Assembly of the Tricyclic Core of Alopecurone C by Asymmetric Donor/Donor Carbene C–H Insertion

Two routes to assemble the complete tricyclic core of alopecurone C are described. In the first-generation route, an efficient synthesis of the "eastern" half of the target, including a decagram-scale rhodium-catalyzed C-H insertion reaction, was developed. When this route proved intractable for assembling the final flavanone ring, a successful second-generation route was developed from a flavanone precursor (naringenin) employing a later stage C-H insertion. Although the second route was ultimately unsuccessful for preparation of the final target, it does provide the basis for the efficient assembly of the complete tricyclic core of alopecurone C and related flavonostilbenoid natural products.