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Die Diimethylsulfilimine (I) bilden mit Diketen (II) ein Gemisch der Verbindungen (III)-(V).

Diketene-acetone adduct (1) generates acetylketene (2) under heating. In order to compare the reactivity of 2 with that of diketene, the reaction of 1 with electron-rich olefins was investigated. On heating with 1, primary enamines (3a-d) produced the corresponding 3-substituted 2, 6-dimethyl-4 (1H)-pyridones (4a-d), while the tertiary enamine 3e gave the 4-pyrone derivative (7). The reaction of 1 with ketene acetals (8) gave the 2, 2-diethoxy-2, 3-dihydro-4-pyrone derivatives (9). The vinyl ether derivatives 13 similarly reacted with 1 to give the 4-pyrone derivative 15 or 16 as the major product. The result shows that both diketene and 2 react with electron-rich olefins in a similar manner.

Reaction of diketene (1) with alkyl, alkenyl, alkynyl, and aryl organometallics proceeded under catalysis of nickel (Ni)- or palladium (Pd)-phosphine complex to give 3-substituted 3-butenoic acids (2a-k).

The synthesis of 1, 3-dimethoxyfluoren-9-ones (7a-f) from ethyl 2-aryl-4, 6-dihydroxybenzoates (4a-d), prepared by the reaction of diketene with ethyl 3-aryl-3-oxopropionates (3a-d), is described. Reaction of diketene with 3a-d in the presence of sodium hydride in tetrahydrofuran gave 4a-d. Methylation of 4a-d with methyl iodide, followed by treatment with alcoholic sodium hydroxide, gave 2-aryl-4, 6-dimethoxybenzoic acids (6a-d). Cyclization of 6a-d with trifluoroacetic anhydride gave 7a-f.

A new method for the preparation of diketene is described. The main feature of the procedure is the dimerization of ketene in the presence of tetramethylethylenediamine (TMEDA) and the direct use of crude diketene in the syntheses of acetoacetic esters.

A preparative method for the N-benzyloxycarbonyl hydroxy amino acid t-butyl esters using the aceto-acetyl group as a protecting group for the hydroxyl group of hydroxy amino acids is described. The acetoacetyl group is readily introduced into the hydroxyl group with diketene and effectively deprotected from the O-protected compounds using hydrazine.

A new synthesis for 1,3-dichloro-2-propanone (symm-dichloroacetone) is described using diketene and chlorine as starting materials. The chlorination product of diketene, 2,4-dichloro-3-oxobutyryl chloride, was converted into the corresponding butyric acid derivative. Subsequent decarboxylation by heating gave 1,3-dichloro-2-propanone in 77% overall yield, without isolation of intermediate products.

Reaction of diketene with ethyl pyridineformimidates (Ia-e) resulted in the formation of 6-methyl-2-pyridyl-4H-1, 3-oxazin-4-one (IVa-c) and 2-ethoxy-6-methyl-2-pyridyl-2H-1, 3-oxazin-4 (3H)-one (IIIb, c). Similar reaction with ethyl 2-quinolineformimidate (Id) and methyl 2-pyridineacetimidate (Ie) gave 6-methyl-2-(2-quinolyl)-4H-1, 3-oxazine-4-one (IVd) and 2-methoxy-6-methyl-2-(2-pyridylmethyl)-2H-1, 3-oxazin-4 (3H)-one (IIIe), respectively. The products obtained were treated with ammonia to give 6-methyl-2-substituted-4 (3H)-pyrimidone (Va-e). Hydrolysis of IIIe gave 6-hydroxy-4-methyl-3 (or 5)-(2-pyridyl)-2 (1H)-pyridone (VIII).

Photoreaction of diketene with benzoyl azide (1a) gave 1-benzoyl-4-hydroxy-3-pyrrolin-2-one (2a). Similarly, diketene reacted with p-anisoyl azide (1b), p-chlorobenzoyl azide (1c), and p-toluoyl azide (1d) to give the corresponding 1-aroyl-4-hydroxy-3-pyrrolin-2-ones (2b,c and d).

