alkynes react with ruthenium carbonyl to form the Ru4( --alkyne)(CO)i2, which form an octahedral RU4C1 arrangement with the metal atoms in a butterfly geometry. Since the synthesis cannot be adapted to arynes, another method is needed. Oxidative addition of aryl iodides to Ru3(CO)i2 gives the aryl complexes described in Sec. 1.14.4.5. Flowever, we have... 

Following earlier studies by Kappe and Lube and Potts and Sorm , Gotthardt and coworkers h32 investigated the cycloaddition of pyrimidiniumolates, which can be regarded as 1,4-dipolar species, to alkynes. Example of addition to an electron-rich alkyne is shown in equation 5. The authors compared their experiments with MO calculations. These calculations indicate that the HOMO of an electron-rich alkyne interacts with the LUMO of the pyrimidiniumolate, whereas the reverse is true for an electron-poor alkyne. 

Halopyridines take part in palladium-catalysed reactions, for example Heck, carbonylation, and coupling reactions, with, for example, alkynes. ... 

Equations 16.122 and 16.123 show convenient routes to [NS2][SbF6] this product is soluble in liquid SO2 and is readily separated from AgCl which precipitates out of solution. The [NS2] ion (16.73) is isoelectronic (in terms of valence electrons) with [N02] (see structure 15.50). The [N 2] ion is a useful synthon, undergoing cycloaddition reactions with, for example, alkynes, nitriles and alkenes. 

The usual stereochemistry of the insertion is syn, and so the stereochemistry at both carbons is retained, as shown by the alkyne example in Eq. 7.20, but the initially formed cis-vinyl complex can sometimes rearrange to the trans isomer, probably via an Ti -vinyl (Eq. 7.21). This can lead to a net anti addition of a variety of X—H groups (Eq. 7.22, where X = RaSi) to alkynes ... 

Reactions A carbyne can couple with another carbyne to give an alkyne or alkyne complex.For instance, Br(CO)4Cr CPh reacts with Ce(IV) to give free PhC CPh. Carbynes also have extensive photochemistry. In the Fischer series, the carbyne carbon is electrophilic and subject to nucleophilic attack, for example, by PMcj, pyridine, RLi, or isonitrile (= Nu) to give a carbene of the type L M=CR(Nu). Alternatively, the nucleophile may attack the metal in L (CO)M=CR and produce a ketenyl complex... 

Alkynes in which the triple bond is between carbons 1 and 2 are commonly referred to as terminal alkynes. Examples of terminal alkynes are propyne and Terminal alkyne 1 -butyne. alkyne in which the triple bond... 

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