Alkynes aliphatic terminal

The aldol (23) on treatment with benzenesulphonyl chloride yields the oxetanone ((3-lactone) (24) which is an intermediate in the synthesis of the butenolides (25) (95SC479). Aliphatic terminal alkynes or arylalkynes react with nitrones in the presence of a copper based catalyst system to give 1,3,4-trisubstituted [3-lactones (95JOC4999). 

Tetrasubstituted silanes are also sources of silylene. Suginome and coworkers reported that palladium catalyzed the transfer of dimethylsilylene, formed from silylborane 44, to alkynes [equation (7.8)], 60 Exposure of silylborane 48 and alkyne 49 to substoichiometric amounts of palladium and P(7-Bu)2(2-biphenyl) afforded 2,4-disubstituted silole 50. This process tolerates a variety of functionality including silyl ether-, dimethylamino-, and trifluoromethyl groups. In addition to aliphatic terminal acetylenes, arylacetylenes were also competent substrates. For... 

Under these conditions, a variety of linear aliphatic terminal alkynes were transformed into aldehydes with good selectivity. The efficiency, regioselec-tivity of the addition and substituent tolerance were improved by using RuCl(Cp)(phosphine)2, where Cp is cyclopentadienyl, or RuCl(Cp)(diphos-phine) as catalyst precursors [30]. The best results were obtained with diphenylphosphinomethane as a ligand, which made possible the preparation of aldehydes from bulky aliphatic alkynes (tert-BuC=CH), aromatic alkynes (PhC=CH), diynes [HC=C(CH2)6C=CH] and functional terminal alkynes [NC(CH2)3C=CH, PhCH20(CH2)2C=CH,...]. The mechanism of this reaction was investigated in details by isolation of intermediates, deuterium-... 

Tetrahydrofuran was coupled to a variety of aromatic and aliphatic terminal alkynes under microwave irradiation to provide a mixture of cis- and t/ an5-2-vinyltetrahydrofuran. A representative example is shown below <04TL7581>. 

Similarly, aliphatic terminal alkynes (76) can also be oxygenated (272,273],... 

In the same year, Zhang also reported a gold-catalyzed synthesis of 2-alkylindoles 46 from iV-arylhydroxylamines 44 and aUphatic terminal alkynes (Scheme 12.22) [26]. The addition of M-arylhydroxylamines to aliphatic terminal alkynes in the presence of gold catalyst affords 0-alkenyl-M-arylhydroxylamines 45, which undergo facile in situ sequential 3,3-rearrangement... 

PhNH2 react in the presence of HgCl2 (5%) to produce the same anils as those obtained with the HgO/BFj.OEtj system (Eq. 4.63), but at room temperature and with a higher TOP (12 h ) [259]. Phenylacetylene and secondary aromatic amines afford enamines hke those of Eq. (4.64), but aliphatic terminal alkynes and secondary aromatic amines give rise to a mixture of enamines (Eq. 4.65) [259]. 

As in the case of secondary aromatic amines, aliphatic terminal alkynes and secondary aliphatic amines give rise to mixtures of enamines like those of Eq. (4.65) [260]. 

The increased Markovnikov selectivity in the hydroamination of aliphatic terminal alkynes with aniline derivatives seems to be universal for a number of titanium-based hydroamination catalysts, such as Ind2TiMe2 (49) [184], the di-(pyrrolyl) amine complex 50 [186, 187], and the di(pyrrolyl)methane complex 51 [188]. The bis(amidate) titanium complex 43 exhibited enhanced catalytic activity compared to titanocene catalysts, thus combining high a ri-Markovnikov selectivity with high catalytic activity [191]. 

The reaction time between 4-iodopyrazoles and 1-alkynes varies from 5 to 25 h and the yield of products is 55-95%. It is noteworthy that the nature of the terminal acetylene has a greater effect on the rate of halogen atom substitution for low-reactive 4-iodopyrazoles. Thus, the reaction time for ethynylarenes is 5-6 h, and for less acidic aliphatic 1-alkynes is 10-25 h (Table XTT). 

