Z‐bpy, a New C₂‐Symmetric Bipyridine Ligand and Its Application in Enantioselective Copper(I)‐Catalyzed Cyclopropanation of Olefins

Abstract

Summary of main observation and conclusion A rigid C2‐symmetric chiral bipyridine ligand Z‐bpy with a triptycene‐like backbone was designed and synthesized from simple chemicals in a scalable route. Using this new ligand, copper(I) catalyzed cyclopropanation of styrenes with commercial ethyl diazoacetate produced various corresponding cyclopropanes in high yields, diastereoselectivity and enantioselectivity up to 97% ee.

Development of a Tunable Chiral Pyridine Ligand Unit for Enantioselective Iridium-Catalyzed C–H Borylation

“…With an N,B-ligand PL7 incorporating You’s chiral pyridine moiety, however, only a trace of the desired product was detected under the same conditions, likely due to the high steric hindrance of the pyridine ligand (Table , entry 12). Similarly, low reactivity was also observed with a chiral preligand PL8 incorporating the rigid polycyclic chiral pyridine moiety developed by our group (Table , entry 13) …”

“…Von Zelewsky, Kočovský, and others used a natural chiral pool as the chiral source to build chiral pyridines such as CP4 to CP7 . Recently, we have reported a rigid polycyclic chiral pyridine unit CP8 . Although the above ligands have been successfully applied in benchmark reactions such as cyclopropanation, allylic oxidation, and so forth, further development of asymmetric reactions using them has been significantly retarded, most likely due to the difficulty in their structural modification .…”

“…Racemic ketone 3 could be readily obtained by known methods in a decagram quantity . Based on a method recently developed by us, using the commercial inexpensive Ellman’s chiral tert -butanesulfinamide, ketone 3 was successfully resolved in a two-step procedure. Optically active ketone 3 could be transformed into the corresponding chloropyridine by a sequence involving the formation of the oxime and the enamide, and then treatment with phosphoryl chloride in DMF.…”

“…4 Recently, we have reported a rigid polycyclic chiral pyridine unit CP8. 5 Although the above ligands have been successfully applied in benchmark reactions such as cyclopropanation, allylic oxidation, and so forth, further development of asymmetric reactions using them has been significantly retarded, most likely due to the difficulty in their structural modification. 6 Moreover, common strategies to increase stereoselectivity by introducing large substituents at local sites could fail for pyridine ligands because the increased steric hindrance also decreased the catalyst's activity (such as CP4).…”

“…Similarly, low reactivity was also observed with a chiral preligand PL8 incorporating the rigid polycyclic chiral pyridine moiety developed by our group (Table 1, entry 13). 5 We next explored the substrate scope of the above asymmetric C−H borylation, and the results are summarized in Table 2. In most cases, the mono-borylation reaction of a diaryl(2-pyridyl)methane selectively took place and 1 H NMR analysis of the concentrated reaction mixture showed little side products.…”