Benzazetines and their derivatives (review)

Published information on methods for the production of benzazetines and their dehydro derivatives (benzazetes) and their chemical transformations is reviewed and analyzed. It was noted that benzazetines with an unsubstituted NH group are unstable and their stable representatives have only became accessible in recent years. The tendency of benzazetines to undergo opening of the four-membered heterocycle and isomerization processes was demonstrated. The wide-ranging synthetic possibilities of benzazetines and benzazetes are indicated. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1763–1783, December, 2007.     

Synthesis of Sybstituted Isoxazoles and Pyrazoles Based on 1-Aryl-3,4,4-trichloro-3-buten-1-ones

3-Aryl-5-methylenehydroxyiminoisoxazoles were synthesized by reaction of 1-aryl-3,4,4-trichloro-3-buten-1-ones with hydroxylamine. Reactions of ketones with hydrazine provided pyrazole structures; therewith two pyrazole molecules underwent coupling affording 3-arylpyrazole-5-carbaldehyde azines.     

Synthesis of 4,5-Dichloroisothiazole-3-carboxylic Acid Amides and Esters

Previously unknown 4,5-dichloroisothiazole-3-carboxylic acid amides and esters were synthesized by reactions of 4,5-dichloroisothiazole-3-carbonyl chloride with ammonia, heterocyclic and aromatic amines, and functionally substituted alcohols and phenols.     

Synthesis and Properties of Copper,Mercury, and Silver (2-Naphthyl)acetylenides

(Z)-2-Naphthylacetylene was synthesized by the reaction of (Z)-3-(2-naphthyl)-3-chloropropenal (prepared from 2-acetylnaphthalene) with aqueous NaOH in dioxane. The reactions of 2-naphthylacetylene with CuCl, [Ag(NH₃)₂]NO₃, and K₂[HgI₄] gave copper, silver, and mercury 2-naphthylacetylenides, respectively. Silver naphthylacetylenide reacts with iodine to give the iodoethynyl derivative, which readily takes up bromine across the triple bond.     

Reaction of 4-Ethoxy-2-(2,3,3-trichloro-1-nitro- 2-propenylidene)benzazetine with Methyl- and Phenyllithium

The reactions of 4-ethoxy-2-(2,3,3-trichloro-1-nitro-2-propenylidene)benzazetine with methyl- and phenyllithium at a ratio of 1:2 result in replacement of one chlorine atom and formation, respectively, of 4-ethoxy-2-(2,3-dichloro-3-methyl-1-nitro-2-propenylidene)benzazetine and 4-ethoxy-2-(2,3-dichloro-1-nitro-3-phenyl-2-propenylidene)benzazetine in 45 and 52% yield. With excess phenyllithium (reactant ratio 1:5), a mixture of products is formed due to replacement of one, two, and three chlorine atoms by phenyl groups. An analogous reaction with methyllithium is nonselective.     

Crystal and molecular structure of 3-trichloromethyl-4-chloro-5-isopropoxyisothiazole and 4,5-dichloroisothiazole-3-carboxylic acid

X-ray structural data are used to demonstrate that the chlorine in the 5-position of the heterocycle is replaced on reaction of 3-trichloromethyl-4,5-dichloroisothiazole with sodium isopropoxide. The S-N and C-S bond lengths are lengthened in the resulting 3-trichloromethyl-4-chloro-5-isopropoxyisothiazole whereas the C-N and C-C bonds are shortened compared with analogous bonds in 4,5-dichloroisothiazole-3-carboxylic acid. This is explained by conjugation of the carboxylic acid with the heterocycle.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 399–402, March, 1992.     

Synthesis of 5-alkyl(aryl)sulfanyl-4-chloro-3-trichloromethyl-1,2-thiazoles and 5-Alkyl(aryl)sulfanyl-4-chloro-1,2-thiazole-3-carboxylic acids

Butane-, phenylmethane-, and benzenethiols reacted with 4,5-dichloro-3-trichloromethyl-1,2-thiazole in the presence of sodium ethoxide to give the corresponding 5-alkyl(aryl)sulfanyl-4-chloro-3-trichloromethyl-1,2-thiazoles. The reaction of 4,5-dichloro-1,2-thiazole-3-carboxylic acid with the same thiols under similar conditions resulted in the formation of sodium 4,5-dichloro-1,2-thiazole-3-carboxylate, while in the presence of pyridine 5-alkyl(aryl)sulfanyl-4-chloro-1,2-thiazole-3-carboxylic acids were obtained.     

Azolyl Derivatives of Nitrohalobutadienes: V. A New Route to Functionally Substituted Benzazetines

Heating of 1-azolyl-1-(4-R-phenylamino)-2-nitro-3,4,4-trichloro-1,3-butadienes and 1-azolyl-1-(4-R-phenylamino)-2-nitro-3,4-dichloro-4-bromo-1,3-butadienes (R = BuO, EtO, MeO, Me; azolyl = 1-benzotriazolyl, 3,5-dimethyl-1-pyrazolyl, and 1,2,4-triazol-1-yl) in methanol or acetic acid gave the corresponding 2-(1-nitrotrihalopropenylidene)-4-R-benzazetines. The latter reacted with amines, sodium alkoxides, and sodium thiolates, affording salts of the aci-nitro form. The reactions with benzoyl chloride and chloroacetyl chloride in the presence of pyridine led to formation of mixed anhydrides.     

Synthesis of 3,4-dibromo-3,4,4-trichloro-1-phenylbutan-1-one and 1-aryl-2-bromo-3,4,4-trichlorobut-3-en-1-ones from 3,4,4-trichlorobut-3-enoic acid

Bromination of 3,4,4-trichlorobut-3-enoic acid in boiling carbon tetrachloride led to the formation of 2-bromo-3,4,4-trichlorobut-3-enoic acid as a result of replacement of hydrogen in the CH₂ group. The reaction at 40°C involved the double C=C bond to give 3,4-dibromo-3,4,4-trichlorobutanoic acid. The brominated acids were converted into the corresponding chlorides which were used to acylate benzene, toluene, and bromobenzene according to Friedel-Crafts. The acylation was not selective, and only the reaction of 3,4-dibromo-3,4,4-trichlorobutanoyl chloride with benzene gave 3,4-dibromo-3,4,4-trichloro-1-phenylbutan-1-one as the only product. 1-Aryl-2-bromo-3,4,4-trichlorobut-3-en-1-ones were synthesized by bromination of the corresponding 1-aryl-3,4,4-trichlorobut-3-en-1-ones which were prepared previously by Friedel-Crafts acylation of substituted benzenes with 3,4,4-trichlorobut-3-enoyl chloride.     

Synthesis of 3-aryl-5-dichloromethyl-1H-pyrazole-1-carboxamides from 1-aryl-3,4,4-trichlorobut-3-en-1-ones

The reaction of 1-aryl-3,4,4-trichlorobut-3-en-1-ones with semicarbazide hydrochloride in the presence of sodium acetate is accompanied by prototropic allylic rearrangement, leading to the formation of two isomeric products, semicarbazones of the initial ketones and 1-aryl-3,4,4-trichlorobut-2-en-1-one semicarbazones. The latter undergo heterocyclization in the presence of triethylamine to give the corresponding 3-aryl-5-dichloromethyl-1H-pyrazole-1-carboxamides.