Electrochemical Synthesis of Heterocyclic Compounds. XI. Annelation of Coumarin Ring via Cathodic Reduction of 3-Nitrocoumarin Derivatives

Annelation of the coumarin ring was performed via cathodic reduction of 3-nitrocoumarin derivatives (1-4) by controlled potential. The reduction of 3-nitro-4-aminocoumarin, 1, gave 3,4-diaminocoumaDin, 5, and subsequent treatment with formic acid furnished tlie novel 4H [1] benzopyrano [3,4-b] imidazole-4-on ring system 6. The condensation of 5 with trifluoracetic acid anhydride, acetic acid anhydride, and benzil gave products 7, 8 and 9, respectively. The reduction of 3-nitro-4-carbetoxymethylthiocoumar.in, 2, gave the cyclic product 3H, 5H [1] benzopyrano[3,4-b]l,4-thiazine (2H)-3,5-dion, 10. The r.eduction of 3-nitro-4-(2-formylphenoxy)coumarin, 3, and subsequent intramolecular condensation of amino derivative 11 gave the novel SH [1] benzopyrano[3,4-b]l,4-benzoxazepin- 8-on ring system 13. The same compound 13 was obtained through reduction of 3-ruitro-4-chlorcoumarin, 4, to 3-amino-4- -chlorocoumarin, 12, acid and subsequent ·condensation of 12 with salicylaldehyde

Electrochemical Synthesis of Heterocyclic Compounds. XI. Annelation of Coumarin Ring via Cathodic Reduction of 3-Nitrocoumarin Derivatives

Annelation of the coumarin ring was performed via cathodic reduction of 3-nitrocoumarin derivatives (1-4) by controlled potential. The reduction of 3-nitro-4-aminocoumarin, 1, gave 3,4-diaminocoumaDin, 5, and subsequent treatment with formic acid furnished tlie novel 4H [1] benzopyrano [3,4-b] imidazole-4-on ring system 6. The condensation of 5 with trifluoracetic acid anhydride, acetic acid anhydride, and benzil gave products 7, 8 and 9, respectively. The reduction of 3-nitro-4-carbetoxymethylthiocoumar.in, 2, gave the cyclic product 3H, 5H [1] benzopyrano[3,4-b]l,4-thiazine (2H)-3,5-dion, 10. The r.eduction of 3-nitro-4-(2-formylphenoxy)coumarin, 3, and subsequent intramolecular condensation of amino derivative 11 gave the novel SH [1] benzopyrano[3,4-b]l,4-benzoxazepin- 8-on ring system 13. The same compound 13 was obtained through reduction of 3-ruitro-4-chlorcoumarin, 4, to 3-amino-4- -chlorocoumarin, 12, acid and subsequent ·condensation of 12 with salicylaldehyde

Chemistry of Coumarins. Some Novel Heterocycles from Deoxygenation of 4-Arylamino-3-nitrocoumarins

Reaction of 4-arylamino-3-nitrocoumarins with triethyl phosphite was investigated. The yet unreported 6-H-1-benzopyrano- -[4,3-b]quinoxalin-6-one (2a) system was synthesized and characte- rized on the basis of spectral and analytical data. Four derivatives (2a-2d) were obtained in good yields ranging from 68 to 76

Syntheses of New Pyrazolo-, and Tetrazolopyridines

By the reaction of cyanoacetamide and acetylacetone we prepared some new pyrazolo(3,4-b) pyridines (8, Sa, 9) and tetrazolo( l,5-a) pyridines (6, 12, 16) over several reaction steps. Azido- tetrazolo isomerisation of tetrazolo (l,5-a) pyridines (6, 12, 16) has been investigated on the basis of their i. r. and n. m. r. spectra in three solvents (dimethyl sulfokside, chloroform and trifluoroacetic acid). Compound 8 can be detected as a tetrazolo tautomer in the solid state as well as in solutions. Compound 16 in the solid state exists only in the tetrazolo form, while in solutions it exists in both forms. Compound 12 in the solid state exists only in the azido form, while in solutions it exists in both forms

Electrochemical Synthesis of Keto and Enol Forms of Tetraketones of the Type 3,4-Diaroyl-2,5-hexanedione by Oxidative Dimerization of Aroylacetones

