Tris silyl ester protect acids

Like the silyl ethers, the stability of the silyl esters parallels the steric bulk of the substituents on the silicon atom. Tris(2,6-diphenylbenzyl)siiy1 esters confer extraordinary steric protection upon the carboxyl group.234 For example, the tris(2,6-diphenylbenzyl)silyl ester of 4-phenylbutanoic acid 104.1 [Scheme 6.104] does not react with butyllithium (2.5 equiv) after 5 h at -78 °C or methylmag-nesium bromide (2,5 equiv) at room temperature. Nor did it react with lithium aluminium hydride after 30 min at 0 °C l M HC1 in THF at 40 °C, or aqueous sodium hydroxide at 50 °C after 5 h. Ester 104.1 was reduced with diisobutyl-aluminium hydride in 99% yield to give the 4-phenyl-l-butanol (99%) and HF pyridine in THF (1 2) at 50 aC cleaved it back to the acid after 5 h. Unfortunately, the penalty for such unusual stability is high the tris(2 6-diphenyl-... 

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