Ebe Y, Nishimura T * Kyoto University, Japan
Iridium-Catalyzed Annulation of Salicylimines with 1,3-Dienes.
J. Am. Chem. Soc. 2014;
136: 9284-9287
Key words
iridium - diene ligands - salicylimines
Significance
Enantiomerically enriched 4-aminochromanes are a structurally unique and biologically
important class of molecules. In this report the authors describe a novel annulation
reaction of salicylimines with 1,3-dienes in the presence of an iridium catalyst.
Utilizing a chiral diene ligand led to a highly enantioselective process.
Comment
Although the authors do not provide an explanation, a completely different set of
conditions for the achiral examples was used (NaOAc as base, toluene as solvent, 80
°C instead of 20 °C and cyclooctene as achiral ligand). The proposed catalytic cycle
includes the formation of a six-membered ring where the iridium center is coordinated
to both oxygen and nitrogen. After oxidative cyclization and reductive elimination,
the nitrogen–iridium bond is protonated to release the product and regenerate the
catalyst.
