pH-Controlled selective protection of polyaza macrocycles

Piperazine (1), tetraazacyclododecane 3 and pentaazacyclopentadecane 4 react with chloroformates in acid solution to give the selectively protected carbamate derivatives 1a,3a-d, and 4a. The benzyloxycarbonyl derivatives 3d and 4a were alkylated with tertbutyl bromoacetate and removal of the benzyloxycarbonyl protection by catalytic hydrogenation afforded tert-butyl esters 5b and 6b in good yields.