Modification and optimization of the bis-picolylamide-based relay protection for carboxylic acids to be cleaved by unusual complexation with Cu ~(2+) salts

摘要

A simple modification of our recently published protection scheme for carboxylic acids as amides resulted in a new protecting group with significantly improved properties. It requires shorter reaction times for deprotection and allows us to replace Cu(OTf) _2 by CuCl _2, indicating at the same time the importance of the nature of the anion of the Cu ~(2+) source. Since the new scheme fulfills all criteria required for an ideal protection group it should find widespread application in synthetic organic chemistry.