A facile and mild synthesis of sterically hindered esters.

Abstract

We report a Brønsted acid-catalyzed synthesis of sterically hindered esters via a putative acylium intermediate. N-Methyl-N-tosyl ynamide is employed as a coupling reagent to convert a carboxylic acid into a stable α-acyloxyenamide adduct, the protonation of which with catalytic HNTf2 liberates a reactive acylium that acylates congested alcohols and phenols in good to excellent yields with good functional group tolerance. Interception by electron-rich arenes to afford hindered ketones via the Friedel-Crafts acylation confirms acylium intermediacy.

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