I'm having trouble with the following set of reactions and their products.

enter image description here Product A is achieved by exploiting the unique aromaticity of cycloheptatriene cations. When A is treated with the Grignard reagent $\ce{MeMgI}$, a mixture of B and C is obtained. Treating A with catalytic amount of $\ce{HCl}$ in $\ce{CCl_4}$ furnishes isomer A’, which is again converted into a mixture of B and C upon treatment with Lewis-acidic Grignard reagents.

For A I got the following structure, since I could not figure out how the aromaticity of the first structure is affecting the reaction.

enter image description here

This cannot be correct, since the grignard reaction would produce only one product and not a mixture of two.

enter image description here

Having done some reasearch online on the resonance structures of cycloheptatriene, I thought of the following structure for A. But this would not produce two different products either if I am not mistaken.

enter image description here

  • 6
    $\begingroup$ I think your initial structure for A is correct. Consider that MeMgI can attack A in a 1,2 mode or 1,4 $\endgroup$
    – Waylander
    May 14, 2021 at 11:27
  • $\begingroup$ Would that result in the products B and C being 1) the one below my structure for A and the other 2) being the same as 1) but with methyl group moved to the adjacent carbon in the cycloheptatriene structure? $\endgroup$ May 14, 2021 at 12:10
  • 3
    $\begingroup$ 1) correct 2) Me group in the benzylic position on benzocycloheptadiene ring - like your last structure but without the OH $\endgroup$
    – Waylander
    May 14, 2021 at 13:23

1 Answer 1


The product A, shown below, is formed by first reducing the ketone to a secondary alcohol with $\ce{LiAlH_4}$ and then by adding a methyl group to form an ether using the reagent $\ce{CH_3I}$.

$\hskip2in$ A

Next the grignard reaction with product A will form two products. The grignard reagent $\ce{MeMgI}$ can attack A in a $1$,$2$ or in a $1$,$4$ mode, due to the unique aromaticity of cycloheptatriene, giving a mixture of products B and C, the structures of which are shown below.

$\hskip1in$B C


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