Photochemistry of azole N-oxides. Facile photoisomerisation of 2H-imidazole N-oxides to 1,3-diaza-6-oxabicyclo[3.1.0]hex-3-enes and synthesis of a 1,3-diaza-4,7-dioxatricyclo[4.1.0.1,603,5]heptane

Ultraviolet irradiation of a series of 2H-imidazole N-oxides 2 has been shown to effect a clean isomerisation to derivatives of the new ring system, 1,3-diaza-6-oxabicyclo3.1.0]hex-3-ene, 7 . Epoxidation of a representative 7 has given access to the hitherto inaccessible trans-fused 1,3-diaza-4,7-dioxatricyclo4.1.0. ^1,60^3,5]-heptane ring system 9 .