Cyclopentadienone, tetraphenyl

Group IV substituted, 1, 614-620 Cyclopentadiene-spiropyrazolenine photolysis, 5, 251 Cyclopentadienone, 2,3-epoxy-photochromic compound, 1, 385 Cyclopentadienone, tetraphenyl-diepoxide, 7, 191... 

The reaction of 9 (generated thermally from 7 in toluene) with tetraphenyl-cyclopentadienone is more complex. Both the [6 + 2]-cycloadduct 3416), for which an X-ray structure analysis is available, and the [12 + 2]-cycloadduct 3516), whose constitution has been assigned primarily on the basis of H-NMR evidence, are obtained. The two cycloadducts presumably have a common intermediate which, in accord with the general reactivity of 9, should possess betaine character (.31 - 32) it is caused by nucleophilic attack by the carbonyl oxygen atom on the phosphorus of the heterocumulene. Ring closure of the carbanionic carbon atom... 

This double Claisen-Schmidt reaction takes place under the influence of ethano-lic potassium hydroxide (Expt 7.7) and presumably proceeds in the stepwise manner (cf. formulation in Section 6.12.2, p. 1032). The four aryl groups in tetra-cyclopentadienone effectively stabilise the cyclopentadienone system, which otherwise has only a transient existence and readily undergoes dimerisation by way of a diene-dienophile interaction (Diels-Alder reaction, Section 7.6). The use of tetracyclone as a dienophile for the preparation of 3,4,5,6-tetraphenyl-dihydrophthalic anhydride is noted on p. 1121. 

Some molecules are studied for their theoretical interest one being cyclopentadienone 16. But it turns out that this dimerises instantly by a Diels-Alder reaction and cannot be studied. The simplest cyclopentadienone that can be made is the tetraphenyl compound 17. Aldol disconnection gives 18 but we can now do a second aldol disconnection to reveal the two symmetrical starting materials 19 and 20. 

Diphenylacetylene with Mo(CO)a (298) in a sealed tube at 160°-170°C produces, in addition to two cyclobutadiene complexes, a yellow compound with the empirical formula [C9(CgH5)gO]Mo(CO)2, the infrared spectrum and chemical properties of which suit the tetraphenyl-cyclopentadienone complex of structure (11). On the other hand, the interaction of 3-hexyne with (CH3CN)gMo(CO)3 yields only the alkyne complex (570). 

Example 2.15. Loss of carbon monoxide in the thermal reaction of tetraphenyl-cyclopentadienone with maleic anhydride. 

In contrast to earlier interpretations gas phase decarbonylation of ionized 2,3,4,5-tetraphenyl-2,4-cyclopentadienone (147) does not result in the formation of an ionized tetraphenyl-substituted tetrahedrane (148), but yields exclusively the isomeric cyclo butadiene derivative (149) (Scheme 24). 

Cyclopentadienone is an elusive compound that has been sought for many years but with little success. Molecular orbital calculations predict that it should be highly reactive, and so it is it exists only as the dimer. The tetraphenyl derivative of this compound is to be synthesized in this experiment. This derivative is stable, and reacts readily with dienophiles. It is used not only for the synthesis of highly aromatic, highly arylated compounds, but also for examination of the mechanism of the Diels-Alder reaction itself. Tetraphenylcyclopentadienone has been carefully studied by means of molecular orbital methods in attempts to understand its unusual reactivity, color, and dipole moment. In Chapter 48 this highly reactive molecule is used to trap the fleeting benzyne to form tetraphenylnaphthalene. Indeed, this reaction constitutes evidence that benzyne does exist. 

Prepared by the method of Dilthey, the reagent is more efficient than tetraphenyl-cyclopentadienone as a reagent for trapping benzyne generated from diphenyl-iodonium carboxylate. In experiments with equimolar quantities of reactants, the yields of tetraarylnaphthalenes isolated by chromatography were 19 and 57%, respectively. 

Other aromatic transition metal complexes for which electronic spectra and assignments have been reported are (CsHs TiXb [X=C1, Br, I] 96), (C6He)2Cr 59), [(C6H6)2Cr]+I- 3io.42i.526), (C5H5)2Ni 17,422), and tetramethyl- and tetraphenyl-cyclopentadienone cobalt cyclopenta-... 

Also, the 2-siloxetane adducts of several substituted cyclopentadienones with the relatively stable silenes l,l-bis(trimethylsilyl)-2-(trimethylsiloxy)-2-phenylsilene and 1,1-bis(trimethylsilyl)-2-(trimethylsiloxy)-2-terf-butylsilene, generated in situ from their dimers by refluxing in dioxan or toluene, were isolated (equation 125)298, while similar reactions with fluorenone and tetraphenyl-a-pyrone yielded products of further transformations of the 2-silaoxetanes. 

The conversion of these substrates into phthalazines is interesting rather than useful in its present state of development. The lead tetracetate oxidation of 4,7-diphenyl-17/-1,2,3-triazolo[4,5-tf]pyridazin-l-amine (301) in the presence of 2,3,4,5-tetraphenyl-l-cyclopentadienone (302) gave 1,4,5,6,7,8-hexaphenylphtha-lazine (303) [reactants, CaO, CH2CI2, Pb(OAc)4 portionwise, 20°C, min 20% see original with respect to mechanism]. ... 

The kinetic product of sodium diphenylphosphite addition to tetraphenyl-cyclopentadienone is a 1,6-adduct (21). 

Coronene 16 can be viewed as a superbenzene. The series was continued with the synthesis of supemaphthalene 53 and supertriphenylene 56, using different phenylacetylenes and tetraphenyl substituted cyclopentadienone. Two selected examples 53 and 56 are shown in Scheme 15 [39,40]. 

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