Recyclization of 1,4-dihydropyridine derivatives in acidic medium

The recyclization of 1,4-dihydropyridines in aqueous-alcoholic hydrochloric acid medium proceeds with cleavage of a C-N bond and pyridine ring opening. Cyclohexenone derivatives are formed as a result of the subsequent intramolecular crotonic condensation of the acyclic intermediate. The leaving carbonyl substituents depart simultaneously with recyclization, depending on the acidity of the reaction medium. Dedicated to Prof. Dr. E. Lukevics on the occasion of his 70th birthday. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 49–58, January, 2007.     

Reaction of natural isoflavonoids and their analogs with hydroxylamine

Recyclization of the chromone ring in several natural isoflavonoids and their analogs by reaction with hydroxylamine was studied. It has been found that the most suitable base for carrying out the reaction is N-methylmorpholine. Several derivatives of 4-aryl-5-(2-hydroxyphenyl)isoxazole were synthesized. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 332–336, July–August, 2007.     

Recyclization of pyrimidinium salts into 1,2,4-triazole derivatives

The interaction of the iodomethylates of pyrimidinyl-2-acetic acid derivatives with monosubstituted hydrazines, in addition to the products of a Kost-Sagitullin rearrangement, leads also to N-substituted triazoles. The structure of the triazoles was demonstrated by NOESY NMR experiments. The structure of the reaction products was determined on the basis of the response observed in the spectra between the methyl group protons of the triazole ring and the spatially close proton of the substituent in position 1 and a conclusion was drawn on the direction of the primary attack of nucleophile in the recyclization process of the pyrimidinium salts into a 1,2,4-triazole. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1175–1179, August, 2007.     

New rearrangement of benzo[d]isoxazoles: recyclization of 4-R-6-nitrobenzo[d]isoxazole-3-carbaldehyde arylhydrazones into 2-aryl-4-(2-hydroxy-4-nitro-6-R-phenyl)-1,2,3-triazoles

The previously unknown recyclization of nitrobenzo[d]isoxazoles into 1,2,3-triazoles was found. A general method for the synthesis of 2-aryl-4-(2-hydroxy-4-nitro-6-R-phenyl)-1,2,3-triazoles from 4-R-6-nitrobenzo[d]isoxazole-3-carbaldehyde arylhydrazones was developed.     

Recyclization of Condensed Carbethoxypyrimidines Accompanied by Substitution of a Carbon Atom into the Heterocycle

Condensation in ethanol of ethyl ethoxymethyleneacetoacetate with systems containing an amidine fragment (substituted 3-aminopyrazoles and 3-amino-1,2,4-triazole) gave 6-carbethoxy-7-methylpyrazolo[1,5-a]pyrimidines. Addition of base to solutions of the obtained bicyclic carbethoxy derivatives in the course of several minutes caused rearrangement to 6-acetyl-7-hydroxypyrazolo[1,5-a]pyrimidine and 6-acetyl-7-hydroxy-1,2,4-triazolo[1,5-a]pyrimidine respectively. A more prolonged refluxing in 15% aqueous alcohol solution of base caused 6-carbethoxy-7-methyl-2-phenylpyrazolo[1,5-a]pyrimidine and 6-acetyl-7-hydroxy-2-phenylpyrazolo[1,5-a]pyrimidine to recyclize to 7-methylpyrazolo[1,5-a]pyrimidine.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 569–576, April, 2005.     

Transformations of sym-octahydroxanthene-1,8-diones and 1,8-dioxo-sym-octahydroxanthylium salts in recyclization under the influence of amines

The chemical behavior of 9-R-sym-octahydroxanthene-1,8-diones and salts based on them in recyclization reactions under the influence of amines was studied. The effect of the basicity of the amines on the direction of recyclization was established. A method is proposed for the single-stage synthesis of sym-octahydroacridine-1.8-dione oximes based on 1,8-dioxo-sym-octahydroxanthenes. Conditions were worked out for the oxidation of sym-octahydroxanthene-1,8-diones and N-R-decahydroacridinediones to the corresponding salts. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 32–38, January, 2006.     

Synthesis and intramolecular recyclization of 2,2-dialkyl-6-chloro-4-hydroxymethyl-benzo[<Emphasis Type="Italic">f</Emphasis>]isoindolinium salts

The intramolecular cyclization of dialkyl(2-butynyl-4-hydroxy)[3-(p-chlorophenyl)propargyl]ammonium chlorides, catalyzed by aqueous KOH, was realized. It was shown that the obtained products — 2,2-dialkyl-6-chloro-4-hydroxymethylbenzo[f]isoindolinium chlorides — readily undergo recyclization under the action of a twofold molar amount of KOH in aqueous solution with heating with the formation of 4-dialkylaminomethyl-8-chloro-1,3-dihydronaphtho[1,2-c]furans. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 834–840, June, 2007.     

Thioureas from 3-aminoquinazolin-4(3H)-one. 2. Unusual alkaline recyclization of 3-(N",N",S-trialkylisothioureido)quinazolin-4(3H)-ones into new 1,3,4-oxadiazoles

3-(N",N",S-trialkylisothioureido)quinazolin-4(3H)-ones obtained by the reactions of 3-(N",N"-dialkylthioureido)quinazolin-4(3H)-ones with alkyl halides undergo unusual recyclization into 5-(2-aminophenyl)-2-dialkylamino-1,3,4-oxadiazoles under the action of aqueous solutions of alkali, hydrazine, and primary aliphatic amines. A plausible mechanism of the recyclization was proposed.