Enantioselective Palladium‐Catalyzed Ring‐Opening Reaction of Azabenzonorbornadienes with Methyl 2‐Iodobenzoate: An Efficient Access to cis‐Dihydrobenzo[c]phenanthridinones

Abstract

AbstractThe palladium‐catalyzed asymmetric ring‐opening (ARO) reaction of azabenzonorbornadienes with iodobenzoate derivatives was realized by using chiral spirophosphine ligands with zinc powder as a reducing reagent. Various enantiomerically enriched cis‐dihydrobenzo[c]phenanthridinones, the core structure of numerous chiral natural products, were prepared by the ARO reaction and tandem amidation from easily obtained starting materials with favorable enantioselectivity (up to 86% ee) under mild reaction conditions. The present palladium‐catalyzed ARO reaction avoids the direct use of organometallic reagents, enables tandem cyclization, and thus improves synthetic efficiency. The formal total synthesis of a chiral natural product, (+)‐chelidonine, was accomplished with the ARO reaction as a key step, which demonstrates the potential synthetic applications of the present methodology.magnified image