Collect. Czech. Chem. Commun. 1985, 50, 1982-1993

Photo-induced rearrangement of isoxazolines - A pathway to 2,4,5,8-tetrahydro-1,3-dioxa-5-azocine derivatives

Lubor Fišeraa, Vladimír Oremusa, Ladislav Štibrányia, Hans-Joachim Timpeb and Alena Máťušováa

a Department of Organic Chemistry, Slovak Institute of Technology, 812 37 Bratislava, Czechoslovakia
b Department of Photochemistry, Technical University, 42 Merseburg, G.D.R


4-R-Substituted-8-X-phenyl-3,5,10-trioxa-9-azabicyclo[3,5,0]dec-8-enes (X = H, 4-CH3, 4-OCH3, 4-Cl, 4-Br, 4-F, 3-NO2, 3-Cl, 3-Br) have been prepared by cycloaddition of substituted benzenenitriloxides with 2-R-substituted 1,3-dioxep-5-enes (R = H, CH3, C6H5). A mixture of the endo and exo adducts is formed, if R is CH3 or C6H5. Their irradiation produces high yields of the title compounds as the single products. High selectivity of the photo-rearrangement is due to resonance stabilization of the biradical with p electrons of the oxygen atom. The quantum yields of the photoreaction vary from 0.02 to 0.04 depending on the substituent X. An unexpected dependence has been found between the quantum yield of the photo-rearrangement and stereochemical arrangement of the 4-R-substituent: exo derivatives exhibit higher values than the endo derivatives. Also different are UV spectra of the endo and exo derivatives. A new synthesis principle is described enabling preparation of (n + 1)-membered heterocycles from n-membered heterocycles.