Irradiation of 3-hydroxy-l,2-benzisoxazole (3) results in the formation of benzoxazolinone (4). This photoisomerization is shown to occur predominantly via the keto tautomer 3b since facile rearrangements of the Nalkyl-l,2-benzisoxazolinones (19) occur under similar photolytic conditions. A mechanism involving a diradical species is proposed for this reaction. Low temperature photolysis-infrared measurements support this mechanism while arguing against an isocyanate (12) or a spiro-a-lactam (13) intermediate. Sensitization studies conducted on 3 and 19a indicate that the rearrangement occurs predominantly from the triplet state.
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