2(1H)-Pyrazinones bearing a X-(o-C6H4)-C=C-R moiety (X=NH, NAc) are shown to undergo an intramolecular cycloaddition-elimination reaction on thermolysis in refluxing bromobenzene yielding alpha-caarbolines or beta-carbolinones. The product distribution depends strongly on the substitution pattern of the pyrazinone precursors and the solvent used for thermolysis. A high yield and selective formation of beta-carbolinones is possible when heating in tetrahydronaphthalene at reflux. Use of acetic anhydride as solvent facilitated the reaction and made it possible to realise a carbolin(on)e unaccessible by thermolysis in the previously mentioned solvents. (C) 1998 Elsevier Science Ltd. All rights reserved.