Catalytic Reduction of Oximes to Hydroxylamines: Current Methods, Challenges and Opportunities

Abstract

Catalytic reduction of oximes represents a direct efficient approach to synthesize valuable hydroxylamine derivatives. However this transformation presents significant challenges: oximes are hard to reduce and, if reactive, reductive cleavage of the weak N−O bond often leads to primary amine side products. The first suitable systems involved the use of platinum‐based heterogeneous catalysts with hydrogen as reductant and stoichiometric amounts of a strong Brønsted acid. More recently metal‐free and transition‐metal‐based homogeneous catalysts have been developed, which display the highest turnovers (up to 4000). In the asymmetric variants, the E/Z‐geometry of the oxime double bond affects significantly the stereoselectivity, sometimes requiring extra synthetic efforts in substrate preparation. This minireview provides an overview of the advances and limitations in catalytic oxime to hydroxylamine reduction. Emphasis is put on highlighting and comparing the practical aspects of the existing methods, such as their reaction conditions and substrate scope. Additionally, future directions for improving this young research area are suggested.

The diacetyliminoxyl radical in oxidative functionalization of alkenes

“…Phenylacetylene and 1-phenyl-1-pentyne were found unreactive towards diacetyliminoxyl: zero conversion of starting alkynes was observed after 24 h of the reaction by NMR monitoring. The synthesized C–O coupling products could be catalytically converted into hydroxylamine derivatives 71–73 or further employed as substrates for iminyl radical chemistry. 74–76…”

Reductive Denitrogenation of Six‐membered Cyclic Nitronates to Densely Substituted Dihydrofurans with Raney® Nickel/AcOH System

“…In this case, the conversion of oxime 4 to amine 3 would bypass intermediate Int‐1 and the formation of dihydrofuran 2 would not occur (pathway (3) in Scheme 4, c). Examples of the hydrogenation of oximes to hydroxylamines over palladium catalysts are known from the literature [27] …”

Selective Electrocatalytic Conversion of Nitric Oxide to High Value‐Added Chemicals

“…At present, NH 2 OH is typically prepared by the hydrolysis of ketoxime. [ 94 ] This approach is not only complicated in process but also requires the use of hydrogen peroxide, acid, and precious ammonia, which does not align with the principles of green and sustainable development. [ 95 ] Therefore, researchers have been exploring alternative approaches for NH 2 OH production.…”