Intermolecular [5 + 1]-Cycloaddition between Vinyl Diazo Compounds and -Butyl Nitrite to 1,2,3-Triazine 1-Oxides and Their Further Transformation to Isoxazoles.

1,2,3-Triazine 1-oxides are formed by nitrosyl addition from -butyl nitrite to the vinylogous position of vinyl diazo compounds. This transformation, which is a formal intermolecular [5 + 1] cycloaddition, occurs under mild conditions, with high functional group tolerance and regioselectivity, and can be employed for late-stage functionalization. Upon heating at refluxing chlorobenzene temperature, these triazine--oxides undergo dinitrogen extrusion to form isoxazoles in very high yields.