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12.4.5 Benzimidazoles (Update 2019)

DOI: 10.1055/sos-SD-112-00338

Irudayanathan, F. M.; Lee, S.Science of Synthesis Knowledge Updates, (201921.

General Introduction

The benzimidazole unit occurs widely in drugs, fungicides, and herbicides, as well as in natural products and there are therefore many methods for the synthesis of benzimidazoles. The literature up until approximately 2000 is covered in Section 12.4, which also includes an overview of the general physicochemical and spectroscopic properties of benzimidazoles. The current chapter provides an update, describing new methods, as well as improvements to previously reported approaches, for example using more effective or more environmentally friendly catalysts.

The approach starting from a benzene-1,2-diamine and a one-carbon synthon is still probably the most versatile route to benzimidazoles. The one-carbon synthons covered here include aldehydes, alcohols, amines, Weinreb amides, (alkoxymethylene)hydrazinecarboxylates, (dibromomethyl)arenes, nitriles, ortho esters, and carbon dioxide, but earlier methods use many other synthons including carbonic and carboxylic acid derivatives, and imidates. Previously published information can be found in Section 12.4.1.1.1.1.