Enantioselective Synthesis of Chromanones through Organocatalytic Tandem Reactions

An enantioselective approach to lactone-fused chromanone derivatives from 1-(2-hydroxyaryl)-1,3-diketones and alpha,beta-unsaturated aldehydes under mild conditions has been developed, which included organocatalytic stepwise Michael addition/ cycloketalization/hemiacetalization and followed by oxidation reaction. In the presence of chiral amine organocatalyst and an additional salicylic acid, a wide range of 1-(2-hydroxyaryl)-1,3-diketones and alpha,beta-unsaturated aldehydes were tolerated, furnishing a spectrum of lactone-fused tricyclic chromanones bearing three contiguous stereocenters in high yields with good to excellent selectivities (90->99% ee, >19:1 d.r.).