Chen W, Chen M, Hartwig JF * University of California, Berkeley, USA
Diastereo- and Enantioselective Iridium-Catalyzed Allylation of Cyclic Ketone Enolates:
Synergistic Effect of Ligands and Barium Enolates.
J. Am. Chem. Soc. 2014;
136: 15825-15828
Key words
iridium - phosphoramidites - asymmetric allylic alkylation - barium enolates
Significance
The transition-metal-catalyzed asymmetric allylic alkylation (AAA) reaction is a versatile
and powerful method for the construction of C–C bonds. Although palladium catalysts
are routinely used in this reaction, iridium catalysts have been shown to have complementary
and comparable reactivity to palladium (see Review below). Within this area of research,
the diastereo- and enantioselective allylic alkylation of unstabilized ketone enolates
remains a significant challenge. Herein, Hartwig and co-workers report a diastereo-
and enantioselective iridium-catalyzed allylation of barium enolates derived from
cyclic ketones.
Comment
The branched-selective allylic alkylation method developed by the authors provides
access to products containing a vicinal quaternary and a tertiary stereogenic center
– a difficult class of molecules to access using traditional Pd-catalyzed methods.
The method is highly efficient and demonstrates a broad substrate scope. The authors
show that good levels of diastereoselectivity can be achieved in this reaction simply
through the facial selectivity of the prochiral barium enolate without necessitating
coordination of the enolate directly to the metal center.
Review
J. F. Hartwig, L. M. Stanley Acc. Chem. Res.
2010, 43, 1461–1475.
