Acetylene/norbornene

Copolymerizations of benzvalene with norbornene have been used to prepare block copolymers that are more stable and more soluble than the polybenzvalene (32). Upon conversion to (CH), some phase separation of nonconverted polynorbomene occurs. Other copolymerizations of acetylene with a variety of monomers and carrier polymers have been employed in the preparation of soluble polyacetylenes. Direct copolymerization of acetylene with other monomers (33—39), and various techniques for grafting p oly acetylene side chains onto solubilized carrier polymers (40—43), have been studied. In most cases, the resulting copolymers exhibit poorer electrical properties as solubility increases. 

Difunctionalization of Unactivated Alkenes and Acetylenes 8.2.1.1 Carbopalladation of Norbornene and its Analogues... 

Interesting evidence supporting the mechanism of polymerisation of acetylenes via carbene species is provided by the block and random copolymerisation of acetylenic monomers with cycloolefins. For instance, block copolymers of acetylene and cyclopentene with the WC —AlEtCT catalyst [41] and block copolymers of acetylene and norbornene with the (MeA. Oj2W(=NAr)= CHMe3 catalyst [42] have been obtained moreover, random copolymers of phenylacetylene and norbornene with the WC16 catalyst have also been obtained [149, 150],... 

The initial catalytic version of the PK reaction actually appeared in 1973, in the first paper detailing the preparation of cyclopentenones by Pauson and co-workers.3 By stirring a solution of dicobalt octacarbonyl (10 mol % with respect to the alkene) and norbornene (or norbornadiene), first under a pressure of acetylene and then under a pressure of mixed acetylene/CO (1 1), it was possible to obtain a good yield of the desired cyclopentenone products (42 and 8 - Scheme 16). It was possible to lower the loading of dicobalt octacarbonyl to 2.5 mol % and still obtain a 62% yield of the cyclopentenone. When norbornadiene was employed as the alkene, a lower yield of the desired cyclopentenone was obtained but this was due to the product reacting further under the conditions employed. 

Ethynylcyclopropanes, like normal acetylenes, react with dicobalt octacarbonyl in ether to form stable dinuclear cluster-like hexacarbonyl complexes (equation 170). The complex with l-chloro-2,2,3,3-tetramethylethynylcyclopropane reacts stereo- and regioselec-tively with norbornene in a typical Pauson-Khand reaction to give the xo-2-cyclopropyl substituted cyclopentenone (equation 171). Similarly, the reaction of 2-ethoxycyclo-propylacetylene with cyclopentene in the presence of Co2(CO)8 under CO gave 3-(2-ethoxycyclopropyl)-c/.y-bicyclo[3.3.0]oct-3-en-2-one (equation 172) ... 

Koltzenburg et al. report the synthesis of AB block copolymers of acetylene and norbornene derivatives bearing mesogenic moieties [68]. A norbornene... 

Considerable effort has been devoted to achieving the intermolecular catalytic Pauson-Khand reaction. The mthenium complex-catalyzed reaction of an alkyne with an alkene such as ethylene or 2-norbornene under CO gave hydroquinone derivatives [79], with CO (2 mol) being introduced into the products (Eq. 11.36). This reaction is the first example of the preparation of hydroquinone derivatives by the reaction of alkynes and alkenes with CO, while hydroquinone is synthesized by the ruthenium-catalyzed reaction of 2 mol acetylene with 2 mol CO (Eq. 11.37) [80]. 

The cycloaddition reaction of the adduct 575, obtained from -Bu3P and CS2, to a strained double bond such as in norbornene, gave the stable zwitterionic product 576. The latter dissociated to yield 577, which could be trapped with aldehydes in a Wittig reaction to give the tricyclic alkylidenedithiolanes 578 (Scheme 81). The compound 575 also reacted with acetylenic dipolarophiles to give dihydro-TTF derivatives <1996PS593, 1997T10441>. 

The first report of a catalytic intermolecular cyclization was made by Pauson and Khand in 1974 [22], but the scope was limited to gaseous acetylene as the alkyne partner, strained olefins such as norbornene and norbornadiene as the alkene component, and TON s (turnover numbers) were modest (8-11). Several subsequent reports detailed the production of cyclopentenones from a substoi-chiometric amount of Co2(CO)g, but none were as efficient as Pauson s initial work [23,24]. Using ethylene as the alkene component, Rautenstrauch demonstrated the first efficient catalytic Pauson-Khand cyclization with a TON of 220, Eq. (5) [25]. A more general catalyst system employing (indenyl)Co(cod) was recently reported by Chung and Jeong, Eq. (6) [26]. The reaction was quite effec-... 

