Michael reaction of methylenemalonaldehydes: Synthetic approach to 4H-pyran-5-carboxaldehydes and 2-amino-4H-pyran-5-carboxaldehydes

Base-catalyzed addition of β-dicarbonyl compounds to methylenemalonaldehydes led to tetracarbonyl compounds II which were dehydrated in an acid medium to 4H-pyran-5-carboxaldehydes III. In the addition of compounds containing a nitrile group, the primarily formed addition products were immediately cyclized to give directly 2-amino-4H-pyran-5-carboxaldehydes V.