Singh VK, Zhu C, De CK, Leutzsch M, Baldinelli L, Mitra R, Bistoni G, List B. Taming secondary benzylic cations in catalytic asymmetric S
N1 reactions.
Science 2023;
382:325-329. [PMID:
37856595 DOI:
10.1126/science.adj7007]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2023] [Accepted: 09/05/2023] [Indexed: 10/21/2023]
Abstract
Benzylic stereogenic centers are ubiquitous in natural products and pharmaceuticals. A potentially general, though challenging, approach toward their selective creation would be asymmetric unimolecular nucleophilic substitution (SN1) reactions that proceed through highly reactive benzylic cations. We now report a broadly applicable solution to this problem by identifying chiral counteranions that pair with secondary benzylic cations to engage in catalytic asymmetric C-C, C-O, and C-N bond-forming reactions with excellent enantioselectivity. The critical cationic intermediate can be accessed from different precursors via Lewis- or Brønsted acid catalysis. Key to our strategy is the use of only weakly basic, confined counteranions that are posited to prolong the lifetime of the carbocation, thereby avoiding nonproductive deprotonation pathways to the corresponding styrene.
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