Cyclohexene is treated with $\ce{RCOOOH}$ and 'A' is formed. A is treated with $\ce{CH3MgBr}$ and 'B' is formed. On hydrolysis of B we get 'C'. Identify A,B,C.

I identify A as cyclohex-1,2-diol. Could someone give me assistance after that please.


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  • $\begingroup$ I suggest you read "the reaction of alkenes with peracids" first, then Grignard reaction (assuming you are in OCHEM II class). $\endgroup$ – Mathew Mahindaratne Apr 3 '18 at 16:42

First of all, A is not Cyclohexane-1,2-diol. Because, when you treat a peroxy acid with any alkene, first an epoxide is formed, and it is stable under slightly acidic or basic medium, as it is an ether. But if you hydrolyse the compound under highly acidic conditions then cleavage of this ether happens and the ring opens to form trans-Cyclohexane-1,2-diol. But, here no hydrolysis is being performed under any acidic conditions. So, the treatment with peroxy acid will yield only Cyclohexene-oxide. So, A) is Cyclohexene-Oxide
enter image description here

Now when you treat this with $\ce{CH_3MgBr}$, there is a nucleophilic attack( $S_N2$ ) by $\ce{CH_3^-}$ at one of the two carbons to which oxygen is attached, and the ring opens to form 2-methyl cyclohexanoxide Magnesium Bromide.As, in this case the substitution mostly occurs through $S_N2$, it is most probable to get a trans product. So, In B), major is the following compound
enter image description here

Now, when you hydrolyse it, you will get trans-2-methylcyclohexanol as a major product in C)
enter image description here

  • $\begingroup$ A cautionary note: With Grignard reagents and other coordinating metals, beware of rearrangement of the epoxide to a carbonyl group. In this case cyclohexanone may be formed and add the Grignard reagent to form 1-methylcyclohexan-1-ol. $\endgroup$ – user55119 Apr 3 '18 at 16:11
  • $\begingroup$ How can Cyclohexanone be formed ? I didn't get what you said!! $\endgroup$ – Soumik Das Apr 3 '18 at 16:12
  • $\begingroup$ Mg++ coordinates with oxygen and opens C-O bond leaving cation on carbon. Hydride migrates 1,2 to give cyclohexanone (as enol) coordinated to Mg. Mg++ is lost. Mg++ can be MeMgBr as well. 1,1-Carbon substituted epoxides are notorious in this regard giving aldehydes as intermediates. I do think that your answer is correct as the major product. PS: The mechanism is similar to this. Substitute -H for -CO2H. chemistry.stackexchange.com/questions/86726/… $\endgroup$ – user55119 Apr 3 '18 at 16:23
  • $\begingroup$ Oxygen can still coordinate to $Mg^{2+}$ being in that epoxide (ether) form, why does the ring need to open up for that?? $\endgroup$ – Soumik Das Apr 3 '18 at 16:48
  • $\begingroup$ I don't know the intentions of an epoxide. Just competitive rates, direct addition vs. rearrangement. $\endgroup$ – user55119 Apr 3 '18 at 17:22

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