Recent Developments in the Reduction of Aromatic and Aliphatic Nitro Compounds to Amines

The reduction of the nitro group represents a powerful and widely used transformation that allows to introducing an amino group in the molecule. New synthetic strategies for complex functionalized molecular architectures are deeply needed, including highly efficient and selective nitro reduction methods, tolerant of a diverse array of functional moieties and protecting groups. Since chiral amino groups are ubiquitous in a variety of bioactive molecules such as alkaloids, natural products, drugs, and medical agents, the development of reliable catalytic methodologies for the nitro group reduction is attracting an increasing interest also in the preparation of enantiomerically pure amines. In this context, the modern reduction methods should be chemoselective and respectful of the stereochemical integrity of the stereogenic elements of the molecule. The review will offer an overview of the different possible methodologies available for this fundamental transformation, with special attention on the most recent contributions in the field, especially in the last ten years: hydrogenations, metal dissolving and hydride transfer reductions, catalytic transfer hydrogenations, and metal-free reductions. The main advantages or limitations for the proposed methods will be briefly discussed, highlighting in some cases the most important features of the presented reduction methodologies from an industrial point of view.