Carbamoylnitrile Oxide and Inverse Electron‐Demand 1,3‐Dipolar Cycloaddition

1,3-Dipolar cycloaddition has been employed as a powerful synthetic procedure by which five-membered heterocyclic frameworks are constructed together with forming two bonds in a single manipulation. Among the various functionalized nitrile oxides reported, the ethoxycarbonyl derivative 1 is commonly used in organic synthesis. In this chapter, another generation method for 6 from easily available nitroisoxazolone 10 is introduced, which proceeds under mild conditions without using any special reagents. 2-Methyl-4-nitroisoxazol-5(2H)-one 10 having multifunctionalities reveals versatile reactivity to serve as a precursor for polyfunctionalized systems. The carbamoyl group of the nitrile oxide plays an important role not only as an electron-withdrawing group but also as an accelerator in the cycloaddition by forming a hydrogen bond with a dipolarophilic nitrile. The electron-withdrawing carbamoyl group realizes the cycloaddition with electron-rich dipolarophiles, which is inverse electron-demand 1,3-dipolar cycloaddition.