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

Abstract

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 retro‐Diels‐Alder 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.