Terminal aliphatic alkynes (e.g., 1-octyne) react with iron(III) halides (FeCls and FeBrs) to give the corresponding 2-halovinyl derivatives (route A, Scheme 10). The moderate yields were remarkably improved upon addition of stoichiometric amounts of carboxylic acids. 

Both aliphatic and aromatic terminal alkynes reacted with aliphatic aldehydes giving exclusively a mixture of ( ,Z)-1,5-dihalo-1,4-dienes and disubstituted ( )-a,p-unsaturated ketones, the former being the major products in all cases. When nonterminal aromatic acetylenes were used, the trisubstituted ( )-a,p-unsat-urated ketones were the exclusive compounds obtained. The procedure was not valid for ahphatic and unsaturated alkymes. However, the catalytic system was found to be compatible with alcohols and their corresponding acetates although limited yields were obtained. 

To check the scope of this coupling reaction, a study with different combinations of aldehydes, amines, and terminal alkynes was performed. Aromatic alkynes turned out to be more reactive than aliphatic ones. This study included aliphatic... 

A catalytic system comprising TiCNMe ), LiNCSilVIej) and IMes has been developed for the intermolecular hydroamination of terminal aliphatic alkynes (1-hexyne, 1-octyne, etc.) with anilines [toluene, 100°C, 10 mol% TiCNMe ) ]. Markovnikov products were dominant. Substituted anilines reacted similarly. High conversions (85-95%) were observed with specific anilines. The optimum Ti/IMes/ LiN(SiMe3)2 ratio was 1 2 1. However, the nature of the active species and especially the role of LiN(SiMe3)2 are unclear [74]. 

Derivatives of aliphatic alkynes (14 and 15) are more thermally unstable than 12, but they show SmA and N phases at low temperatures (below 130 °C). The type of phase and the mesophase stability depend on the length of both the terminal and the lateral chains. When both chains are elongated, the mesomorphism becomes metastable and compounds 14 display monotropic N and SmA transitions. Complexes IS, which contains an ester group with an opposite direction to that of complexes 14, display less stable nematic mesophases. 

Liquid crystals based on aliphatic isocyanides and aromatic alkynyls (compounds 16) show enantiotropic nematic phases between 110 and 160 °C. Important reductions in the transition temperatures, mainly in clearing points (<100 °C), areobtained when a branched octyl isocyanide is used. The nematic phase stability is also reduced and the complexes are thermally more stable than derivatives of aliphatic alkynes. Other structural variations such as the introduction of a lateral chlorine atom on one ring of the phenyl benzoate moiety or the use of a branched terminal alkyl chain produce a decrease of the transition temperatures enhancing the formation of enantiotropic nematic phases without decomposition. 

Pt-catalyzed hydration of various aliphatic and aromatic alkynes under phase transfer conditions in (CH2C1)2/H20 in the presence of Aliquat 336 led to either a Markovnikov product, mixtures of two ketones, or ketones with the carbonyl group positioned away from the bulky side.72 In the absence of the phase transfer reagent, Aliquat 336, hardly any reaction took place. Recently, a hydrophobic, low-loading and alkylated polystyrene-supported sulfonic acid (LL-ALPS-SO3H) has also been developed for the hydration of terminal alkynes in pure water, leading to ketones as the product.73 Under microwave irradiation, the hydration of terminal arylalkynes was reported to proceed in superheated water (200°C) without any catalysts.74... 

