1,8-Diazabicyclo[5.4.0]undec-7-ene: A Highly Efficient Catalyst for One-Pot Synthesis of Substituted Tetrahydro-4H-chromenes, Tetrahydro[b] pyrans, Pyrano[d] pyrimidines, and 4H-Pyrans in Aqueous Medium

We have reported 1,8-diazabicyclo[5.4.0]undec-7-ene catalyzed one-pot synthesis of tetrahydro-4H-chromenes, tetrahydro[b]pyrans, pyrano[d]pyrimidines and 4H-pyrans from aldehydes, active methylene compounds malononitrile/ethyl cyanocacetate and activated C-H acids such as dimedone, 1,3-cyclohexanedione, 1,3-cyclopentanedione, 1,3-dimethylbarbituric acid, and ethyl acetoacetate in water under reflux. The attractive features of this process are mild reaction conditions, reusability of the reaction media, short reaction times, easy isolation of products, and excellent yields.