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Page 4 of 8 Liu et al. Chem Synth 2023;3:11 https://dx.doi.org/10.20517/cs.2022.46

Scheme 2. Evaluation of different N-protecting groups and substituents on iminoquinones.

Scheme 3. Substrate scope with respect to iminoquinones.

Inspired by the above results, we then turned our attention to investigating the generality of indole
substrates [Scheme 4]. From the selected examples (3p, 3s, 3t and 3u), it could be recognized that the
electronic properties of the indole substituents presented limited impact on the product yields and
enantioselectivities. However, a more pronounced structural variation of substrates such as disubstitution (
3v) and an additional fused ring (3w) could negatively affect the product yields. As expected, 2-(tert-
pentyl)-1H-indole and 2-(1-adamantyl)-1H-indole were also effective nucleophiles to give the
corresponding products 3x and 3y. Our method thus represents one of the most straightforward ways to
access axially chiral C3-arylindoles. The absolute configuration of the product 3s was confirmed by X-ray
crystallography (CCDC: 2225458) and the stereochemistry of other products has been assigned by analogy.

To further demonstrate the utility of this strategy, the scale-up synthesis of 3c and a series of chemical
transformations were conducted. First, the gram-scale reaction could deliver product 3c with nearly the
same yield (87%) and enantioselectivity (93% ee) as the small-scale reaction [Scheme 5A]. The oxidative
treatment of compound 3c with Ag O gave the atropisomeric heteroaryl-p-quinone monoimine 4c in 90%
2
yield without any erosion of enantioselectivity [Scheme 5B]. The unsaturated nature of this novel axially
chiral heteroaryl-p-quinone monoimine compound sets the stage for nucleophilic addition: With indoles as