Cyclopropenone 2,3-diphenyl

Diphenyl-cyclopropenon ergibt nach Reaktion mit Diboran und Protonolyse mit Bu-tansaure in 45%iger Ausbeute cis-1,2-Diphenyl-cyclopropan9 ... 

The first synthesis of a cyclopropenone was reported in 1959 by Breslowls who achieved the preparation of diphenyl cyclopropenone (11) by reacting phenyl ketene dimethylacetal with benzal chloride/K-tert.-butoxide. The phenyl chloro carbene primarily generated adds to the electron-rich ketene acetal double bond to form the chlorocyclopropanone ketal 9, which undergoes 0-elimination of HC1 to diphenyl cyclopropenone ketal 10. Final hydrolysis yields 11 as a well-defined compound which is stable up to the melting point (120—121 °C). 

Independently Volpin17 synthesized diphenyl cyclopropenone from diphenyl-acetylene and dibromo carbene (CHBr3/K-tert.-butoxide). This reaction principle of (2 + 1) cycloaddition of dihalocarbenes or appropriate carbene sources ( caibenoids ) to acetylenic triple bonds followed by hydrolysis was developed to a general synthesis... 

Furthermore, the addition of dichlorocarbene to ene-ynes proved to be remarkably sensitive to substituent effects. Trans-1,4-diphenyl butenyne gave only the cyclopropenone 17 via hydrolysis of dichlorocyclopropene 16, however, 2-methyl-pentene-l-yne-3 favored the formation of the dichlorocyclopropane 18 with only traces of products resulting from addition to the triple bond ... 

Cyclopropenone formation should involve the bisketene 46 and its decarbonylation to the monoketene 47 (a valence tautomer of cyclopropenone 44), since photolysis in protic media like ethanol produces diethoxy diethyl tartrate 45) (meso and d,l). This method was also successful in the case of l,2-diphenyl-3,3-dichloro-cyclo-butene dione (48) giving rise to diphenyl cyclopropenone49 (but as for 44 only a moderate yield was produced) ... 

The formal relationship between cyclopropenone and an a,a -biscarbene of a ketone (R—C—CO—C—R ) initiated investigations on photolytic and Ag-catalyzed decomposition of a, a -bisdiazo dibenzyl ketone (49) (Trost50 ). Indeed, diphenyl-cyclopropenone was formed in addition to other products (52 and tolane) derived from it furthermore, products resulting from solvent insertion and Wolff rearrangement of the monocarbene 50 were isolated (51) ... 

One of the first syntheses of a triafulvene utilized the Wittig reaction, when diphenyl cyclopropenone was reacted with triphenyl carbomethoxymethylene phos-phorane giving 696 ) ... 

The Wittig reaction of diphenyl cyclopropenone with the phosphorane 68 failed to give the methylene cyclopropene instead a hydrocarbon of probable structure 67 was obtained71. ... 

Triafulvenes derived from cyclic 0-dicarbonyl systems like 84/85ia 861S and S779 are conveniently prepared from cation 75 by the DIPEA method and in some cases (5780,81), 8862 8983 ) from diphenyl cyclopropenone by condensation in acetic anhydride. 

The reaction of diphenyl cyclopropenone with aryl malononitriles75 or aryl cyano acetone84 unexpectedly gave rise to 4-cyano-4-aryl triafulvenes 90, as well as the formation of quinocyclopropenes (see later) ... 

A final type of cyclopropenium cyanines is found in the azatriapentafulvalenium ions 145,146, and 147/148, which have been prepared93,112,113 from diphenyl and di-n-propyl cyclopropenone or ethoxy cation 75 and indole derivatives as well as from diphenyl methylthio cyclopropenium cation and phenyl-substituted pyr-roles114> ... 

The synthesis of cyclopropenone imines 3 has been accomplished by several methods. Thus aromatic amines, e.g. p-nitraniline, can be reacted either with diphenyl cyclopropenone in HCl/ethanol or with the ethoxy cation 75 forming the immonium cation 150, which is deprotonated by tertiary bases to the N-(p-nitro-phenyl)-imine /5/llsl ... 

Diphenyl cyclopropenone reacts readily with isocyanates activated by p-toluene-sulphonyl, trichloroacetyl, and chlorosulphonyl116 or benzenesulphonyl117 groups giving rise to cyclopropenone imines 152 and carbon dioxide ... 

Diphenylcyclopropene thione (156) was prepared11S-12°) from 3,3-dichloro-1,2-diphenyl cyclopropene (154) by reaction with thioacetic acid, since transformation of the carbonyl function of diphenyl cyclopropenone with P4S10121 was complicated by ring expansion to the trithione 155122 In a useful recent thioketone synthesis123) 156 was obtained directly from diphenyl cyclopropenone in a quantitative yield by simultaneous treatment with HC1 and H2S. 

