Bisoxazoline ligands with an axial-unfixed biaryl backbone: the effects of the biaryl backbone and the substituent at oxazoline ring on Cu-catalyzed asymmetric cyclopropanation

Recent Applications of Oxazoline-Containing Ligands in Asymmetric Catalysis

“…Ligand 154 with an axial-unfixed biaryl backbone has been applied in the enantioselective Cu(I)-catalyzed cyclopropanation of styrene (Scheme 1.74), with a trans/cis ratio of 83:17 and enantiomeric excesses of 96% and 89%, respectively. 133 Ligand 155 has furnished an enantiomeric excess of 82% in the Cu(I)-catalyzed cyclopropanation of styrene (Scheme 1.74), with a trans/cis ratio of 59:41 and yield of 41%. 134 Bis(oxazoline) ligand 156 with a 3,3′-bithiophene backbone has also been applied in the Cu(I)-catalyzed cyclopropanation of styrene (Scheme 1.74) with an enantiomeric excess of 67%, a yield of 81%, and a trans/cis ratio of 67:33.…”

“…Ligand 154 with an axial-unfixed biaryl backbone has been applied in the enantioselective Cu(I)-catalyzed cyclopropanation of styrene (Scheme ), with a trans / cis ratio of 83:17 and enantiomeric excesses of 96% and 89%, respectively …”

Modular Synthesis of a New Class of Bis(amino-oxazoline) Using Palladium-Catalyzed Buchwald−Hartwig Amination Methodology

“…However, such metal-accelerated racemization appears to be unique to bipyridyl and biisoquinoline ligands, the origin of which is poor overlap of the nitrogen lone-pair orbitals with those of the metal and the increase in M−N bond strength on going from the ground state to the transition state. Ikeda has recently investigated the coordination chemistry of a series of 2,2‘-biaryl-bridged tropos 2-(5-alkyl)bis(oxazolines) and demonstrated that coordination to copper(I) occurs with high diastereoselectivity for all oxazolines examined, while the selectivity for other metal such as Ag(I), Pd(II), and Zn(II) depended on the oxazoline substituent . Patti observed a similar level of selectivity for coordination of the S ,a S , S -diastereoisomer of the 2-(5-ferrocenyl)-substituted 8 to zinc .…”

“…The biphenyl-bridged 2-(5-alkyl)- and 2-(5-ferrocenyl)bis(oxazolines), 8 (R = alkyl, C 5 H 4 FeCp), developed by Ikeda 38 and Patti, respectively, also belong to the tropos class of ligand, as do the 3,3‘-bithiophene-bridged analogues 9 recently introduced by Banaglia (Chart ). Even though 8 (R = alkyl) exists as an interconverting equilibrium mixture of two diastereoisomers, only one coordinates to copper(I), and the resulting complex catalyzes the highly enantio- and diastereoselective cyclopropanation of styrene with ethyl diazoacetate, giving ee values up to 84% 38b. In marked contrast, their 2-(5-ferrocenyl) counterpart gave a much lower ee, even though its solution behavior and coordination properties paralleled its alkyl-substituted counterparts .…”

Convenient synthesis of tropos phosphine-oxazoline ligands

“…In view of atom economy, traditional axialfixed ligands require inconvenient enantiomer resolution or diastereomer separation in their synthetic processes, and generally, only one enantiomeric or diastereomeric pure form of the ligands works effectively in asymmetric catalytic reactions for industrial uses. Since Zhang and Ikeda reported the first type of tropos ligand 1 [19][20][21][22], several types of such ligands have been developed by Ikeda, Mikami, Zhang and other chemists [23,24]. These axial flexible (tropos) ligands could form single enantiomeric or diastereomeric metal catalysts, which showed excellent asymmetric catalytic activity for several types of reactions [23,24], due to chirality-inducement in complexing process.…”