Reactions of hydrazidoyl halides: synthesis of imidazo[2,1-b]thiazole, thiazolo[2,3-c]-as-triazole and heterocyclic enaminonitriles

The Chemistry of Heterocyclic Hydrazonoyl Halides

Abstract: Publisher Summary Hydrazonoyl halides have emerged as an important class of intermediates, particularly for the synthesis of heterocyclic compounds. This chapter discusses the synthesis, properties, and reactions of Hydrazonoyl Halides. The mechanisms of some of the reactions and the structures of some of the products are outlined. Direct halogenation of arylhydrazone derivatives of both aliphatic and aromatic aldehydes with the appropriate halogen in glacial acetic acid is an excellent method for the synthesis of the corresponding hydrazonoyl halides. Halides are also obtained by refluxing with N- bromosuccinimide in dry carbon tetrachloride. Furthermore, bromination of aldehyde N-heteroarylhydrazones in acetic acid in the presence of sodium acetate sometimes leads to intramolecular cyclization of the initial hydrazonoyl bromides to yield the corresponding cyclized products. However, from the foregoing survey of heterocyclic hydrazonoyl halides, it appears that the main emphasis has been restricted to both their preparation and use as intermediates for further synthesis. Large areas of their chemistry, particularly regarding their physical and biological properties, remain to be developed.

Synthesis and tautomerism of aryl- and hetaryl-azo derivatives of bi- and tri-heterocycles

Abstract: This review summarizes results from the literature concerning synthesis and azo-hydrazone tautomerism of arylazo- and hetarylazo-derivatives of various bi- and tri-heterocycles reported by us and other research groups from 1981 to mid 2009.

Reactions with hydrazidoyl halides. IV. Synthesis of thiazolo[3,2-a]benzimidazoles, imidazo[2,1-6]thiazoles and pyrazolo[4,3-b]thiazines†

Abstract: Hydrazidoyl halides were condensed with 2- mercaptobenzimidazole yielding 4a-c and 7a,b which were cyclized to the corresponding 2-arylhydrazonothiazolo[3,2-a]benzimidazol-3-ones 5a,b and 3-substituted 2-arylazo thiazolo[3,2-a]benzimidazoles 8a,b respectively. Imidazo[2,1-b]thiazoles were obtained by the reaction of hydrazidoyl halides with 2-mercapto-4,5-dihydroimidazole. Also, hydrazidoyl halides 6a,b were reacted with 3-amino-4-mercapto-5-phenylpyrazole to give pyrazolo[4,3- b]thiazines 15a,b. The structures of the products were assigned on the basis of their elemental analysis and spectral data

An Efficient One-pot Synthesis of Aryl-substituted 1-(Thiazol-2-yl)-1H-pyrazole-3-carboxylates via a Hantzsch Synthesis-Knorr Reaction Sequence

Abstract: The treatment of α-bromoalkyl aryl ketones and 2-(propan-2-ylidene)hydrazine carbothioamide afforded 4-aryl2-(2-(propan-2-ylidene)hydrazinyl)thiazoles via a Hantzsch-thiazole synthesis, which reacted with 4-aryl-2,4-diketoesters via a sequential Knorr-pyrazole reaction to deliver a variety of aryl-substituted ethyl 1-(thiazol-2-yl)-1Hpyrazole-3-carboxylates in a one-pot fashion with moderate to high yields. The key intermediates 4-aryl-2,4-diketoesters, existing as its enolic lithium salt, were synthesized in situ by a high-yield tert-BuOLi-mediated Claisen condensation of alkylphenones and diethyl oxalate. This class of elegant molecule comprises aryl groups on the two different heterocyclic cores, and the configurations of two representative molecules were determined by single crystal X-ray crystallography.

Reaction of dimethylphenacylsulfonium bromide with N-nitrosoacetarylamides and reactions of the products with nucleophiles.

Abstract: The azo coupling of dimethylphenacylsulfonium bromides (I) with N-nitrosoacetanilides in nonaqueous solvents, and with diazotized aniline in aqueous media gave 2-bromophenylglyoxal 2-arylhydrazones (V) and the tetrazine (VI), respectively. V reacted with nucleophiles displacing the bromide. Treatment of V with bases gave VI via benzoylphenylnitrilimine (X). 1,3-Dipolar cycloadditions of X onto ethyl acrylate and acrylonitrile afforded the expected cycloadducts. The mechanisms of the reactions are outlined.