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A convenient and efficient route for the chemoselective synthesis of carbohydrazide, arenesulfonylhydrazide, and thiosemicarbazone derivatives of 5 H -pyrrolo[3,4- b ]pyrazine and 1 H -pyrrolo[3,4- b ]quinoxaline from the corresponding dinitriles and substituted hydrazines was elaborated. The synthesis of starting pyrazine-2,3-dicarbonitrile was sufficiently improved by using concentrated HCl as a catalyst.

6 Title compounds of type (II) are prepared and the reaction mechanism is discussed using also the results of quantum-chemical calculations.

The reaction of 2-substituted 7,7-dimethyl-5-oxo-5,6,7,8-tetrahydroquinoline-4-carboxylic acids with hydrazine was studied. This reaction gave 5-substituted 8,8-dimethyl-3,7,8,9-tetrahydro-2H-pyrido-[4,3,2-de]cinnolin-3-ones in good yields. A possible reaction mechanism was discussed using nonempirical quantum-chemical calculations.

The direction of the process depends on the temperature regime and on the structure of the starting materials.

An efficient method for the synthesis of dicarbonitrile (IV) and its conversion into pyrrolopyridinylidene carbohydrazides such as (VI) are described.

A simple procedure in suitable solvents allows the selective synthesis of pyrimidopyridone products.

The selective formation of the products (III) and (IV) depends on the solvents and the reaction time.

Various 1-substituted cyclopentylamines (25 examples, 10― 89 % yield) have been prepared according to a one-pot procedure by the addition of tetramethylenebismagnesium dibromide in the presence of Ti(OiPr) 4 to aliphatic, aromatic and heteroaromatic nitriles, respectively.

N0,N00-1H-Isoindole-1,3-diylidenedialkyl(aryl,heteroaryl)carbohydrazides were prepared in good yields via 1,1,3-trichloro-1H-isoindole, which was shown to be a versatile reagent for their synthesis. Tautomeric structure and conformational behaviour of dicarbohydrazides in solid state as well as in solution have been studied by X-ray crystallography, NMR spectroscopy and quantum calculations. The dependence of Z/E amide-type isomerism upon steric effects and solvent polarity is discussed.

Vinyl cations, generated by protonation of the triple bond of α,β-alkynylcarbonyl compounds in the superacid HSO 3 F, react efficiently with arylammonium (anilinium) ions at low temperatures −75 and −30 °C in 30–75 min with the formation of Friedel–Crafts-type products of anilinium ring alkenylation in 14–62% yields. Regio- and stereoselectivity of such electrophilic aromatic substitution has been studied in detail.

According to the 1H and 13C NMR data, 3-arylpropynoic acids and their esters XC6H n -C≡C-CO2R (R = H, Me, Et) having electron-withdrawing substituents in the benzene ring (X = NO2, CN, COMe, CO2Me) exist in HSO3F at −80 to 0°C as XC6H n -C≡C-C+(OH)OR ions. Derivatives with other substituents (X = H, F, Me, MeO) in HSO3F or CF3SO3H above −40°C undergo protonation at the acetylenic carbon atom neighboring to the acid group to give unstable vinyl-type XC6H n -C+=CH-CO2R cations which are then transformed into mixtures of stereoisomeric (Z and E) fluorosulfonates or triflluoromethanesulfonates XC6H n -CY=CH-CO2R (Y = OSO2F, OSO2CF3), the E isomer prevailing.

Vinyl type carbocations ArC+=CHX [X = CO2H, CO2Alk, C≡N, P(O)(OAlk)2] generated from alkyl 3-arylpropynoates and related compounds in fluorosulfonic acid at −75 to −20°C react with various benzene derivatives, following the mechanism of electrophilic substitution of hydrogen. A new procedure for the synthesis of alkyl 3,3-diarylpropenoates having various substituents in the aryl fragments has been developed on the basis of protonation of the triple bond in alkyl 3-arylpropynoates.

1,3-Diarylpropynones ArC≡CCOAr′ in superacids with H0 ranging from −20 to − 14 undergo protonation at the carbonyl oxygen atoms to give stable ArC≡CC(O+H)Ar′ ions or at the acetylenic C2 atom with formation of reactive ArC+=CHCOAr′ species. The effects of the Ar and Ar′ substituents and reaction conditions on the intramolecular cyclization of ArC+=CHCOAr′ to 3-arylinden-1-ones are discussed.

Nitration of phenylpropiolic acid derivatives ArC≡CX (X=CN, CO2Me) in HSO3F at −75...−50°C afforded mononitro compounds, for instance, m-O2NC6H4C≡CX. Vinyl type cations generated in HSO3F from methyl 3-arylpropiolates ArC+=CHCO2Me react along two pathways. The first among them results in formation of fluorosulfonates ArC(OSO2F)=CHCO2Me, and the second one after the attack of vinyl cation on the aryl moiety of the substrate affords a dimer that on nitration is converted into a nitro product with conserved triple bond.

We recently reported on an unusual low-temperature dimerization of methyl 3-(4-methylphenyl)propynoate (I), which involved intermediate formation of cation A [1]. It seemed reasonable to estimate the scope of the revealed reaction as applied to other acetylene compounds, and (what is the most important) to use the vinyl-like cations generated therefrom by the action of HSO3F as addends to foreign organic substrates. Such processes would provide a simple synthetic route to various practically important compounds. For this purpose, we examined reactions of cation A with 2,3,5,6-tetramethylbenzenesulfonyl fluoride (II, R = FSO2) and (2,3,5,6-tetramethylphenyl)acetonitrile (III, R = NCCH2). These substrates do not react with HSO3F but are characterized by considerably different reactivities in electrophilic substitution processes.