Addition onto acetylenes

Scheme 1-32. syn-Selective cuprate addition onto acetylene followed by trapping with organic iodides, with acetyl chloride and with elemental iodine. 

Similarly, electrogenerated MeS and PhS may afford [298] electrophilic substitution with phenols and ethers (Scheme 66). The addition of such electrophiles onto acetylenic bonds was also reported [297]. 

In a later study. Swanson and coworkers [81] studied the cure of acetylene-terminated poly(imide)s selectively labelled at various positions with nuclei. Curing of the sample, labelled at the imide carbonyl group, confirmed the completion of the imidization reaction on heating. The product of addition onto the carboxyl group was not observed. Four new peaks were identified in the spectrum of the cured sample labelled at the Ci-acetylene group, while a similar result was obtained for the sample labelled at the C2-acetylene position. Analysis of these results rules out the participation of coupling reactions and the biradical mechanism, which would produce triple-bond structures, but confirms the presence of the product of cyclotrimerization and Friedel-Crafts reactions. The latter mechanism is confirmed from the presence of small peaks due to aliphatic carbons in the spectra of the materials labelled at the acetylene groups. 

Monomer (VA). It is an enol ester that is obtained either by addition of acetic acid onto acetylene in the presence of a mercury, zinc, or cadmium salt (catalyst). 

A unique feature of organocuprate chemistry is the perfectly xyn-selective addition of lithium dialkylcuprates onto acetylene (Scheme 1-32). The 1-alkenylcuprates 40 thus generated are most attractive intermediates in reactions with alkyl... 

Lithium acetylide reacts very smoothly with ketones. For example, it combines rapidly with 2-norbomanone (bicyclo[2.2.1]heptan-2-one) to give 1-exo-ethynyl-2-e (io-norbomanol. If camphor is the substrate the ethinyl groups enters on the endo face. The addition of acetylene onto ketones can even be brought about by catalytic amounts of potassium ter/-butoxide. ... 

The XPS survey spectrum of a 75 nm thick film of plasma polymerized acetylene that was deposited onto a polished steel substrate is shown in Fig. 18 [22]. This film consisted mostly of carbon and a small amount of oxygen. Thus, the main peaks in the spectrum were attributed to C(ls) electrons near 284.6 eV and 0(ls) electrons near 533.2 eV. Additional weak peaks due to X-ray-induced O(KVV) and C(KLL) Auger electrons were also observed. High-resolution C(ls) and 0(ls) spectra are shown in Fig. 19. The C(ls) peak was highly symmetric. 

The hydration of triple bonds is generally carried out with mercuric ion salts (often the sulfate or acetate) as catalysts. Mercuric oxide in the presence of an acid is also a common reagent. Since the addition follows Markovnikov s rule, only acetylene gives an aldehyde. All other triple-bond compounds give ketones (for a method of reversing the orientation for terminal alkynes, see 15-16). With allqmes of the form RC=CH methyl ketones are formed almost exclusively, but with RC=CR both possible products are usually obtained. The reaction can be conveniently carried out with a catalyst prepared by impregnating mercuric oxide onto Nafion-H (a superacidic perfluorinated resinsulfonic acid). ... 

Lavallee, J.-F. Berthiaume, G. Deslongchamps, P. Grein, F. Intramolecular Michael addition of cyclic P-keto esters onto conjugated acetylenic ketones. Tetrahedron Lett. 1986, 27, 5455-5458. 

A significant part of the examples of transition metal catalyzed formation of five membered heterocycles utilizes a carbon-heteroatom bond forming reaction as the concluding step. The palladium or copper promoted addition of amines or alcohols onto unsaturated bonds (acetylene, olefin, allene or allyl moieties) is a prime example. This chapter summarises all those catalytic transformations, where the five membered ring is formed in the intramolecular connection of a carbon atom and a heteroatom, except for annulation reactions, involving the formation of a carbon-heteroatom bond, which are discussed in Chapter 3.4. 

The intramolecular addition of the N-H bond onto the acetylene moiety in ethynylanilines is presumed to lead to the formation of an indolylpalladium complex (c.f Chapter 1.2.). Trapping of this intermediate in subsequent transformations leads to the introduction of a substituent into... 

The amino benzopyran of step 5 (2.0 g) and dimethyl acetylene dicarboxylate (1.24 g 1.01 ml) were refluxed in ethanol (30 ml) for 26 hours. The reaction mixture was cooled to 0°C and the insoluble yellow-brown solid was collected by filtration and washed with a little ethanol and dried to give 2.0 g of a product which was a mixture of maleic and fumaric esters obtained by Michael addition of the amine to the acetylene. This mixture of esters (2.0 g) was treated with polyphosphoric acid (30 ml) and heated on the steam bath with stirring for 20 minutes. The reaction mixture was then poured onto ice and stirred with ethyl acetate. The organic layer was separated, washed with water and dried. The solvent was evaporated to leave 1.6 g of a yellow orange solid. Recrystallisation of this solid from ethyl acetate gave the required product as fluffy orange needles, mp 187°-188°C. 

Addition of dienophiles preferentially occurs onto the heterocyclic rings of tropones [c]-fused onto furan and pyrrole [cf. 84CHEC(4)67], Furotro-pone 307a and dimethyl acetylene dicarboxylate (DMAD) give a dimerized adduct that undergoes cycloreversion at higher temperature to form monomeric adduct 527 (Scheme 138 91CB2465). The 5,7-bis(carbomethoxy)... 

On the other hand, the cyclization reaction of a vinyllithium onto an acetylenic unit provides an efficient route to five- and six-membered bis-exocyclic 1,3-dienes, which react stereoselectively with a wide range of dienophiles157. The 5-exo carbolithiation reaction of vinyllithiums 369, derived from the corresponding vinyl bromides, is syw-stereospecific giving, after hydrolysis, the /(-isomer of five-membered outer-ring dienes 370 and tolerates aryl-, silyl- or alkyl-substituents at the distal acetylenic carbon (Scheme 97). However, the alkyl-substituted alkynes are far more resistant to rearrangement than the aryl- or silyl-substrates and the addition of TMEDA and longer reaction times are needed for the latter... 

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