Phosphomolybdic Acid Supported on Silica Gel: An Efficient, Mild and Reusable Catalyst for the Chemoselective Hydrolysis of Acetonides

Abstract

Carbohydrate acetonides were chemoselectively cleaved to the corresponding diols by using environmentally benign phosphomolybdic acid (H₃PMo₁₂O₄₀) supported on silica gel (PMA-SiO₂) at ambient temperature in a short span of 5-7 minutes in acetonitrile. Acid-labile protective groups such as THP, TBS, TBDPS, MOM, OMe and PMB were found to be stable under the reaction conditions.

acetonides - phosphomolybdic acid - chemoselective hydrolysis - silica gel

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12

Typical Experimental Procedure. (a) Preparation of PMA/SiO ₂ Catalyst. PMA-SiO₂ catalyst was prepared following the published procedure. [11]
(b) Preparation of Terminal Diols. To a solution of glucose diacetonide (260 mg, 1 mmol) in MeCN (2 mL) were added the 1 mol% PMA/SiO₂ (0.01 mmol, based on PMA) followed by 40 µL of H₂O, and the reaction mixture was stirred at ambient temperature for 5-7 min. After completion of the reaction as indicated by TLC, the solvent was removed under reduced pressure and the residue was dissolved in THF (2 mL) and filtered. The filtrate was concentrated under reduced pressure and purified by column chromatography (100-200 silica gel mesh) using hexane and EtOAc as solvent system to afford the pure diols. The filtered catalyst was reused without prior drying.
Spectral Data.
Entry b: [α]_D +6 (c 1.76, CHCl₃). ¹H NMR (200 MHz, CDCl₃): δ = 7.38 (s, 5 H), 5.75 (d, J = 3.8 Hz, 1 H), 4.64 (dd, J _1,2 = J _2,3 = 3.7 Hz, 1 H), 4.54 (s, 2 H), 3.40-4.00 (m, 6 H), 2.00-2.40 (m, 1 H), 1.48 (s, 3 H), 1.29 (s, 3 H). MS-FAB: m/z = 325.
Entry c: [α]_D +2.8 (c 1, MeOH). ¹H NMR (200 MHz, CDCl₃): δ = 7.78 (d, J = 8.0 Hz, 2 H), 7.38 (d, J = 8.0 Hz, 2 H), 4.83 (d, J = 7.0 Hz, 1 H), 4.15 (d, J = 5.5 Hz, 1 H), 4.05 (d, J = 5.5 Hz, 1 H), 3.90 (d, J = 5.0 Hz, 1 H), 3.52-3.70 (m, 2 H), 2.60 (br s, 1 H), 2.50 (s, 3 H), 2.00 (br s, 1 H), 1.50 (s, 3 H), 1.32 (s, 3 H). MS-FAB: m/z = 389 [M⁺ + 1].
Entry d: [α]_D -16.2 (c 0.4, CHCl₃). ¹H NMR (200 MHz, CDCl₃): δ = 7.35-7.24 (m, 5 H), 6.98-6.82 (m, 1 H), 5.85 (d, J = 15.6 Hz, 1 H), 4.69 (d, J = 11.1 Hz, 1 H), 4.46 (d, J = 11.1 Hz, 1 H), 4.18 (q, J = 7.4 Hz, 2 H), 3.86-3.78 (m, 2 H), 3.50 (dd, J _1,2 = 11.1, J _2,3 = 5.9 Hz, 1 H), 3.35 (dd, J _1,2 = 11.1 Hz, J _2,3 = 5.9 Hz, 1 H), 2.52 (t, J = 6.7 Hz, 2 H), 1.58-1.43 (m, 2 H), 1.28 (t, J = 7.4 Hz, 3 H). MS-FAB: m/z = 331 [M⁺ + 23], 309 [M⁺ + 1].