Benzyne-Promoted Curtius-Type Rearrangement of Acyl Hydrazides in the Presence of Nucleophiles

A protocol has been developed for the Curtius-type rearrangement of acyl hydrazides in the presence of nucleophiles by activating acyl hydrazides with benzyne to generate aminimide intermediates. A wide variety of N'-methyl-N'-phenyl acyl hydrazides were treated with various alcohols in the presence of 2-(trimethylsilyl)phenyl triflate and CsF under mild conditions to afford structurally diverse carbamates in moderate to excellent yields. Importantly, complete retention of configuration was observed in the reaction of enantioenriched alpha-chiral alkanoyl hydrazides. Replacing the alcohol with water, an amine, an N'-unsubstituted acyl hydrazide, an alkoxyamine, or a thiophenol in the reaction permitted facile synthesis of ureas and analogues.