Li X, Wodrich MD, Waser J. Accessing elusive σ-type cyclopropenium cation equivalents through redox gold catalysis.
Nat Chem 2024;
16:901-912. [PMID:
38783040 PMCID:
PMC11164686 DOI:
10.1038/s41557-024-01535-8]
[Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 04/15/2024] [Indexed: 05/25/2024]
Abstract
Cyclopropenes are the smallest unsaturated carbocycles. Removing one substituent from cyclopropenes leads to cyclopropenium cations (C3+ systems, CPCs). Stable aromatic π-type CPCs were discovered by Breslow in 1957 by removing a substituent on the aliphatic position. In contrast, σ-type CPCs-formally accessed by removing one substituent on the alkene-are unstable and relatively unexplored. Here we introduce electrophilic cyclopropenyl-gold(III) species as equivalents of σ-type CPCs, which can then react with terminal alkynes and vinylboronic acids. With catalyst loadings as low as 2 mol%, the synthesis of highly functionalized alkynyl- or alkenyl-cyclopropenes proceeded under mild conditions. A class of hypervalent iodine reagents-the cyclopropenyl benziodoxoles (CpBXs)-enabled the direct oxidation of gold(I) to gold(III) with concomitant transfer of a cyclopropenyl group. This protocol was general, tolerant to numerous functional groups and could be used for the late-stage modification of complex natural products, bioactive molecules and pharmaceuticals.
Collapse