Approaches to N- and O-Debenzylation (A Microreview)

Protective groups are of great importance when choosing a strategy for the synthesis of organic substances. The multi-stage nature of syntheses of target organic molecules, various conditions, lability and reactivity of substrates, intermediate and target products, and individual functional groups of molecules force chemists to use a variety of protective groups to prevent decomposition of the desired substances, increase the regioselectivity of the synthesis processes, and eliminate the influence of aggressive reagents on labile reactive centers in the molecule. Along with this, the process of removing protective groups involves selecting conditions that reduce or eliminate undesirable side reactions. Among these methods is hydrogenation, one of the special cases of which is reductive debenzylation. This reaction of introducing and removing a benzyl group is one of the most common reactions in organic synthesis, since the relative ease of introduction and the chemical and thermal stability of the benzyl group and the possibility of its indirect introduction are the preferred factors for using this method by synthetic chemists. This reaction is used for the synthesis of a wide range of compounds, such as drugs, high-energy substances, and polymers [1–11]. Since the reaction is universal, many organic molecules can act as a substrate for this process. Removal of the benzyl group involves the use of various methods, depending primarily on the structure and properties of the original substrates. This review considers the methods of reductive and oxidative N- and O-debenzylation using catalysts of various types and addresses approaches to the removal of benzyl protection in different classes of organic substances, such as aromatic compounds, crown ethers, tetrazoles, triazoles, substituted hexoses, and isowurtzitanes.