3-HYDROXYPYRROLES AND 1H-PYRROL-3(2H)-ONES .13. REACTIONS OF METHOXYMETHYLENE MELDRUM ACID WITH 3-HYDROXYPYRROLES, WITH 3-METHOXYPYRROLES AND WITH OTHER ACTIVE SUBSTRATES, AND PYROLYTIC HETEROCYCLIZATIONS OF THE PRODUCTS

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 3-hydroxypyrroles 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.