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

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?

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    $\begingroup$ For formation of D, electrophilic nature of double bond is considered. $\endgroup$
    – Zenix
    May 10, 2020 at 13:30
  • $\begingroup$ @Zenix I just tried doing that now, it leads to the formation of that 3 mem-ring but for me the 3-mem ring's position was different. It came directly opposite to the c double bond o. Could u help me out pls? $\endgroup$
    – booma vijay
    May 10, 2020 at 13:48
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    $\begingroup$ C is a bogus result . Only five carbons. D is doable. If your 3-membered ring is the obvious one bearing two geminal phenyls, have the radical fragment it such that the diphenyl methyl radical is formed. Now couple this radical with the one on the oxygen resonance form. $\endgroup$
    – user55119
    May 10, 2020 at 15:43
  • $\begingroup$ @user55119 I cant believe that i didn't notice that c had only 5 c atoms. thanks. But the next part i dont get. Do you mind posting an answer? Thanks a lot! $\endgroup$
    – booma vijay
    May 10, 2020 at 16:51

2 Answers 2

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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.

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1) A. G. Schultz and S. A. Hardinger, J. Org. Chem., 1991, 56, 1105.

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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

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