I- -1 -alkynes

More recently, decarbonylation of the bridging // -alkyne complex [Rh2(//5-C5H5)2(CO)2(CF3CCCF3)] with Me3NO gave the z/2-complex, which, when treated with PF3, afforded high yields of the i 1-alkyne mixed carbonyl-trifluorophosphine derivative (8), in which the ligands are mutually trans 103). 

CH,),QH,]2BH (1). Mol. wt. 250.20, m.p. 68°, air stable, in 70% yield by reduction of fluorodimesitylborane with LiAlHj. This borane is recommended for hydroboration of alkynes, par-e hydroboration of unsymmetrical alkynes (equation I). 1-Alkynes khydes in high yield. Since alkcnes react only slowly with this iwration of alkynes in the presence of alkenes is possible. 

The 1 1 complexes of alkynylgold compounds (L)AuC=CR with strong donors L can also be conveniently prepared from the corresponding gold halides (L)AuX (X = C1, Br, I), an alkyne HC=CR, and a base. For many representative examples, the reactions with an alkali alkanolate in an alcohol58 or with triethylamine in dichloro-methane are the methods of choice (Equation (13)).59... 

Platinum on carbon did almost exactly the same thing but required a temperature of about 100°C to do so. With excess acetylene, only III formed. With tcrt-butylacetylene no II formed, probably because of steric hindrance, but I and III formed readily. 3-Hexyne reacted more slowly, required heat with chloroplatinic acid, and formed exclusively c/s-3-di-chlorosilyl-3-hexene. Trichlorosilane with platinum on carbon also added (57) to 1-alkynes or to phenylacetylene exclusively by cis addition to give only trans adducts. Later works (55) indicate that chloroplatinic acid and other soluble catalysts also give exclusively cis addition with a wide variety of Si—H compounds. 

It is of interest to mention that DFT study performed, prior to experimental observations, revealed for Cu(I)-catalyzed cycloaddition of nitrile oxides to 1-alkynes, a stepwise mechanism involving unprecedented metalacycle intermediates, which appear to be common for a variety of dipoles (382). 

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. 

Khand and Pauson reported a Co-mediated intermolecular [2-I-2-I-1] cycloaddition of an alkyne, an alkene and carbon monoxide (the Pauson-Khand reaction) [4, 26] wherein an alkyne-Co2(CO)6 complex, which had been prepared from Co2(CO)g... 

The rhodium-entrapped cage compound which is formed using a stoichiometric amount of [RhCl(CO)2]2 is a notable paradigm of the rhodium-catalyzed [2-I-2-I-1] al-kyne-alkyne and CO coupling [35]. Heating 57 in acetone at 50 °C for 8 h or irradiation by a tungsten or mercury lamp provided the cage compound in 50% yield based on NMR spectroscopy. However, due to mechanical losses it was isolated in only 16% yield from the reaction mixture, by crystallization as the hexafluorophosphate salt 58 (Eq. 13). 

Rhodium-catalyzed silylformylation proceeds smoothly in branched 1-alkynes at 25 °C as shown in Table 3. The stereochemistry at the chiral carbon involved in alkynes is retained intact under the silylformylation conditions. (A)-28, (rhodium particles co-condensed with mesitylene. 3-Trimethylsilyl-l-propyne 40 reacts similarly to give 41 (Equation (7)). " / //-Butylacetylene does not work as a substrate for the silylformylation because of the bulky tert-huty group on the i/>-carbon. In contrast to /< r/-butylacetylene, trimethylsilylacetylene 42 gives 43 in a fair yield (Equation (8)). ... 

Homoaliyttc alcohols,An efficient synthesis of homoallylic alcohols of type I involves carbometallation of 1-alkynes (8, 506) followed by reaction of the alkcnyl-aluminate (a) with an epoxide.2... 

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