Question

(1) Draw the products of Diels-Alder reaction of maleic anhydride with α-phellandrene, β- phellandrene, and α-terpinene, assuming that endo product is formed. In each structure, mark all chiral carbons present (if any).

(2) Using a reaction of 1,3-cyclohexadiene with maleic anhydride, explain endo selectivity in Diels-Alder reaction (include a clear drawing of orbitals overlap in transition state as a part of your answer)

Answer 1

Question 2:

The Diels-Alder reaction is facilitated by the presence of electron donating groups on the diene and by the presence of electron withdrawing groups on the dienophile. For instance, maleic anhydride is a very good dienophile because it contains two highly electron withdrawing carbonyl groups. In fact, maleic anhydride was one of the original dienophiles that Diels and Alder used in their studies. It will react with a variety of dienes to afford the corresponding cyclohexene system. The reaction of maleic anhydride and cyclohexadiene is shown as an example (see picture below)

In this case, the endo is well favored because of steric effect. The H atoms would not exert steric effect with the left side of the ring, while the exo it does, because the maleic anhydride it's on the upper side.

Question 1.

I have a doubt of the final product with the Beta, but the other two are there: