Synthesis of Benzochromenes by Visible Light Electron Transfer

MICAELA D. HEREDIA; MARÍA E. BUDÉN; ROBERTO A. ROSSI

Venecia

Congreso; Green Chemistry Posgraduate Summer School; 2020

6H-benzo[c]chromene ring is widely present in pharmaceutical and natural products. For example, Cannabinol is one of the most common cannabinoids and has an antimicrobial property.Thus many different synthetic methodologies are known for the construction of benzochromenes. Catalysts such as Pd, Co and Au have been used to obtain the benzochromene skeleton. Morever, a metal-free strategy has been developed to approach the desired ring using neocuproine-KOtBu complex in benzene at 100°C.Due to the biological importance of benzo[c]chromenes, the development of an eco-friendly synthetic protocol that avoids the use of high temperatures, toxic solvents, ligands, and even transition metals is still desired. Nowadays, the new application of visible light in organic synthesis pretends to replace the uses of ligands and high temperatures. Recently, it has been reported the use of iridium catalysts and visible light to initiate an intermolecular radical addition to biaryl vinyl ethers. It is known that the homolytic aromatic substitution (HAS) reaction promoted by base and light efficiently works in intermolecular coupling reactions in the synthesis of biphenyls and stilbenes. However, no heterocycle has been obtained by using this strategy. Herein, we demonstrate that 6H-benzo[c]chromenes can be easily obtained from the corresponding 2-halobenzylphenyl ether and using blue light-emitting diode to promote the cyclization at room temperature.