Carboxylic acids were activated in the presence of DMAP with tert-butyl carbonates (BOC-OX) 1 , which were prepared in situ by reaction of X-OH and di- tert-butyl dicarbonate (BOC 2O). The most efficient active carbonate proved to be tert-butyl 3-(3,4-dihydrobenzotriazine-4-on)yl carbonate 1a , leading to efficient formation of benzotriazinonyl esters 3 and 6 , which are intermediates in reactions with primary and secondary amines to afford amides or peptides in good yield. By-products in the formation of 3 or 6 are the environmentally safe tert-BuOH and CO 2. The hindered amino acid AIB also forms a dipeptide in good yield.