Diphenylketenes

Diphenylketene (253) reacts with allyl carbonate or acetate to give the a-allylated ester 255 at 0 °C in DMF, The reaction proceeds via the intermediate 254 formed by the insertion of the C = C bond of the ketene into 7r-allylpalla-dium, followed by reductive elimination. Depending on the reaction conditions, the decarbonylation and elimination of h-hydrogen take place in benzene at 25 °C to afford the conjugated diene 256(155]. 

Diphenylketene (283) adds to terminal alkynes to form the diphenylmeth-ylalkyne 285 via the Pd-carbene intermediate 284[140],... 

Alkoxythiazoles are prepared by heterocyclization (274, 462). The Williamson method using catalytic amounts of KI and cupric oxide is also possible (278. 288, 306). 5-Acetoxy-4-alkenylthiazoles are obtained by treatment of 242 with acetyl chloride and triethylamine or with acetic anhydride and pyridine (450). Similarly, the reaction of diphenylketene with 242 affords 5-acyloxy-4-alkenylthiazoles (243) (Scheme 120) (450). The readiness of these o-acetylations suggests that 4-alkylidene thiazoline-5-one might be in equilibrium with 4-alkenyl-5-hydroxythiazoles (450). 

Physical Properties. Ketenes range ia their properties from colorless gases such as keteae and methylketene [6004-44-0] to deep colored hquids such as diphenylketene [525-06-4] and carbon subsulftde [627-34-9]. Table 1 lists the physical state mp, and bp for certain ketenes, thioketenes, and ketenimines. 

StericaHy hindered or very electrophilic substituted ketenes, such as diphenylketene, di-Z rZ-butylketene [19824-34-17, and bis(trifluoromethyl)ketene, are quite stable as monomers. Ketenimines tend to polymerize. The dimerization of thioketenes results in 1,3-dithiacyclobutanones (6) (45), a type of dimer not observed with ketenes. 

An unusual reaction leading to a Ti—C bond is unrelated to those just discussed. Diphenylketene adds Ti(OR)4 (199) as follows ... 

Thermolysis of the aziridine (446) in the presence of diphenylketene gave a mixture of the pyrrolidone (447 minor product) and the oxazolidine (448 major product). In this instance the preferential addition to the C=0 bond is explained in terms of steric effects (72CC199). Similar addition to diphenylacetaldehyde takes place with the same orientation and the oxazolidine (448a) was obtained. When the reaction of the aziridine with the aldehyde was carried out in the presence of hydrogen selenide a selenazolidine was obtained (72BSB295). 

Diazoalkanes and ynamines react with the electrophilic C(4)—C(5) double bond of pyrazolenine (359) to afford the cycloadducts (360) and (361), respectively, whereas diphenylketene yields the bicyclic diazetidinone (362) by reaction with the c/s-azo system of (359) (79CC568). 

The Hash thermolysis of the dioxolene (124) gave diphenylketene among the products (Scheme 107) (70CC206), and it is conceivable that diphenyloxirene is the precursor of this product. 

The lithium chloride-catalyzed addition of 2-phenylthiirane to diphenylketene may involve attack on carbon by chloride ion followed by addition of the anion of 2-chloro-l-phenylethanethiol to the ketene, but no data about the mechanism were given (69TL259). 

Phenyl isocyanate reacts with (82) to form (83) by ring enlargement (74JOC948). Reaction of oxaziridines with diphenylketene proceeds less obviously. Isolated products (84) and (85) contain only the R—N group of the starting material (69TL263). 

A modified amidine structure can be seen in (166), the product of reaction of 1,2-diethyldiaziridine (165) with diphenylketene. A second molecule of diphenylketene may have formed the four-membered ring of (166) (75JAP75117765). 

Triphenylethylene has been prepared by the reaction of phenylmagnesium bromide with benzyl benzoate, with desoxy-benzoin, or with ethyl pheaniylacetate, and by the reaction of diphenylketene-quinoline with benzaldehyde. The above procedure is an adaptation of that described by Hell and Wiegandt. ... 

