Steroidal thiazoles,isothiazoles, thiazolines and thiazolidines

In order to discover new useful steroids in which the cyclopentanoperhydrophenanthrene system is condensed with various heterocyclic rings, many new compounds are continually being synthesized and tested for physiological action. The thiazole, isothiazole, thiazoline and thiazolidine ring condensed on several positions of the steroidal skeleton, has shown great interest due to the physiological properties. Literature coverage for this review includes publications which appear from 1946 to the 1980′s.     

Functionally substituted isoxazoles and isothiazoles: Synthesis,palladium(II) complexes and their catalytic activity

Functionally substituted 5-(p-tolyl)isoxazoles and 4,5-dichloroisothiazoles, whose molecules contain azomethine, amino, carboxyl, and ester moieties in various combinations in the aromatic ring in the position 3 of heterocycle, were synthesized. Synthesis of complexes of Pd(II) with carboxyl derivative of 1,2-azoles was performed. They show high catalytic activity in the Suzuki reaction in aqueous media.     

Direct preparation of thiazoles, imidazoles, imidazopyridines and thiazolidines from alkenes

A range of heterocycles, namely thiazoles, imidazoles, imidazopyridines, thiazolidines and dimethoxyindoles, have been synthesised directly from alkenes via a two-step ketoidoination/cyclisation protocol. The alkene starting materials are themselves readily accessible using many different and well-established approaches, and allow access to a variety of heterocycles with excellent yields and regioselectivity.     

A bifurcated pathway to thiazoles and imidazoles using a modular flow microreactor

A scalable method for the preparation of 4,5-disubstituted thiazoles and imidazoles as distinct regioisomeric products using a modular flow microreactor has been devised. The process makes use of microfluidic reaction chips and packed immobilized-reagent columns to effect bifurcation of the reaction pathway.     

Organocatalytic strategies for the construction of optically active imidazoles, oxazoles, and thiazoles

This study demonstrates the first enantioselective synthesis of hydroxyalkyl- and aminoalkyl-substituted imidazoles, oxazoles, and thiazoles. The approach developed utilizes a highly effective one-pot reaction cascade that consists of either an organocatalytic epoxidation or aziridination of α,β-unsaturated aldehydes coupled with a [3+2]-annulation, in which amidines, ureas, or thioureas act as effective 1,3-dinucleophilic species. The methodology described benefits from low catalyst loadings, commercially and readily available starting materials, and mild reaction conditions.     

Synthesis of trisubstituted imidazoles via a convergent reaction network from methyl ketones and benzoins

A novel method for constructing trisubstituted imidazoles has been created using simple and readily available aromatic ketones, benzoins, and ammonium acetate as starting materials. The new synthetic strategy utilized a convergent integration of two self-labor domino sequences, providing a typical example for logical self-organization synthesis.     

Photoaddition of chloroform to ketones via a singlet exciplex: A photo-CIDNP study

Photolysis of 4-acetyl-4-ethoxyformylcyclohexanone, 4-acetyl-4-phenylcyclohexanone and 1-acetyl-1-phenylcyclohexane in deuteriochloroform using a high pressure Hg—Xe lamp showed unusual polarizations. The results are explained by the formation of a singlet exciplex of the ketone with deuteriochloroform and the photoaddition of deuteriochloroform to the ketone.     

Synthesis of substituted esters of imidazoles,oxazoles, thiazoles,and diethyl pyrazine-2,5-dicarboxylate from a common acyclic precursor employing C-formylation strategy

A novel synthetic route to substituted esters of imidazoles, oxazoles, thiazoles, and diethyl pyrazine-2,5-dicarboxylates via C-formylation of glycine ethyl ester hydrochloride is reported. This methodology is simple, robust, and gives good yields of different heterocyclic esters in one or two steps from a common acyclic precursor and is amenable to large scale synthesis.     

Reaction of aryl-β-nitrovinyl ketones with hydrogen halides. Preparation of isoxazoles

A study is made of the reactions of aryl--nitrovinyl ketones with hydrogen chloride, hydrogen bromide, and hydriodic acid. It is shown that reaction leads to cyclization forming substituted isoxazoles, and that with hydrogen bromide and hydriodic acid, cyclization is accompanied by reduction. The action of hydrogen chloride on phenyl--nitrovinyl ketone gives 3, 4-dichloro-5-phenylisoxazole, while hydrogen bromide gives 5-phenyl- and 3-bromo-5-phenylisoxazoles, and hydriodic acid 5-phenylisoxazole. Chlorination of 3-chioro-5-phenylisoxazole and bromination of 3-bromo-5-phenyl-isoxazole are methods of synthesizing 3, 4-dichloro- and 3, 4-dibromo-5-phenylisoxazole, respectively. The general equations for the reactions are given.     

Directed metalation of pyridinesulphonamides. Synthesis of pyridine-fused isothiazoles and 1,2-oxathioles

4-Lithio-N-t-butylpyridine-3-sulphonamide reacted with benzophenone and carbon dioxide respectively to give the corresponding intermediates which on appropriate treatment gave isothiazolo[5,4-c]pyridin-3-one 1,1-dioxides. Metalation of 2- and 4-(N,N-dialkylaminosulphonyl)pyridines with lithium diisopropylamide (LDA) gave anions which reacted with benzophenone to give carbinols which thermally cyclised to 1,2-oxathiolo[3,4-b]pyridine and 1,2-oxathiolo[4,3-c]pyridine respectively.     

Synthesis and properties of azoles and their derivatives. 34. Synthesis of 4-substituted 2-(3-indolyl)thiazoles

4-Substituted 2-(3-indolyl)thiazoles were synthesized by condensation of indole-3-thiocarboxamide with halomethyl ketones. Reactions involving the nucleophilic substitution of the chlorine atom in 4-chloromethyl-2-(3-indolyl)thiazole were examined.See [1] for communication 33.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp, 761–764, June, 1984.     

Synthesis of condensed thiazoles. (Review)

Data on the synthesis of thiazoles systems condensed with heterocycles are classified. The principal directions in the practical application of these substances are briefly discussed. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 167–190, February, 2006.     

Novel two step synthesis of pyrazoles and isoxazoles from aryl methyl ketones

Various acetyl aromatics when reacted with dimethylformamide dimethyl acetal gave 1-aryl-3-dimethylamino-2-propen-1-ones. These intermediates are masked β-ketoaldehydes and react with hydrazine hydrate or hydroxylamine at room temperature to give in good yields pyrazoles or isoxazoles.     

Synthesis of bromodifluoromethyl substituted pyrazoles and isoxazoles

Bromodifluoromethyl substituted β-diketone 3a-3d, prepared from corresponding ketones and ethyl bromodifluoroactate in the presence of sodium methoxide, reacted with aryl hydrazine derivatives affording bromodifluoromethyl substituted pyrazoles in high regioselectivity. The reaction of 3a-3d with hydroxylamine hydrochloride gave dihydroisoxazoles, which afforded bromodifluoromethyl substituted isoxazoles through dehydration by PPA or concentrated sulfuric acid.     

Synthesis of new isoxazoles derivatives attached to sugar moieties

This work reports the synthesis of isoxazoles linked to sugar derivatives in different positions of furanosidic rings, by intramolecular oxidative cyclization of α,β‐unsaturated oximes with iodine, potassium iodide and sodium hydrogen carbonate. These oximes were obtained from aldehyde‐sugar derivatives.