Abstract
A bicyclo[4.1.0]heptane framework consisting of cis-fused cyclopropane and cyclohexane rings is found in several bioactive compounds.
Given the symmetry of this core, catalytic desymmetrization can be considered as the
most straightforward strategy for its enantioselective synthesis. Known desymmetrization
reactions of meso-bicyclo[4.1.0]heptane derivatives proceed with opening of the cyclopropane ring.
We now report the first ring-retentive desymmetrization of bicyclo[4.1.0]heptane derivatives,
namely meso-cyclopropane-fused cyclohexene-1,4-diones, through a formal C(sp2)-H alkylation using a nitroalkane as the alkylating agent. This reaction is catalyzed
by a dihydroquinine-derived bifunctional tertiary aminosquaramide and generates the
products with up to 97:3 er. An application of this reaction is demonstrated by the
first catalytic enantioselective synthesis of the natural product (–)-car-3-ene-2,5-dione.
Key words
organocatalysis - desymmetrization - cyclopropanes - bicycloheptanes - fused ring
systems