The acylation of enamines derived from cyclic ketones, which can lead to the acyl ketone or ring expansion (692-694), was studied by NMR and mass spectroscopic analysis of the products (695,696). In a comparative study of the rates of diphenylketene addition to olefins, a pronounced activation was observed in enamines (697). Enamine N- and C-acylation products were obtained from reactions of Schiff s bases (698), vinylogous urethanes (699), cyanamides (699), amides (670,700), and 2-benzylidene-3-methylbenzothiazoline (672) with acid chlorides, anhydrides, and dithio-esters (699). 

Support for this mechanism " comes from the reaction of diphenylketene with the phosphine 125 leading to 23 (Y = CPho), from... 

Analogously to ynamines and o, /3-acetylenic ketones, 4-aminobut-3-yn-2-ones react with 1,3-dipoles (68HCA443 73HCA2427 92KGS867). The reaction of 4-dimethylaminobut-3-yn-2-one with diphenylketene follows a route of [2-1-21-cycloaddition (30°C, THF, 1 h) to give 2-acetyl-3-dimethylamino-4,4-diphenyl-cyclobut-2-en-l-one (377) in 15% yield. With ethyl azidoformate (30°C, THF, 3 h), the tiiazole 378 is formed in 82% yield, whereas with phenyl isocyanate, the quinoline 379 is the product (by a [2- -4] scheme) in 70% yield (68HCA443). 

Cycloaddition of diphenylketene to the benzothiazepinones 1 gives the fused /J-lactams 2 re-giospecifically.47... 

Staudinger observed that the cycloaddition of ketenes with 1,3-dienes afforded cyclobutanones from a formal [2+2] cycloaddition [52] prior to the discovery of the Diels-Alder reaction. The 2+2 cycloadditions were classified into the symmetry-allowed 2+2 cycloaddition reactions [6, 7], It was quite momentous when Machiguchi and Yamabe reported that [4+2] cycloadducts are initial products in the reactions of diphenylketene with cyclic dienes such as cyclopentadiene (Scheme 11) [53, 54], The cyclobutanones arise by a [3, 3]-sigmatropic (Claisen) rearrangement of the initial products. 

Staudinger H (1907) Zur Kenntnis der Ketene. Diphenylketen. Liebigs Ann Chem 356 51-123... 

A crystal structure of the C02 derivative of (8), K[Co(salen)( 71-C02)], haso been reported in which the Co—C bond is 1.99 A, the C—O bonds are both equivalent at 1.22 A and the O-C-O angle is 132°.125 Carboxylation of benzylic and allylic chlorides with C02 in THF-HMPA was achieved with (8) electrogenerated by controlled-potential electrolysis,126 in addition to reductive coupling of methyl pyruvate, diethyl ketomalonate and / -tolylcarbodiimide via C—C bond formation. Methyl pyruvate is transformed into diastereomeric tartrates concomitant with oxidation to the divalent Co(salen) and a free-radical mechanism is proposed involving the homolytic cleavage of the Co—C bond. However, reaction with diphenylketene (DPK) suggests an alternative pathway for the reductive coupling of C02-like compounds. 

Several unusual cycloaddition reactions of 9 with unsaturated ketones should be mentioned in conclusion the heterocumulene generated photolytically from 7 undergoes [8 + 2]-cycloaddition with tropone to form 33 (40%) the structure of the product has been unequivocally established by X-ray structure analysis 22,23). Once again, the affinity of phosphorus for oxygen is manifested an entirely analogous cycloaddition reaction is known for diphenylketene 26). 

Unsubstituted l,5-diazabicyclo[3.1.0]hexane 331 reacts with diphenylketene to give a good yield of 332. In contrast, the same treatment with arylketenes leads to the formation of 333 (Scheme 48) <2006JHC881>. 

When a ketene acetal is used instead of a ketene, e.g. diphenylketene glycol acetal 22... 

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