The photosensitized rearrangement of aryl-substituted tricyclo[2.2.0.02,6]hexanes to bicyclo[3.1.0]hex-2-enes

✍ Scribed by Albert Padwa; Thomas J. Blacklock; Roman Loza

• Publisher: Elsevier Science
• Year: 1979
• Tongue: French
• Weight: 187 KB
• Volume: 20
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)93620-2

✦ Synopsis

The triplet sensitized irradiation of 3-allyl-diaryl-substituted cyclopropenes to m.l.O]hex-2-enes proceeds via an intramolecular [2+2]-cycloaddition followed by a subsequent rearrangement of the initially formed tricycl0[2.2.0.0~~~]hexane skeleton. Previous work from this laboratory has shown that the direct irradiation of 3-allyl-3methyl-1,2-diphenylcyclopropene (1) afforded 1,2-diphenyl-3-methylbicyclo[3.l.O]hex-3-ene (3) as the exclusive photoproduct.' The most reasonable explanation to account for the formation of 2 involves ring opening of the electronically excited singlet state of 1 to a vinylcarbene intermediate (g).2-4 Attack of the carbene carbon on the neighboring double bond generates the bicyclo[3.l.O]hexene skeleton. The photochemical reaction encountered on direct irradiation proceeds through the singlet manifold since irradiation of 1 in the presence of a triplet sensitizer gave rise to the isomeric bicyclohexene i.5 Subsequent studies showed that 3 is not a primary reaction product but is formed by a secondary photoreaction of tricyclohexane 3. With short exposures , tricyclohexane 3 accounts for nearly