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29.6.2.2.2.3 Variation 3: From Alcohols with Removal of Water by Chemical Means

DOI: 10.1055/sos-SD-129-00001

Fowler, L. S.; Sutherland, A.Science of Synthesis Knowledge Updates, (20103126.

The equilibrium of the acetalization process can also be shifted toward the acetal by removing the water formed by a dehydration process or a chemical reaction. Molecular sieves and magnesium sulfate are commonly used dehydrating agents for the formation of acetals.[‌45‌,‌46‌] However, the most common procedure involves a chemical reaction with an ortho ester, typically a trialkyl orthoformate. To ensure a clean reaction, the alcohol component of the ortho ester should be the same as the alcohol used for acetalization. The same catalysts as used in the previously mentioned acetalization processes from aldehydes or ketones and alcohols can be used, including 4-toluenesulfonic acid,[‌47‌‌49‌] camphorsulfonic acid,[‌50‌,‌51‌] cerium(III) trifluoromethanesulfonate,[‌52‌‌54‌] zinc(II) chloride,[‌55‌] and copper(II) tetrafluoroborate.[‌56‌] The Lewis acid ytterbium(III) trifluoromethanesulfonate can be used to convert aldehydes and ketones into the corresponding O/O diethyl acetals 12 in the presence of triethyl orthoformate (Scheme 9).[‌57‌] This process, which uses extremely low catalyst loading of the ytterbium(III) trifluoromethanesulfonate (0.1 mol%), generally produces the acetals in excellent yields.

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8-M8MM8M8 M 8 88 [‌88‌]
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M8 M8 Meee Meee (e) Meeee (%) Mee
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Me M ee 8.8 >88 [‌88‌]
8-MeM8M8 M ee 8.8 >88 [‌88‌]
(M)-MM=MMMe M ee 8 88 [‌88‌]
Me Me ee 8 88 [‌88‌]
(MM8)8Me (MM8)8Me ee 8 88 [‌88‌]
MM=MMMe MM=MMMe eeeeee 8 88 [‌88‌]
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e 8 eee% ee Me(MMe)8 eee eeee.

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Meeeeee Meeeeee 88; Meeeeee Meeeeeeee Meeee Meeeeeeee(MMM) Meeeeeeeeeeeeeeeeeeeeeeee:[‌88‌]

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Meeeeeee Meeeeee 88; Meeeeee Meeeeeeee Meeee Meee(MMM) 8-Meeeeeeeeeeeeeee:[‌88‌]

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