Bifunctional Ammonium Salt Catalyzed Asymmetric α-Hydroxylation of β-Ketoesters by Simultaneous Resolution of Oxaziridines
作者:Johanna Novacek、Joseph A. Izzo、Mathew J. Vetticatt、Mario Waser
DOI:10.1002/chem.201604153
日期:2016.11.21
Chiral bifunctional urea‐containing ammonium salts were found to be very efficient catalysts for asymmetric α‐hydroxylation reactions of β‐ketoesters with oxaziridines under base‐free conditions. The reaction is accompanied by a simultaneous kinetic resolution of the oxaziridine and a plausible and so far unprecedented bifunctional transition‐state model has been obtained by means of DFT calculations
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.