Research Article

Enantio- and Diastereodivergent Dual Catalysis: α-Allylation of Branched Aldehydes

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Science  31 May 2013:
Vol. 340, Issue 6136, pp. 1065-1068
DOI: 10.1126/science.1237068

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Independent Chiral Catalysts

Synthetic catalysts can be prepared in their mirror-image form and thereby furnish the mirror-image (enantiomer) of the reaction product. In practice, however, this versatility is largely limited to products featuring a single stereocenter that accounts for the dissymmetry. Krautwald et al. (p. 1065; see the Perspective by Schindler and Jacobsen) now report a pair of chiral catalysts—an iridium complex and an amine—that operate in concert to facilitate carbon-carbon bond formation, while retaining independent stereoselectivity toward their respective sides of the bond.

Abstract

An important challenge in asymmetric synthesis is the development of fully stereodivergent strategies to access the full complement of stereoisomers of products bearing multiple stereocenters. In the ideal case, where four products are possible, applying distinct catalysts to the same set of starting materials under identical conditions would in a single step afford any given stereoisomer. Herein, we describe the realization of this concept in a fully stereodivergent dual-catalytic synthesis of γ,δ-unsaturated aldehydes bearing vicinal quaternary/tertiary stereogenic centers. The reaction is enabled by chiral iridium and amine catalysts, which activate the allylic alcohol and aldehyde substrates, respectively. Each catalyst exerts high local stereocontrol irrespective of the other's inherent preference.

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