ChemInform Abstract: Substituent Effect on Oxidative Cyclization of Aldehyde Thiosemicarbazones with Ferric Chloride.

The reactivity of aldehyde thiosemicarbazones 1 with ferric chloride solutions was examined. When compounds 1 are not substituted on the N-2 nitrogen atom formation of 1,3,4-thiadiazole 3 heterocyclic ring was observed. In contrast 1,2,4-triazoline 4 and/or 1,3,4-thiadiazoline 5 heterocyclic rings were afforded when N-2 nitrogen atom carried a methyl or a phenyl group. The reaction mechanism is also discussed.

Addition reactions of heterocycles. VI. Reactions of 1,2-dimethylpyrrole and 1-methyl-2-carbomethoxypyrrole with nitrilimines

Addition reactions of 1,2-dimethylpyrrole and 1-methyl-2-carbomethoxypyrrole with C-acetyl-N-phenylnitrilimine, have been investigated. 1,2-Dimethylpyrrole gives three different types of adducts: i.e. bis-cycloadducts (Vc) and (VIc), spirocycloadduct (IX), and non cyclic bis-adduct (XII). On the other hand, 1-methyl-2-carbomethoxypyrrole gives the bis-cycloadduct (VIb) only. Compound XII arises probably through a double 1,3-addition reaction, whereas the formation of cycloadducts Vc, VIc, and IX depends on the substituents present at C2 of the pyrrole ring and consequentially on the intermediary occurence of mono-cycloadduct (IIIc), its methylenic tautomer VII, VIc, and XL The behaviour of …

A study of the behaviour of 2,4-substituted thiosemicarbazides toward orthoesters: Formation of mesoionic compounds

The reactions beetwen 2,4-disubstituted thiosemicarbazides and orthoesters in refluxing xylene led to the formation of the 1,2,4-triazoline-5-thione ring and to the 1,2,4-triazolium-5-thiolate ring. The formation of the mesoionic componds is due to rearrangement of the easily available 2,4-disubstituted thiosemicarbazides to 1,4-disubstituted thiosemicarbazides under the reaction conditions adopted. This method can be usefully used for the synthesis of mesoionic compounds, especially in the case of the 2-methyl-4-phenylthiosemicarbazide.

ChemInform Abstract: Methylation of 2-Phenylamino-1,3,4-thiadiazole. A Structure Debated.

The true identity of the 4-methyl-5-phenylimino-δ2-1,3,4-thiadiazoline (A) has been demonstrated. The reactions, previously reported in the literature to give A have been repeated and the structure of the compounds obtained has been established.

Cycloadditions in the pyrrole series

Oxidative cyclization of some aldehyde semicarbazones induced by metallic salts

The oxidative cyclization of some aldehyde semicarbazones 10 with four different oxidizing agents has been effected. The structure of the semicarbazones and the nature of cyclizing agent affected the rate and yield of cyclization but they did not show any influence on the regiochemistry of reaction. In fact, 1,2,4-triazoline 20 was the only heterocyclic ring obtained by the cyclization reaction.

Polycondensed nitrogen heterocycles. Part21. Complete13C NMR assignment of annelated phenanthridines

Two-dimensional nmr techniques were used for the complete assignment of 13C nmr spectra of pyrrolo-[1,2-f]-, pyrazolo[1,5-f]-, and 1,2,4-triazolo[1,5-f]phenanthridines.

Addition reactions of heterocycles—IV

Abstract The reactivity of indole derivatives towards nitrilimines has been studied. Substituents at positions 1, 2 and 3 of the indole ring greatly affect the course of the reaction. 1,3-Dipolar cycloaddition products (3a,8a,dihydropyrazole-[3,4-b]-indole derivatives) and non-cyclic addition products (3-indolyl derivatives) were obtained depending on these substituents. The structures reported were assigned on the basis of satisfactory analytical, spectroscopic and chemical data.

Heterocyclic photorearrangements. Photoinduced rearrangement of 3-styryl-1,2,4-oxadiazoles

The photochemical behaviour of 3-styryl-5-phenyl-(5-methyl)-1,2,4-oxadiazoles in methanol at 254 nm has been investigated. A photoinduced rearrangement to the quinoline system has been pointed out and explained as proceeding through an initial photolysis of the ring ON bond, followed by a six membered ring closure reaction involving the styryl moiety.

Mononuclear heterocyclic rearrangements. Part 12. Rearrangement of 1,2,4-oxadiazoles into indazoles

The first example of a mononuclear heterocyclic rearrangement involving an XYZ = CCN side-chain sequence is reported. The 3-(o-aminophenyl)-, and 3-(o-methylaminophenyl)-5-methyl-1,2,4-oxadiazoles (3a,b) gave a thermally induced rearrangement into 3-acylaminoindazoles (4a,b). On the other hand, the 3-(o-acetylaminophenyl)-5-methyl-1,2,4-oxadiazole (3c) produced a base induced rearrangement into 3-acetylaminoindazole (4a).

