Journal
ACS CATALYSIS
Volume 9, Issue 7, Pages 6522-+Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.9b01502
Keywords
asymmetric catalysis; Friedel-Crafts reaction; conjugate addition; chiral phosphoric acids; chiral proton-transfer shuttle
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Funding
- National Natural Science Foundation of China [21625204, 21790332, 21532003]
- 111 project of the Ministry of Education of China [B06005]
- National Program for Special Support of Eminent Professionals
- Fundamental Research Funds for the Central Universities
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Asymmetric Friedel Crafts conjugate addition reactions that generate an alpha-chiral center are challenging because the configuration-determining step is a proton-transfer reaction of a highly active enol intermediate. Herein, we report a protocol for highly enantioselective Friedel Crafts conjugate addition of indoles and pyrroles to exocyclic enones catalyzed by chiral spiro phosphoric acids. This protocol provides a straightforward, efficient approach to synthetically important indole-containing cyclic ketones with an alpha-chiral center and features with high yields (up to 99%) and high enantioselectivities (up to 98% ee) for a broad substrate scope. Density functional theory calculations suggest that the Spiro phosphoric acid initially catalyzed the addition reaction by acting as a Bronsted acid and then catalyzed an enantioselective proton-transfer reaction of the enol intermediate by acting as a chiral proton-transfer shuttle. The enantiocontrol strategy described herein may be widely applicable to other addition reactions in which a proton transfer is the configuration-determining step.
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