Photolysis of 3,5‐diphenylisoxazole in argon matrices

Broadband irradiation of 3,5‐diphenylisoxazole 1 in an argon matrix results in formation of azirine 3. Further irradiation of the matrix reduces the amount of azirine 3 with concurrent formation of ylide 4. Thus, it is theorized that the conversion of isoxazole 1 to azirine 3 goes through a triplet vinylnitrene 2 that does not intersystem cross to ketenimine 6. Hence, the reactivity of triplet vinylnitrene 2 is different from similar vinylnitrene intermediates with α‐methyl substituents that intersystem cross to form corresponding ketenimines. Density functional theory calculations support the notion that the conjugation of the α‐phenyl group to the vinylnitrene moiety in vinylnitrene 2 renders it more flexible than vinylnitrenes with α‐methyl substituents, and therefore, vinylnitrene 2 intersystem crosses to azirine 3, rather than ketenimine 6. Copyright © 2016 John Wiley & Sons, Ltd. Broadband irradiation of 3,5‐diphenylisoxazole 1 in an argon matrix results in formation of azirine 3. Further irradiation of the matrix reduces the amount of azirine 3 with concurrent formation of ylide 4. Thus, it is theorized that the conversion of isoxazole 1 to azirine 3 goes through a triplet vinylnitrene 2 that does not intersystem cross to ketenimine 6.