Cooperative Palladium/Brønsted Acid Catalysis toward the Highly Enantioselective Allenylation of β-Keto Esters
作者:Henning J. Loui、Christoph Schneider
DOI:10.1021/acs.orglett.2c00179
日期:2022.2.25
We report the first enantioselective allenylation of Pd enolates enabled by cooperative Pd/Brønsted acid catalysis employing β-keto esters and propargyl alcohols. The enantioselectivity originates solely from an in-situ-generated chiral metal enolate in an open transition state with no additional binding of the propargyl component to the catalyst. Thus a broad substrate scope was established, furnishing
Palladium-Catalyzed Enantioselective Addition of Chiral Metal Enolates to In Situ Generated <i>ortho</i>
-Quinone Methides
作者:Fabian Göricke、Christoph Schneider
DOI:10.1002/anie.201809692
日期:2018.11.5
describe herein a conceptually novel, cooperative Brønsted acid/base catalyzed process for the conjugate addition of cyclic β‐keto esters to ortho‐quinone methides both generated in situ. Upon hemiacetalization, densely functionalizedchiral chromans with two adjacent quaternary and additionally a tertiary stereogenic center were obtained with very good diastereoselectivity (up to >95:5 d.r.) and typically
Delineating Origins of Stereocontrol in Asymmetric Pd-Catalyzed α-Hydroxylation of 1,3-Ketoesters
作者:Alexander M. R. Smith、Henry S. Rzepa、Andrew J. P. White、Denis Billen、King Kuok (Mimi) Hii
DOI:10.1021/jo1002906
日期:2010.5.7
Systematic studies of reaction conditions and subsequent optimization led to the identification of important parameters for stereoselectivity in the asymmetric alpha-hydroxylation reaction of 1,3-ketoesters. Enantioselectivities of up to 98% can be achieved for cyclic substrates and 88% for acyclic ketoesters. Subsequently, the combination of cyclic/acyclic ketoester, catalyst, and oxidant was found to have a profound effect on reaction rates and turnover-limiting steps. The stereochemistry of the reaction contradicts that observed for other similar electrophilic substitution reactions. This was rationalized by transition-state modeling, which revealed a number of cooperative weak interactions between oxidant, ligand, and counterion, together with C-H/pi interactions that cumulatively account for the unusual stereoselectivity.