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TCI Practical Example: Regioselective Acylation of a Carbohydrate Utilizing the Benzoxaborole Catalyst

We are proud to present the 3-position-selective benzoylation of the fucopyranoside catalyzed by the benzoxaborole derivative (1).

Used Chemicals

• 5-Fluoro-3,3-bis(4-fluorophenyl)benzo[c][1,2]oxaborol-1(3H)-ol (1) [F1259]
• Benzoyl Chloride [B0105]
• N,N-Diisopropylethylamine (= DIPEA) [D1599]
• Methyl α-L-Fucopyranoside [M1051]
• acetonitrile

Procedure

To a solution of methyl α-L-fucopyranoside (250 mg, 1.4 mmol), N,N-diisopropylethylamine (217 mg, 1.68 mmol, 1.2 eq.) and 1 (48 mg, 0.14 mmol, 10 mol%) in acetonitrile (7 mL) was added benzoyl chloride (237 mg, 1.68 mmol, 1.2 eq.) at r.t. and the mixture was stirred for 20 hours. Methanol (1 mL) was added to the reaction mixture. The solvent was removed under reduced pressure and the residue was purified by column chromatography (ethyl acetate:hexane = 0:1 - 3:1 on silica gel) to give methyl 3-O-benzoyl-α-L-fucopyranoside as a white solid (362 mg, 91% yield).

Experimenter’s Comments

The reaction mixture was monitored by TLC (dichloromethane:methanol = 10:1, Rf = 0.50).

Analytical Data

Methyl 3-O-Benzoyl-α-L-fucopyranoside

¹H NMR (270 MHz, CDCl₃); δ 8.12-8.08 (m, 2H), 7.61-7.56 (m, 1H), 7.49-7.43 (m, 2H), 7.19 (brd, 1H, J = 8.1 Hz), 5.30 (dd, 1H, J = 10.3, 3.0 Hz, H-3), 4.85 (d, 1H, J = 4.3 Hz, H-1), 4.17 (dd, 1H, J = 10.3, 4.3 Hz, H-2), 4.07 (q, 1H, J = 6.5 Hz, H-5), 3.98 (brs, 1H, H-4), 3.47 (s, 3H), 1.32 (d, 3H, J = 6.5 Hz, H-6).

Lead Reference

• Benzoxaborole Catalyst for Site-Selective Modification of Polyols
• • S. Kusano, S. Miyamoto, A. Matsuoka, Y. Yamada, R. Ishikawa, O. Hayashida, Eur. J. Org. Chem. 2020, 2020, 1598.