Enantioselective CpRu‐Catalyzed Carroll Rearrangement – Ligand and Metal Source Importance

• Published in: European Journal of Organic Chemistry Vol. 2008; no. 34; pp. 5778 - 5785
• Main Authors: Linder, David, Buron, Frédéric, Constant, Samuel, Lacour, Jérôme
• Format: Book Review Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag 01-12-2008
• Subjects: Air‐stable precatalyst; Allylic compounds; C–C coupling; Enantioselective catalysis; N ligands; Ruthenium
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.200800854

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 as2 mol‐%. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
A combination of [CpRu(η6‐naphthalene)][PF6] and enantiopure pyridine‐mono‐oxazoline ligands catalyze the regio‐ and enantioselective decarboxylative Carroll rearrangement of allyl β‐keto esters into γ,δ‐unsaturated ketones.