106. Enantioselective CpRu-Catalyzed Carroll Rearrangement. Metal Source Importance and Ligand Optimization
     David Linder, Frédéric Buron, Samuel Constant, Jérôme Lacour
     Eur. J. Org. Chem. 2008, 5778-5785

The addition of unstabilized carbonyl nucleophiles to unsymmetrical allyl-metal fragments still represents a challenge to generate stereogenic centers enantio- and regioselectively. In this context, the decarboxylative Carroll rearrangement of allyl β-keto esters is particularly interesting, since chiral γ,δ-unsaturated ketones are obtained. Herein, we show that CpRu half-sandwich complexes can, with selected enantiopure pyridine-monooxazoline ligands, catalyze this transformation and afford complete conversions along with good levels of regioselectivity and enantioselectivity. Even more challenging (electron-poor) substrates react (up to 86 % ee, branched/linear ratio ≥ 97:03). In addition, the use of an air-stable metal precursor, namely [CpRu(η⁶-naphthalene)][PF₆], allows the reaction to be carried out reproducibly evenin non-anhydrous THF with a catalyst loading as low as 2 mol-%.

DOI : 10.1002/ejoc.200800854 

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