2,3,4,5-Tetraphenylcyclopentadienone

Prelab Exercise Write a detailed mechanism for the formation of tetraphenylcyclopentadienone from benzil and 1,3-diphenylacetone. To which general class of reactions does this condensation belong  

Louis Fieser introduced the idea of using very high-boiling solvents to speed up this and many other reactions 

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. 

The literature procedure for condensation of benzil with 1,3-diphenyl-acetone in ethanol with potassium hydroxide as basic catalyst suffers from the low boiling point of the alcohol and the limited solubility of both potassium hydroxide and the reaction product in this solvent. Triethylene glycol is a better solvent and permits operation at a higher temperature. In the procedure that follows, the glycol is used with benzyl-trimethylammonium hydroxide, a strong base readily soluble in organic solvents, which serves as catalyst. 

Measure into a 25 x 150-mm testtube 2.1 gofbenzil,2.1 gof 1,3-diphenyl-acetone, and 10 mL of triethylene glycol, using the solvent to wash the walls of the test tube. Support the test tube in a hot sand bath, stir the mixture with a thermometer, and heat until the benzil is dissolved, then remove it from the sand. Measure 1 mL of a commercially available 40% solution of benzyltrimethylammonium hydroxide (Triton B) in methanol into a 10 X 75-mm test tube, adjust the temperature of the solution to exactly 100°C, remove from heat, add the catalyst, and stir once to mix. Crystallization usually starts in 10-20 s. Let the temperature drop to about 80°C and then cool under the tap, add 10 mL of methanol, stir to a thin crystal slurry, collect the product, and wash it with methanol until the filtrate is purple-pink, not brown. The yield of deep purple crystals is 3.3-3.7 g. If either the crystals are not well formed or the melting point is low, place 1 g of material and 10 mL of triethylene glycol in a vertically supported test tube, stir with a thermometer, raise the temperature to 220°C to bring the solid into solution, and let stand for crystallization (if initially pure material is recrystallized, the recovery is about 90%). 

Submitted by John R. Johnson and Oliver Grummitt. Cheeked by Nathan L. Drake and Stuart Havwood. 

In a 500-cc. round-bottomed flask, 21 g. (0.1 mole) of benzil (Org. Syn. Coll. Vol. 1, 1941, 87) and 21 g. (0.1 mole) of dibenzyl ketone (Note 1) are dissolved in 150 cc. of hot alcohol. The flask is fitted with a reflux condenser, the temperature of the solution is raised nearly to the boiling point, and a solution of 3 g. of potassium hydroxide in 15 cc. of alcohol is added slowly in two portions through the condenser. When the frothing has subsided the mixture is refluxed for fifteen minutes and then cooled to 0°. The dark crystalline product is filtered with suction and washed with three 10-cc. portions of 95 per cent alcohol. The product melts at 218-220° and weighs 35-37 g. (91-96 per cent of the theoretical amount) (Note 2). 

This product is sufficiently pure for most purposes. It may be crystallized from a mixture of alcohol and benzene using 155— 160 cc. solvent for 5 g. of tetraphenylcyclopentadienone the melting point of the recrystallized material is 219-220°. 

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C ( propyl) N phenylmtrone to N phenylmaleimide, 46, 96 semicarbazide hydrochloride to ami noacetone hydiochlonde, 46,1 tetraphenylcyclopentadienone to diphenyl acetylene, 46, 44 Alcohols, synthesis of equatorial, 47, 19 Aldehydes, aromatic, synthesis of, 47, 1 /3-chloro a,0 unsaturated, from ke tones and dimethylformamide-phosphorus oxy chloride, 46, 20 from alky 1 halides, 47, 97 from oxidation of alcohols with dimethyl sulfoxide, dicyclohexyl carbodumide, and pyndimum tnfluoroacetate, 47, 27 Alkylation, of 2 carbomethoxycyclo pentanone with benzyl chloride 45,7... 

Tetramethvlethylene, 47, 36 Tetraphenylcyclopentadienone, from dibenzyl ketone and benzil, 46, 45... 

