Cycloaddition of 3-Amino-5-chloro-2(1<i>H</i>)-pyrazinones and Olefins:  Ring Transformation into 3-Amino- or 6-Cyano-Substituted 2-Pyridinone Systems

Abstract

The cycloadducts formed from the Diels−Alder reaction of 3-amino-5-chloro-2(1 H )-pyrazinones with methyl acrylate in toluene are subject to two alternative modes of ring transformation yielding either methyl 6-cyano-1,2-dihydro-2-oxo-4-pyridinecarboxylates, e.g. 12a,b (loss of amine substituent), or the corresponding 3-amino-6-cyano-1,2,5,6-tetrahydro-2-oxo-4-pyridinecarboxylates, e.g. 15a,b . From the latter compounds, 3-amino-2-pyridinones can be generated through subsequent loss of HCN. A mechanism accounting for the loss or retention of the amine substituent is based on (1) the effects observed for each reaction mode when varying the substituents in both reaction partners and (2) the exclusive retention of the amine substituent when replacing toluene with the basic solvent pyridine.