Chiral 6,6′‐Bis(oxazolyl)‐1,1′‐biphenyls as Ligands for Copper(I)‐Catalyzed Asymmetric Cyclopropanation

Abstract

A series of chiral bis(oxazoline)s with biphenyl backbones were synthesized from enantiomerically pure (S)-and (R)-hexabenzyloxydiphenic acid (1) and their utility in copper(I)-catalyzed asymmetric cyclopropanation was investigated.

Recent Applications of Oxazoline-Containing Ligands in Asymmetric Catalysis

“…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. 135 Ligand class 157 has been applied in the asymmetric pinacol coupling reaction.…”

“…Ligand 155 has furnished an enantiomeric excess of 82% in the Cu(I)-catalyzed cyclopropanation of styrene (Scheme ), with a trans / cis ratio of 59:41 and yield of 41% …”

Synthesis of Chiral and Modifiable Hexahydroxydiphenoyl Compounds

“…The residue was dissolved in CH 2 Cl 2 (80 mL), and the solution was successively washed with H 2 O and brine. After the general drying procedure, the mixture was purified by preparative TLC (CHCl 3 / MeOH = 30/1) to give 13 (106 mg, 49% yield for two steps) as a yellow solid, which was recrystallized from a mixture of CH (14). (2S,3S)-1,4-Bis(benzyloxy)-2,3-butanediol (4) (1.00 g, 3.31 mmol) was azeotropically dried using C 6 H 6 before use.…”

“…The hexahydroxydiphenoyl (HHDP) group is a motif component of ellagitannins, exemplified by (−)-corilagin ( 1 ) (Figure ), a class of polyphenolic natural products with a broad range of biological activities. − Interestingly, several activities have been attributed to the HHDP moiety, , including inhibitions of recombinant rat squalene epoxidase and of protein kinase C and anti-HIV activities. − Additionally, HHDP compounds with axial chirality have attracted much attention as possible asymmetric catalysts. − The easily modifiable phenolic hydroxy groups of the HHDP group allow potential derivatization of a wide variety of systematically designed analogues. Despite the biological and chemosynthetic importance of the chiral HHDP compounds, their availability from natural sources is low because the isolation of a substantial amount of pure ellagitannin is generally difficult .…”

Preparation and DFT studies of chiral Cu (I)-complexes of biphenyl bisoxazolines and their application in enantioselective Kharasch–Sosnovsky reaction

“…Furthermore, both great diversity in amino alcohols and diacid structures lead to a wide range of BOX ligands with unique features. On the other hand, literature surveys have implied that the introduction of an additional chiral element in the ligand backbone is capable of effectively controlling asymmetric induction [12][13][14][15][16][17] . It has demonstrated that the combination of a biaryl backbone and chiral oxazoline rings at ortho-position leads to a mixture of atropisomeric diastereomers of BOX ligands bearing a chiral axis close to the stereogenic centers of the oxazoline moieties [18][19][20][21][22][23][24][25] .…”