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

Abstract

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

Lewis acid/CpRu dual catalysis in the enantioselective decarboxylative allylation of ketone enolates

“…As expected, these compounds reacted at 25 • C under the new set of conditions to afford the branched regioisomer with excellent regioselectivity and ee values of 83 and 82% for 4c and 4d, results better than those at 60 • C (ee 77% in both cases). 9 In the case of substrate 3e similar results to 3b were, not too surprisingly, obtained due to their structural similarities (entry 3). 9…”

“…[CpRu(h 6 -C 10 H 8 )][PF 6 ] 1) 8 and chiral diimine ligands 7f,g were shown to catalyze this type of reaction with high selectivities, but with somewhat unsatisfactory reactivity; pyridine mono-oxazolines of type 2 (Table 1) being nevertheless better ligands than pyridine imines. 9 It is this lack of reactivity that we decided to tackle. Mechanistically, it is considered that, for CpRu allyl complexes, the ionization of the substrate to form a p-allyl metal complex, separated from the b-ketocarboxylate moiety, is the rate-determining step (Scheme 1, grey external cycle).…”

(Cyclopentadienyl)ruthenium‐Catalyzed Regio‐ and Enantioselective Decarboxylative Allylic Etherification of Allyl Aryl and Alkyl Carbonates

“…[18b,26] In the context of allylation reactions, this complex has been shown to be an effective catalyst for the related enantioselective Carroll rearrangement. [27] However, in this case, we quickly found out that it was necessary to add 30 mol% of acetonitrile to the reaction mixture prior to the addition of the substrates. This provided a homogeneous solution for the whole duration of the catalysis and assured high reproducibility, something that was difficult to achieve without the Lewis basic additive.…”

Preparation and Structural Characterization of [CpRu(1,10‐phenanthroline)(CH3CN)][X] and Precursor Complexes (X=PF6, BArF, TRISPHAT‐N)

“…Of importance for the current study, combinations of [CpRu] and nitrogen‐based ligands [1,3,13,14] such as diimines [15–26] were also found to catalyze original processes [7,27,28] . For example, [CpRu(CH 3 CN) 3 ][PF 6 ] and pyridine‐imine/pyridine‐oxazoline ligands are effective catalysts in enantioselective decarboxylative rearrangements of allylic β‐ketoesters and carbonates [26,29–32] . Kitamura successfully applied enantiopure dipyrroloimidazole ligands and [CpRu] in enantioselective dehydrative C‐, N‐, and O‐allylation [14,33,34] .…”

“…[7,27,28] For example, [CpRu(CH 3 CN) 3 ][PF 6 ] and pyridine-imine/pyridine-oxazoline ligands are effective catalysts in enantioselective decarboxylative rearrangements of allylic β-ketoesters and carbonates. [26,[29][30][31][32] Kitamura successfully applied enantiopure dipyrroloimidazole ligands and [CpRu] in enantioselective dehydrative C-, N-, and Oallylation. [14,33,34] CpRu(bipyridine) complexes were shown to be active catalysts for both deoxygenation of 1,2-hexanediol and glycerol [35] and hydrogenation of ketone in acidic conditions.…”