Metal‐Free O‐Selective Direct Acylation of Amino Alcohols Through Pseudo‐Intramolecular Process

Efficient α‐aryl‐β‐keto ester acylation of amine accompanied by the elimination of ethyl phenylacetate was achieved owing to the pseudo‐intramolecular process. The eliminated ethyl phenylacetate could be recycled by conversion into an α‐aryl‐β‐keto ester upon treatment with an acyl chloride in the presence of lithium bis(trimethylsilyl)amide, by which the atom economy considerably increased. Acylation using an α‐aryl‐β‐keto ester is highly sensitive to the bulkiness of the nucleophile, which facilitated the regioselective‐acylation of the less hindered amino group in diamine without protecting the other. The transacylation of α‐aryl‐β‐keto ester with N‐alkylamino alcohol resulted in chemoselective O‐acylation without protecting the amino group because the hydroxy group was attracted to the reaction site of the keto ester by forming an ammonium salt. Transacylation was demonstrated to be a practically useful tool for organic synthesis because this protocol can be conducted under mild conditions with simple manipulations in the absence of any additives such as metal catalyst and base. Acylation of diamines using α‐aryl‐β‐keto esters occurs regioselectively at the less hindered amino group. The transacylation using N‐alkylamino alcohol resulted in chemoselective O‐acylation in the absence of metal catalyst. Protection of the amino group is not necessary. These reactions proceed efficiently because of the pseudo‐intramolecular process.