Diastereo- and Enantioselective Iridium-Catalyzed Allylation of Ketone Enolates

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.