Cocyclodimerizations of norbornene with butadiene or acetylene dicarboxylates, like many other examples, reveal an exo stereoselectivity in addition reactions25. 

Similarly, thioselenation of olefins can be achieved with the diphenyl disulfide/ diphenyl diselenide binary system [26] (Eq. 9). The radical chain addition of disulfides to olefins is quite inefficient because of the competition of yff-elimination with the attack of the /S-thioalkyl radical on the disulfide diphenyl diselenide is a far better radical trap. As shown in Eq. (10), the reaction has been extended to thio-telluration. With the exception of norbornene and vinylcyclopropanes, for which the addition step is followed by the fast opening of the three-membered ring, thio-telluration does not proceed with olefins. In contrast, the thiotelluration of acetylenes is highly efficient. 

Risse and S. Breunig, Transition metal catalyzed vinyl addition polymerizations of norbor nene derivatives with ester groups, Makromol. Chem. 193, 2915 (1992) C. Mehler and M. Risse, Addition polymerization of norbornene catalyzed by palladium(2- -) compounds. A polymerization reaction with rare chain transfer and chain termination, Macromol. 25, 4226 4228 (1992) R.G. Schulz, Polym. Lett. 4, 541 (1966). C. Tanielian, A. Kiennemann, and T. Osparpucu, Influence de differents catalyseurs abase d elements de transition du groupe VIII sur lapol3mierisation du norbor nene, Can. J. Chem. 57, 2022 (1979) A. Sen and T. W. Lai, Catalytic polymerization of acetylenes and olefins by tetrakis(acetonitrile)palladium(II) ditetrafluoroborate, Organometallics 1, 415 (1982) C. Mehler and W. Risse, Pd(II) catalyzed polymerization of norbornene derivatives, Mak romol. Chem. Rapid Commun. 12, 255 (1991). 

Norbornene reacts with dimethyl acetylenedicarboxylate in the presence of ruthenium(cyclooctadiene)(cyclooctatriene) to form the xo-cycloadduct 418. The ability to activate norbornene is unique to low-valent ruthenium . The photochemical addition of symmetrical acetylenes RC=CR (R = H, Me, Ph or SiMes) to 3,6-... 

Three synthetic approaches toward 3-trifluoromethylpyrazole 41 are summarized in Scheme 12.5, all of which involve [2 + 3] cycloaddition. Either combinations of diazotrifluoroethane 39 with acetylene 40 or trifluoroacetimidoyl chloride 43 with ethyl vinyl ether leads to 41. However, cycloaddition of a zwiterionic intermediate 45 with norbornadiene affords 47 (after removal of norbornene fragment), but only as a minor product. Intermediate 45 is generated by the dehydrobromination of imi-doylbromide 44 with triethylamine. 

We could thus expect that this reaction terminated the palladium- and nor-bornene-catalyzed reaction sequence in place of the acrylic ester or terminal olefins in general. Considerable difficulties were met, however, because the alkyne interacted with all the palladium complexes of the sequence, giving rise to a number of by-products. Starting from 1 equivalent of aryl iodide, 2 equivalents of alkyl bromide, 1 equivalent of norbornene, 0.3 equivalents of aryl-acetylene, 8 equivalents of KOAc, and 0.1 equivalent of Pd(OAc)2 and adding gradually 2 equivalents of alkyl bromide and 0.7 equivalents of arylacetylene (to keep the concentration of the latter low) satisfactory results were obtained. Equation 30 reports the reaction withp-fluoroiodobenzene, n-propyl bromide, and phenylacetylene, which gave a 79% yield (71% with iodobenzene) [37]. 

This number was calculated based on Hartree-Frock energy minimization and frequency calculations for acetylene, ethylene, propene, E 2-butene, norbornene, ds 1,3-divinylcyclopentene, and 1,6-heptadiene using Gaussian 03. The -31G basis set was used. Frisch, M. J. Trucks, G. W. Schlegel, H. B. Scuseria, G. E. Robb, M. A. Cheeseman, J. R. Zakrzewski, V. G. Montgomery, J. A. Stratmann, R. E. Burant, J. C., et al. Gaussian, Inc., Pittsburgh, PA, 1998. 

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