Phenyl ketenes

On the other hand, l-(phenylethynyl)cyclopropanol 9 (R = Ph) underwent a C3 -> C4 ring expansion and subsequent decarboxylation when treated with MCPBA to yield the 2-phenylcyclobutanone 47, likely via the intermediate 2-(l-hydroxy-cyclopropyl)-2-phenyl ketene 44, formed by migration of the cyclopropyl group in the vinyl cation 43. The ketene 44 thus resulting could be attacked by a second equivalent of MCPBA and ring expanded to the (3-ketoacid 46 which would easily decarboxylate to yield 47, Eq. (15) 14>. 

Bielectrophiles have found appreciable applications in the synthesis of ring-fused systems, especially those involving [5,6] fused systems. The following serve to illustrate these applications. Reaction of pyrazole with (chlorocarbonyl)phenyl ketene (214) (Type 1, Scheme 6) readily formed the zwitterionic pyrazolo[l,2-a]pyrazole derivative (215) (80JA3971). With l-methylimidazole-2-thione (216), anhydro-2-hydroxy-8-methyl-4-oxo-3-phenyl-4//-imidazo[2,l-6][l,3]thiazinium hydroxide (217) was obtained (80JOC2474). 

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). 

The standard method of preparation of phenylacetic acid is by the hydrolysis of benzyl cyanide with either alkali1 or acid.2 The acid hydrolysis runs by far the more smoothly and so was the only one studied. There are numerous other ways in which phenylacetic acid has been formed, but none of them is of practical importance for its preparation. These methods include the following the action of water on phenyl ketene 3 the... 

The first synthetically useful levels of stereoinduction can be dated back to 1960, when Pracejus systematically studied the addition of various alcohols such as methanol to phenyl ketene. In the presence of O-acetylquinine 115 as catalyst, the respective (-)-a-phenyl methylpropionate was isolated in 74% ee in nearly quantitative yield (Scheme 6.111) [271]. 

The flash vacuum thermolysis of 4-hydroxy-2,5-diphenyl-l,3-oxazin-6-one resulted in carboxy(phenyl)ketene and benzonitrile as the major and benzoyl isocyanate as the minor product. This was interpreted in terms of the influence of the tautomeric forms on the thermal fragmentation pathways <2007JOC1399>. 

Somewhat better results are obtained by employing a chiral phosphonate in reactions with alkyl(phenyl)ketenes, which results in destruction of the chiral phosphonate and in the enantioselective formation of allenecarboxylic esters with 15-20% optical purity114-115. 

Die Thermolyse in aromatischen Kohlenwasserstoffen > 110° setzt ofFenbar (Nitroso-thio)-phenyl-keten (s.S. 394) frei, das weiter zu l,3-Dithiolium-4-olaten reagiert (vgl. Bd. E8a, S.630, 637fF.)14 ... 

Die Photolyse von 4-Phenyl-l,3,2-oxathiazolium-5-olat ergibt Benzonitril (77%), Schwefel (91%) sowie Kohlendioxid3,7. In einer Matrix lassen sich als primare Zerfallsprodukte Benzonitril-sulfid sowie (Nitroso-thioj-phenyl-keten (s. Bd. E15, S. 2850) spektroskopisch identifizieren16 ... 

Pyrolysis of the ethylene acetal of bicyclo[4.2.0]octa-4,7-diene-2,3-dione yields a-(2-hydroxyphenyl)-y-butyrolactonc 11 a mechanism involving a phenyl ketene acetal is proposed. Tartrate reacts with methanediol (formaldehyde hydrate) in alkaline solution to give an acetal-type species (9) 12 the formation constant was measured as ca 0.15 by H-NMR. Hydroxyacetal (10a) exists mainly in a boat-chair conformation (boat cycloheptanol ling), whereas the methyl derivative (10b) is chair-boat,13 as shown by 1 H-NMR, supported by molecular mechanics calculations. 

Diketones and a-(chlorocarbonyl)phenyl ketene react to provide the intermediate ketene 645, which can cyclize to afford 2/7-pyran-2-ones in high yield (Scheme 150) <2004T5931>. Similarly, silyl enol ethers react with ot-(chlorocarbonyl)mesitylketene to afford 2//-pyran-2-ones (Equation 260) <2001T4133>. 

How can one explain the origin of these products in which one finds, aside from the former carbene ligand and the pyrrolidone, just an additional carbonyl group It seems plausible that the carbene ligand first of all reacts with carbon monoxide to form methoxy (phenyl) ketene. This, in turn, forms with the polarized olefin a cyclobutanone derivative which by ring opening goes over to the observed product (Fig. 6). 

The generation of ketenes was confirmed, as illustrated in Scheme 29, by trapping experiments with methanol or benzylamine, producing the methyl ester or amide 196. Upon photolysis of precursor 194 (R = Ph R = H), the formation of phenyl ketene, which was monitored by IR spectroscopy, was indicated by the appearance of the C=C=0 band at 2120 cm. The even more efficient generation of ketenes was also achieved by photolysis of the selenium analogues of compounds 194. 

