Chemistry of thienopyridines. XXIII. Mass spectra of some N-oxides,sulfoxides, and sulfones

The mass spectral fragmentation patterns of a series of thienopyridine N-oxides, S-oxides, and S,S-dioxides were elaborated as a means of structural determination. Observation of a significant (M-16) peak is diagnostic for the presence of either an N-oxide or an S-oxide function (indistinguishable from one another by this method) but does not occur for an S,S-dioxide function. For a substituted thieno2,3-b]pyridine 7-oxide, structural rearrangement to a pyridone (followed by emission of carbon monoxide or formyl radical) or side-chain fission may be competitive with de-N-oxygenation. For two tricyclic parent S-oxides, rearrangement and de-S-oxygenation are competing initial processes. For parent S,S-dioxides structural rearrangement precedes fragmentation, wherein the oxygen is ejected in such forms as sulfur monoxide, carbon monoxide, formyl or cyanate radicals, and ketene.