Palladium-Catalyzed Enantioselective Three-Component Dearomative Coupling of Bromoarenes: Modular Construction of Terpenoid Scaffolds

Abstract

We report a palladium-catalyzed asymmetric three-component coupling of bromoarenes, diazoalkanes, and malonates. It represents a significant advancement in catalytic enantioselective dearomative 1,4-difunctionalization of unactivated arenes. A palladium catalyst of a novel phosphoramidite enables a domino reaction consisting of enantiofacial aryl insertion of a bound diazoalkane and regioselective and stereospecific allylic substitution. The new reaction was readily applied in short total syntheses of three terpenoids, including (+)-erogorgiaene, (-)-7-hydroxy-3,4-dihydrocadalin, and (-)-odongrossin C. Mechanistic studies establish that stereocontrol arises from a concerted aryl migration/N₂ extrusion, which forms the key cyclic π-allyl palladium intermediate. The C4-regioselectivity of the malonate attack is governed by a combination of ligand effects, silyl group sterics, and stabilizing noncovalent interactions between the naphthyl ring and sodium malonate.

Keywords: Catalytic asymmetric dearomatization; Diazo compound; Difunctionalization; Palladium catalysis; Terpenoids.