亞苄基縮醛是1,2-二醇和1,3-二醇常用的保護基團。當反應底物是1，2，3-三醇時，1,3-縮醛是優先產物，這和丙酮化合物相反。亞苄基縮醛的優越性在於它可以在中性條件下通過氫解去除，或者在酸性條件下水解去除。由於1,2-二醇的亞苄基縮醛比1,3-二醇的亞苄基縮醛更容易被氫解去除，所以1,2-二醇的亞苄基縮醛可以在1,3-二醇的亞苄基縮醛存在下被選擇性除去。
1,2-二醇製備亞苄基縮醛示例 (J. Am. Chem. Soc. 2010, 132, 9900)
To a vigorously stirred solution of diol 1 (2.18 g, 4.86 mmol, 1.0 equiv) in CH2Cl2(24 mL) at 25 °C was added PhCH(OMe)2 (2.2 mL, 14.6 mmol, 3.0 equiv) and camphorsulfonic acid (56 mg, 0.24 mmol, 0.05 equiv), and the reaction mixture was stirred at 25 °C for 24 h. The mixture was then quenched with Et3N (2 mL), concentrated under vacuum and directly subjected to flash column chromatography (silica gel, hexanes:EtOAc 7:3 to 1:1) to afford benzylidene 2 (1.96 g,3.65 mmol, 75% yield) as an amorphous yellow solid.
1,3-二醇亞苄基縮醛在酸性條件下脫保護示例 (J. Am. Chem.Soc. 2010, 132, 9900)
To a stirred solution of 1 (6.00 g,11.4 mmol, 1.0 equiv) in CH2Cl2/ MeOH (240 mL, 2:3) at 25 °C was added camphorsulfonic acid (592 mg,2.5 mmol, 0.2 equiv), and the reaction mixture was stirred for 12 h. The reaction was quenched with Et3N (0.5 mL) and the resulting reaction mixture was concentrated under vacuum. The residue was purified by flash column chromatography (silica gel, hexanes:EtOAc 1:1 to 1:5) to afford diol 2 (4.50 g, 10.3 mmol, 90% yield) as a white foam.
對甲氧基亞苄基縮醛也是二醇普遍使用的保護基團。它的酸水解比亞苄基縮醛快10倍。和亞苄基縮醛一樣，1,3-衍生物比1,2-衍生物在熱力學上更穩定。除了酸水解和催化氫化，使用單電子氧化劑（CAN，DDQ等）進行脫保護也很常見。
1,3-二醇的對甲氧基亞苄基縮醛製備示例 (Org. Lett.2012, 14, 314)
To a solution of diol 1 (1.9 g,5.4 mmol) in CH2Cl2 (50 mL) was added p-anisaldehydedimethylacetal (1.3 mL, 7.6 mmol) followed by p-TsOH (51.3 mg, 0.27mmol). The resulting pink solution was stirred for 2 h at rt and filtered over alumina. The solvent was then removed under reduced pressure and the resulting crude residue was purified by flash column chromatography (PE/Et2O:95/5) to afford the desired acetal 2(2.56 g, 98%) as a colourless oil.
1,3-二醇的對甲氧基亞苄基縮醛在酸性醇溶液中脫保護示例 (Angew. Chem. Int. Ed. 2012, 51,4695)
The acetal 1 (12.0 mg, 19 μmol) and (±)-10-camphorsulfonic acid (0.4 mg, 1.9μmol, 0.1 equiv.) were stirred in MeOH (0.4 mL, 0.05 M) for 45 min. Solid NaHCO3 (~50 mg) was added and the mixture stirred for 5 min, then concentrated in vacuo. SiO2 flash column chromatography (petroleum ether: EtOAc, 9 : 1 → 4: 1) afforded the diol 2 (9.0 mg, 92%, 18 μmol).
相關連結：
【醇的保護】環縮醛和環縮酮——環亞戊基和環亞己基縮酮
【醇的保護】環縮醛和環縮酮——亞甲基縮醛
【醇的保護】環縮醛和環縮酮——丙酮化合物
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