Ketene dimethyl

The initial reaction between a ketene and an enamine is apparently a 1,2 cycloaddition to form an aminocyclobutanone adduct (58) (68-76a). This reaction probably occurs by way of an ionic zwitterion intermediate (75). The thermal stability of this adduct depends upon the nature of substituents Rj, R2, R3, and R. The enolic forms of 58 can exist only if Rj and/or R4 are hydrogens. If the enamine involved in the reaction is an aldehydic enamine with no 3 hydrogens and the ketene involved is di-substituted (i.e., R, R2, R3, and R4 are not hydrogens), then the cyclo-butanone adduct is thermally stable. For example, the reaction of dimethyl-ketene (61) with N,N-dimethylaminoisobutene (10) in isopropyl acetate... 

Dihydropyrans have been produced by the 1,3 cycloaddition of methyl vinyl ketone (77) or acrolein (29-J7) with enamines (see Section II.A.2). S-Lactones have been formed as a side product in the reaction of dimethyl ketene with enamines (77), and as the primary products in the reaction of excess ketene with enamines derived from ketones (75) (see Section II.A.4). 

Analogously, the reactions of ketene aminals with ketene or dimethyl ketene gave y-amino-a-pyrones and the linear acylation products, respectively 422). 

On the other hand y-pyrones or 1,3-diketones could be obtained from the reactions of ketone derived enamines with diketene 423-426). The addition of dimethyl ketene dimer to aldehyde or ketone derived enamines produced cyclohexanediones 425,426). 

Safety. Since organic peroxides can be initiated by heat, mechanical shock, friction or contamination, an enormous problem in safety presents itself. Numerous examples of this problem have already been shown in this article. Additional examples include the foilowing methyl and ethyl hydroperoxides expld violently on heating or jarring, and their Ba salts also are extremely expl the alkylidene peroxides derived from low mw aldehydes and ketones are very sensitive and expld with considerable force polymeric peroxides of dimethyl ketene, -K>-0-C(CH3)2C(0)j-n, expld in the dry state by rubbing even at —80° peroxy acids, especially those of low mw, and diacetyl, dimethyl, dipropkmyl and methyl ethyl peroxides, when pure, must be handled only in small amts and... 

On thermolysis of bis(trimethylsilyl) malonate 337 at 160°C in the presence of P4O10 carbon suboxide 339 is formed in 54% yield, via 338 two equivalents of tri-mefhylsilanol 4 are also formed and react in situ with P4O10 to give polyphosphoric acid trimethylsilylester (PPSE) 195 [118] (Scheme 4.44). Pyrolysis of trimethylsilyl 2,2-dimefhylmalonate at 700°C gives dimethyl ketene and HMDSO 7 [118a]. 

Zinc chloride in conversion of dimethyl-ketene /3-lactone dimer to 2,2,4-trimethyl-3-oxovaleryl chloride, 48,126... 

Two or more unsaturated groupings e.g, dimethyl ketene (CH3)2 = C = O often enhance one another and so visible colour is produced. Similar is the case of triketones. 

Scheme 54 Photoreaction of aromatic carbonyl compounds with p,p-dimethyl ketene silyl acetals.

The mechanisms for nucleophilic GTP and electrophilic GTP are not the same. Electrophilic GTP proceeds by an associative or concerted mechanism that does not involve anionic propagating centers. Initiation involves a concerted addition of methyl trimethylsilyl dimethyl ketene acetal to monomer to form species XXV. The overall effect is to transfer... 

The syntheses of many Co3(CO)9X compounds from dicobalt octacarbonyl and XCCI3 have been optimized 347), and further reactions starting from 0(60)4 and XCCI3 360), or RCF —Co(CO)4 46) have been investigated in order to determine the mechanism of formation of the clusters. Methinyltricobalt enneacarbonyls are also formed from Co2(CO)g and such apical carbon precursors as acetylenes 140), dimethyl ketene 408), or carbyne chromium complexes (7 73). In several cases (7 72,... 

Dimethyl-2-iodobutane, 31, 67 Dimethyl ketene, 33, 29 Dimethyl mercaptoacetal, 35, 54... 

A new route to mono- and dioxo derivatives of 1,3-oxazine was given by Martin et a/.96-97 addition of 2 moles of ketene to the C=N of azomethines. (This reaction was described by Staudinger98-100 in 1906, but piperidinedione structures were assigned to these compounds.) When the SchifFs base PhCH=NEt reacted with 2 moles of dimethyl-ketene a good yield of a derivative of 2-isopropylidenetetrahydro-l,3-... 

In an analogous manner dimethyl ketene acetal (176) gave a polyester under the influence of boron trifluoride ... 

Irradiation of tetramethyl-1,3-cyclobutanedione in nonhydroxylic solvents results in decarbonylation as the major course of reaction with g-cleavage being observed as a minor reaction path. A low yield of the lactone [115] has also been reported (73) however, since this material might result from dimerization of dimethyl-ketene, it may not be a primary photoproduct (i.e., ketene dimer is isolated from irradiation of [69]. 

Aluminum amalgam in reduction of oximinomalononitrile, 48, 2 Aluminum chloride, 46, 109 in conversion of tetramethy 1-1,3-cyclobutanedione to dimethyl-ketene d-lactone dimer, 48, 72 with lithium aluminum hydride, in reduction of l,4-dioxaspiro[4.5 -decane, 47, 37... 

LACTAMS Catecholboranc. Dimethyl-ketene. Hexamethyldisila2ane. Hydroxyl-aminc-O-sulfonic acid. o-Nitrophenyl thiocyanate. Palladium(II) acetate. Rhodiuin(H) acetate dimer. Sodium hydride. 

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