Indole-based atropisomers are a very important class of axially chiral
compounds. However, the atroposelective synthesis of axially chiral
2-arylindole remains largely unexplored. In this study, we report the
successful synthesis of atropisomeric 2-arylindoles using direct
amination of indoles with
p-quinonediimines
in the presence of chiral phosphoric acid as a catalyst. Quinonediimine
acts as an aminating reagent through formal polarity inversion of imine.
The malonate group on the 2-aryl of 2-indoles was found to be essential
for high enantioselectivity of the products. This could be due to the
additional interaction between the ester group and the catalyst, as well
as the intramolecular hydrogen bonding. Our findings provide a new
strategy for the asymmetric construction of 2-arylindole atropisomers.
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