Insights on the synthesis and organisational phenomena of twisted pyrazine-pyridine hybrids

Pyrazine-pyridine hybrids containing two different oligopyridyl chains, 2,3-disubstituted onto the pyrazine ring nucleus are prepared from appropriate mixed alpha-diketone precursors. The latter were obtained by epoxidation of the enols of corresponding 1,2-disubstituted ethanones. The structures of the pyrazine derivatives were investigated by detailed proton NMR spectroscopic and X-ray crystallographic methods. These indicated a twisting of the oligopyridyl chains about one another to result in a pre-double helical topology. This phenomenon occurred up to two pyridin-2,6-diyl groupings from the pyrazine ring and is accompanied by edge-on-face stacking of spatially proximate pyridyl rings. Parallel stacking of pyrazine and weak C-H ... N acid interactions are significant in their crystal lattices and may also figure in their metallosupramolecular self-assembly behaviour patterns.