Enaminones in heterocyclic synthesis: A novel route to tetrahydropyrimidines, dihydropyridines, triacylbenzenes and naphthofurans under microwave irradiation

Abstract

Condensation of phthalimidoacetone (1) with DMFDMA (N,NDimethylformamide dimethyl acetal) has afforded enaminone 2. Refluxing 2 with equimolecular amounts of benzaldehyde and urea in acetic acid afforded a mixture of tetrahydropyrimidine 5 and the dihydropyridine 6. Compound 2 undergoes selfcondensation on heating in acetic acid or under microwave irradiation in presence of acidic zeolite to give 1,3,5-triacylbenzene 9. Reacting enaminone 11a with naphthoquinone 15 afforded the naphthofuran 18. The possible formation of the aldehyde 19 was excluded based on an HMQC experiment, which revealed that the carbonyl carbon is not linked to any hydrogen.