A. Lichtblau et al., 1ST STRUCTURAL CHARACTERIZATION OF AN EASILY OXIDIZED DERIVATIVE OF 1,4-DIHYDROQUINOXALINE, Zeitschrift fur Naturforschung. B, A journal of chemical sciences, 48(6), 1993, pp. 713-718
The first crystal structure analysis of a 1,4-dihydroquinoxaline is de
scribed by example of the 1,4-bis(tert-butyldimethylsilyl) derivative.
In the solid state, this molecule exhibits a non-planar heterocycle w
ith a dihedral angle of 156.3-degrees along the N-N axis in the boat-s
haped 8 pi electron ring system. The alkyl groups of the Si(tert-Bu)Me
2 substituents are arranged as to minimize steric repulsion. Despite t
he reduced pi electron conjugation due to non-planarity, the compound
is oxidized reversibly to an EPR detectable radical cation at -0.59 V
vs. ferrocene in dichloromethane. However, the second oxidation to the
fully aromatic dication is electrochemically irreversible. A comparis
on with previously obtained results illustrates the structural flexibi
lity of the non-aromatic 1,4-dihydro-1,4-diazine ring system which is
strongly affected by rather weak non-bonded interactions.