What will be the product when 3,4-dibromocyclohexene is reacted with sodium followed by heating with selenium? I'm tutoring few Class 12 students for their chemistry exams. I'm stuck with few problems. I don't know, if the key is wrong or I am wrong. 


  


According to me product (A) must be the cyclic diene, as given in option (A). Now, I don't know, what happens when you heat cyclic diene with selenium. But I do know that,  $\ce{SeO2}$  oxidizes allylic positions of alkenes into alcohols. But, none of the options given are fitting into that argument.

The answer given in the book is option (B).
How can that be explained?
Assuming your Product A is correct then product B should be benzene. Selenium act as a mild oxidizing agent at temperature 220 °C to 330 °C. In the above reaction selenium oxidizes cyclohexadiene to form benzene.

Below is a reaction in which 1-methyl-1,3-cyclohexadiene is converted into toluene.


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