Of the further functional derivatives of cyclopropenones in the diphenyl series, the oxime115,121) and several hydrazones115) (e.g. 158/159), and a2ines (e.g. 760U5)), are easily available from the ethoxy cation 75 and hydroxylamine, hydrazines, and hydrazones, respectively. Sometimes oximation of cyclopropenones produces unexpected results (see later and Ref.42 ). 

Whilst anhydrous hydrazine is reported124) to give products of nucleophilic ring opening and cyclization (7 62/7 63) with diphenyl cyclopropenone, hydrazine hydrochloride yielded the azine 16112s ... 

Attempts were reported119,129 to synthesize the ortho-linked diphenyl cyclo-propenone phenanthreno cyclopropenone 173 by dehydrohalogenation of the dibromo derivative 174 of dibenzo cyclohepta-l,3-diene-6-one. The only product isolated was the anhydride 175 of phenanthrene-9-carboxilic acid, which was shown not to arise from 173l29 ... 

Cyclopropenones are markedly more basic than other a,0-unsaturated compounds131 tropone, however, exhibits higher basicity than cyclopropenones due to its half-protonation value of —0.4. As shown in Table 4, basicity of cyclopropenones is increased by alkyl substituents relative to phenyl substitution. This is also demonstrated by the observation132 that di-n-propyl cyclopropenone is extracted by 12N HC1 from CCI4 solution, but diphenyl cyclopropenone is not. 

As comparison with Table 3 shows, dipole moments and basicities of cyclopropenones are not correlated di-n-propyl and di-cyclopropyl cyclopropenone are stronger bases than diphenyl cyclopropenone the latter, however, possesses the higher dipole moment. 

Finally, calculations of dipole moments for cyclopropenone, dimethyl cyclopropenone136), and diphenyl cyclopropenone (Table 4) have been reported. The earlier results markedly suffer from the uncertainties of cyclopropenone bond lengths which have only recently been established (see following chapter). 

The molecular structures of diphenyl cyclopropenone (anhydrous148 and as hy-drate13s 149 diphenylcyclopropene thione1501, 1,2-diphenyl-13S and 1,2-dimethyl-lsu 4,4-dicyano triafulvene, l,2-di-(p-tolyl)-4,4-di-(trifluoromethyl) triafulvenelslb), 5,6-diphenyl-1 S2 and 5,6-di-n-propyl-153 1,2,3,4-tetrachlorocalicene and 8-cyano-8-(diphenylcyclopropenyl)-heptafulvenylium tetrafluoroborate111 have been determined by X-ray analysis15 4). 

The carbonyl distances in diphenyl cyclopropenone and cyclopropenone (1.225/1.212 A) are larger than in cyclopropanone and indicate enhanced singlebond character. The same is true for the C=S bond in the thione 156 (1.63 A) compared to the C=S distance in thioketones (1.56 A1S7 ). 

In diaryl cyclopropenones, the UV data are not very characteristic and resemble those of diaryl cyclopropenones and stilbenes as well as diaryl cyclopropenium cations, as shown in Table 8. Recently a new long-wave absorption band was found164) in diphenyl cyclopropenone [362 nm, log e = 3.06 (cyclohexane)] which was assigned tentatively to an intramolecular charge-transfer. 

Generally diaryl cyclopropenones are thermolyzed at lower temperatures than dialkyl cyclopropenones, e.g. diphenyl cyclopropenone 150 °C, di-n-propyl cyclopropenone 190 °C, due to the better stabilizing properties of alkyl substituents. 

At temperature below the decarbonylation level cyclopropenones are preferentially transformed to stable dimers, which do not eliminate CO at higher temperatures. Thus, thermolysis of diphenyl cyclopropenone at temperatures above 160 °C gives mainly diphenyl acetylene, whilst heating in the molten state to 145— -... 

It should be noted that codimerization was achieved from diphenyl cyclopropenone and unsubstituted cyclopropenone (2JS)197. Phenyl hydroxy cyclopropenone, which appears to be an associated dimer in (dioxane) solution52, formed a dimeric pulviniv acid lactone 260 on treatment with thionyl chloride51, probably via oxidative rearrangement of a dimer 259 ... 

Another type of dimerization was observed by Japanese authors198. In the presence of Ni°, compounds like bis(l,5-cyclooctadiene) nickel(0), diphenyl and di-n-propyl cyclopropenone, and cyclohepteno cyclopropenone are transformed to tetra-substituted p-benzoquinones (261/262) by formal (2 + 2) or (3 + 3) cycloaddition of two cyclopropenone moieties effected by metal complexing. 

Dimerization of cyclopropenones has also been found to occur under reductive conditions. Tetraphenyl resorcinol is formed in addition to a small amount of tetra-phenyl p-benzoquinone on treatment of diphenyl cyclopropenone with aluminum amalgam200 its formation can be rationalized via dimerization of the cyclopropenone ketyl 266 and subsequent aromatization, possibly according to a prismane mechanism. 

Thermolytic and photolytic transformations are reported for several diphenyl cyclopropenone imines and diphenylcyclopropene thione. 

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