Perrhenic Acid-Catalyzed Dehydration from Primary Amides, Aldoximes, N-Monoacylureas, and [alpha]-Substituted Ketoximes to Nitrile Compounds

The dehydration reaction of primary amides is one of the most fundamental methods for the synthesis of nitriles, and the development of environmentally benign catalytic reaction processes is needed. We surveyed a variety of metal catalysts and found that perrhenic acid was extremely effective for the dehydration of not only primary amides but also aldoximes. Typically, 1 mol % of perrhenic acid gave the corresponding nitriles from amides or aldoximes under azeotropic reflux conditions with the removal of water in toluene or mesitylene. In addition, perrhenic acid is an extremely efficient catalyst for the Beckmann fragmentation of α-substituted ketoximes to functionalized nitriles. This new catalytic system can be applied to the gram-scale synthesis of nitriles without further modifications.