Strain‐Driven [3+2] Cycloaddition of Triazine 1‐Oxides with Arynes/Cyclooctyne: Access to Benzisoxazoles/Cyclooctene‐Fused Isoxazoles

The 4‐carboxylates of 1,2,3‐triazine 1‐oxides undergo [3+2] cycloaddition with in situ generated benzynes and naphthyne and also with cyclooctyne that, following extrusion of dinitrogen, form isoxazole‐3‐propenoate derivatives in high yields and diastereocontrol. This practical method occurs at room temperature and provides a wide range of isoxazole‐based heterocycles with diverse functionality. 1,2‐Naphthyne, an unsymmetrical alkyne, forms only one regioisomeric product, exemplifying inherent regioselectivity. Although high, stereoselectivity is not 100 % in most cases, indicating that the loss of dinitrogen is stepwise. Derivative reactions of benzisoxazoles suggest their versatility. A practical and convenient method has been developed for the synthesis of a wide range of isoxazole based heterocycles having diverse functionality by cycloaddition reactions of 1,2,3‐triazine 1‐oxides with arynes and cyclooctyne.