Organocatalytic asymmetric conjugate addition of malonates to 3-nitro-2H-chromenes

The conjugate addition of malonates to 3-nitro-2H-chromenes has been studied in the presence of a number of chiral organocatalysts. A bifunctional thiourea-tertiary amine was found to be an efficient catalyst for the reaction. Good yields and enantioselectivities were obtained for a variety of substituted 3-nitro-2H-chromenes. Diethyl malonate and diisopropyl malonate were applicable for the reaction with lower yields and similar enantioselectivities. 1,3-Diphenylpropane-1,3-dione also provided the corresponding product, however with a low yield and enantioselectivity.