Cyclooctatetraene addition

Dimethyl acetylenedicarboxylate (DMAD) (125) is a very special alkyne and undergoes interesting cyclotrimerization and co-cyclization reactions of its own using the poorly soluble polymeric palladacyclopentadiene complex (TCPC) 75 and its diazadiene stabilized complex 123 as precursors of Pd(0) catalysts, Cyclotrimerization of DMAD is catalyzed by 123[60], In addition to the hexa-substituted benzene 126, the cyclooctatetraene derivative 127 was obtained by the co-cyclization of trimethylsilylpropargyl alcohol with an excess of DMAD (125)[6l], Co-cyclization is possible with various alkenes. The naphthalene-tetracarboxylate 129 was obtained by the reaction of methoxyallene (128) with an excess of DMAD using the catalyst 123[62],... 

Section 11 19 An additional requirement for aromaticity is that the number of rr elec Irons m conjugated planar monocyclic species must be equal to An + 2 where n is an integer This is called Huckel s rule Benzene with six TT electrons satisfies Huckel s rule for n = 1 Square cyclobutadiene (four TT electrons) and planar cyclooctatetraene (eight rr electrons) do not Both are examples of systems with An rr electrons and are antiaromatic... 

The addition of benzonitrile oxide to cyclooctatetraene produced a monoadduct which was induced to undergo valence tautomerism to produce a tricycloisoxazoline (Scheme 104). A similar reaction with tropone gave a minimum of eight adducts from which two monoadducts were isolated (Scheme 104) (70T5113). 

Cyclooctatetraene provides a significant contrast to the preference of aromatic hydrocarbons for one-electron reduction. It is converted to a diamagnetic dianion by addition of two electrons. It is easy to understand the ease with which the cyclooctatetraene radical accepts a second electron because of the aromaticity of the 10-7t-electron aromatic system which results (Section 9.3). 

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. 

Additions of benzene, not to olefins but to acetylenes have been utilized in the synthesis of cyclooctatetraenes (4.38)443). 

In addition to cycloheptatriene, cyclooctatriene and cyclooctatetraene systems can be used as six-carbon components in the [6 + 2]-cycloaddition with 7t-systems (Scheme 36). Interestingly, in these cases, dienes react exclusively... 

If the cycloaddition and cycloreversion steps occurred under the same conditions, an equilibrium would establish and a mixture of reactant and product olefins be obtained, which is a severe limitation to its synthetic use. In many cases, however, the two steps can very well be separated, with the cycloreversion under totally different conditions often showing pronounced regioselectivity, e.g. for thermodynamic reasons (product vs. reactant stability), and this type of olefin metathesis has been successfully applied to organic synthesis. In fact, this aspect of the synthetic application of four-membered ring compounds has recently aroused considerable attention, as it leads the way to their transformation into other useful intermediates. For example aza[18]annulene (371) could be synthesized utilizing a sequence of [2 + 2] cycloaddition and cycloreversion. (369), one of the dimers obtained from cyclooctatetraene upon heating to 100 °C, was transformed by carbethoxycarbene addition to two tetracyclic carboxylates, which subsequently lead to the isomeric azides (368) and (370). Upon direct photolysis of these, (371) was obtained in 25 and 28% yield, respectively 127). Aza[14]annulene could be synthesized in a similar fashion I28). 

Uranocene itself was prepared by allowing cyclooctatetraene (COT) to react with potassium in dry, oxygen-free tetrahydrofuran (THF) at —30° followed by the addition of a THF solution of anhydrous uranium tetrachloride ... 

In systems of conjugated double bonds catalytic hydrogenation usually gives a mixture of all possible products. Conjugated dienes and polyenes can be reduced by metals sodium, potassium, or lithium. The reduction is accomplished by 1,4-addition which results in the formation of a product with only one double bond and products of coupling and polymerization. Isoprene was reduced in 60% yield to 2-methyl-2-butene by sodium in liquid ammonia [357]. Reduction of cyclooctatetraene with sodium in liquid ammonia gave a... 

A solution of l-(a-chlorobenzylidene)-2-phenylhydrazine (0.2 g, 0.87 mmol) and Et3N (0.6 mL, 4.3 mmol) in cyclooctatetraene (5 mL, 43 mmol) was kept in the dark at 25 X for 48 h. The precipitated hydrochloride was filtered off and the excess cyclooctatetraene and Et, N were evaporated under normal pressure in the dark to give a residue which was dissolved in EtOAc, then precipitated by addition of MeOH at — 10 X yield 0.16 g (62%) mp 128 131 X yellow needles. 

Tetrahaptocyclohexatriene- and cyclooctatetraene-metal-tricarbonyl complexes undergo some unusual cyclo-addition reactions with tetracy-anoethylene in which the dienophile undergoes a 1,3 addition across the coordinated ligand and causes a rearrangement of the metal-carbon bonds, for example (99),... 

The 18 n-electron system furo[3,4-c]octalene (356) is available by a Wittig reaction starting from cyclooctatetraene-1,2-dicarboxaldehyde it is obtained as an unstable pale yellow liquid, which is rapidly oxidized in air. The electronic spectrum resembles that of 353, showing little extended conjugation. Compound 356 underwent Diels-Alder addition at the terminal cyclooctatetraene ring thus treatment with dimethyl fumarate leads to monoadduct 357. ... 

Cyanogen azide reacts with cyclooctatetraene (112) at room temperature in ethyl acetate to give alkylidenecyanamide.326 At 78°, a 31% yield of a mixture of the alkylidenecyanamide (113) (68%) and the 1,4-adduct 114 (32%) is obtained. Since cyanogen azide decomposes above 40° and since the alkylidenecyanamide does not rearrange to the 1,4 adduct under the reaction conditions, one may believe that the 1,4 adduct forms directly from cyanonitrene and cyclooctatetraene. This is a case of 1,4 addition studied by Anastassiou.328... 

With dichlorosilylene, similar products result along with smaller amounts of the 2-silaindane. These are thought to result from insertion, or addition, of the silylene to the bicyclo valence isomer (11) of cyclooctatetraene (Scheme 24) (75ZOB2221), although a similar route to that in Scheme 23 is also possible. 

When additional formally noncoordinating double bonds are added to the ligands as in (cycloheptatriene)Fe(CO)3 and (cyclooctatetraene)Fe(CO)3, two further peaks are apparent in the UPS at 10.23 and 10.61 eV, respectively. These are attributable to the ionization of the 7r-type MOs of the uncoordinated olefin... 

Access to homotropenylium ions can be achieved by two general routes. The first involves the addition of an electrophile to a cyclooctatetraene or cyclooctatetraene derivative, an approach which can be considered to correspond to a homoallyl route (Scheme 4). In this route the electrophile is generally attached stereoselectively to the endo position on C(8)18 7,1 74. The second approach involves the ionization of a bicyclo[5.1.0]octadienyl derivative. This is the cyclopropylcarbinyl approach (Scheme 4). This route has the potential of generating a wide range of differently substituted cations however, the starting materials can be difficult to access75 . 

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... 

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