β-Keto Esters Derived from 2-(Trimethylsilyl)ethanol: An Orthogonal Protective Group for β-Keto Esters

Abstract

β-Keto esters derived from 2-(trimethylsilyl)ethanol undergo cleavage and decarboxylation when treated with 0.75 equivalents of tetrabutylammonium fluoride trihydrate in tetrahydrofuran at 50 ˚C, while β-keto esters derived from methanol, tert-butyl alcohol, allyl alcohol, or benzyl alcohol stay intact. Conversely, methyl­-, tert-butyl-, allyl-, or benzyl β-keto esters can be cleaved and decarboxylated without the 2-(trimethylsilyl)ethyl β-keto esters being affected. Similarly, mixed bis(β-keto esters) derived from 2-(trimethylsilyl)ethanol and methanol, tert-butyl alcohol, allyl alcohol, or benzyl alcohol can be defunctionalized chemoselectively under the same reaction conditions.

Key words

chemoselectivity - dealkoxycarbonylation - deprotection - β-keto esters - ketones

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4

Moreover, we determined the absolute amounts (i.e., the absolute yields) of the up to four species detected in each reaction mixture under scrutiny by weighing this mixture. Thereafter, the mole fraction of each component, its molecular weight, and the gram amount of the mixture allowed us to calculate the yields listed in Tables  [¹] - [8] .

11

For representative examples of chemoselective deprotections of TMSE esters besides methyl esters, see footnote 3 in ref. 2.

12

For representative examples of chemoselective deprotections of TMSE esters besides tert-butyl esters, see footnote 4 in ref. 2.

13

For representative examples of chemoselective deprotections of TMSE esters besides allyl esters, see footnote 5 in ref. 2.

14

For representative examples of chemoselective deprotections of TMSE esters besides benzyl esters, see footnote 6 in ref. 2.

20

THF solutions of Et₃NH⁺HCO₂ ^- were prepared from Et₃N (2.5 equiv) and HCO₂H (2.0 equiv).

23

Without the addition of the base, the reaction furnished the β-keto acid exclusively.