Li J, Lear MJ, Hayashi Y. Direct Cyclopropanation of α-Cyano β-Aryl Alkanes by Light-Mediated Single Electron Transfer Between Donor-Acceptor Pairs.
Chemistry 2021;
27:5901-5905. [PMID:
33565170 DOI:
10.1002/chem.202100341]
[Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2021] [Revised: 02/08/2021] [Indexed: 12/21/2022]
Abstract
Cyclopropanes are traditionally prepared by the formal [2+1] addition of carbene or radical based C1 units to alkenes. In contrast, the one-pot intermolecular cyclopropanation of alkanes by redox active C1 units has remained unrealised. Herein, we achieved this process simply by exposing β-aryl propionitriles and C1 radical precursors (N-oxy esters) to base and blue light. The overall process is redox-neutral and a photocatalyst, whether metal- or organic-based, is not required. Our findings support that single electron transfer (SET) from the α-cyano carbanion of the propionitrile to the N-oxy ester is facilitated by blue-light via their electron donor-acceptor (EDA) complex. The α-cyano carbon radical thus formed can then lose a β-proton to form a π-resonance stabilised radical anion that preferentially couples at the benzylic β-position with a decarboxylated C1 radical unit. This new transition metal-free chemistry tolerates both electron rich and electron deficient (hetero)aryl systems, even sulfide or alkene functionality, to afford a range of cis-aryl/cyano cyclopropanes bearing congested tetrasubstituted quaternary carbons.
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