Microwave-assisted novel synthesis and structural confirmation of Pyrido[1,2-a]pyrazin-5-ium (N-Oxide) Salts

Pyrido[1,2-a]pyrazin-5-ium (2-oxide) salts are an interesting class of compounds that contain unique moieties: a bridgehead quaternary nitrogen, an amino group, and an N-oxide functionality. These compounds were efficiently constructed in a one-pot reaction within minutes, yielding good yields. The microwave-assisted reaction of 2-pyridinecarboxaldehyde oxime with bromoacetonitrile yields these unique structures. The compounds were characterized, and their structures confirmed, by single-crystal XRD, NMR, FTIR, and other spectroscopic techniques. ¹H-¹⁵N HMQC for directly bonded ¹H to N clearly shows the presence of an amino group in both compounds. These compounds crystallize in the triclinic p-1 and Cc space groups, revealing the presence of several intermolecular interactions.