Catalytic Asymmetric Syntheses of Quinolizidines by Dirhodium-Catalyzed Dearomatization of Isoquinolinium/Pyridinium Methyl ides-The Role of Catalyst and Carbene Source

摘要

Convenient access to highly enantioenriched substituted quinolizidines has been achieved by chiral dirhodium(Ⅱ) carboxylate-catalyzed dearomatizing formal [3 + 3]-cycloaddition of isoquinolinium/pyridinium methylides and enol diazoacetates. Coordination of Lewis basic methylides to dirhodium(Ⅱ) prompts the rearrangement of the enol-carbene that is bound to dirhodium to produce' a donor-acceptor cyclopropene. The donor-acceptor cyclo-propene is in equilibrium with the dirhodium-bound enol- carbene and undergoes both enantioselective [3 + 3]-cycloaddition from the dirhodium-bound enol-carbene and diastereoselective [3 + 2]-cycloaddition by uncatalyzed reaction of the cyclopropene with isoquinolinium or pyridinium methylides. Increasing the mol % of catalyst loading suppresses the [3 + 2]-cydoaddition pathway.