Assembly of\nthe Tricyclic Core of Alopecurone C by\nAsymmetric Donor/Donor Carbene C–H Insertion

Two routes to assemble the complete tricyclic core of\nalopecurone\nC are described. In the first-generation route, an efficient synthesis\nof the “eastern” half of the target, including a decagram-scale\nrhodium-catalyzed C–H insertion reaction, was developed. When\nthis route proved intractable for assembling the final flavanone ring,\na successful second-generation route was developed from a flavanone\nprecursor (naringenin) employing a later stage C–H insertion.\nAlthough the second route was ultimately unsuccessful for preparation\nof the final target, it does provide the basis for the efficient assembly\nof the complete tricyclic core of alopecurone C and related flavonostilbenoid\nnatural products.