When the optimized reaction condition was obtained (
Table, entry 14), we further explored the substrate scope of the atropoenantioselective nitrile formation process using a variety of biaryl dialdehydes
1 (Fig.
2). Whether one or two methyl groups are installed in ring A, with the corresponding aryl monoaldehydes obtained in improved yields with no erosion of the product er values (
3b to
3e). However, the electron-donating group 4′-OCH
3 introduced in ring A led to a lower enantioselectivity (
3f). The halogen (F, Cl) could be attached to ring A of the benzaldehydes
1 to give corresponding products in moderate yields with retaining high optical purities (
3g to
3j). Notably, the presence of 5′-Cl of ring A in the biaryl dialdehyde resulted in a lower er value of aryl aldehyde product
3k, albeit with a moderate yield. The 2′-methyl group on ring A played an important role in restricting axial rotation. For instance, when ethyl, -SMe, or alkenyl groups were incorporated at the 2′-position of ring A, the product yields of the aryl monoaldehydes were slightly changed (
3l to
3n). Moreover, an obvious reduction in both product yields and er values could be observed when the 2′-halogen or 2′-phenyl group was introduced to ring A (
3o to
3q). Furthermore, the NHC-catalyzed atropoenantioselective reaction exhibited promising performance even in the presence of aromatic fused rings in the dialdehydes, and all the corresponding aryl monoaldehydes could be obtained with excellent optical purities (
3r to
3t). However, a slight decrease in the product er value occurred when 2′-CH
3O-naphthyl was used to replace ring A (
3u). In addition, we also tested substrate scope on the dialdehyde aromatic ring (ring B). Electron-donating (OMe) and halogen (F) groups were tolerated well and given corresponding aryl monoaldehyde products
3v and
3w in moderate yields and excellent er values.