A New Approach to Mechanistic Organic Photochemistry. IV. Photochemical Rearrangements of 4,4-Diphenylcyclohexadienone

1962 ◽  
Vol 84 (23) ◽  
pp. 4527-4540 ◽  
Author(s):  
Howard E. Zimmerman ◽  
David I. Schuster
Keyword(s):  
New Approach ◽  
Organic Photochemistry ◽  
Photochemical Rearrangements

Some photochemical rearrangements of vinylcyclopentadienes. Mechanistic and exploratory organic photochemistry

1984 ◽  
Vol 62 (11) ◽  
pp. 2592-2611 ◽  
Author(s):  
Howard E. Zimmerman ◽  
William D. Ramsden
Keyword(s):  
Cope Rearrangement ◽  
Direct Irradiation ◽  
Organic Photochemistry ◽  
Photochemical Rearrangements

The photochemistry of 2,3-diphenyl-1,4,5-trimethyl-5-vinylcyclopentadiene and 1,2-diphenyl-3,4,5-trimethyl-5-vinylcyclopentadiene was studied. The triplet of the 2,3-diphenyl isomer was found to undergo a 1,5-vinyl migration; in contrast, the 1,2-diphenyl diene was unreactive. On direct irradiation, in addition to vinyl migration, four photoproducts were formed from the cyclopentadienes. These were shown to be 5,6-diphenyl-1,2,7-trimethylbicyclo[3.2.0]hepta-2,6-diene, 1,5-diphenyl-2,6,7-trimethylbicyclo[3.2.0]hepta-2,6-diene, 6,7-diphenyl-1,2,5-trimethylbicyclo[3.2.0]hepta-2,6-diene, and 1,7-diphenyl-2,5,6-trimethylbicyclo[3.2.0]hepta-2,6-diene. A number of experimental observations led to a mechanism involving: (a) electrocyclic closure of the vinylcyclopentadienes to give vinyl housenes, (b) bicycling which interconverts isomeric housenes, and (c) thermal Cope rearrangement of the vinyl housenes to afford bicyclo[3.2.0]hepta-2,6-dienes. In addition, evidence was adduced for 1,5-vinyl shifts occurring in the vinylcyclopentadiene reactants.

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