Rapid Access to an Enantioenriched Spiro Bisindole Directly from Indole and Acetone
Jing-Yi Wang1, Jie Lin1, Chaoshen Zhang1
1Department of Chemistry and the Hong Kong Branch of Chinese National Engineering Research Centre for Tissue Restoration & Reconstruction, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, 999077, Hong Kong SAR (China).
Abstract:
Disclosed here is a "one-pot self-assembly" strategy for the enantioselective synthesis of a spiro bisindole molecule directly from indole and acetone. This convenient synthesis contrasts drastically to the typical long sequence required for other privileged C2-symmetric spirocycles. The use of an alcohol additive in cooperation with chiral phosphoric acid (CPA) catalysis proved crucial to the good efficiency and enantioselectivity. The favorable interaction between the additive and CPA was confirmed by nuclear magnetic resonance (NMR) and density functional theory (DFT) studies. The obtained enantiopure C2-symmetric bisindole was demonstrated as a useful backbone of chiral catalysts/ligands.
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