Photochemical generation of nitrosocarbonyl intermediates on solid phase: synthons toward hetero Diels-Alder and Ene adducts through photocleavage.

The synthesis of 1,2,4-oxadiazole-4-oxides on polystyrenic solid phase docked at the position 3 of the heterocyclic ring has been performed through the cycloaddition of stable supported nitrile oxides to amidoximes. The photochemical cycloreversion of these heterocycles afforded the free nitrosocarbonyl intermediates that were trapped by suitable dienes or enes. The method is proposed as a clean and environmental friendly approach to the fleeting nitrosocarbonyl intermediates, which afford valuable adducts for various synthetic applications. The isomeric heterocycles docked at the position 5 of the ring have also been obtained by cycloaddition of nitrile oxides to supported amidoximes. Their photolysis afforded resin-bound nitrosocarbonyls that were trapped with dienes affording valuable supported adducts suitable for further elaboration on solid-phase chemistry.