Bicyclo octa-2,4-dienes

Ring-opening metathesis polymerization (ROMP) of substituted bicyclo octa-dienes or paracyclophane-enes initiated by Gmbbs molybdenum, tungsten-based carbenes have been used to prepare PPV s [178—181]. The living character of ROMP has been exploited to prepare soluble well-defined precursors, which can be converted into XI. Yu and Turner have used ROMP of tetra octyloxy-substituted paracyclo-phanedienes initiated by reactive ruthenium-based carbenes to prepare monodisperse, soluble yellow fluorescent PPV with an alternating cis-trans microstructure and molecular weights as calculated [178] (Fig. 9.21). 

Another application of catalyst 8 is to the reaction of acetylenic aldehydes [10c] (Scheme 1.18, Table 1.6). Two acetylenic dienophiles have been reacted with cyclo-pentadiene or cyclohexadiene to give bicyclo[2.2.1]heptadiene or bicyclo[2.2.2]octa-diene derivatives in high optical purity. A theoretical study suggests that this reaction proceeds via an exo transition state. 

The intramolecular photochemical [2+2] cycloaddition of bicyclo[3.3.0]octa. dienes has been examined by several groups.128 197, 99) A striking example of a synthetic application of this chemistry is given in Scheme 22. 

Neben 2-Methyl-buten-(2) bildet auch Athyl-vinyl-ather mit Benzonitril ein 1 1-Photo-addukt, bei dem es sieh wahrscheinlich ebenfalls um ein Dcrivat des Bicyclo[4.2.0]octa-diens-(2,4) handelt2 Versuche mit Essigsaurc-vinyl ester und cw-l,2-Dichlor-athyicn verliefen dagegen erfolglos2. 

When a small ring was fused to the bridge of TBP precursor 44a, strained cycloalkene would be formed in the rDA reaction. Thus, the rDA temperamre was expected to be raised in this case. Such precursors were prepared from cycloheptatriene 49e [55] and cyclooctatriene 49f [56]. The DA reaction of these diene equivalents with disulfonylethy-lene 4b proceeded via norcaradiene and bicyclo[4.2.0]octa-diene forms to give the tricyclo adducts 51e and 51f, which were transformed to precursors 53e-H2 and 53f-H2 in the usual manner (T. Okujima et al., manuscript in preparation). The rDA temperatures of 53e-H2 and 53f-H2 were proved to be extremely raised. Cyclopropane-fused 53e-H2 and cyclo-butane-fused 53f-H2 did not undergo the thermal rDA reaction below 265 and 180 C, respectively, and were successfully metallated with Cu(OAc>2 to give 53e-Cu and 53f-Cu (T. Okujima et al., manuscript in preparation). 

The prediction on the basis of orbital symmetry analysis that cyclization of eight-n-electron systems will be connotatoiy has been confirmed by study of isomeric 2,4,6,8-decatetraenes. Electrocyclic reaction occurs near room temperature and establishes an equilibrium that favors the cyclooctatriene product. At slightly more elevated temperatures, the hexatriene system undergoes a subsequent disrotatory cyclization, establishing equilibrium with the corresponding bicyclo[4.2.0]octa-2,4-diene ... 

Abbreviations acac, acetylacetonate Aik, alkyl AN, acetonitrile bpy, 2,2 -bipyridine Bu, butyl cod, 1,5- or 1,4-cyclooctadiene coe, cyclooctene cot, cyclooctatetraene Cp, cyclopentadienyl Cp, pentamethylcyclopenladienyl Cy, cyclohexyl dme, 1,2-dimethoxyethane dpe, bis(diphenyl-phosphino)ethane dppen, cis-l,2-bis(di[Atenylphosphino)ethylene dppm, bis(diphenylphosphino) methane dppp, l,3-bis(diphenylphosphino)propane eda,ethylenediamine Et,ethyl Hal,halide Hpz, pyrazole HPz, variously substituted pyrazoles Hpz, 3,5-dimethylpyrazole Me, methyl Mes, mesityl nbd, notboma-2,5-diene OBor, (lS)-endo-(-)-bomoxy Ph, phenyl phen, LlO-phenanthroline Pr, f opyl py, pyridine pz, pyrazolate Pz, variously substituted pyrazolates pz, 3,5-dimethylpyrazolate solv, solvent tfb, tetrafluorobenzo(5,6]bicyclo(2.2.2]octa-2,5,7-triene (tetrafluorobenzobanelene) THE, tetrahydrofuran tht, tetrahydrothicphene Tol, tolyl. 

The Cope rearrangement of hexa-l,5-diene does not allow for differentiation of starting material and product this is called a degenerate Cope rearrangement. Another example is the automerization of bicyclo[5,l,0]octa-2,5-diene 7 ... 

Bicyclo[2.2.1]hepta-2,5-diene, nitrosyl chloride adduct, 46, 74 reaction with acetic acid to yield nortricyclyl acetate, 46, 74 Bicyclohexyl, 46, 61 Bicyclohexylidene, 47, 34 ejSO-e s-BlCYCLO[3.3.0]OCTANE-2-CAR-BOXYLIC ACID, 47, 10 Bicyclopentadienylidene, octa-chloro-, 46,93... 

