8‐Oxabicyclo[5.1.0]octa‐2,4‐dien Thermische und lichtinduzierte Isomerisierung

Abstract 8‐Oxabicyclo[5.1.0]octa‐2, 4‐diene ( 1 ) yields 2,4,6‐heptatrienaldehyde as major primary rearrangement product upon pyrolysis in a flow system between 200 and 300°. Above 500° o ‐cresol, benzaldehyde and benzene are obtained. Bicyclo[3.2.0]hept‐2‐en‐7‐one, 2,3‐ and 2, 5‐dihydrobenzaldehyde are shown to be intermediates in this transformation to stable aromatic products. The observed conversions can be rationalized as proceeding mostly through allowed pericyclic reaction steps with heterogeneous, acid catalysed reactions participating to a minor extent. Irradiation of 1 affords 3‐oxatricyclo[4.2.0.0 2,4 ]oct‐7‐ene, 2,4,6‐heptatrienal and 3,5‐cycloheptadienone. Upon sensitized irradiation only the latter two compounds are formed.