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DOI: 10.1055/s-2008-1078635
Enantioselective Iridium-Catalyzed Carbonyl Allylations with Allyl Acetate
Contributor(s):Mark Lautens, Praew ThansandotePublication History
Publication Date:
22 August 2008 (online)
Key words
iridium - enantioselective carbonyl allylation - allyl acetate
Significance
An alternative procedure for carbonyl allylation (C-allylation), that avoids the use of preformed allyl metal reagents, is presented using an iridium catalyst and phosphine ligand. C-Allylation of alcohols or aldehydes can be accomplished in good yields and excellent enantioselectivities for a broad scope of substrates. Carbonyl crotylation of alcohols can also be achieved, although with currently low diastereoselectivities. A drawback of the methodology is that it currently requires a large excess of allyl acetate with respect to the alcohol or aldehyde.
Comment
Allylic substitution through the oxygen of the alcohol (O-allylation) is also a known mode of reactivity. However, low-valent Ir(I) complexes with less acidic phosphine ligands are more nucleophilic and therefore less prone to a nucleophilic attack from an alcohol in an O-allylation. For instance, using the π-acidic phosphoramidite ligands under the standard conditions gave mixtures of O- and C-allylation products in low yield. For a related reaction see: F. Shibahara, J. F. Bower, M. J. Krische J. Am. Chem. Soc. 2008, 130, 6338.