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Nishii, Yuji; Hirai, Takahiro; Fernandez, Sarah; Knochel, Paul; Mashima, Kazushi (2017): Zinc-Catalyzed Esterification of N-beta-Hydroxyethylamides: Removal of Directing Groups under Mild Conditions. In: European Journal of Organic Chemistry, No. 34: pp. 5010-5014
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Amide transformations involving C-N bond cleavage are recognized as difficult reactions owing to the inert nature of amides resulting from resonance. Accordingly, a strong inductive effect and geometrical distortion reasonably decrease the resonance stabilization to attenuate the C-N linkage. Although the conversion of such activated amides has been studied intensively, reaction systems for unactivated amides are underdeveloped. We herein report that a zinc(II) trifluoromethanesulfonate [Zn(OTf)(2)] catalyst achieves the esterification of a wide range of unactivated tertiary amides with the assistance of intramolecular acyl rearrangement. The reaction was applied to the one-pot removal of various amide-based directing groups under mild reaction conditions to afford the corresponding esters in high yields.