for the following products
4-(2-Amino-phenyl)-piperazine-1-carboxylic acid tert-butyl ester | tert-Butyl 4-(2-aminophenyl)piperazine-1-carboxylate | tert-Butyl-4-(2-aminophenyl)tetrahydro-1(2H)-pyrazinecarboxylate and 1-Boc-4-(2-Aminophenyl)piperazine
