CuII-Mediated Synthesis of a New Fluorescent Pyrido[1,2-a]quinoxalin-11-ium Derivative

Pyrazinyl and pyridinyl bis-azomethines formation: an experimental and computational study

Formation of bis-azomethines from hydrazine and heterocyclic aromatic carbaldehydes, namely pyridine-2-carbaldehyde and pyrazine-2-carbaldehyde, is studied using density functional theory. The theoretical investigation is correlated with experimental results obtained by means of NMR spectroscopy. The presence of bis-hemiaminal intermediates is evidenced by NMR spectra while surprisingly stable hemiaminal intermediate was isolated experimentally. Water, methanol and acetic acid were outlined to play a crucial role as active catalysts of elementary steps of the reaction mechanisms. The possible reaction sequences, i.e. addition-dehydration-addition-dehydration or addition-addition-dehydration-dehydration are investigated and discussed. Also, alternative mechanistic path via ionic mechanism was proposed for the formation of hemiaminals.

Crystal structure of 2-amino-1,3-di-bromo-6-oxo-5,6-di-hydro-pyrido[1,2-a]quinoxalin-11-ium bromide monohydrate

In the title hydrated salt, C12H8Br2N3O(+)·Br(-)·H2O, which was synthesized by the reaction of the pyridine derivative Schiff base N (1),N (4)-bis-(pyridine-2-yl-methyl-ene)benzene-1,4-di-amine with bromine, the asymmetric unit contains a 2-amino-1,3-di-bromo-6-oxo-5,6-di-hydro-pyrido[1,2-a]quinoxalin-11-ium cation, with a protonated pyridine moiety, a bromide anion and a water mol-ecule of solvation. The cation is non-planar with the di-bromo-substituted benzene ring, forming dihedral angles of 24.3 (4) and 11.5 (4)° with the fused pyridine and pyrazine ring moieties, respectively. In the crystal, the cations are linked through a centrosymmetric hydrogen-bonded cyclic R 4 (2)(8) Br2(H2O)2 unit by N-H⋯Br, N-H⋯O and O-H⋯Br hydrogen bonds, forming one-dimensional ribbons extending along b, with the planes of the cations lying parallel to (100).

Crystal structure of 2-azaniumyl-3-bromo-6-oxo-5,6-dihydropyrido[1,2-a]quinoxalin-11-ium dibromide

The title salt, C₁₂H₁₀BrN₃O²⁺·2Br⁻, was synthesized from the reaction of N¹,N⁴-bis­(pyridin-2-yl­methyl­idene)benzene-1,4-di­amine and bromine in a methanol solution. All non-H atoms of the 2-aza­niumyl-3-bromo-6-oxo-5,6-di­hydro­pyrido[1,2-a]quinoxalin-11-ium cation are nearly coplanar, the maximum deviation being 0.114 (4) Å. In the crystal, the cations and anions are linked through N—H⋯Br hydrogen bonds and weak C—H⋯Br inter­actions, forming a three-dimensional supra­molecular architecture. A short Br⋯Br contact [3.3088 (9) Å] is observed in the crystal.

Dichlorido[2-(3,5-dimethyl-1H-pyrazol-1-yl-κN)ethanamine-κN]zinc(II)

The amine title complex, [ZnCl₂(C₇H₁₃N₃)], resulted from imine hydrolysis in a Schiff base compound. The Zn metal atom has a distorted tetra­hedral geometry with the most significant deviation identified in the magnitude of the N—Zn—N angle. This deviation stems from the participation of the Zn and N atoms in a six-membered metallocyclic ring. The latter is in an approximate screw-boat conformation. Two strong N—H⋯Cl hydrogen bonds link the mol­ecules into ribbons propagating along the b-axis direction. The ribbons contain two second-order hydrogen-bonded motifs: a chain and a ring. The chain described by the graph set notation C₂²(6) is formed by one hydrogen bond going in the forward direction (donor to acceptor) and the other in the backward direction (acceptor to donor). In the ring motif R₂²(8), both hydrogen bonds propagate in the forward direction.