Enantioselective Synthesis of Tricyclic β-Lactones by NHC-Catalyzed Desymmetrization of Cyclic 1,3-Diketones.

The NHC-catalyzed desymmetrization of cyclic-1,3-diketones allowing the enantioselective construction of tricyclic β-lactones with five contiguous stereocenters, including two quaternary stereocenters, has been developed. The mild and operationally simple addition of α-bromoenals to cyclopentane-1,3-diketone derivatives proceeds via the initial formation of chiral α,β-unsaturated acylazolium intermediates and culminates in a cascade reaction, following the Michael-aldol-lactonization pathway to deliver the β-lactone derivatives in moderate to good yields and excellent selectivity.