Photochemical rearrangement of 4,4‐diphenylcyclohexa‐2,5‐dien‐1‐one


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> [![Photochemical rearrangement of 4,4‐diphenylcyclohexa‐2,5‐dien‐1‐ol](https://i.stack.imgur.com/XqHoK.jpg)](https://i.stack.imgur.com/XqHoK.jpg)
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I can see how the option **A** and **B** are correct as it is just a standard dienone–phenol type reaction which involves a phenyl shift. However, the given answer is **A**, **B**, **C** and **D**.


I do not see how **C** and **D** are formed. Does the presence of light affect the reaction? If so, how?




The formation of structure **6** (your **D**) occurs as follows. Photolysis of dienone **1** affords excited state **2** that forms cyclopropane **3**. In turn, **3** is capable of breaking a different cyclopropane bond to form 5-membered ring **4**. Structure **5** is a resonance structure of **4**. Structure **5** closes to the [3.1.0] product **6** (your **D**). I don't know how you formed **A** (**12** here) but further photolysis of **6** can form **12** via a bridged phenyl migration as shown in structure **9**. A similar migration in structure **2** leads to your **B**. Of course, structure **C** has only five carbons and was added to the choices as a trap. See reference 1 for an example of a dienone phenol rearrangement.  
  

[![enter image description here](https://i.stack.imgur.com/r8QAU.jpg)](https://i.stack.imgur.com/r8QAU.jpg)  
  



1) [A. G. Schultz and S. A. Hardinger, J. Org. Chem., 1991, 56, 1105.](https://pubs.acs.org/doi/abs/10.1021/jo00003a037)


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The above answer is totally Correct but for your information, if light was not there then there would have been a RETRO PINACOLE-PINNACOLON REARRANGEMENT.[![enter image description here](https://i.stack.imgur.com/0RkZr.jpg)](https://i.stack.imgur.com/0RkZr.jpg)


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