N-oxides are a class of compounds with a wide range of biological activity, commonly used as drugs or various pharmaceutical synthesis intermediates; In addition, they also can be used as organic chemical intermediates or catalyst and play a very important role in organic synthesis. The traditional approaches to prepare N-oxides is via oxidation of nitrogen in nitrogen-containing compounds with suitable oxidant. Besides, by direct synthesis approaches, namely generating the nitrogen-containing compounds, the N-oxidation occurs simultaneously, can also to give the corresponding N-oxides. Considering the advantages of direct synthesis approaches and the disadvantages of traditional approaches, this paper especially summarized the direct synthesis approaches of ten kinds of N-oxides, such as pyrimidine N-oxides and quinoxaline N-oxides, etc. Further more, the applications of the ten kinds of N-oxides were described.
