title: Palladium-N-heterocyclic carbene (NHC)-catalyzed asymmetric synthesis of indolines through regiodivergent C(sp3)-H activation: scope and DFT study.
abstract: Two bulky, chiral, monodentate N-heterocyclic carbene ligands were applied to palladium-catalyzed asymmetric C-H arylation to incorporate C(sp(3))-H bond activation. Racemic mixtures of the carbamate starting materials underwent regiodivergent reactions to afford different trans-2,3-substituted indolines. Although this CAr-Calkyl coupling requires high temperatures (140-160 °C), chiral induction is high. This regiodivergent reaction, when carried out with enantiopure starting materials, can lead to single structurally different enantiopure products, depending on the catalyst chirality. The C-H activation at a tertiary center was realized only in the case of a cyclopropyl group. No C-H activation takes place alpha to a tertiary center. A detailed DFT study is included and analyses of methyl versus methylene versus methine C-H activation is used to rationalize experimentally observed regio- and enantioselectivities.
authors.affiliation: Department of Organic Chemistry, University of Geneva, 30 Quai Ernest Ansermet, 1211Geneva 4 (Switzerland), Fax: (+) 41 22-237-3215.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Katayev
authors.forename: Evgeny
authors.initials: E
authors.lastname: Larionov
authors.forename: Masafumi
authors.initials: M
authors.lastname: Nakanishi
authors.forename: Céline
authors.initials: C
authors.lastname: Besnard
authors.forename: E Peter
authors.initials: EP
authors.lastname: Kündig
keywords: CH activation; asymmetric catalysis; carbenes; chirality; density functional calculations