Enantioselective Hydrogenation of Olefins with Iridium-Phosphanodihydrooxazole Catalysts

Abstract

High turnover numbers and up to 98% ee were obtained in the catalytic hydrogenation of unfunctionalized aryl-substituted olefins with iridium-phosphanyldihydrooxazole complexes 1 (see reaction scheme). The anion of the complex-for example, hexafluorophosphate or tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BARF )-has a remarkable effect on the reactivity and longevity of the catalyst.

Reducing Challenges in Organic Synthesis with Stereoselective Hydrogenation and Tandem Catalysis

“…In 1998, Pfaltz developed this technology using a cationic Ir−BAr F complex bearing a chiral phosphinooxazoline (PHOX) ligand. 36 In this report, several tri-and tetrasubstituted styrene and stilbene derivatives were hydrogenated in up to 98% ee. Since this pioneering work, numerous reports have emerged showcasing the power of chiral variants of Crabtree's catalyst for the AH of unfunctionalized and sterically hindered olefins.…”

A modular approach to neutral P,N-ligands: synthesis and coordination chemistry

“…P,N-ligands have been applied in a wide variety of chemical reactions ranging from hydrogenations [1–2] and allylic substitutions [3–4] to Heck reactions [5] and conjugate additions to enones [6]. Their popularity arises from the inherent electronic disparity of the phosphorus and the nitrogen donor groups, rendering one binding site a soft π-acceptor featuring a pronounced trans effect and the other site a hard σ-donor [7].…”

Synthesis of Chiral 2-Substituted 1,4-Benzoxazin-3-ones via Iridium-Catalyzed Enantioselective Hydrogenation of Benzoxazinones

“…Transition-metal-catalyzed enantioselective hydrogenation has gained much attention in academia, and great success has been achieved in industrial applications owing to its atom economy, excellent enantioselectivity, and simple operation for the construction of enantioenriched compounds . Since the Pfaltz group’s pioneering work, iridium-catalyzed enantioselective hydrogenation has attracted much attention due to its excellent performance in the enantioselective reduction of different types of CC bonds with/without functional groups. Our group has developed axis-unfixed biphenylphosphine-oxazoline ligands ( BiphPHOX ) that have shown excellent performance in several types of transition-metal-catalyzed enantioselective catalytic reactions, especially for iridium-catalyzed enantioselective hydrogenations. − ,− Considering the importance of 1,4-benzoxazin-3-ones and to further explore our developed axis-unfixed biphenylphosphine-oxazoline ligands in the enantioselective hydrogenation reactions and the methods for the construction of chiral heterocycles, herein we report an Ir/ BiphPHOX -catalyzed enantioselective hydrogenation of 2-alkylidene 1,4-benzoxazin-3-ones for the preparation of chiral 2-substituted 1,4-benzoxazin-3-ones (Scheme ).…”