Stereochemical features of addition of O- and C-nucleophiles to 5-(Het)aryl-2,3-dicyano-1-ethylpyrazinium salts

Synthesis, X-ray crystal structure and antimycobacterial activity of enantiomerically pure 1-ethyl-2,3-dicyano-5-(het)aryl-6-hetaryl-1,6-dihydropyrazines

“…We have earlier carried out a series of studies on the properties of substituted pyrazinium salts 5a-c. 22,23,[44][45][46][47][48][49][50] It has been shown that they are capable of reacting with various types of nucleophiles under mild conditions to form products of nucleophilic addition to the unsubstituted positions of the pyrazine ring. The aim of the present study is to examine the further modifications of 6-alkoxy adducts 6-8 derived from the reaction of 5-(het)aryl-2,3-dicyano-1-ethylpyrazinium tetrafluoroborates 5a-c with O-nucleophiles (water and alcohols) (Scheme 2).…”

“…17,18 Indeed, it has recently been shown that 1-alkyl-1,4-diazinium cations are prone to add carbo-and heteroatomic nucleophiles to give mono-and diadducts, or to be transformed into condensed tetrahydropyrazines through the tandem addition reactions with bifunctional nucleophiles. [17][18][19][20][21][22][23][24][25][26] On the other hand, the Petasis reaction is one of the multicomponent condensation reactions, which provides a convenient method for the preparation of α-amino acids by reacting an amine 1 with a carbonyl compound 2 and a boronic acid 3. [27][28][29][30][31][32][33][34] The reaction proceeds via the formation of aminal intermediate 4 (Scheme 1).…”

σH-Adducts of N-alkylpyrazinium and quinoxalinium salts with nucleophiles. The 1H and 13C NMR spectra and the crystal structures of P-adducts

“…20 The synthesis of 1,2 dihydro and 1,4 tetrahydropyrazines by the addition of O and C nucleophiles to 1 alkyl 2,3 dicyanopyrazinium salts was also documented. 21, 22 Data on the involvement of P nucleophiles in the reac tions with 1,4 diazines are lacking, although examples of the addition of P nucleophiles to π deficient nitroarenes 12 and azines 23-26 were reported. The structures of the P adducts of isoquinoline, 23 phthalazine, 24 and 4,7 phe nanthroline 25, 26 were established by X ray diffraction.…”

“…A comparative analysis of the 1 H and 13 C NMR spectra of the P adducts, the spectra of the O and C σ H adducts of 5 aryl and 5 hetaryl 2,3 dicyano 1 ethylpyrazinium salts prepared previously, 22 and the spectra of the already known O adducts of pyrazinium and quinoxalinium salts 20 showed that the chemical shifts of the sp 3 hybridized car …”

A facile, metal-free, oxidative coupling of new 6-(hetero)aryl-[1,2,5]-oxadiazolo[3,4-b]pyrazines with pyrroles, indoles and carbazoles

“…The absorption maxima of the four dyes 21a-d in the solid state were red-shifted (Table 2) by 2-5 nm compared with those for the corresponding dyes in CH 3CN. For D-π-A fluorescent dyes, in general, the redshifts of absorption or fluorescence maxima by changing from solution to the solid state are quite common and explained in terms of the formation of intermolecular π-π interactions 27 or continuous intermolecular hydrogen bonding 28 in the crystalline state leading to delocalization of excitons or eximers.…”