Another important click reaction is the cycloaddition of azides. The addition of sodium azide to nitriles to give l//-tetrazoles is shown to proceed readily in water with zinc salts as catalysts (Eq. 11.71).122 The scope of the reaction is quite broad a variety of aromatic nitriles, activated and nonactivated alkyl nitriles, substituted vinyl nitriles, thiocyanates, and cyanamides have all been shown to be viable substrates for this reaction. The reaction of an arylacetylene with an azide in hot water gave 1,4-disubstituted 1,2,3-triazoles in high yields,123 while a similar reaction between a terminal aliphatic alkyne and an azide (except 111 - nitroazidobenzcnc) afforded a mixture of regioisomers with... 

Addition of diphenyl disulfide (PhS)2 to terminal alkynes is catalyzed by palladium complexes to give l,2-bis(phe-nylthio)alkenes (Table 3)168-172 The reaction is stereoselective, affording the (Z)-adducts as the major isomer. A rhodium(i) catalyst system works well for less reactive aliphatic disulfides.173 Bis(triisopropylsilyl) disulfide adds to alkynes to give (Z)-l,2-bis(silylsulfanyl)alkenes, which allows further transformations of the silyl group to occur with various electrophiles.174,175 Diphenyl diselenide also undergoes the 1,2-addition to terminal alkynes in the presence of palladium catalysts.176... 

Addition of a phosphorus-sulfur bond to a carbon-carbon triple bond is catalyzed by a palladium(O) complex (Equation (130)).298 Terminal aliphatic alkynes having various functional groups undergo the addition with PhS-P(0)(OPh)2 to afford (Z)-adducts in high yield. In contrast to aliphatic alkynes, phenylacetylene gives a mixture of E Z adducts. Internal alkynes and alkenes are unreactive. 

Success was obtained with Ru3(CO)i2 as catalyst precursor [6], but the most efficient catalysts were found in the RuCl2(arene)(phosphine) series. These complexes are known to produce ruthenium vinylidene spedes upon reaction with terminal alkynes under stoichiometric conditions, and thus are able to generate potential catalysts active for anti-Markovnikov addition [7]. Similar results were obtained by using Ru(r]" -cyclooctadiene)(ri -cyclooctatriene)/PR3 as catalyst precursor [8]. (Z)-Dienylcarba-mates were also regio- and stereo-selectively prepared from conjugated enynes and secondary aliphatic amines (diethylamine, piperidine, morpholine, pyrrolidine) but, in this case, RuCl2(arene) (phosphine) complexes were not very efficient and the best catalyst precursor was Ru(methallyl)2(diphenylphosphinoethane) [9] (Scheme 10.1). 

The formation of a ruthenium vinylidene is proposed as the key intermediate in the regioselective addition of hydrazine to terminal alkynes [55]. This reaction, which proceeds via addition of the primary amino group of a 1,1-disubstituted hydrazine followed by deamination, provides an unprecedented access to a variety of aromatic and aliphatic nitriles. The tris(pyrazolyl)borate complex RuCl(Tp)(PPh3)2 gave the best catalytic activity in the absence of any chloride abstractor (Scheme 10.17). 

Silylstannylation is also observed in the Pd(PPh3)4-catalyzed reaction of alkynes with disilanyl stannanes, in which both Si-Si and Si-Sn bonds are present. The alkynes undergo insertion into the Si-Sn bond, to regio-and stereoselectively yield (/8-disilanylalkenyl)stannanes [Eq. (25)].73 With terminal alkynes, the stannyl group adds regioselectively to the internal carbon atom. Aliphatic alkynes are not reactive in this system. 

A regioselective iodoperfluoroalkylation of terminal alkynes (R—C = CH) has been reported, and is based on photolysis ofthe C—I bond in perfluoroalkyl iodides (Rp-I). Addition of the thus-formed RF" radical onto the alkyne afforded a vinyl radical that in turn abstracts an iodine atom from the starting Rp—I to form the end olefin R-C(I)= CH-Rf. A xenon lamp through Pyrex (hv > 300 nm) was used for the reaction, where aliphatic alkynes gave a better alkylation yield with respect to phenylacetylene [81],... 

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