Recent advances in iridium-catalyzed enantioselective allylic substitution using phosphoramidite-alkene ligands

Abstract

Enantioselective allylic substitution is one of the most important and reliable reactions for the synthesis of chiral building blocks. While various transition metal catalysts have been studied for use in...

Development of Immobilized Carreira (Phosphoramidite, Olefin) Ligands and Application in Iridium-Catalyzed Asymmetric Allylic Amination

“…Among them, Pd-catalyzed versions (Tsuji–Trost reactions) are the most widely studied and have an inherent tendency of forming chiral, linear substitution products . In contrast, Ir-catalyzed allylic substitutions usually favor the formation of the branched product with excellent regio- and enantioseletivities …”

“…For instance, a general interest is to develop protocols that employ a lower loading of the Ir-ligand catalytic complex. Complementary to this is the development of strategies that can allow a facile recovery of the catalyst, both the metal and the ligand . The implementation of these strategies would result in a rather ideal process from the practical, economical, and sustainability points of view, which would favor an eventual use at the industrial level.…”

“… 2 In contrast, Ir-catalyzed allylic substitutions usually favor the formation of the branched product with excellent regio- and enantioseletivities. 3 …”

Ir-Catalyzed Asymmetric Cascade Allylation/Spiroketalization Reaction for Stereoselective Synthesis of Oxazoline-Spiroketals

“…5-Methyleneoxazolines are widely utilized as useful reagents/intermediates in a variety of chemical reactions . In particular, You and co-workers achieved an iridium-catalyzed asymmetric allylic aromatization reaction by using allylic alcohols as π-allyl-iridium precursor , and 5-methyleneoxazolines as a nucleophilic reagent (Scheme b). Inspired by this elegant report, we hypothesized that 2-aryl-5-methyleneoxazolines bearing 4,4-disubstitution could avoid the aromatization reaction and act as stable exocyclic vinyl ethers engaging the allylation/spiroketalization reaction with 2-(1-hydroxyallyl)­phenol to synthesize the unique oxazoline-spiroketals (Scheme c).…”

Iridium-Catalyzed Enantioselective Ring Opening of Alkenyl Oxiranes by Unactivated Carboxylic Acids

“…Iridium-catalyzed asymmetric allylic substitution reaction is a powerful tool for the synthesis of valuable organic compounds. Since the first iridium-catalyzed allylic substitution discovered by Takeuchi in 1997, this research field has steadily evolved with the development of advanced chiral ligands. , Chiral iridium catalyst efficiently promotes high branch-selectivity and excellent enantioselectivity. ,, Thus, we began the initial investigations with commercially available vinyl oxirane ((±)- 1a ) and benzoic acid ( 3a ) using [Ir­(cod)­Cl] 2 and various nonracemic phosphoramidite ligands ( L2 to L5 and ( S )- L ) in dichloromethane as solvent (Table ). With ligands L2 to L5 , product ( 4aa ) was obtained in very low conversions and the enantioselective outcome was poor.…”