Q 14-14-56 E - Organic Chemistry (Mcmurry)

Question

Norboradiene (Problem 14-55) can be prepared by reaction of chloroethylene with 1,3-cyclopentadiene, followed by treatment of the product with sodium ethoxide. Write the overall scheme and identify the two kinds of reactions.

Step-by-Step Solution

Answer

The first step and second step reactions are Diels-Alder reaction and E2 elimination reaction respectively.

Diels-Alder reaction

Diels-Alder reaction is an important organic reaction which includes a substituted alkene in the form of a dienophile and a conjugated diene. It proceeds via concerted mechanism (simultaneous bond breaking and bond formation). Diels alder reaction generates a 6 membered ring.

It is a pericyclic reaction between a conjugated diene and a dienophile. The reaction is stereospecefic i.e., the cis dienophile will give cis stereochemistry in product and trans dienophile will generate product with trans stereochemistry.

                                 Diels-Alder reaction

Diene and dienophile

Diene is an organic compound which comprises of two or more double bonds separated by a single bond while dienophile is a diene loving compound or ( a substituted alkene with electron withdrawing group). When the interaction between them, occurs a transition state without any additional energy barrier, is obtained.

Explanation

The formation of  Norboradiene (Problem 14-55)  by the reaction of chloroethylene with 1,3-cyclopentadiene first forms aldrin which is a Diels-Alder reaction and can be shown as follows-

After the Aldrin is formed, it undergoes dehydrohalogenation with sodium ethoxide to form norboradiene. It is an elimination reaction (E2).