American Chemical Society
ja406482q_si_001.pdf (7 MB)

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

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journal contribution
posted on 2013-08-21, 00:00 authored by Xichen Xu, Peter Y. Zavalij, Michael P. Doyle
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 cyclopropene 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]-cycloaddition pathway.