ChemInform Abstract: Tris(2,6-diphenylbenzyl)silyl Group as a New and Highly Effective Protector for Carboxylic Acids: Unusual Behavior of such Carboxylic Esters Toward Common Nucleophiles and Bases.
Abstract
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ChemInform Abstract
Protection of carboxylic acids with the title silyl group leads to carboxylic acid esters such as (I), which are unusually stable towards a variety of nucleophiles and bases, e.g. methyl-, butyl-, and tert-butyllithium, methylmagnesium bromide, and lithium diisopropylamide, by treatment at -78°C for several hours. The high shielding effect of the bowl-shaped tris(2,6-diphenylbenzyl)silyl moiety is elucidated by single-crystal X-ray diffraction analysis of acetate (Ia). Deprotection is conveniently achieved as exemplified for ester (Id) with potassium tert-butylate in DMSO or with pyridine hydrofluoride in THF.
