Work

Divergent reactivity of intramolecular cycloadditions of keteniminium ions with alkynes: [4+2] or [2+2]?

Year: 2025

Type: article

Abstract: We describe here divergent reactivity in the intramolecular cyclizations of a family of keteniminium ions (KIs) that contain a tethered alkyne. The KI precursors were tertiary amides having (i) unsaturation (arene or alkene) located β,γ to the amide carbonyl and (ii) an alkyne tethered through the amide nitrogen atom. The KIs were generated by the action of triflic anhydride and a pyridine base at 0 °C. Substrates having a three-atom linker between the central carbon atom of the KI undergo unprecedented [4 + 2] cycloadditions between the alkyne and the styrenic/dienic subunit of the conjugated KI leading to indoline or carbazole derivatives. DFT computations suggest that the reaction proceeds by a stepwise mechanism. In contrast, substrates with a four- or five-atom tether undergo [2 + 2] cycloaddition to afford isolable, fused, cyclobutenyl iminium ions further useful as synthons.

Source: Chemical Science

DOI: 10.1039/d5sc02212f

Authors: Sangjun Lee, Thomas R. Hoye

Institution: University of Minnesota

Language: English

Topic: Chemical synthesis and pharmacological studies

Subfield: Organic Chemistry

Field: Chemistry

Domain: Physical Sciences

Open Access status: diamond

Funders: University of Minnesota, National Institutes of Health, National Cancer Institute, National Institute of General Medical Sciences