Photocatalytic C(sp³)-H and C(sp²)-H Carboxylation of Amines with CO₂ Using a Sustainable Covalent Organic Framework/gC₃N₄ Composite

Carboxylation of amines is an important route to obtain amino acids. Herein, we have reported the synthesis and characterizations of a new COF/gC3N4 composite which acted as a heterogeneous photocatalyst for the carboxylation of unprotected indoles and N-Boc-benzyl amines. We have used SnO2 nanoparticles as the cocatalyst and CO2 as the carbon source under visible light irradiation. This gave a range of carboxylated products both with unprotected indoles and N-Boc-benzylamines with high yield. Control experiments gave the optimum reaction conditions for this photocatalytic carboxylation. Light dependency of this reaction was confirmed by altering the intensity of light. Here, we have synthesized two different catalysts, TpBpy and Tz COF, and the gC3N4 heterojunction which showed excellent photocatalytic activity. The photocatalysts, COF/gC3N4, are recyclable and reusable for several cycles without a significant loss in performance. The synthesis of a drug compound Clopidogrel and drug formation unit Tirofiban is demonstrated with these photocatalytic protocols.