PMGB

Case 1 (where the amine is nucleophilic, example-piperazine):

To a stirred suspension of the amine with a phenolic OH group (0.01 mol) in 20 mL tetrahydrofuran (in a round bottom flask fitted with a gas bubbler) was added a solution of di-tert-butylcarbonate (0.012 mol) in 10 mL tetrahydrofuran at room temperature. Soon it became a clear solution and a gas was evolved. The resulting mixture was heated at 60 ^oC for 6 h. The solvent was evaporated, the residue was dissolved in ethyl acetate and washed with water, dried (Na₂SO₄) and evaporated to give the corresponding BOC protected amine (with phenolic OH group) which was purified by triturating with hexanes (white solid, 92% yield).

Case 2 (where the amine is not nucleophilic, example-benzimidazole):

To a suspension of the amine containing phenolic OH group (0.001 mol) in 30 mL DMF was added triethylamine (0.001 mol) followed by di-tert-butyldicarbonate (0.001 mol) in 10 mL DMF followed by 4-(dimethylamino)pyridine (DMAP) (0.001 mol). The solution became clear after the addition of DMAP and a gas was evolved. The resulting mixture was stirred for 1 h at room temperature. The reaction mixture was diluted with 100 mL water, the white solid (product) precipitated was filtered, washed with water and hexanes, dried under suction to give the corresponding BOC protected amine with the free phenolic OH group (white solid, 100%).