Ring-opening, cyclooctatetraene

A general entry into the azonine system, c.g. 4, is by photoinduced electrocyclic ring opening of the bicyclic valence isomer 3,9 11-13 which is readily prepared by earboethoxynitrene addition to cyclooctatetraene. 

Much yet remains to be done as regards the choice of the pendent radicals. The ring-opening metathesis polymerization of cyclooctatetraenes (Gins-burg et ai, 1989 Klavetter and Grubbs, 1988) has not yet been applied to the construction of high-spin polyacetylenes. 

Langsdorf BL, Zhou X, Lonergan MC. Kinetic study of the ring-opening metathesis polymerization of ionically functionalized cyclooctatetraenes. Macromolecules 2001 34 2450-2458. 

The reaction of arc generated atoms with cyclooctatetraene (37) produces indene (22) in which the label is on C9. An initial DBA followed by ring opening to cyclononapentaene (38) is proposed. In analogy with known reactions of 38, electrocychc closure followed by H migration leads to 22- C9 (Eq. 25). 

Substituted polyacetylenes may be produced through the ring-opening metathesis polymerization of substituted cyclooctatetraenes.127... 

The photodimerization of a silylalkynylbenzene to cyclooctatetraenes has been reported by West and coworkers194. It was proposed that this occurred via intermolecular [2 + 2] dimerization followed by ring opening to the cyclooctatetraene (equation 44). 

Partially substituted derivatives of polyacetylene are synthesized via the ring-opening metathesis polymerization (ROMP) of cyclooctatetraene (COT) and its derivatives. Certain poly-COT derivatives afford soluble, highly conjugated poly acetylenes. These materials exhibit large third-order optical nonlinearities and low scattering losses. 

Ortho photocycloaddition was first reported in a U.S. patent [1] dated September 3, 1957. Irradiation of benzonitrile in the presence of various alkenes resulted in the formation of derivatives of l-cyanobicyclo[4.2.0]octa-2,4-diene. The first ortho photocycloaddition to benzene was reported in 1959 by Angus and Bryce-Smith [2], who discovered that benzene and maleic anhydride react to form a stable adduct at 60°C under the influence of ultraviolet radiation. This 1 2 adduct was formed from one molecule of benzene and two molecules of maleic anhydride. Two years later, Bryce-Smith and Lodge [3] found that acetylenes could also be photoadded to benzene. The isolated products were cyclooctatetraenes, formed by ring opening of the primarily formed bicyclo[4.2.0]octa-2,4,7-trienes. Since those early years, hundreds of examples of ortho photocycloadditions of alkenes to the benzene ring and many mechanistic investigations have been reported and they will be discussed in this chapter. 

Bryce-Smith and Lodge [3] have discovered that methyl propiolate, dimethyl acetylenedicarboxylate, and phenylacetylene add to benzene upon irradiation at 50°C. The products are cyclooctatetraenes, formed via initial ortho addition of the acetylene to benzene followed by ring opening (Scheme 9). 

Atkinson et al. [73] have described the photochemical addition of 3-hexyne and 5-decyne to benzonitrile. The products were 2,3-diethylcyclooctatetraene-l-carbonitrile and 2,3-n-butylcyclooctatetraene-l-carbonitrile, respectively. The ortho addition apparently takes place at positions 1 and 2 of benzonitrile. Subsequent ring opening of the initial bicyclo[4.2.0]octa-2,4,7-trienes leads to the 1,2,3-trisubstituted cyclooctatetraenes. 

The carbon-nitrogen triple bond can also undergo ortho photocycloaddition to derivatives of benzene. Al-Jalal et al. [86] found that irradiation of 4-cyanoanisole in acrylonitrile produced three 1 1 adducts. Two of these were formed by the addition of the carbon-carbon double bond of acrylonitrile to positions 1,2 and 3,4, respectively, of 4-cyanoanisole. The third product was an aza-cyclooctatetraene, apparently formed by the addition of the carbon-nitrogen triple bond to the arene, followed by ring opening [87],... 

In this case, only a thermal pathway for the formation of the cyclooctatetraene is proposed, in agreement with many other publications (for references, see Sec. II and Table 3). Tinnemans and Neckers [62], however, describe the ring opening of the ortho adduct from methyl phenylpropiolate and benzene as well as the reverse reaction as photochemical processes. The formation of this ortho adduct can also be accomplished in a xanthone-sensitized photoreaction [63], and in that case, the authors consider the ring opening as a thermal or a triplet-sensitized reaction and the reverse reaction as one proceeding via the singlet. 

An alternative approach to the preparation of polyacetylene is provided by the ring-opening polymerisation of 1,3,5,7-cyclooctatetraene in the presence of a metathesis catalyst, e.g. WCU—AlEt2Cl-epichlorohydrin (Cl4W[OCH(CH2Cl)2 —AlEt2Cl) [157-163] ... 

Tris(cyclopentadienyl)lanthanide complexes with steri-cally more crowded Cp ligands such as C5Me4R (R = Me, Et, Tr, and SiMe3) are not assessable by simple metathesis between lanthanide trihalides and the respective alkali metal salt of the bulky Cp ligand. For instance, Cp 3Sm, obtainable from Cp 2Sm and cyclooctatetraene, reacts with THF with ring-opening forming Cp 2Sm[0(CH2)4Cp ](THF) (equation 14). 

Optically active polyacetylene derivatives 97 were synthesized through ring-opening polymerization of the corresponding cyclooctatetraene derivatives.25 A twisted conformation of the main chain was proposed on the basis of CD and UV absorptions. Various optically active polyacetylenes have also been prepared from chiral monomers.24,25,263,177-183 The examples include a phenylacetylene derivative (98),26a alkylacetylenes 99,24 propionic esters such as 100,177,178 a Si-containing monomer (101),179 and disubstituted monomers such as 102.180 Poly-(A)-98 synthesized using a [RhCl(norbornadiene)]2 catalyst shows intense CD bands in the UV—vis region, probably based on a predominant helical sense of the main chain.263 This polymer effectively resolves several racemic... 

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