Vilsmeier reactions of ethyl 2-benzimidazoleacetate (4), ethyl 2-benzothiazoleacetate (5), and ethyl 2-benzoxazoleacetate (6) gave ethyl α-(dimethylaminomethylene)-2-benzimidazoleacetate (7), ethyl α-(dimethylaminomethylene)-2-benzothiazoleacetate (8), and ethyl α-(dimethylaminomethylene)-2-benzoxazoleacetate (9), respectively. Reaction of the enamines (7, 8 and 9) with diketene, acetic anhydride, propionic anhydride, and active methylene compounds such as ethyl cyanoacetate and malononitrile gave rise to the corresponding pyrido [2, 1-b] benzoazoles (10-19).

Acridin-N-Oxid (I) reagiert mit Diketen (II) uber diskutierte Zwischenstufen zum 9-Acetonyl-acridin (III), das unabhangig aus Acridin (V) durch Reaktion mit Aceton/ Methylat zu (IV) und dessen Oxidation mit Chloranil entsteht.

A number of new aryl esters of acetoacetic acid were obtained in the reaction of phenols with diketene in the presence of triethylamine. Reaction of the esters thus obtained with hexamethylenetetramine gave, for the first time, aryl esters of 1,4-dihydropyridine-3,5-dicarboxylic acid, the oxidation of which with chloranil gave the corresponding pyridines.

The reaction of 2-amino-1, 5-benzodiazocines (1) with diketene (2) gave two isomeric products 3 and 4, whereas 2-amino-1, 4-benzodiazepines (16) afforded 2-acetoacetamidodiazepines (17). Treatment of the acetoacetylated derivatives (3, 4, 17) with methanolic hydrogen chloride or thionyl chloride afforded the corresponding fused pyrimidine derivatives (5, 6, 18). Thermal dehydration of both 3a and 4a, on the other hand, gave the same cyclized compound (5a), indicating that acyl migration took place in the reaction of 4a. Similarly, 17a gave the rearranged product (19a).

The products formed by the reaction of benzenethiols with diketene in the presence of H2SO4 are (E)-β-(arylthio)crotonic acids (2) and/or isomeric (Z)-β-(arylthio)crotonic acids and not, as has been reported, S-phenyl 3-oxobutanethioates (1). Compounds 1a–k, as the precursor of thiocoumarins, were prepared from benzenethiols and diketene in the presence of triethylamine. The reaction of 1 with various condensing agents has been examined to prepare 2H-1-benzothiopyran-2-ones (thiocoumarins). It is found that 4-methyl(thiocoumarins) were conveniently prepared by the reaction of 1 with anhydrous aluminium chloride in yields of 16–48%. When 1 was treated with PPA, isomeric 2-methyl(thiochromones) were preferentially obtained in yields of 5–66%, and compound 2 was isolated as an intermediate. The spectral characteristics of 4-methyl(thiocoumarins) have also been described.

Reaction of several conjugated C-N double bond compounds with diketene was carried out with a view to establishing the structure-reactivity relationship of the 1, 3-diaza-1, 3-butadiene system. Formamidine derivatives (IIIa-h) reacted with diketene in benzene to form the products (Va-h) through 1, 4-dipolar cycloaddition with the elimination of dimethylamine, respectively. Similarly, reaction of diketene with 2-(p-dimethylaminobenzylideneamino) benzothiazole (IXa) and 2-(p-dimethylaminobenzylideneamino) benzimidazole (IXb) respectively afforded 3-acetyl-2-(p-dimethylaminophenyl)-2, 3-dihydro-4-oxo-4H-pyrimido [2, 1-b] benzothiazole (Xa) and 3-acetyl-2-(p-dimethylaminophenyl)-2, 3-dihydro-4-oxo-4H-pyrimido-[1, 2-a] benzimidazole (Xb).