Tetraphenylcyclopentadienone, Diels-Alder

Thiete sulfones show an irregular behavior pattern when involved in cycloaddition reactions. With 1,3-dienes, dienamines, enamines, ynamines, diazoalkenes, cyclopropadiene, and its substitution products, furan, and anthracene, the addition proceeds in the normal fashion. With certain Diels-Alder reagents such as tetraphenylcyclopentadienone (tetracycloneX however, the cyclic sulfones react anomalously. The Diels-Alder adducts undergo decomposition with SO 2 and CO extrusion to a seven-membered ring, the tetraphenylcycloheptatriene 223. Bicyclic octadienone is produced as well (Eq. 62). The mechanism of this unusual reaction is proposed by... 

Diels-Alder addition of the benzazete (168) to tetraphenylcyclopentadienone (169) followed by CO loss yields the pentaphenylbenzazocine (170) (75JCS(PI)45). Intramolecular Wittig reaction of (171) gives some 3,4-dihydro-27/-benzoxocin (74JOC3038). 

The synthetic method applied is that of a repetitive Diels—Alder reaction whereby ethynyl-substituted tetraphenylcyclopentadienones 105 and 106 serve as branching reagents, since they contain one diene and two to four dienophile functions, respectively. The... 

When thermolysis was performed in the presence of dienophiles, Diels-Alder products were formed, some of which at the high temperature underwent further transformation for example, tetraphenylcyclopentadienone gave directly 1,2,3,4-tetraphenylnaphthalene (90%) [52]. The use of 2-phenyliodonio benzoate as a source of benzyne was especially suitable with some zwitterionic and mesoionic compounds of low reactivity, which did not react with other benzyne precursors [53]. Another iodonium zwitterion was used for the generation of 2,3-dehydro-naphthalene, which on reaction with tetraphenylcyclopentadienone afforded 1,2,3,4-tetraphenylanthracene. 

Mullen and coworkers utilized the Diels-Alder reaction to prepare hb-PPs (hb-P25 to hb-P27) with Mw up to 107000 from ethynyl-, propynyl-, and phenylethynyl-substituted tetraphenylcyclopentadienones (Scheme 13) [47]. Despite their high molecular weights and rigid phenyl rings, all the polymers showed good solubility in common aromatic solvents such as toluene and benzene. 

Polyphenyls. Another means of carrying the cyclopentadienone Diels-Alder reaction to the monoadduct stage (III, Reaction 6) is to use an acetylenic dienophile and obtain a product which is no longer a diene but an aromatic. The reaction of tetraphenylcyclopentadienone (V) with diphenylacetylene (XII) affords hexaphenylbenzene (XIV) by loss of carbon monoxide from the intermediate adduct XIII (Reaction 10). In certain cases the intermediate adduct XIII can be isolated. 

The thermally stable furan adducts undergo a second Diels-Alder reaction with tetraphenylcyclopentadienone. The tetracyclic product obtained turns out to be thermolabile and breaks down on heating to give the trifluoromethyl-substituted furan together with 1,2,3,4-tetraphenylben-zene and carbon monoxide [91JFC(53)297]. 

Conjugated diynes can function as dienophiles in Diels-Alder reactions, and adducts have been obtained in which one or both of the triple bonds participates. Most of the studies have involved the use of substituted cyclopentadienones, e.g. tetraphenylcyclopentadienone ( tetracyclone ), which form adducts that undergo decarbonylation to give aromatic hydrocarbons. Butadiyne itself reacts with tetracyclone to give hexaphenylquaterphenyl (221) while diphenylbutadiyne gives the mono(222)- and di(223)-adduct . Bis(4-biphenylyl)butadiyne gives the monoadduct 224 . 

Diels-Alder reactions of thiete 1,1-dioxides occur readily as exemplified by the syntheses of 151 ° and 152. Adducts of thiete 1,1-dioxide with tetraphenylcyclopentadienone or a-pyrone ° are thermally unstable. Thiete 1,1-dioxides also undergo 1,3-dipolar additions with diazoalkanes, (e.g., the formation of 153 from which the strained bicyclic thietane sulfone 154 is obtained) " nitrile oxides, and cycloadditions with the MA -dimethylenamine of isobutyraldehyde (e.g., the formation of 155). ° ... 

Diels-Alder cycloadditions involving thiete sulfones as dienophiles occur with butadiene,cyclopentadiene, 1,2,3,4-tetraphenylcyclopentadiene, anthracene. tetraphenylcyclopentadienone, l,3-diphenyl-2H-cyclopenta[l]-phen-anthrene-2-one, a-pyrone, l-(Af,Af-dimethyl)- and l-(7V,A -diethyl)-l,3-butadiene, furan, 2,5-dimethylfuran, l,3-diphenylisobenzofuran, isobenzofuran," and l,3-diphenylnaphtho[2,3-c]furan. Generally, thiete... 

Both the organometallic methods of phenyl-phenyl coupling (PPP synthesis) and the repetitive Diels-Alder reaction between tetraphenylcyclopentadienones and arylacetylenes toward branched polyphenylenes can be modified for the synthesis of structurally related oligomers (see also section 1.4.). Thus,... 