Toluene carrier technique products in toluene were carbon dioxide and 1,2-diphenylethane with smaller amounts of carbon monoxide, hydrogen and methane intramolecular elimination of water was also thought to occur from phenyl acetic acid to give phenyl ketene and water. 

When dimethoxyphosphinyl phenyl ketene, prepared by an Rh-catalyzed Wolff rearrangement of dimethyl l-diazo-2-oxo-2-phenylethylphosphonate, is submitted to the action of (trimethylsi-lyl)diazomethane, it gives rise to the corresponding dimethyl 2-(trimethylsilyl)-l-phenylvinylphos-phonate in reasonable yield (44%, Scheme 2.9). ... 

From 1960, Pracejus studied the base-catalyzed methanolysis of ketenes in depth [45]. Using 0-acetylquinine as a catalyst, he obtained (S)-methyl hydrat-ropate in 74% ee at -110 °C from methyl phenyl ketene. An inversion of absolute configuration occurred on raising of the temperature. 

Bei 3,5-Dimethoxy-4-phenyl-lH-pyrazol gelingt mit Chlorcarbonyl-phenyl-keten (5 min in Di-ethylether) der RingschluB zu 5,7-Dimethoxy-2,6-diphenyl-l-oxo-lH-(j)yrazolio[l,2-a]pyrazo-liumy-3-olat (Schmp. 150°)2388, analog reagieren eine Rcihe weiterer 1-unsubstituierter 1H-Pyrazole mit Chlorcarbonyl-ketenen oder Kohlensuboxid zu den mesomeren Betain-Strukturen der 1 H--3-olate2389 2399 2400-2403. 

Reaction of 1,2-allenyl esters and 1, catalyzed by potassium carbonate, gave 456a through a tandem nucleophilic addition-lactoniza-tion process (06S2731). The (chlorocarbonyl)phenyl ketene was condensed with 1 to give 456 (R = Ph) (04T5931). 

Methyl-phenyl-keten addiert optisch aktives 1-Phenyl-ethanol in Gegenwart von Basen zu 2-Phenyl-propansaure in e.e. 73%38. 

The power of column-like reactors for continuous flow processes lies in the possibility to sequentially link them up in order to carry out multistep syntheses in solution in one run (see also Schemes 1 and 2). Lectka and coworkers utilized conventional fritted and jacketed columns for this purpose. These columns were filled with conventional functionalized polymeric beads [47]. The continuous flow was forced by gravity. En route to / -lactams polymer beads functionalized with the Schwesinger base 17, a cinchona alkaloid derivative 18 as a chiral catalyst, and a primary amine 19 were sequentially employed. They first guaranteed the generation of phenyl ketene from phenyl... 

To a solution of 0.8 g dimethyl A -[l-(2-azidophenyl)ethyl]dithiocarbonimidate (3 mmol) in 15 mL dry toluene, was added 3 mL 1 M trimethylphosphane in toluene (3 mmol), and the mixture was stirred at room temperature until the evolution of nitrogen ceased (15-30 min). Then, 0.40 g methyl phenyl ketene (3 mmol) was added, and the reaction mixture was stirred at room temperature until the ketenimine band 2000 cm was not observed by IR spectroscopy (3-4 h). Upon removal of the solvent under reduced pressure, the residue was purified by silica gel column chromatography using hexanes/EtOAc (4 1 v/v) as the eluent to afford 0.90 g frans-2,8-dimethyl-l,l-bis(methylthio)-2-phenyl-l,2-dihydroazeto[2,l-i ]quinazoline as colorless prisms (Et20), in a yield of 85%, m.p. 141-142°C. 

For cumulenic skeletons one observes linear correlations of the asymmetric stretching frequencies i>as with the nuclear charges for the series allene (11) (106), N-phenyl-ketene imine (188) (896), and ketene (43) (107), ketene imine 188 (896), dimethylcarbodiimide (213) (108), and phenylisocyanate (218) (110) as well as allene (11), dimethylcarbodiimide (213), and carbon dioxide (204) (109fl) (Fig. 19). From the first two series one sees that the introduction of a nitrogen atom into the cumulenic skeleton has a constant effect of shifting Vas by 100 cm" to longer wavenumbers. 

Another way of looking at isoelectronic substitutions within the pheny-lallene chromophore would be the change of the a CH unit in phenylaliene (16) by N to give N-phenyl-ketene imine (188). This kind of substitution within the phenylaliene chromophore is associated with a hypsochromic shift of the ir,rr" band (e.g. from 40400 cm in 16 to 44000 cm" in 218 (114)). The isoelectronic substitution of the methylene group in N-phenyl-ketene imine (188 - 217 - 218) results in a relatively small tt.tt band variation (190 43300 cm" (115), 218 44000 cm" (114)). 

C-Phenyl ketene imine (2-phenyl-vinylidene-amine) (215)... 

Isobutyl-methyl-phenyl-ketene imine isobutyl-N-(2-phenyl-l-propenylidene)amine) (197)... 

H-Phenyl-phenyl-ketene imine (N-(2-phenyl-l-vinylidene)aniline) (191) Carbon chemical shift 386. 

N-Phenyl-methyl-phenyl-ketene imitte (N- 2-phenyl-I-propenylidene)-aniline) (195)... 

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