Bicyclo octa-2,3,7-triene

Dimethylamino-2.3,4,5-tetrafluo-ro- EI0b2, 267 (l-NR2-2,3,4,5-F4 - [Pg.863]

The chemistry of cyclooctatetraene is interesting and unusual. Particularly noteworthy is the way in which it undergoes addition reactions to form products that appear to be derived from the bicyclic isomer, bicyclo[4.2.0]2,4,7-octa-triene, 8. In fact, there is an electrocyclic equilibrium between cyclooctatetraene and 8 (Section 21-10D) and, although the position of equilibrium lies... 

Complex 105 cydizes with DMAD to give the diastereomeric bound bicyclo[2.2.2]octa-trienes 109A and 109B in a 1 1 ratio (Scheme 14). Oxidation of these complexes liberates the corresponding triene 110 as well as the disubstituted anisole 111, presumably generated with acetylene from the cycloreversion of 110. 

COT is prepared by the polymerization of ethyne at moderate temperature and pressure in the presence of nickel salts. The molecule is non-planar and behaves as a typical cyclic olefin, having no aromatic properties. It may be catalytically hydrogenated to cyclo-octene, but with Zn and dil. sulphuric acid gives 1,3,6-cyclooclairiene. It reacts with maleic anhydride to give an adduct, m.p. 166 C, derived from the isomeric structure bicyclo-4,2,0-octa-2,4,7-triene(I) ... 

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. 

Again, the bicyclic valence isomer coexists in sufficient concentration, that the bicyclic peroxide 19 was readily accessible in ca. 20% yield. Alternatively, the thermally labile bicyclic valence isomer of cyclooctatetraene, namely bicyclo[4.2.0]-octa-2,4,7-triene, was converted into the corresponding endoperoxide on low temperature singlet oxygenation and reduced with diimide to yield 19. 

Scheme 6.28 Precursors and reactions of bicyclo[3.2.1]octa-2,3,6-triene (117).

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. 

Benzocyclobutenone Bicyclo[4.2.0]octa-1,3,5-trien-7-one (8,9) (3469-06-5) 2-Toluic acid chloride o-Toluoyl chloride (8) Benzoyl chloride, 2-methyl- (9) (933-88-0)... 

One case of some interest for which kinetic data are not available, but for which equilibrium data are, is that of cyclo-octa-l,3,5-triene. At 100° there is a rapid equilibration between the triene and bicyclo[4,2,0] octadiene ... 

Norbornadiene adds typical dienophiles in a homo-Diels-Alder reaction whereby, for example, the adduct 86 is obtained with tetra-cyanoethylene. Dimethyl acetylenedicarboxylate and dicyanoacetyl-ene add to barrelene (bicyclo[2.2.2]octa-2,5,7-triene) in a similar way. °... 

Treatment of tungsten hexacarbonyl with a mixture of cyclo-octa-1,3,5-and -1,3,6-triene gives the complex [W(OO iCslIiohJ (85). The hydrocarbon is believed to be the 1,3,6-triene, acting as a diene, but for the reasons mentioned (see Section III,H) it is possible that the ligand is bicyclo[4,2,0]-octa-2,4-diene (XV). 

Chelate complexes of the type [PdX2(diene)] (X = Cl, Br) are readily formed by the dienes hexa-1,5-diene (124), bicyclo 2,2,lJhepta-2,5-diene (1, 7) tricyclo[4,2,2,0]-deca-triene and -diene derivatives (10), cyclo-octa-1,5-diene and dicyclopentadiene, but not dipentene (43). These may be converted to complexes of the types [Pd2X2(dieneOR)2] and [PdCl(dieneOR)-(amine)] (R = alkyl) (43), and their properties indicate that they have similar structures to the platinum complexes (XXXI) and (XXXIII). 

For example, the electrocyclic ring closure of cycloocta-1,3,5-trienes 1 to bicyclo[4.2.0]octa-2,4-dienes 2 has been widely used for the preparation of cyclobutanes (see Houbcn-Weyl, Vol. 4/4,... 

Cyclooctatetraene (3) reacts via its valence isomer, bicyclo[4.2.0]octa-2,4,7-triene, as a dienophile towards tetrachlorocyclopentadienone acetals to form 1 2 adducts (e.g., 10) with four-membered saturated rings.63... 

In this review, the term benzocyclobutene is used to refer to structure I, with the numbering system shown below. This was done to be as consistent as possible with the majority of the references used in the preparation of this review. It should be noted however, that according to CAS, the name benzocyclobutene actually refers to benzocyclobutadiene 130 and what is commonly called benzocyclobutene is 1,2-dihydrobenzocyclobutadiene. The prefered CAS name for what is commonly called benzocyclobutene 1 is bicyclo[4.2.0]octa-l,3,5-triene with the numbering system shown below in 130. Benzocyclobutene 1 has also been referred to as benzocyclobutane, cardene, benzocyclobutene-1,2-dihydro, cyclobutabenzene and generically as a cyclobutarene. 

Roedig et al, described the treatment of polyhalogenated bicyclo-[4,2,0]octa-l,5,7-trienes (323) with aniline to give first 324 and then 325, which with DMAD formed the naphthoquinonebisimine 326.198... 

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