Enantioselective cyclopropanation of styrene with optically active nitrogen ligands based on the pyridine framework

Catalytic Applications of Terpyridines and their Transition Metal Complexes

“…The best results were achieved with ligand 1 f, giving the trans ‐isomer (90 % ee ) and cis ‐isomer (94 % ee ) in a 70:30 ratio (96 % isolated yield). The ligands 1 a – c did not provide any convincing enantioselectivity; this poor performance was attributed to the conformational mobility ( 1 a/b )49 and the remote position ( 1 c )38 of the chiral substituent, respectively. As a result, the steric interaction between the stereogenic centers on the ligand and the substrate, a crucial requirement for the enantioselective formation of the transition state, was decreased; consequently, the more rigid frameworks 1 d – h offered improved enantioselectivity 38.…”

“…The Chelucci and Kwong groups utilized the Cu I complexes of chiral terpyridine ligands 1 , as catalysts, in the asymmetric cyclopropanation of styrene derivatives with ethyl diazoacetate (EDA) according to Scheme 38. 49…”

Chiral 2,2‘-Bipyridines, 1,10-Phenanthrolines, and 2,2‘:6‘,2‘ ‘-Terpyridines: Syntheses and Applications in Asymmetric Homogeneous Catalysis

“…101 It was found that the 6,6-dimethylnorpinen-2-yl group was unable to provide satisfactory enantioselectivity (up to 5% ee) ( Table 4). This disappointing result was ascribed to the conformational mobility of this group which can minimize the steric interaction between the stereogenic centers on the ligand and the sub- Recently, the use of more effective tpy ligands, bearing substituents on the rigid asymmetric framework, has been independently studied by Kwong 94 and our group.…”

Mononuclear and Tetranuclear Copper(II) Complexes Bearing Amino Acid Schiff Base Ligands: Structural Characterization and Catalytic Applications

“…As a control in these catalytic evaluations, we used copper (II) sulfate; we found that after 160 h, the IR signal from the EDA had not completely disappeared. Carbene transfer can lead to two possible products, the trans and cis diastereomers; the comparison of the mass fragmentation patterns and the use of the NIST Standard Reference database, as well as the congruence of the retention times obtained and their comparison with those reported in the literature [ 49 ], allowed the diastereomers’ identification by GC-MS. The chromatogram was achieved using a chiral column (β™-DEX) and showed two peaks, at 13.28 and 13.48 min, for the cis isomer, and two peaks, at 12.63 and 12.90 min, for the trans isomer.…”