It has been reported that irradiation of bicyclo[5.1.0]octa-3,5-dien-2-one (63) in methanol leads to a mixture of racemic tricyclo[4,2.0.03,5]oct-7-en-2-one (65), 37, and cyclohepta-l,3,5-triene35). Control of the reaction was also tried in expectation... 

Table 1. Preparation and Anionic Polymerization of Masked Disilene, 1-Phenyl-7,8-disila-bicyclo[2.2.2]octa-2,5-diene...

D. W. Rogers, S. A. Loggins, S. D. Samuel, M. A. Finnerty and J. F. Liebman, Struct. Chem., 1, 481 (1990). Admittedly, the authors did not separate 74 from the isomeric bicyclo[3.3.0]octa-2,6-diene but it is unlikely that these two species are that different. 

As shown in Table 6 and Figure 1, the oxidation potentials of 2-substituted norbornadienes (1), 2-substituted bicyclo[2.2.2]octa-2,5-dienes (2) and 4-substituted [2.2]paracyclophanes (3) clearly indicate that the transannular interaction between two double bonds contributes already at the stage of the first electron transfer. Namely, in compounds 1-3, the electron is transferred from the unsaturated bond which is not substituted by the electron-withdrawing group, Figure 1 shows the... 

Dai et al. (1990) have reported direct spectroscopic measurements on a similar bishomobenzene radical cation. The system they studied was the bicyclo[3.3.0]octa-2,6-diene-4,8-diyl radical cation [159] generated by radiolytic oxidation of semibullvalene [83] in Freon matrices. The hydrogen... 

Scheme 6.29 Generation of bicyclo[3.2.1 ]octa-2,3-diene (123) and trapping by KOtBu and styrene.

Scheme 6.30 Structure ofthe trapping products of bicyclo[3.2.1]-octa-2,3-diene (123) with 1,3-cyclopentadiene, (Z)-l, 3-pentadiene and 2,3-dimethyl-l, 3-butadiene and ofthe dimers of123.

Dimers with a 1,2-bismethylenecyclobutane structure were obtained from 585 [240], 590 [238], 591 [241], 592 [242], 593 [243] and from the pinene derivative 597 [244]. The interception of 592 by 1,3-diphenylisobenzofuran (DPIBF) afforded two diastereomeric [4+ 2]-cycloadducts [245], Bicyclo[5.1.0]octa-3,4-diene (594) was generated by /3-elimination and trapped by sodium pyrrolidide because of the question of the extent to which the corresponding bicyclooctyne is formed in addition to 594 [184], Liberated by /3-elimination from ll,ll-dichloro-l,6-methano[10]annulene in... 

These results have been interpreted in terms of trans addition of mercuric ion and nucleophile where the attack of the mercuric ion takes place from the more hindered side of the diene molecule. A transition state 197, involving an endo attack of mercuric ion with some stabilization by coordination to the 8,9-ethylenic bond to the mercury atom, has been proposed to support the suggested mechanism. Analogously, and in sharp contrast to the results obtained167 in the mercuration of norbomadiene which reacts with mercury salts via the usual scheme of exo-syn addition, the principal pathway in the mercuration of bicyclo[2.2.2]octa-2,5-diene is the formation of endo-syn products (equation 165). 

The thermolysis of the bicyclodiene 109 at 225 °C gives rise to equilibrium mixture of cyclooctatriene and its transformation products (see below)54. More recently the influence of a methoxy group on the thermal behavior of the bicyclo[5.1.0]octa-2,4-diene system was studied56. Heating of 8-ewdo-methoxydiene 115 in cyclooctane at 95 °C gaves rise to methoxy substituted diene 117 and not to the product 116 of butadienylcyclopropane rearrangement (equation 41). The thermolysis of the 8-exo-isomer 118 has taken place as an equilibrium reaction to give 6-ewdo-methoxy diene 119 (equation 42)56. These two reaction partners were separated by TLC. 

The numerous transformations of cyclooctatetraene 189 and its derivatives include three types of structural changes, viz. ring inversion, bond shift and valence isomerizations (for reviews, see References 83-85). One of the major transformations is the interconversion of the cyclooctatetraene and bicyclo[4.2.0]octa-2,4,7-triene. However, the rearrangement of cyclooctatetraene into the semibullvalene system is little known. For example, the thermolysis of l,2,3,4-tetra(trifluoromethyl)cyclooctatetraene 221 in pentane solution at 170-180 °C for 6 days gave three isomers which were separated by preparative GLC. They were identified as l,2,7,8-tetrakis(trifluoromethyl)bicyclo[4.2.0]octa-2,4,7-triene 222 and tetrakis(trifluoromethyl)semibullvalenes 223 and 224 (equation 71)86. It was shown that a thermal equilibrium exists between the precursor 221 and its bond-shift isomer 225 which undergoes a rapid cyclization to form the triene 222. The cyclooctatetraenes 221 and 225 are in equilibrium with diene 223, followed by irreversible rearrangement to the most stable isomer 224 (equation 72)86. 

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