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

Abstract

Quinoxalines are heterocyclic compounds with potential application as drugs or fluorophores. However, few quinoxalinylium salts have been reported in the literature. This manuscript describes the synthesis and structural characterization of a previously unknown quinoxalinylium derivative, 2-aminopyrido[1,2-a]quinoxalin-11-ylium ([1](+)), as perchlorate and thiocyanate salts from the Cu(II)-mediated reaction of a Schiff base. The reaction is most efficient with Cu(II). The formation of a small quantity was observed spectroscopically in the presence of either a strong oxidizer or Mn (II). No product formation was observed with Zn(II), Cd(II), Fe(II), or Ni(II). [1](+) emits at 580 nm, with a quantum yield estimated as 0.23, upon excitation at 470 nm.

Crystal structure of 2-amino-1,3-dibromo-6-oxo-5,6-dihydropyrido[1,2-a]quinoxalin-11-ium bromide monohydrate

“…There are very few examples of similar compounds in the literature, a search of the Cambridge Structural Database (Version 5.35, May 2014; Groom & Allen, 2014) revealing the structure of 2-azaniumyl-3-bromo-6-oxo-5,6-dihydropyrido-[1,2-a]quinoxalin-11-ium dibromide (Faizi et al, 2015), in which the 2-amino-1,2-dibromide ring in the title compound is replaced by a 2-azaniumyl-3-bromo ring. Other similar structures have been reported (Faizi & Sen, 2014;Koner et al, 2008).…”

“…A shorter C10-N3 distance of 1.367 (9) Å , compared to the usual aromatic C-N amine single bond distance of 1.43 (3) Å , might be due to the electronwithdrawing effect of the positively charged pyridine N atom, and the ortho-substituted bromine atom which decreases the C-N amine bond order. Other C-C and C-N bond distances are well within the limits expected for aromatic rings (Koner & Ray, 2008;Kanderal et al, 2005;Fritsky et al, 2006). Present also in the cations are intramolecular N3-HÁ Á ÁBr1 and N3-HÁ Á ÁBr2 interactions [3.048 (7), 3.006 (7) Å , respectively, Table 1].…”

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

“…For applications of quinoxalines, see: Duffy et al (2002); Gazit et al (1996); Harmenberg et al (1991); Naylor et al (1993). For types of quinoxalines and a structure similar to title compound, see: Eiden & Peter (1966); Koner & Ray (2008); Fritsky et al (2006); Kanderal et al (2005); Moroz et al (2012). For background to and applications of related compounds, see: Faizi & Sen (2014); Symmetry codes: (i) Àx þ 1; Ày; Àz þ 1; (ii) x þ 1; Ày þ 1 2 ; z À 1 2 ; (iii) x; Ày þ 1 2 ; z À 1 2 ; (iv) Àx þ 2; y þ 1 2 ; Àz þ 3 2 ; (v) x þ 1; Ày þ 1 2 ; z þ 1 2 .…”

Dichlorido[2-(3,5-dimethyl-1H-pyrazol-1-yl-κN2)ethanamine-κN]zinc(II)

“…For imine hydrolysis in Schiff base compounds, see: ; Czaun et al (2010); Bu et al (1997); Koner & Ray (2008); Sinha et al (2003). For graph-set analysis, see: Bernstein et al (1995).…”

“…Imine hydrolysis in Schiff base compounds is quite common. It is usually driven by traces of water and the presence of acidic metal ions, especially in the case of the first row transition metal chlorides such as Co II (Guzei et al, 2010), Ni II (Czaun et al, 2010) and Cu II (Bu et al, 1997;Czaun et al, 2010;Koner & Ray, 2008;Sinha et al, 2003). In a recent attempt to prepare a Zn II complex from the reaction of 2-{[2-(3,5-dimethylpyrazol-1-yl)ethylimino]}-4,6-ditertbutylphenol with zinc(II) chloride, we isolated the title compound (I), a hydrolysis product of the imine to an amine.…”