环状的缩醛(酮)由醛酮在酸催化下与二醇脱水而成，有代表性的结构如：

环状缩醛(酮)较非环缩醛(酮)酸性条件下稳定性更好，保护和脱保护速度不仅与羰基本身活性有关，且跟环的大小和取代基有关。如：对相同的底物缩醛(酮)的形成速度：

在酸性条件下(0.003M HCl in dioxane/H₂O)水解相对速度：

环的大小不一样，缩醛(酮)水解速度也不一样，如酸催化缩酮的水解速度：

缩醛则正好相反。

取代的乙二醇或者丙三醇与羰基形成的缩醛(酮)的方法基本类似，根据取代基不同其酸性稳定性也各异，脱保护条件也可以更温和，如：

环状缩醛(酮)中，由于五元环缩醛(酮)形成比较方便，稳定性好，在多个羟基存在下，通过采用合适的条件也能具有一定的选择性，所以五元环缩醛(酮)，可能是羰基保护中使用最多的方法。其形成和脱除的典型操作如下：

应用举例1：

4-Cyanobenz aldehyde(15 g, 114.4 mmol) was placed in a round flask together with ethyleneglycol (11.5 mL, 206 mmol, 1.8equiv.), dry toluene (300 mL), and p-toluenesulfonic acid as catalyst (1.5 g, 8.7 mmol). The solution was heated at reflux in a Dean–Stark apparatus with water trap for 18 h. It was then neutralized with saturated aqueous NaHCO₃ solution (100 mL), and the phases were separated. The aqueous layer was extracted with toluene (3*50 mL), and the combined organic layers were collected, dried with MgSO₄, and filtered. The toluene solution was concentrated under reduced pressure, and the desired compound was obtained as a pale yellow solid (20.04 g, yield 99 %). (N. Boyer,P. Gloanec, Euro. J. Org. Chem., 2008, 4277)

应用举例2

A solution of acetal (1.00 g,3.16 mmol) and p-toluenesulfonic acid monohydrate (59 mg, 0.31 mmol) in acetone(100 mL) was stirred at room temperature for 2 days. The reaction mixture was poured into saturated ammonium sulfate solution. The organic layer was concentrated in vacuum and the residue was dissolved in EtOAc. The aqueous layer was extracted with EtOAc. Combined organic layers were washed with saturated NaHCO₃ solution and brine, dried over anhydrous magnesium sulfate and concentrated in vacuum. The residue was chromatographed over silica gel. Elution with hexane–ethyl acetate (1/1) gave desired ketone (0.86 g, quant.) as a colorless oil.(I. Ken; K. Ryo, W. Hidenori, Tetrahedron, 2006, 62, 2224)

应用举例3

A mixture of H₂O (15 mL) and TFA (15 mL) was added to a stirred solution of pentacycle (427 mg, 0.78 mmol) in THF (3.5 mL). After 1 h, the reaction mixture was diluted with EtOAc (100 mL), the organic layer was washed with H₂O(50 mL), cautiously basified by washing with saturated aqueous solution of Na₂CO₃(3*100 mL), washed with brine (200 mL), dried, concentrated in vacuum and purified by flash column chromatography (gradient elution: 0–50% EtOAc/petroleum ether) to give ketone (346 mg, 88%) as a colorless foam. (B.Aurelien, H. Shuji, Q-S. Beatrice, R. Louis, Tetrahedron, 2009, 65, 6730)

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