Keywords: Density functional calculations / Isocyanides / Reaction mechanisms / E/Z isomerism / GlycosylationWe present a computational investigation of the reaction between isocyanides and carboxylic acids. Our results indicate that this reaction begins with a stereoselective concerted α-addition of the acid to the isocyanide, leading exclusively to a Z-acyl imidate. Isomerization to the E isomer and successive rate-limiting 1,3 OǞN acyl migration yields an N-formyl