Diketene, reactions structure

With diketene, intermediates of type (III) were isolated and subsequently cyclized under basic conditions following step (b). In the case of 3-oxo-carboxylic acid esters or 3-acyl Meldrum s acids, cyclization step (b) immediately follows reaction step (a), if a slight excess of amine is employed (85TH1 87TH1). Note that conversion of (III) to (V) involves the (IH)-enol (Table I cf. 75BSF2731). The relatively low yield in the case of malonic acid ester, as well as the failure of the reaction with the non-enolizable diphenyl phosphinylacetic ester and cyanoacetate, points to the participation of an enol structure of (III). 

In most reactions diketene appears to react as acetylketene or one of its tautomeric forms. This is one of the reasons for the correct structure of diketene being firmly established only in 1952, 45 years after its discovery (97,98). 

Dimeric aldoketenes and ketoketenes of p-lactone structure show a chemical behavior which is not much different to that of diketene. Thus nucleophiles add in similar fashion to give derivatives of 3-ketoacids which are mono- or dialkylated at C-2 (aldo- and ketoketene dimers, respectively), but the reaction can often be slower than with the parent compound and, in case of long-chain or bulky substituents, may not proceed at all. Other reactions can proceed differently than those with diketene. For an overview of important reactions of aldoketene and ketoketene dimers see Reference 122. 

The action of a Zn/Cu couple on 1,3-dibromo ketones and secondary amides yields 2-dialkylamino-1,3-dioxolanes (451 equation 208). Fluorosulfonic peracid anhydride adds to trifluoroacetonitrile to give an amide acetal (452 equation 209). In the addition of (Z)-2-butene-l,4-diol to trichloroacetoni-trile, catalyzed by sodium, the 1,3-dioxepin (453 equation 210) is produced. Bicyclic amide acetals (454 equation 211) are byproducts in the reaction of lactim ethers with diketene. TTie methyl esters of perfluorinated carboxylic acids react with diethanolamine to afford bicyclic amide acetals (455 equation 212). Heating of maleic anilides (456 equation 213) with acetic acid anhydride/sodium acetate gives heterocyclic compounds (457) containing an amide acetal structure. ... 

Some exceptions, however, are known for which high selectivities have been observed despite the tertiary allylic alcohol structure. Thus, the reaction of 2-phenyl-3-buten-2-ol with diketene leads to a 9 1 EtZ mixture of 6-phenyl-5-hepten-2-one317. 

This facile crosslinking reaction is due to the extreme ease with which alkoxy groups on an ortho ester linkage transesterify. To prevent this transesterification, a scheme was used where the alkoxy groups were made part of a cyclic structure. In this particular case, two alkoxy groups in the final polymer were made part of a cyclic structure. To prepare such a polymer, the cyclic diketene acetal 3,9-bis (methylene 2,4,8,10-tetraoxaspiro [5,5] undecane) was used. It was prepared as shown in Scheme 8 [23]. 

The allene PrCH=C=CHCH2NH2 isomerizes to the 3-pyrroline (122) under the influence of silver tetrafluoroborate. Photolysis of aroyl azides in the presence of diketen (123) yields the hydroxy-pyrrolinones (124).AT-Ray analysis has shown that the adduct of the imine Pr"CH=NPr to N-phenylmaleimide has structure (125). Treatment of dichloromaleimide with ethoxycarbonyl-methylenetriphenylphosphorane affords the Wittig product (126). The formation of the pyrrolidinone (128) in the thermolysis of the iV-cyclohexenylacryl-amide (127) represents an intramolecular ene-reaction (see arrows). The perfluoropyrrolidinone (130) results from the reaction of the cyclobutane (129) with potassium fluoride. Pyrrolidinols (131) are obtained in moderate yields by photochemical cyclization of the amides ArCOCH2CH2NBzCH2Ph. ... 

Besides the more often-used acyl donors mentioned above, others which would also ensure an irreversible type of reaction have been investigated [170]. Bearing in mind that most of the problems of irreversible enzymatic acyl transfer arise from the formation of unavoidable byproducts, emphasis has been put on finding acyl donors that possess cyclic structures, which would not liberate any byproducts at all. However, with candidates such as lactones, lactams, cyclic anhydrides (e.g., succinic acid anhydride [171]), enol lactones (e.g., diketene [172, 173]), and oxazolin-5-one derivatives [174], the drawbacks often outweighed their merits. 

When quinoline was allowed to react with diketene, 6a,7-dihydro-5,9-dimethylbenzo[f]pyrano[2,3-b]quinolizine-ll,12-dione (XXX) was formed and this on dehydrogenation gave (XXXI) [20]. The structure and reactions of (XXX) were also investigated [22]. In a similar manner, the isomeric system, 1 l-methylbenzo[a]pyrano[3,2-g]quinolizine-8,9-dione (XXXII), was synthesised by the reaction of isoquinoline and diketene [20]. 

Apparently there is yet no agreement among students of the problem of the diketene structure, - " and it is possible that the substance actually is a mixture of readily interchangeable isomeric forms. The use of the acylketene formula I in the sequel is for convenience only. The dimers of aldoketenes undergo the same reactions as diketene and present the same problems of structure. ... 

The tendency of ketene to undergo cyclodimerization reactions was noted as early as 1908 by Chick and Wilsmore , and by Staudinger and Klever . The unsymmetrical structure of the ketene dimer 3 was established by spectroscopical methods The mechanism of this cycloaddition reaction was studied recently and the chemistry of diketene was reviewed... 

Ethanolysis of diketene to produce ethyl acetoacetate (etacH) is catalyzed by [PdC ], and yellow crystals separated at the end of the reaction were identified as [PdCl(>/ -etac)]2 (38) in which the monoanion of ethyl acetoacetate coordinates to Pd(II) in an -allylic fashion. This complex is also prepared by the direct reaction between PdCl2 and etacH in water at 70°C in an 85% yield, and its structure was confirmed by X-ray crystallography. ... 

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