Catalytic Asymmetric Synthesis of Chromene Derivatives by Iminium Ion Catalysis

The diarylprolinol TMS ether catalyzed enantioselective addition-acetalization cascade reaction of 1,3-diketones with α,β-unsaturated aldehydes provides access to biologically active hydroxychromenone derivatives. These chromenones can be converted into the corresponding lactones, oxadecalinones, and benzopyranes in good yields without loss of enantiomeric excess. The usefulness of this newly developed methodology was demonstrated in the synthesis of the core structure of a Δ ⁹-tetrahydrocannabinol analog.