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DOI: 10.1055/s-0030-1258795
Ruthenium-Catalyzed Asymmetric Claisen Rearrangement
Contributor(s):Mark Lautens, Jane PanteleevUniversity of Pittsburgh, USA
Catalytic Asymmetric Claisen Rearrangement of Unactivated Allyl Vinyl Ethers
J. Am. Chem. Soc. 2010, 132: 11875-11877
Publication History
Publication Date:
21 October 2010 (online)
Key words
Claisen rearrangement - allyl vinyl ethers - ruthenium
Significance
While considerable effort is invested into the development of asymmetric Claisen rearrangements, examples of reactions leading to products bearing vicinal stereocenters remain uncommon. The authors disclose a ruthenium-catalyzed Claisen rearrangement of E-substituted allyl vinyl ethers to yield products with two stereocenters in high yields and enantioselectivities. A variety of aryl substituents are tolerated at the allyl side chain, but aliphatic substituents give the undesired [1,3]-regioisomer.
Comment
The metal-catalyzed rearrangement is proposed to go through a C-O bond cleavage to give an allyl metal species, which is subsequently recombined with the enolate. In contrast to the concerted process, this mechanism introduces regio- and diastereoselectivity issues. The authors find that addition of a Lewis acid [B(OPh)3] is essential for high yields, presumably because it facilitates the initial oxidative addition. Furthermore, the alcohol in the ligand is proposed to participate in this step by H-bonding to the oxygen in 1. Addition of acetonitrile further improves the reactivity, potentially by reducing product inhibition. Notably, subjecting substrates with Z-alkenes yields the opposite diastereomer, albeit in lower dr.