Cobalt(II)-Catalyzed Enantioselective Propargyl Claisen Rearrangement: Access to Allenyl-Substituted Quaternary β-Ketoesters

Abstract

Highly enantioselective propargyl Claisen rearrangement of O-propargyl β-ketoesters was achieved under 2.5 mol % of the chiral cobalt complex as the catalyst under mild reaction conditions. With Co(OTf) 2 as the Lewis acid and C 1 -symmetric imidazoline-pyrroloimidazolone pyridine as the ligand, diverse chiral allenyl-substituted all-carbon quaternary β-ketoesters were obtained in good yields (up to 97% yield) and high enantioselectivities (up to 98% ee).

Reversal of enantioselectivity in cobalt(ii)-catalyzed asymmetric Michael–alkylation reactions: synthesis of spiro-cyclopropane-oxindoles

“…Based on the above experimental results and references, 13,14 the Co(acac) 2 -PyIPI-catalyzed Michael–alkylation reaction mechanism was explored using the density functional theory (DFT), and a preliminary stereochemical model was proposed (Fig. 4).…”

“…In 2023, inspired by Uozumi 11 and Arai, 12 we developed and used tridentate imidazolidine-pyrroloimidazolone pyridine (PyIPI) as the chiral ligand for asymmetric dearomative [3 + 2] annulation and propargyl Claisen rearrangement. 13 While developing asymmetric catalysis promoted by a PyIPI-metal complex, herein, we report the asymmetric Michael–alkylation reaction of 3-chlorooxindoles with β,γ-unsaturated-α-ketoesters, which could be applied for the synthesis of chiral spiro-cyclopropane-oxindoles with three contiguous stereocenters with reversed enantioselectivity (Scheme 2b).…”