Cycloaddition Reactions - Multi-Step Synthesis

The diene shown on the left can be converted into the product shown by performing a simple [4+2] cycloaddition reaction, followed by a reaction of the cyclic alkene. For each problem, draw the structure of the diene and dienophile which would be required for the synthesis, the structure of the intermediate product, and the reaction conditions necessary to convert the intermediate into the final product.

Click the mouse on the buttons to view the synthetic logic, the structure of the intermediate and the solution to the problem.

The final product is an dicarboxylic acid and a bromine has been introduced into the molecule. Alkenes can be converted into carboxylic acids by oxidation in acidic MnO₄^-; the bromine must have come from the dienophile.

This intermediate was formed from the starting diene and a dienophile. To identify the reactants in a [4+2] cycloaddition reaction, identify the carbons of the dienophile (they will be the two carbons in a six-member ring which are opposite to the double bond in the product) and mentally split the bonds, separating the carbon skeletons of the diene and the dienophile.

1,3-cyclopentadiene undergoes [4+2] cycloaddition with 1-bromoethene (vinyl bromide) to give the bicyclic addition product. Oxidation with acidic MnO₄^- gives the final product. No stereochemistry is indicated, but all of the substituents on the cyclopentane ring must be cis-relative to each other. cis-