Cyclooligomerization of alkynes

A number of models for the cyclooligomerization of alkynes by early transition metal catalysts have been prepared by reducing sterically hindered aryloxide... 

A couple of prototypical examples of the cyclic version of the Heck reaction, defined as a process consisting of alkene carbopalladation followed by -elimination, were reported during the 1984-1985 period [9,10]. Almost concurrently, seminal examples of both the non-Heck cyclic carbopallation reactions [10,30] were reported during the 1983-1985 period. Thus, with due respect paid to earlier discoveries of alkyne cyclooligomerization via cascade carbopalladation [7,8] as well as copolymerization [24] and cocyclization [25,... 

In the case of reactions such as valence isomerization, metathesis reactions of alkenes and alkynes, oligomerization or cyclooligomerization of olefins, metallacycloalkanes are of special importance. Their catalytic efficiency depends on the ease of the M—C bond cleavage, which is the result of reductive elimination of the organic substrate or of /J-hydrogen transfer. Also a- or / -C—C bond rupture has been reported. Heterocycles with an aliphatic carbon skeleton and a donor atom adjacent to the metal are suitable model compounds for the study of individual catalytic steps and structural properties. In connection with the activation of C—H bonds, cyclometa-lation has become a very general reaction and was reviewed in 1977. ... 

Thermal cyclooligomerizations of olefins and alkynes require severe and often dangerous reaction conditions and the yields of cyclic products are usually very low. Acetylene ean be trimerized to benzene at 500 °C [1] and butadiene (BD) dimerizes at 270 °C and under high pressure to give small amounts of 1,5-cyclo-octadiene [2]. Reppe s discovery in 1940 that acetylene can be cyclotetramerized to cyclooctatetraene (COT) using a nickel catalyst [3] shows that transition metals can act as templates for the synthesis of cyclic hydrocarbons from acetylenic or olefinic building blocks (Scheme 1). 

Cyclopentanones, Cyclopentenones and Cyclopentadienones via Carbonylative [2 + 2 + 1 Cyclooligomerization of Alkenes and Alkynes with Carbon Monoxide... 

Use of CpV(CO)4 under photoirradiation affords CpV(rj -CgFsC CCeFs)(00)2 (Scheme 34). Cyclooligomerization of diphenylacetylene with Cp2V2(CO)5 affords the )] -cydobutadiene complex (60), V(C4Ph4)Cp(CO)2 (Scheme 35). The above-mentioned side-on monomeric complex is obtained with the more basic alkyne like dimethyl-acetylene. 

A rhodium-catalyzed protocol of alkyne cyclooligomerization provides an alternative route for the preparation of indenocorannulenes 100 [27] (Scheme 29). The key step of the synthesis starts with 2,3-diethynylcoranulenes 99, which are accessed by Pd-catalyzed cross-coupling reactions of the corresponding 2,3-dichlorocorannulenes 19/23 with trimethyltin-substimted alkynes. The... 

Another class of transition metal complexes studied by our group consists of alkyne and vinylidene complexes of tungsten and molybdenum in high oxidation states. Alkyne complexes are interesting from a theoretical point of view because they may be considered to be either side-on coordinated ligand complexes or metallacyclopropenes. They are also important as possible intermediates in the cyclooligomerization and polymerization of alkynes. o " Scheme 3 shows the two types of alkyne complex that were studied. 

Polymerization Reactions (Including Cyclooligomerization) of Alkenes and Alkynes Using Polymeric Transition Metal Catalysts... 

Metallocycles, as noted earlier, frequently are intermediates in the cyclooligomerization of acetylenes. In several cases, e.g., Fe (Hoogzand and Hiibel, 1968), Ru (Sears and Stone, 1968), Os (Ferraris and Gervasio, 1974), Co (Wakatsuki and Yamazaki, 1973), Rh (Muller et al., 1971), Ir (Collman et al., 1968), Ni (Zeiss and Tsutsui, 1959), and Pd (Ito et al, 1972), these compounds have been isolated and found to undergo several interesting and synthetically important reactions [Eq. (78)]. When unsymmetrical alkynes... 

The Pd-catalyzed alkynylation is one of the most widely used —C bond formation reactions. It has been thoroughly and extensively reviewed recently15-17. So only a brief overview and a discussion of some of the most recent advances will be presented in this section. As in the case of alkenyl-alkenyl coupling, Ni catalysts have rarely been used for alkynylation, even though Ni catalysts do affect the desired alkynylation in some cases. One main reason for disfavoring Ni is that Ni can readily react with alkynes to undergo alkyne cyclooligomerization represented by arene formation. The Pd-catalyzed alkynylation can, in principle, be performed in three discrete manners, as shown in Scheme 40. 

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