Mass spectral studies on mesoionic imidazo [1,2‐a] pyrid‐2 and ‐3‐one derivatives

The mass spectral fragmentation patterns for 1‐substituted derivatives of anhydro (3‐chloroacetyl‐2‐hydroxyimidazo[1,2‐a]pyridinium hydroxide) (Ia to Ie) and 2‐acyl substituted derivatives of anhydro(1‐benzyl‐3‐hydroxyimidazo[1,2‐a]pyridinium hydroxide) (IIa and IIb) are reported. In all cases the mass spectra may be interpreted on the basis of initial cleavage of the ‘carbonyl‐heteroatom’ bond of the mesoionic system, followed by fragmentation.