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Methoxymethylene Meldrum's acid 2 in acetonitrile solution acts as a useful C-electrophile for active substrates such as pyrrole, indole or tertiary enaminones to give substitution products (e.g. 5, 6 or 12, respectively). Primary enaminones react exclusively at the nitrogen atom under these conditions. The effect of ring substituents on the regiochemistry of electrophilic substitution of 3hydroxypyrroles and 3-methoxypyrroles was studied using methoxymethylene Meldrum's acid as the electrophile. Flash vacuum pyrolysis of the Meldrum's acid derivatives obtained in many of these reactions gave access to a range of heterocyclic systems, including the pyridone 48, quinolinedione 43, benzazepinedione 41 and fused pyrones 50,52 and 54.

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Photolysis of the azepinone (2) gives the bicyclic photoproduct (5) in 64% yield; this compound reverts cleanly t o the starting material (2) on thermolysis in toluene. Cycloaddition reactions of the azepinones (1) or (2) with maleic anhydride generate the endo adducts ( 7) or (8), respectively, whereas treatment of (1) with acetylenic dienophiles gives rise t o bentenoid compounds after cleavage of the three-atom bridge.