The palladium catalysed coupling of aryldiazonium salts with beta-gamma-unsaturated lactones under basic conditions has been investigated. Both (3H)-furanone and alpha-angelicalactone were evaluated as substrates in the Fleck Matsuda reaction but both failed to afford the desired arylated butenolides. Under basic conditions, beta-gamma-unsaturated lactones generate highly nucleophilic enolates that preferentially undergo azo coupling reactions with arenediazonium salts to afford aryldiazene butenolides. The electronic and steric effect of the substituents on the aryldiazonium salt in the azo coupling reaction is described. Aryldiazene-lactone derivatives were obtained in good yields from a highly facile and straightforward procedure. An aminoisomaleimide was formed from (3H)-furanone and cyclised to the corresponding pyridazinones in modest yield.331020702074