Tetraketones of the type 3,4-diaroyl-2,5-hexanedione: Ar = CsH;-, p-CHs-CsH4-, 3,4-(CHsh-CsHs-, p-CHaO-CsH4-, p- Cl-CsH4-, p-Br-C6H4- and 2-C4H3S- were prepared in good yield by oxidative anodic dimerization of aroylacetones. Electrochemical oxidation was carried out at constant current (4-5 A) in cylindrical cell without diaphragm with Pt-gauze anode and Ni-cathode. Depending on the method used (A or B) and depending on the properties of the electrolysed aroylacetones, dimer-products were isolated as stable keto or enol tautomers. Electrolysis in 80°/o aqueous methanol (Method A) gave keto or enol tautomers, while electrolysis in absolute methanol (Method B) yielded only enol tautomers

Electrochemical Synthesis of Heterocyclic Compounds: X. Anodic Synthesis of s-Triazolo [3,4-a)pyridinium Salt Derivatives

A novel way of preparing s-triazolo[3,4-a] pyridinium salts by . anodic oxidation of aryl hydrazones of 2-acetylpyridine, 2-benzoylpyridine and 2-formylpyridine is described. Controlled potential electrolysis was carried out in CH3CN-Et4NX media using a Pt- electrode and a divided cell. The products were obtained in high yield (79-91°/o) and purity. It has been shown that the conformation of the starting hydrazone does not affect the yield of products and s-triazolo [3,4-a]pyridinium salts differing in anions can be prepared merely by using a supporting electrolyte carrying the desired anion (Clo4- , Tso-, BFn

Electrochemical Reduction of Acetonylacetone in Hydrochloric Acid

The electrochemical reduction of acetonylacetone on a mercury cathode in aqueous hydrochloric acid medium has been studied. It has been shown that the electroactive species is the protonated form of acetonylacetone. The experimental results indicate -that the rate of electrochemical reduction is dependent upon the preceding chemical protonation step and/or adsorption of the electroactive species. The electrolysis at controlled potential (- 1.2 V vs. S. C. E .) yielded the following products : acetaldehyde; acetone, acetic acid, 2,5-hexanediol and 2,5-dimethyltetrahydrofuran. Possible mechanistic routes leading to the formation of these products are discussed

Electrochemical Synthesis of Heterocyclic Compounds. Part 21.1 Anodic Oxidation of 1-Arylmethylenesemicarbazides in Methanol

Anodic oxidation of 1-arylmethylenesemicarbazides (1-5) was performed in methanol-tetraethylammonium perchlorate electrolyte solution by constant-current electrolysis. As a result of anodic oxidation, the corresponding oxadizoles (la-3a) were isolated in good yields, ranging from 51 to 65%. The anodic oxidation represents a novel efficient conversion of an aromatic aldehyde to an aromatic methyl ester (3b-5b) through oxidation of its semicarbazones

Electrochemical Synthesis of Keto and Enol Forms of Tetraketones of the Type 3,4-Diaroyl-2,5-hexanedione by Oxidative Dimerization of Aroylacetones

Tetraketones of the type 3,4-diaroyl-2,5-hexanedione: Ar = CsH;-, p-CHs-CsH4-, 3,4-(CHsh-CsHs-, p-CHaO-CsH4-, p- Cl-CsH4-, p-Br-C6H4- and 2-C4H3S- were prepared in good yield by oxidative anodic dimerization of aroylacetones. Electrochemical oxidation was carried out at constant current (4-5 A) in cylindrical cell without diaphragm with Pt-gauze anode and Ni-cathode. Depending on the method used (A or B) and depending on the properties of the electrolysed aroylacetones, dimer-products were isolated as stable keto or enol tautomers. Electrolysis in 80°/o aqueous methanol (Method A) gave keto or enol tautomers, while electrolysis in absolute methanol (Method B) yielded only enol tautomers

Rapid prototyping of art sculptural shapes according to the sample

The aim of this paper is to spread the use of Rapid Prototyping technology (RP)-Additive Manufacturing (AM), into design, restauration and making Art sculptural shapes according to the sample. Rapid prototyping is being used since its origin in designers' fields for a product design, and here it is presented in art design according to the sample, and it has been proved that it is a crucial tool in any design process. In this paper presents a procedure for the rapid prototyping of two models of monuments, the preparation of the model in the STL format and the making of scaled real models of the monuments