Chiral pyridyl phosphinites with large aryl substituents as efficient ligands for the asymmetric iridium-catalyzed hydrogenation of difficult substrates

Abstract

Using a flexible synthesis, new chiral iridium N,P complexes with sterically demanding aryl substituents were synthesized and used in the asymmetric hydrogenation of difficult substrates. Unprecedented enantioselectivities were obtained in the asymmetric hydrogenation of a-substituted a,b-unsaturated esters and dihydronaphthalenes. The variety of aryl substituents incorporated into the catalyst has made it possible to obtain useful structure selectivity relationships for important classes of substrates.

8.17 Homogeneous Catalytic Hydrogenation of CåC and CåC

“…Esters of α,β-unsaturated acids act more like unfunctionalized alkenes, where Ir-based systems have enjoyed some success (see Section 8.17.5.5). [296][297][298][299][300] The BINAP family of ligands provided the first success for the reduction of α,β-unsaturated acids. This has led to the majority of the ligand systems used to perform this reduction being based on hindered biaryl systems.…”

Synthesis and Catalysis

“…[11a] Iridium complexes with pyridine-phosphinite ligands also proved to be active catalysts for the asymmetric hydrogenation of a wide range of functionalized olefins including , -unsaturated carboxylic esters and ketones, as well as imines, furans and indoles. [10][11][12][13] Another long-standing problem that was recently solved, was the hydrogenation of tetrasubstituted olefins, which were known to be notoriously unreactive substrates. Certain iridium P,N complexes showed unexpectedly high activity and allowed the hydrogenation of a range of tetrasubstituted olefins with high enantioselectivity.…”

Gold(I)‐Catalyzed Synthesis of Indenes and Cyclopentadienes: Access to (±)‐Laurokamurene B and the Skeletons of the Cycloaurenones and Dysiherbols

“…[22,23] The gold(I)-catalyzed reaction between 5i and cycloheptatriene 1f was most efficient with [(IPr)Au(PhCN)]SbF 6 (F)a st he catalyst and gave spiroindene 13 as am ixture of four stereoisomers (Scheme 4). [23] Cleavage of the benzoate and oxidation of the secondary alcohols with Dess-Martin periodinane (DMP) delivered ketones 14 a and 14 b in a1:1 ratio and 36 %y ield over three steps,a fter only one chromatographic purification.…”