Organocatalytic Enantioselective Tandem Michael Addition and Cyclization Reaction of Trisubstituted 2-Nitro-1,3-enynes with Cyclic 1,3-Diketones

An enantioselective tandem Michael addition/ cyclization reaction between trisubstituted 2-nitro-1,3-enynes and cyclic 1,3-diketones catalyzed by a chiral organosquaramide catalyst in the presence of Ag2CO3 was developed. The chiral functionalized chromene products could be obtained in good yield and in 80-99% enantiomeric excess. The structures and absolute configurations of some of the products were confirmed by X-ray crystallographic analysis.