Synthesis of Isoxazoles via [2+3]-Dipolar Cycloaddition Using Alkyne Surrogates

Significance

The reaction of α-chlorobenz­aldoximes with 1-substituted 1-bromoalkenes ­under mild conditions in the presence of triethyl­amine affords 3-arylisoxazoles in good to excellent yields. This application of the well-known [2+3] cycloaddition of nitrile oxides, generated in situ from the α-chlorohydroxylamines, has a new wrinkle in that the bromoalkenes act as surrogate alkynes. Although the intermediate bromoisoxazolines were not isolated, the lack of reaction of the bromoalkene with triethylamine to produce alkynes was demonstrated. A key advantage of the reported method is the regioselectivity, apparently supported by FMO calculations, which often troubles the normal [2+3] cycloaddition process. The generality of the reaction was insufficiently investigated from both starting component points of view.