1ST STRUCTURAL CHARACTERIZATION OF AN EASILY OXIDIZED DERIVATIVE OF 1,4-DIHYDROQUINOXALINE

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.