Mass spectra of α,β‐substituted butenolides

The mass spectra of twenty‐six β‐ and α,β‐substituted butenolides have been examined. Fragmentation of the butenolide ring can be rationalised on the basis of the fragmentation pathways described for β‐hydroxybutenolides. However, a number of butenolides, e.g. the α‐(substituted)benzamido‐β‐hydroxymethyl‐butenolides, show a weak fragmentation of the ring. The fragmentations in which the substituents are involved are more favourable and interactions between the substituents on the α‐ and β‐positions complicate these spectra.