Cooperative Catalysis for the Highly Diastereo‐ and Enantioselective [4+3]‐Cycloannulation of ortho‐Quinone Methides and Carbonyl Ylides

We describe herein a highly diastereo‐ and enantioselective [4+3]‐cycloannulation of ortho‐quinone methides and carbonyl ylides to furnish functionalized oxa‐bridged dibenzooxacines with excellent yields and stereoselectivity in a single synthetic step. The combination of rhodium and chiral phosphoric acid catalysis working in concert to generate both transient intermediates in situ provides direct access to complex bicyclic products with two quaternary and one tertiary stereogenic centers. The products may be further functionalized into valuable and enantiomerically highly enriched building blocks. It takes two: A combination of Rh2(OAc)4 and a chiral phosphoric acid catalyzes the in situ generation of transient carbonyl ylides and chiral hydrogen‐bonded ortho‐quinone methides through cooperative catalytic cycles. These transient species then undergo a highly diastereo‐ and enantioselective cycloannulation to afford a broad range of functionalized oxa‐bridged dibenzooxacines featuring two quaternary and one tertiary stereogenic centers.