Synthesis, Application and Kinetic Studies of Chiral Phosphite‐Oxazoline Palladium Complexes as Active and Selective Catalysts in Intermolecular Heck Reactions

Abstract

This study identifies new phosphite-oxazoline ligands that have been successfully applied in the palladiumcatalyzed intermolecular asymmetric Heck reaction. The design of the new phosphite-oxazoline ligands derives from a previous successful generation of phosphine-oxazoline ligands, by replacing the phosphine group with several πacceptor biaryl phosphite moieties. With these simple modifications, the new phosphite-based ligands, unlike previous phosphine-oxazoline, not only present a modular design with numerous potential phosphite groups available, but they are also air-stable solids, which can be made in the same number of synthetic steps as the phosphine analogues. The substitution of the phosphine by a biaryl phosphite group extended the range of substrates and triflates sources that can be coupled with regio-, enantioselectivities and activities comparable to the few best ones reported. In addition, the ligands that provided the best selectivities contained an isopropyl oxazoline moiety instead of the tert-butyl group found in the related phosphine-oxazoline ligands, which is made from a much more expensive precursor. In this paper we have also carried out kinetic studies and a Hammett plot analysis to determine the rate determining step of this system in the regime of interest. We suggest a likely explanation for the fast Heck reaction of the phosphite-oxazoline catalysts.

Recent Advances of Catalytic Enantioselective Heck Reactions and Reductive‐Heck Reactions

“…[ 7 ] Chiral phosphite‐oxazoline ligand L3 also showed excellent asymmetric induction in the arylation of such heterocyclic olefins, leading to excellent enantioselectivities and high conversions. [ 10 ] As shown in Scheme 17,…”

“…In 2018, Pàmies, Leeuwen, and Diéguez synthesized a range of phosphite‐oxazoline ligands derived from 2‐hydroxyphenylacetonitrile, among which ligand L3 could lead to high conversions (up to 99%) and excellent enantioselectivities (up to 96% ee) in the Heck coupling of cyclopentene with aryl triflates (Scheme 5). [ 10 ]…”

Catalytic and antibacterial properties of 3‐dentate carboxamide Pd/Pt complexes obtained via a benign route

“…Therefore, efforts have recently been made to design novel anticancer drugs based on palladium compounds . In addition, these compounds have attracted renewed interest due to their wide applications in catalytic processes, construction of chemical sensors, and antibacterial and cytotoxicity usage …”

“…Therefore, efforts have recently been made to design novel anticancer drugs based on palladium compounds. [20][21][22] In addition, these compounds have attracted renewed interest due to their wide applications in catalytic processes, [23][24][25] construction of chemical sensors, [26] and antibacterial and cytotoxicity usage. [27] Based on the literature, a great number of recent publications have focused on finding suitable alternatives for hazardous solvents, and ionic liquids (ILs) have emerged as appropriate candidates for use in sustainable chemistry.…”

D-Fructose-based spiro-fused PHOX ligands: synthesis and application in enantioselective allylic alkylation

“…These ligands gave up to 96% ee by their application in allylic substitution with dimethyl malonate as nucleophile [ 13 – 14 ]. The design of new PHOX ligands is still subject to current research and the synthesis of a lot of different PHOX ligands have been reported during the last years [ 15 – 18 ]. Kunz reported the preparation of a carbohydrate based PHOX ligand 2 [ 19 ].…”