Investigation of the scope of a [3+2] cycloaddition approach to isoxazole boronic esters

The [3+2] cycloaddition reaction of nitrile oxides and alkynylboronates provides direct access to a wide variety of isoxazole boronic esters. Specifically, this technique has been employed to generate trisubstituted isoxazole 4-boronates and disubstituted isoxazoles where the boronic ester moiety can be installed at C-4 or C-5 with high levels of regiocontrol. The application of this methodology in the synthesis of non-steroidal antiinflammatory agents is also described.