Recent trends in the development of sustainable catalytic systems for the oxidative cleavage of cycloalkenes by hydrogen peroxide

Dicarboxylic acids constitute one of the most important oxygenated intermediates in the chemical industry providing a wide range of daily products: fibers, pharmaceuticals, cosmetics, lubricants, pesticides and plasticizers. A major part of their large-scale production relies on the oxidative cleavage processes of unsaturated acids and cyclic olefins but suffers from severe drawbacks such as the use of harmful compounds, the need of specific set-ups to produce oxidants, expensive catalysts and energy-consuming conditions. In the context of the development of sustainable oxidation reactions, hydrogen peroxide has attracted growing interest thanks to its multiple benefits to replace conventional oxidants: low toxicity, no need of energetic conditions to perform catalytic oxidation and generation of benign H 2 O as a by-product. The present review aims at bringing a critical view on the development of catalytic systems for the H 2 O 2 -mediated oxidative cleavage of cycloalkenes toward green chemistry criteria. Different transition metal-based catalysts investigated for the reaction will be discussed with a special emphasis on tungsten. Next, the performance of different heterogeneous and homogeneous W-based systems on the oxidative cleavage of various cycloolefins will be presented. More specifically, their relevance towards sustainable oxidation will be assessed by studying key reaction features: solvent, H 2 O 2 amount, reaction time and catalyst synthesis, recoverability and activity. The main challenges regarding the oxidative cleavage of medium-sized cycloalkenes with W-H 2 O 2 systems will also be exposed. Finally, the potential of ultrasound as an unconventional activation method will be pointed out to overcome the limits encountered with the conventional thermal heating leading to even more environmentally-friendly cycloalkene oxidative cleavage. This review proposes a comprehensive, critical, and accessible assessment of reaction conditions for cycloolefin oxidative cleavage regarding green chemistry criteria.