Efficient, solventless N-Boc protection of amines carried out at room temperature using sulfamic acid as recyclable catalyst

A simple, rapid, and efficient protocol for the chemoselective N-Boc protection of amines using sulfamic acid as catalyst is described. N-Boc protection of various structurally diverse aliphatic, aromatic, alicyclic, and heterocyclic amines (1°, 2°, 3°) was carried out with (Boc)2O using sulfamic acid as catalyst (5 mol %) at room temperature under solventless conditions. The advantages of this method are simplicity, shorter reaction times (1-15 min), a cost-effective catalyst, and excellent isolated yields (90-100%); it is also environmentally benign. Moreover, the combined use of ultrasound and sulfamic acid achieves a synergic effect that is especially marked in the N-Boc protection of deactivated (sterically hindered and electron-deficient) amines. The catalyst possesses distinct advantages: ease of handling, cleaner reactions, high activity, and excellent chemoselectivity.