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Reactions in microdroplets can be accelerated and can present unique chemistry compared to reactions in bulk solution. Here, we report the accelerated oxidation of aromatic sulfones to sulfonic acids in microdroplets under ambient conditions without the addition of acid, base, or catalyst. The experimental data suggest that the water radical cation, (H2O)+•, derived from traces of water in the solvent, is the oxidant. The substrate scope of the reaction indicates the need for a strong electron-donating group (e.g., p-hydroxyl) in the aromatic ring. An analogous oxidation is observed in an aromatic ketone with benzoic acid production. The shared mechanism is suggested to involve field-assisted ionization of water at the droplet/air interface, its reaction with the sulfone (M) to form the radical cation adduct, (M + H2O)+•, followed by 1,2-aryl migration and C–O cleavage. A remarkably high reaction rate acceleration (∼103) and regioselectivity (∼100-fold) characterize the reaction.
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Accelerated and Concerted Aza‐Michael Addition and SuFEx Reaction in Microdroplets in Unitary and High‐Throughput Formats
Abstract The sulfur fluoride exchange (SuFEx) reaction is significant in drug discovery, materials science, and chemical biology. Conventionally, it involves installation of SO2F followed by fluoride exchange by a catalyst. We report catalyst‐free Aza‐Michael addition to install SO2F and then SuFEx reaction with amines, both occurring in concert, in microdroplets under ambient conditions. The microdroplet reaction is accelerated by a factor of ∼104relative to the corresponding bulk reaction. We suggest that the superacidic microdroplet surface assists SuFEx reaction by protonating fluorine to create a good leaving group. The reaction scope was established by performing individual reactions in microdroplets of 18 amines in four solvents and confirmed using high‐throughput desorption electrospray ionization experiments. The study demonstrates the value of microdroplet‐assisted accelerated reactions in combination with high‐throughput experimentation for characterization of reaction scope.
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- Award ID(s):
- 1905087
- PAR ID:
- 10379773
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 61
- Issue:
- 50
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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