An asymmetric organocatalytic cascade reaction between cyclopentane-1,2-diones and alkylidene malononitriles affords highly substituted 4H-pyrans in moderate to high enantiomeric excess. The selective reduction of a bridged double bond leads to the formation of cis-substituted cyclopentanone with three contiguous stereogenic centres.
Key words
organocatalysis - asymmetric catalysis - diketone - pyran - cascade reaction