Enantioselective Palladium-Catalyzed Ring-Opening Reaction of Azabenzonorbornadienes with Methyl 2-Iodobenzoate: An Efficient Access to<i>cis</i>-Dihydrobenzo[<i>c</i>]phenanthridinones
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
Concise Enantioselective Total Syntheses of (+)-Homochelidonine, (+)-Chelamidine, (+)-Chelidonine, (+)-Chelamine and (+)-Norchelidonine by a PdII-Catalyzed Ring-Opening Strategy
作者:Matthew J. Fleming、Helen A. McManus、Alena Rudolph、Walter H. Chan、Jérémy Ruiz、Chris Dockendorff、Mark Lautens
DOI:10.1002/chem.200701775
日期:2008.2.27
II-catalyzed asymmetric ring-opening reaction of a meso-azabicyclic alkene with an aryl boronic acid as the key step. By screening a variety of functionalized ortho-substituted aryl boronic acids, chiral ligands and reaction conditions we were able to prepare the requisite cis-1-amino-2-aryldihydronaphthalenes in high yield and in up to 90 % ee. Early attempts to complete the synthesis of (+)-homochelidonine