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26.1.6.6.1 Method 1: Hydrolysis of O,O-Acetals

DOI: 10.1055/sos-SD-026-00205

Desmaële, D.Science of Synthesis, (200526333.

Although acetals are easily hydrolyzed by acids, they are extremely resistant to hydrolysis by bases. Acetals of aldehydes or ketones therefore provide protection from bases, and the acetals can be subsequently cleaved by exposure to an acid. In general, acyclic acetals are much more sensitive to acids than their cyclic counterparts; thus, the former are only used when selective or very mild hydrolysis is necessary to conserve the product. The ease of hydrolysis depends on the substitution; for a series of acetals the relative rates of hydrolysis [krel] follow the order CH2(OEt)2 [1]: MeCH(OEt)2 [6000]: Me2C(OEt)2 [1.8×107].[‌220‌] This variability has been exploited to selectively unmask a ketone group in the presence of an aldehyde acetal; for example, the ketone 112 is obtained by simply heating the difunctional acetal 113 in water (Scheme 35).[‌221‌]

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