The reactions of a series of substituted 2(1 H)-pyridones with dimethyl butynedioate have been studied. Cycloadditions across the 3,6-positions can be observed in certain instances and are particularly favoured where steric buttressing occurs between the substituent groups of the starting pyridones. The pyridone could not be induced to react with simple olefins, either by intermolecular or, via incorporation of alkenyl substituents, by intramolecular processes. From the results it is shown that 2-pyridones can be encouraged to behave as reactive classical dienes in cycloaddition reactions.2( ~H)-PYRIL)oNEs have long attracted chemical attention for their hetero-aromatic character.l Studies, on their ability to sustain an induced ring current, led to estimates that they should possess only ca. 35% of the aromaticity of benzene, implying that the conjugated system should act as a diene in Diels-Alder type cycloaddition reactions2 An X-ray crystallographic study on 1-methyl-2-pyridone (1) supports this view, in that it is shown to contain carbon-carbon bonds which are alternately long and short.3 However, early attempts to illustrate such reactivity failed, partly owing to competing nucleophilic addition of the amide group to the dien~phile.~. Thus, ethoxyacetylene produces a mix-

Die Pyridone (I) reagieren mit Acetylendicarbon‐ säuredimethylester bei 80°C unter Bildung der Addukte (II), die bei höherer Temp. in die entsprechenden Phthalsäureester (III) und das Isocyanat (IV) gespalten werden [die Phthalate (III) werden direkt aus den Pyridonen und dem Dienophil unter Thermolysebedingungen ohne Lösungsmittel erhalten].

Szlrnv~zaryThe addition of dimethyl butynedioate to a PREVIOUS reports on cycloadditions involving 2( 1H)pyridones have emphasised the vigorous conditions requ ired for reaction and the low yields of cycloadducts generally 0bserved.l Herein are described some recent results in this variety of 2(1H)-pyridones is reported and the effect of the different substituents discussed.

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