8.22 Partial and Complete Reduction of Pyrroles, Furans, Thiophenes, and their Benzo Analogs, Heterocycles Containing More Than One Heteroatom

This review concentrates on describing methods for the reduction (and partial reduction) of aromatic heterocycles and their benzo-fused analogs. The reaction of a flat, achiral, aromatic starting material to furnish a chiral heterocyclic derivative containing functionality is a very useful theme in organic synthesis. Most attention is given to the transformations of derivatives of furan and pyrrole. The increase in methods for accomplishing the reduction of an achiral arene to give enantiopure heterocycles is a noteworthy development and produces many useful derivatives that will find use in the synthesis of natural products and other biologically active compounds. The challenges that were encountered when reducing arenes containing sulfur and arenes containing more than one heteroatom are also identified and discussed; these will provide interesting problems to solve in the future.