Preparation and photochemistry of furoisoxazolines. An extraordinarily unambiguous photo-induced rearrangement

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Abstract
Preparation and photolysis of furoisoxazoline derivatives is described. The respective compounds IVa, II and VI were obtained by a 1,3-dipolar cycloaddition of benzenenitrile oxide to 5,6-dimethoxycarbonyl-7-oxabicyclo[2,2,1]-2-heptene, 2,5-dihydrofuran and furan; IVb was synthesized from benzoylnitrile oxide. The biradical primarily formed by photolysis was stabilized with respect to the arrangement of the heteroatom and the isoxazoline chromophore. The new 1,3-oxazine derivatives III and V were obtained in high yields as single products. The quantum yield of photoreaction of II, IVa and XXVII was found to be 0.04, 0.26 and 0.07, respectively. Were the stabilization of the radical by conjugation with the lone electron pair of oxygen impossible, oxazoline VII should be formed. Photolysis of the benzoyl derivative IVb had an anomalous course and yielded the β-aminochalcone Xb.

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