Chitosan: An Upgraded Polysaccharide Waste for Organocatalysis

Green chemistry, directed towards the sustainable adaptation of human activity, is part of our society. Catalysis and waste upgrading are central aspects of green chemistry. Bringing them together would afford efficient chemical processes from the point of view of sustainability. Chitosan is a polyglucosamine generated from chitin, an abundant polysaccharide recycled from industrial marine wastes. Organocatalysts show some advantages over metallocatalysts in that they do not involve non-renewable rare metals. However, they have drawbacks such as the need for high loadings and difficulties of recovery. This microreview presents recent achievements in the field of organocatalytic reactions promoted by chitosan as a heterogeneous catalytic material. Various organic reactions are reported, in which chitosan is engaged either as an insoluble organocatalyst or as a support for organocatalysts, being easily recycled and reused. Influences on the reaction outcomes are discussed. Although most reactions produce achiral products, a few asymmetric ones have emerged, demonstrating the capacity of chitosan to transfer its stereochemical information.