The first reported example31,117 involved the diethyltetraphenyl-3//-azepines 18 and 19 which were obtained in 85% overall yield by the reaction of2,3-diethyl-2//-azirine with 2,3,4,5-tetraphenylcyclopentadienone (see Section 3.1.1.1.2.). The two isomeric azepines are separable by column chromatography (alumina or silica gel), and each isomer, on warming in xylene for three days, equilibrates to a 3 8 mixture of the 3//-azepines 18 and 19. 

Benzannulated azocines can be prepared starting from 4-phenyl-l,2.3-benzotriazine (16), flash-vacuum pyrolysis of which leads to 2-phenylbenzazete (17) (cf. Houben-Weyl. Vol. E16c, p 939), which is stable until about 40 °C and easily enters into cycloaddition reactions with dienes. With tetraphenylcyclopentadienone, a nonisolable adduct is formed which, by loss of carbon monoxide, gives an azabicyclo[4.2.0]octatriene derivative that isomerizes to the 1 -benzazocine 18.22... 

The reaction of tetraphenylcyclopentadienone (tetracyclone) with dialkyl phosphites has invoked further interest. Miller has shown that reactions at 20 °C in the presence of sodium bicarbonate lead to products (35) and (36), with phosphorus substituted at carbon rather than oxygen. Quite different products (37) and (38) are obtained at 160 °C, although whether (38) is obtained from initial attack at oxygen or carbon is still unresolved. 

Tetranitromethane as reagent for detecting double bonds, 21, 107 Tetraphenylcyclopentadienone, 23, 92, 93... 

Tetraphenylcyclopentadienone has been prepared by the action of phenylmagnesium bromide on benzaldiphenylmaleide,1 and by reduction, dehydration, and oxidation of the methylene-desoxybenzoin obtained by condensing formaldehyde with desoxy-benzoin.2 The present procedure is essentially that of Dilthey.3... 

Tetraphenylphthalic anhydride has been prepared by condensation of tetraphenylcyclopentadienone and maleic anhydride in nitrobenzene,1 followed by dehydrogenation of the tetraphenyl-dihydrophthalic anhydride with sulfur.2 3... 

Dimethylallene reacted with tetraphenylcyclopentadienone to produce methy-lenecyclohexadiene derivative 180 [146]. The cycloaddition occurred at the more substituted double bond of the allene, which was followed by extrusion of carbon monoxide from the intermediate 179. 

The yields of CO production in the reaction of BrFC with substituted benzaldehy-des are dependent on the electronic effects of para substituents. Carbonyl ylide intermediates were trapped with dimethyl acetylenedicarboxylate. Sterically hindered tetraphenylcyclopentadienone gave a high yield of CO and no ylide could be trapped in this case. 

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... 

Some unusual syntheses of substituted 2,2 -bipyridines deserve mention. Tetracyclone (tetraphenylcyclopentadienone) on heating with picolinonitrile at 215°C affords 3,4,5,6-tetraphenyl-2,2 -bipyridine, whereas 5-methyl-2,2 -bipyridine and some polysubstituted 2,2 -bipyridines are obtained by the oxidative degradation of the antibiotic streptonigrin. 5-Aldehydo-6-amino-2,2 -bipyridines are obtained by acid hydrolysis of pyrido[2,3-[Pg.311]

Cycloaddition of nitriles to tetraphenylcyclopentadienone gives an intermediate which by loss of carbon monoxide gives a pyridine, as shown in equation (74) (35CB1159,52MI20802). 

Is the - state likely to be higher or lower than the - state Explain in less than three lines. Is it plausible that compounds with this structure might be colored (recall tetraphenylcyclopentadienone) ... 

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). 

A 100-ml., round-bottomed, ground-glass flask containing 40 g. of benzophenone is heated over a free flame to melt the bulk of the solid, and then 8.0 g. of tetraphenylcyclopentadienone (0.021... 

Other solvents tried and the liquid temperatures of the refluxing mixtures are stearic acid (340-365°), di- -butyl phthalate (320-325°), phenyl salicylate (290°). The first two solvents are unsatisfactory because of side reactions consuming some of the tetraphenylcyclopentadienone, the third because the addition reaction is too slow. 

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