Nitroisoxazolones Showing Diverse Chemical Behavior: A Use ful Building Block for Polyfunctionalized Systems

Background: 4-Functionalized isoxazolin-5-ones (isoxazolones) have attracted much attentions as precursors of functionalized building blocks because the multiple functionalities. These structural features facilitate the construction of large compound libraries that is important for development of new functional materials. However, the systematic review article dealing with nitroisoxazolone has not been published although they exhibit different reactivity from other functionalized isoxazolones. This review describes the interesting behavior of the nitroisoxazolone motif and its application to the synthesis of polyfunctionalized compounds. Methods: Peer-reviewed research literatures describing the chemistry of nitroisoxazolones were collected, and each paper was appraised using standard criteria. inclusion/exclusion criteria. The papers were analyzed, and divided according to the reaction patterns. Results: This review consists of two parts. In the former part, the chemistry of pyridinium salt of nitroisoxazolone is described, and in the latter part, chemistry of methylnitroisoxazolone is introduced. Sixty-eight papers were included in this review. Twelve papers deal with pyridinium salt or its ring-opened product, cyano-aci-nitroacetate. Nine papers mention the chemistry of methylnitroisoxazolones and derived nitroenamines and nitrile oxide. With regard to each chemistry, reaction mechanism and reactivity are discussed with citing related literatures. Conclusion: The findings of this review confirm the importance of nitroisoxazolones in synthetic chemistry for polyfunctionalized compounds, which are not readily available by alternative methods. This review will provide useful information and synthetic tools for many chemists studying synthetic chemistry and medicinal chemistry.