ChemInform Abstract: Oxidative Cyclization of Some Aldehyde Semicarbazones Induced by Metallic Salts.

The oxidative cyclization of some aldehyde semicarbazones 10 with four different oxidizing agents has been effected. The structure of the semicarbazones and the nature of cyclizing agent affected the rate and yield of cyclization but they did not show any influence on the regiochemistry of reaction. In fact, 1,2,4-triazoline 20 was the only heterocyclic ring obtained by the cyclization reaction.

Substituent effect on oxidative cyclization of aldehyde thiosemicarbazones with ferric chloride

The reactivity of aldehyde thiosemicarbazones 1 with ferric chloride solutions was examined. When compounds 1 are not substituted on the N-2 nitrogen atom formation of 1,3,4-thiadiazole 3 heterocyclic ring was observed. In contrast 1,2,4-triazoline 4 and/or 1,3,4-thiadiazoline 5 heterocyclic rings were afforded when N-2 nitrogen atom carried a methyl or a phenyl group. The reaction mechanism is also discussed.

Methylation of 2-phenylamino-1,3,4-thiadiazole. A structure debated

The true identity of the 4-methyl-5-phenylimino-δ2-1,3,4-thiadiazoline (A) has been demonstrated. The reactions, previously reported in the literature to give A have been repeated and the structure of the compounds obtained has been established.

Photochemical cyclization of some aldehyde thiosemicarbazones

The photochemical behaviour of some substituted aldehyde thiosemicarbazones 1a-k has been investigated in methanol at 254 nm. Thiosemicarbazones of glyoxil methyl ester 1a-f cyclized to furnish the 3-thioxo- 1,2,4-triazin-5-one 2 ring system. The remaining thiosemicarbazones 1g-j gave 1,2,4-triazoline 4 derivatives.

ChemInform Abstract: Heterocyclic Photorearrangements. Photoinduced Rearrangement of 3-Styryl-1,2,4-oxadiazoles.

The photochemical behaviour of 3-styryl-5-phenyl-(5-methyl)-1,2,4-oxadiazoles in methanol at 254 nm has been investigated. A photoinduced rearrangement to the quinoline system has been pointed out and explained as proceeding through an initial photolysis of the ring ON bond, followed by a six membered ring closure reaction involving the styryl moiety.

Mononuclear isoheterocyclic rearrangements. Note I. Interconversion of 3-benzoylamino-5-methyl-1,2,4-oxadiazole and 3-acetylamino-5-phenyl-1,2,4-oxadiazole

The first example of mononuclear isoheterocyclic rearrangement is reported. The 3-benzoylamino-5-methyl-1,2,4-oxadiazole (5) furnishes through a reversible process (slowly at room temperature in methanol, acetone or dioxane, fast in DMSO or in methanol in the presence of strong bases) a mixture of 5 and 3-acethylamino-5-phenyl-1,2,4-oxadiazole (6). The equilibrium process can be achieved also by heating 5 at 181° and the same reaction mixture can be obtained using 6 as the starting material. 3-Trichloroacetylamino-5-methyl-1,2,4-oxadiazole (7) was unaffected by similar treatment. The results obtained are discussed.

Addition reactions of heterocycles. VII. Pyrrole andC-Acetyl-N-phenylnitrilimine

The addition reaction of C-acetyl-N-phenylnitrilimine to pyrrole has been investigated. The products obtained show that the reaction proceeds via two distinct pathways. The 1,3-addition reaction leads to the non-cyclic-adduct III, whereas the 1,3-cycloaddition reaction gives a mixture of regioisomeric Δ2-pyrroline IV and V, and Δ1 -pyrroline VI and VII mono-cycloadducts. These latter compounds cannot be isolated because they undergo a further 1,3-cycloaddition reaction leading to the N-substituted bis-adducts X and XI, and to the bis-adduets XII and XIII. The stereochemical assignment for X, XI, XII and XIII is provided by nmr data which suggest also that in X and XI the rotation around the…

ChemInform Abstract: Photochemical Cyclization of Some Aldehyde Thiosemicarbazones.

The photochemical behaviour of some substituted aldehyde thiosemicarbazones 1a-k has been investigated in methanol at 254 nm. Thiosemicarbazones of glyoxil methyl ester 1a-f cyclized to furnish the 3-thioxo- 1,2,4-triazin-5-one 2 ring system. The remaining thiosemicarbazones 1g-j gave 1,2,4-triazoline 4 derivatives.