Mesoionic azolides

Analogously to these reactions of imidazolium carboxylates, the introduction of urethane-type amino-protecting groups can be accomplished with the following mesoionic azolides [194]... 

The mesoionic azolides are reported to be relatively stable toward hydrolytic decomposition, but more reactive against amines than the corresponding imidazo-lides.[194] -Protection of the amino compounds (for example by the Boc group) takes place smoothly at room temperature in about one to five hours and with high yield. The amino acids are introduced as sodium salts in aqueous acetone. 

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