Synlett 2023; 34(12): 1391-1394
cluster
Special Issue Honoring Masahiro Murakami’s Contributions to Science
Metal- and Additive-Free Synthesis of α-Hydroxyamino Ketones Enabled by Organophotocatalyst
,
Tadachika Matsudaira
,
The authors acknowledge a Grant-in Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS, Grant Number JP20H00380).
Dedicated to Professor Masahiro Murakami on the occasion of his retirement from Kyoto University
Abstract
We report herein a straightforward method for the synthesis of α-hydroxyamino ketones, which involves the benzoylation reaction of nitrones with 2-benzoyl-2-phenylbenzothiazoline under organophotocatalysis. This method offers access to a variety α-hydroxyamino ketones without the use of any transition-metal catalyst or base. Control experiments suggested that the reaction proceeded through a benzoyl radical addition to nitrone. Benzothiazoline was found to be a more suitable radical precursor than Hantzsch ester.
Key words
hydroxyamino ketone -
hydroxylamine -
nitrone -
benzothiazoline -
organophotocatalyst -
metal-free
Supporting Information
Supporting information for this article is available online at https://doi.org/10.1055/a-2059-3003.
Supporting Information
Publikationsverlauf
Eingereicht: 09. Februar 2023
© 2023. Thieme. All rights reserved
Georg Thieme Verlag KG
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Example Synthetic Procedure Sequentially, nitrone 1a (0.050 mmol), benzothiazoline 2a (0.10 mmol), 4CzIPN (1 mol%), and acetonitrile (1 mL, 0.05 M) were added to a dried 20 mL test tube containing a stirrer bar. The mixture was subjected to freeze-pump-thaw process (3 cycles) and back-filled with N2 . The reaction was irradiated with white LED at rt for 14 h. After being exposed to air, the reaction mixture was concentrated and purified by preparative thin-layer chromatography on silica gel (hexane/ethyl acetate, 5:1 v/v) to give the corresponding α-hydroxyamino ketone 3a in 73% yield as a white solid. Spectral Information for Compound 3a
1 H NMR (400 MHz, CDCl3 ): δ = 8.87 (dd, J = 1.3, 8.5 Hz, 2 H), 7.60 (tt, J = 0.9, 7.6 Hz, 1 H), 7.46 (dd, J = 7.7, 8.1 Hz, 2 H), 7.33–7.22 (m, 5 H), 6.08 (br s, 1 H), 4.21 (d, J = 9.0 Hz, 1 H), 4.13 (d, J = 13.4 Hz, 1 H), 3.85 (d, J = 13.4 Hz, 1 H), 2.48–2.33 (m, 1 H), 1.17 (d, J = 6.6 Hz, 3 H), 0.87 (d, J = 6.8 Hz, 3 H) ppm. 13 C NMR (100 MHz, CDCl3 ): δ = 205.7, 138.4, 137.5, 133.6, 129.0, 128.7, 128.4, 128.3, 127.3, 71.6, 61.2, 29.4, 20.3, 19.8 ppm. HRMS (ESI): m/z calcd for C18 H21 NO2 Na: 306.1470; found: 306.1470.
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