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.
