Methyl phenyl ketene

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. 

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

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. 

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

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

Scheme 1.2 The enantioselective addition of MeOH to methyl phenyl ketene reported by Pracejus and the quinine-catalyzed enantioselective Michael reaction reported by Wynberg.

Following the earliest works of Bredig, Pracejus developed the first reactions with good levels of enantioselectivity. Pracejus reported the addition of methanol to methyl phenyl ketene catalyzed by 0-acetyl quinine (Scheme 1.2) [5]. 

Later on, in the 1950s, Prelog reinvestigated this reaction (75) and in the late 1950s Pracejus reported one of the first highly enantioselective reactions ever, by adding methanol to methyl phenyl ketene (5) in the presence of O-acetylquinine (6) (Scheme 2) (76). 

Figure 8.5 depicts the different chiral azaferrocene derivatives synthesized and used in catalysis. The first member in the series bears a TES protected hydroxymethyl group and was prepared in optically pure form in three steps, including a preparative HPLC enantiomer separation (Scheme 8.2) [11]. Optimization studies later showed the greater stereoinduction brought about by bulkier sUyl groups, with the TBS-substituted derivative achieving 77% ee for the addition reaction of methanol to methyl phenyl ketene, whereas the TES derivative shows only 28%...

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). 

KETENES, KETENE DITffiRS AND RELATED SUBSTANCES] (Vol 14) Methyl phenyl ketone [98-86-2]... 

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. 

CHR-CH(OR)2 + C1-S03H] Keten Ethenyl (4-methyl-phenyl-imin) E15/3. 2560 (R-CH2-CO-NH-R + R3PBr2)... 

Hydroxy-1 -methoxy-2-(4-methyl-phenyl)- E17b, 1624 (Ar —CHN2 -I- Keten/R—OH) 2-H ydroxy-2-methoxy-l -methyl-1 -phenyl- E17b, 1624 (Ar—CN2 — R + Keten/R-OH) Cyclopropan--bicyclo[2.2.1] hept-2-en - -6-methoxycarbo-nyl- E17b, 1558 (En —... 

Carben-Ringerweiterung) Keten Ethoxycarbonyl-methyl- -phenylimin E15/3, 2538/2603 (R3P = CH2 + R-NCO) Malonsaure (4-Methyl-phenyl)--ethylester-nitril E5, 1505 (NC-CHNa-COOR +... 

Keten Diethoxyphosphoryl-(4-methyl-phenyl)- E15/3, 2838 ( - CH2 - COOH/S02Cl2/... 

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. 

The most direct method for the preparation of a-peroxylactones is via singlet oxygenation of ketenes (Eq. 25). A few a-peroxylactones have been prepared in this way, including dimethyl, diphenyl, phenyl, and methyl phenyl derivatives. 

Since the 4-phenyl-2-methylene-l,3-dioxolane (XXl) underwent much more extensive ring opening than did the unsubstituted 2-methylene-l,3-dioxolane (I), it was reeisoned that a benzyl ketene acetal would be a more effective chain transfer agent than diethyl ketene acetal. Thus vhen methyl benzyl ketene acetal was used with styrene, a complete addition-elimination occurred to produce an oligomer of styrene. 

Reaction of ketene dithioacetals 260 with thioamides gave 5-substituted 2-methyl(phenyl)-6-methylthio-4-thioxopyrimidine (262) (92H1573). The reaction mechanism involves the addition of the thioamide to the ketene dithioacetal 260 to afford 2-cyano-3-methylthio-3-thioamido-propenoni-trile or -propenoate intermediate, which cyclizes in situ by site-selective nucleophilic attack of the sulfur on the cyano group to give 6-imino-l,3-thiazine 261, which rearranged to 262 (Scheme 84). 

Phenyl-methyl-ethyl-ketene imine (N-(2-methyl-l-butenylidene)-aniline) (193)... 

A detailed study of the cycloaddition of trifluoromethylethene has appeared as has work on a-siloxy-a -unsaturated ketones as dienophiles under Lewis-acid catalysis. Amongst the new dienophiles that have been reported are the two novel ketene equivalents methyl methoxypropiolate (129) and methyl phenyl-thiopropiolate (130). A series of 3-(acyloxy)but-3-en-2-ones (131) has been prepared and used as dienophiles in a route to anthracylinones, and, as part of a route to highly functionalized cyclohexenones, the vinyl sulphone (132) has been used in a Diels-Alder reaction with various dienes. ... 

Vinyl ethers undergo many cycloaddition reactions similar to those which take place with enamines. In general, however, these cycloaddition reactions with vinyl ethers take place less readily than those with enamines. These reactions include cycloaddition of vinyl ethers with ketene (200-205), phenyl isocyanate (206), sulfene (207,208), methyl acrylate (209), diethyl acetylenedicarboxylate (210), and diphenylnitrilimine (183). 

Clive and coworkers have reported a total synthesis of calicheamicinone, the aglycon of the antitumor agent calicheamicin starting from the Diels-Alder reaction of methyl 3-nitro-propenoate with ketene acetal (Eq. 8.32).54 An asymmetric Diels-Alder reaction between ketene acetal presented in Eq. 8.32 and 3-nitropropenoate derived from (-)-8-phenyl-menthol affords the optically pure adduct, which can be converted into either enantiomer of calicheamicinone (Eq. 8.33).55... 

Die Palladium-katalytisierte Hydrierung von 3-Azido-4-aryl-2-oxo- bzw. 3-Acetylamino-4-aryl-2-oxo-azetidinen (/ -Lactamen) fuhrt zu / -Ary 1-a-ami no-carbon saure-a mi-den5 unterschiedlicher optischer Reinheit6. Aus (R)- bzw. (.S )-3-(Chlorcarbonyl-methyl)-2-oxo-4-phenyl-l,3-oxazolidin erhalt man in situ optisch-aktive Ketene. Sie addieren sich diastereoselektiv an achirale Aralkyliden-amine zu homochiralen / -Lactamen7 9 z.B.10 ... 

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