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. 

This experiment illustrates two examples of the Diels-Alder reaction, which synthesizes molecules that would be extremely difficult to synthesize in any other way. Both reactions employ as the diene the tetraphenylcyclopentadienone prepared in the previous chapter. Although the Diels-Alder reaction is reversible, the intermediate in each of these reactions spontaneously loses carbon monoxide (why ) to form the products. 

In the attempted synthesis of twisted polycycle 1,2,3,4-tetraphenylfluorenoM, 9-g/i]quinoline, R.A. Pascal Jr. et al. used the Combes quinoline synthesis to assemble the azaaceanthrene core. Oxidation with DDQ was followed by a Diels-Alder reaction with tetracyclone (tetraphenylcyclopentadienone) to afford the corresponding cycloadduct. However, the last decarbonylation step of the sequence failed to work even under forcing conditions, presumably due to steric hindrance. 

Phenylcyclone. Mol. wt. 382. 43, m.p. 273°, dark green. The reagent is prepared in 90% yield by the condensation of phenanthrenequinone with dibenzyl ketone. Mackenzie found it more reactive than tetraphenylcyclopentadienone in Diels-Alder reactions. 

Diels-Alder dienes 1-Acetoxybutadiene. Butadiene. Cyclopentadiene. (rans,mins-l,4-Diacetoxybutadiene. 2,5-Di-o-anisyl-3,4-diphenylcyclopentadienone. 5,5-Dimethoxy-l, 2,3,4-tetrachlorocyclopentadienone. 2,3-Dimethylbutadiene. 6,6-Dimethylfulvene (see o-Acetoxy acrylonitrile). 2,4-Dimethyl-l,3-pentadiene (see Diethyl azodicarboxylate). 2,3-Diphenyl-butadiene. 1,3-Diphenylisobenzofurane (see Potassium I-butoxide). rrans,/nus-l,4-Diphenyl-butadiene. 1,3-Diphenylisobenzofurane. Hexachlorocyclopentadiene. Isobenzofurane. l-o-Nitrophenylbutadiene-1,3. Oxepin (see Diazabicyclo[3.4.0]nonene-S). Phenylcyclone. Piperylene. n-Pyrone (see also Methyl vinyl ketone). Tetrachlorocyclopentadienone. Tetra-chlorofurane. Tetraphenylcyclopentadienone. 

In addition, [2.2]paracyclophane was transformed into reactive bis-dienes. By reaction of the furan cycloadducts 49 with tetraphenylcyclopentadienone and thermal retro-Diels-Alder reaction [2.2](4,7)isobenzofuranophane 51 was obtained [38]. The highly reactive molecule was trapped in situ with para-ben-zoquinone. The more stable tetraphenylisobenzofuranophane 57 was synthesized via the classical procedure to [2.2]paracyclophanes of Hopf [39] the reaction of 1,2,4,5-hexatetraene 53 with dibenzoylacetylene 54 gave 4,5,12,13-tetra-benzoyl[2.2]paracyclophane (56), that was reduced and cyclized to the target molecule 57 [38]. 

CFs when hydrogenated in controlled fashion in the presence of Pd/C, gives a 1 1 adduct with PhSH in the presence of PhSNa, and readily partakes in thermal Diels-Alder reactions with cyclopentadiene, cyclohexa-1,3-diene, 1,3-diphenyliso-benzofuran, and tetraphenylcyclopentadienone (the last is converted into-PhsCe SOs-CFs at 174°C) it reacts 1.7 times faster with cyclopentadiene in ethyl acetate at room temperature than does dimethyl acetylenedicarboxylate. ... 

This reaction provides quantities of benzoin for use in the multistep synthesis of hexaphenylbenzene (see Experiment [A4ab])- Benzoin is synthesized in this first step of the a series of the Sequential Experiments. In this sequence of reactions, benzoin is converted by oxidation (Experiment [A2a]) to benzil and then to tetraphenylcyclopentadienone (Experiment [A3a]).The latter compound undergoes a Diels-Alder addition with diphenylacetylene (Experiment [A3b]) to give hexaphenylbenzene (Experiment [A4ab]). 

Outline a complete mechanistic sequence to account for the formation of the tetraphenylcyclopentadienone compound. 7-14. Cyclopentadienone is unstable and rapidly undergoes the Diels-Alder reaction with itself. Write the structure for... 

The topology of the twisted precursors must, in a kind of molecular Lego, be made such that all the benzene rings can fall together into one plane. The C60 homologue 24 illustrates how to go beyond C42 (Scheme 7). The precursor of the C222 PAH molecule 28a can be made in different ways using Diels-Alder cycloadditions with tetraphenylcyclopentadienone or cobalt-catalyzed cyclotri-merization of diarylacetylenes [167] (Scheme 8). 

The HBC derivatives with low symmetry were synthesized by an alternative route (Scheme 3.10). The key step was Diels-Alder cycloaddition between suitable tetraphenylcyclopentadienone derivatives 18 and substituted diphenylacetylenes 19 to afford a low symmetric hexaphenylbenzene derivative 20, which was followed by the standard cyclodehydrogenation with FeCls to give the fused HBC derivatives 21. 

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