Revisiting the addition of nitriloxides on protoanemonin. A new access to (2E)-3-(3 '-arylisoxazol-5 '-yl)propenoic acids

Some 4-substituted arylnitriloxides undergo 1,3-dipolar cycloadditions with 5-methylene(5H)furan-2-one (protoanemonin) with formation of spiroisoxazol ines. These spiroadducts can be opened to the corresponding (2E)-3-(3'-aryl isoxazol-5'-yl)propenoic acids 5 and 3-aryl-5[4'-(3'-aryl-4',5'-dihydroisox azolinyl)]isoxazole 6 by various ways, including acidic and basic treatment s, as well as electrooxidation. In the latter case, the electron transfer o ccurs on the 4,5-dihydroisoxazolic ring and is followed by an internal diss ociative electron transfer leading to the opened products.