Enantioselective Cleavage of Cyclobutanols Through Ir-Catalyzed C-C Bond Activation: Mechanistic and Synthetic Aspects.

ABSTRACT: The Ir-catalyzed conversion of prochiral tert-cyclobutanols to β-methyl-substituted ketones proceeds under comparably mild conditions in toluene (45-110 °C) and is particularly suited for the enantioselective desymmetrization of β-oxy-substituted substrates to give products with a quaternary chirality center with up to 95 % ee using DTBM-SegPhos as a chiral ligand. Deuteration experiments and kinetic isotope effect measurements revealed major mechanistic differences to related Rh^I -catalyzed transformations. Supported by DFT calculations we propose the initial formation of an Ir^III hydride intermediate, which then undergoes a β-C elimination (C-C bond activation) prior to reductive C-H elimination. The computational model also allows the prediction of the stereochemical outcome. The Ir-catalyzed cyclobutanol cleavage is broadly applicable but fails for substrates bearing strongly coordinating groups. The method is of particular value for the stereo-controlled synthesis of substituted chromanes related to the tocopherols and other natural products.

SUBMITTER: Ratsch F 

PROVIDER: S-EPMC7986405 | biostudies-literature | 2021 Mar

REPOSITORIES: biostudies-literature