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Copper-Catalyzed Borylation of Styrenes by 1,8-Diaminonaphthalene-Protected Diboronic Acid

Taiga Yasuda, Yusuke Yoshigoe and Shinichi Saito*

*Department of Chemistry, Faculty of Science, Tokyo University of Science, Kagurazaka, Shinjuku, Tokyo 162-8601, Japan, Email: ssaitors.tus.ac.jp

T. Yasuda, Y. Yoshigoe, S. Saito, Org. Lett., 2023, 25, 2093-2097.

DOI: 10.1021/acs.orglett.3c00451



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Abstract

Bench-stable 1,8-diaminonaphthalene-protected diboronic acid (B2(dan)2) can be used for Cu-catalyzed borylation of styrene derivatives. The reactions proceeded in good yields in a highly selective manner.

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proposed mechanism



Preparation of B2(dan)2

A mixture of B2(OH)4 (79 mmol, 7.1 g) and sublimed 1,8-diaminonaphthalene (159 mmol, 25 g, pink) in toluene (160 mL) was refluxed under Ar for 4 h with a Dean-Stark trap. The progress of reaction was monitored by TLC (hexane/AcOEt = 5:1). After the solvent was removed by evaporation, the residue was suspended in hot AcOEt (300 mL) and the insoluble material was removed by filtration. The filtrate was evaporated, and the residue was purified by recrystallization (AcOEt) to afford B2(dan)2 as a white solid (92%, 79 mmol, 24 g). B2(dan)2 is air-stable and it could be purified by column chromathography (hexane/AcOEt = 5:1).

General Procedure for the Cu-catalyzed Borylation Reaction

A mixture of CuCl(SIMes) (6.1 mg, 0.015 mmol, 5.0 mol %), B2(dan)2 (120 mg, 0.36 mmol, 1.2 equiv), and KOtBu (16.8 mg, 0.15 mmol, 0.50 equiv) in toluene (0.85 mL) was stirred at rt for 30 min. To the mixture was added alkene (0.30 mmol, 1.0 equiv) and HOtBu (0.034 mL, 0.36 mmol, 1.2 equiv). The resulting mixture was stirred at 50 C under Ar, and the progress of the reaction was monitored with TLC. The reaction mixture was filtered through a pad of silica gel, and the pad was washed with AcOEt (10 mL X 3). The combined filtrate was evaporated, and the residue was purified by silica gel column chromatography (hexane/AcOEt = 10:1) to afford the desired product.


Key Words

alkylboronates


ID: J54-Y2023