Synthetic routes and fields of application of isohexides: comprehensive perspective of relevant industrial compounds

Isohexides are a class of compounds that can be obtained from natural sources using simple processes, and have interesting properties. Among these, the intrinsic chirality of the rigid bicyclic structural cavity and the presence of two hydroxyl groups in positions 3 and 6, available for functional-group interconversion, appear the most interesting characteristics for real innovative applications. In this review, the strategies for the synthesis of isohexides from polysaccharides and biomasses of different complexities have been analyzed and the alternative processes to the traditional synthetic routes, in terms of sustainability, have been discussed. Secondly, the properties that make isosorbide the most suitable isohexide compound in terms of availability, stability and scalability for innovative production processes have been highlighted. The fields of application of these extremely interesting compounds have been investigated, proceeding with a discussion in which the areas of exploitation of isohexides are analyzed, in terms of their use as building blocks, chiral auxiliaries or constituents of chiral ionic liquids. Finally, the numerous applicative possibilities of isosorbide as a monomer or co-monomer of a wide range of polymeric materials of different natures, have been thoroughly investigated. This review represents a first investigation into the possible uses of isohexide-based compounds by analyzing the positive and negative aspects of their exploitation as ubiquitous alternatives to current oil-based intermediates. Certainly, future studies on the optimization of those production processes that occupy a large share of the chemical-product market will lead to the confirmation of the synthetic potential of compounds with an isohexidic structure.