The problem

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Source : MS Couhan (problems in organic chemistry . Chapter: Alcohols , phenols and ethers).

My Thoughts

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If I proceed along $\ce{path 1}$ , $\ce1a$ is formed . It is unstable due to inductive withdrawing effect of $\ce{C=O}$ neighboring to it. Eventually $\ce2$ is obtained.

However, along $\ce{path 2}$ relatively more stable $\ce{3a}$ (compared to $\ce{1a}$) is formed. $\ce3a$ on ring expansion gives $\ce{3b}$ , leading to $\ce{4}$ ($\ce{3b}$ is relatively unstable compared to $\ce{1b}$).

My question

Which of the two paths should I choose that would lead to a major product ?


The reaction of epoxyketone 1 affords diketone 2 under photochemical and thermal conditions ostensibly through the diradical.1 Boron trifluoride provides the diketone 3 through acyl bond migration and not via alkyl group migration as in your intermediate 3a. I have not located a proton-catalyzed reaction. Unfortunately, diketone 3 was not one of your choices.

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1) John R. Williams, George M. Sarkisian, James Quigley, Aaron Hasiuk, and Ruth VanderVennen, J. Org. Chem., 1974, 39, 1028.

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  • $\begingroup$ @ user55119 this solves my problem. The intermediate formed after reaction with Boron triflouride is more stable then 3b or 1a.This could be the major product. $\endgroup$ – Chakravarthy Kalyan Jul 19 '19 at 23:41
  • $\begingroup$ Cation 1a is a bad choice in any event. $\endgroup$ – user55119 Jul 20 '19 at 0:15

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