Thermochemical and photochemical aerobic oxidation of benzylic alcohols in the presence of Cu(ii) nitrate, DDQ, and their combination

Abstract

The selective oxidation of benzylic alcohols to carbonyl compounds under mild conditions remains a significant challenge in synthetic chemistry. Here, we report four cost-effective and efficient strategies for the selective aerobic oxidation of benzylic alcohols to carbonyl compounds in the presence of Cu(II) nitrate, DDQ, and their combination under thermochemical and photochemical conditions in CH₃CN as a solvent: (1) thermally-assisted DDQ organocatalysis at 60 °C, (2) DDQ photochemical catalysis under light irradiation, (3) Cu(NO₃)₂·3H₂O/DDQ catalyst system, and (4) light-driven (blue LEDs 9 W) Cu(NO₃)₂·3H₂O/DDQ photocatalytic system. Among these methods, the photoactive DDQ/Cu(NO₃)₂·3H₂O catalytic system demonstrated the highest performance. These methods offer several notable advantages, including the use of oxygen as the terminal oxidant and the utilization of commercially available, inexpensive catalysts, making the process both economical and environmentally friendly. Furthermore, they produce environmentally benign water as the sole byproduct, offer 60–98% product yields, and allow for straightforward isolation and purification. The combination of these features makes these protocols both practical and sustainable for the selective oxidation of benzylic alcohols to carbonyl compounds under ambient aerobic conditions.