Chemistry 351, Summer 2019, Winona State University, Dr. T. Nalli 

Expt #3. Diels-Alder Reaction of α-Phellandrene with p-Benzoquinone

Relevant textbook readings - Klein - chapter 17.7. Mohrig - chapter 15.

Literature Reference - Alder, K.; Stein, G.; Pries, P.; Winckler, H. Ber. Dtsch. Chem. Ges. 1929, 2337-2372.

Prelab - Make sure you calculate the volume of phellandrene and the mass of p-benzoquinone to use and include both in your table of reactants and products. Also make sure to include the theoretical yield of the product.

Overview - You will carry out the Diels-Alder reaction of the terpene natural product, (R)-(–)-α-phellandrene, with p-benzoquinone. The resulting product could conceivably be any of four possible diastereomers, however, the configuration of C-5 of the phellandrene must be retained as shown in equation 1.

equation'

We will run the reaction and obtain a crystalline product that will be thoroughly characterized by 1H, 13C, DEPT, COSY, and HMQC NMR. An IR spectrum and mp (lit mp = 119 ºC) will also be obtained.

Procedure 

Reaction:

  1. In a 10-mL round-bottom flask put 5 mmol p-benzoquinone and 5 mmol α-phellandrene.
  2. Add 4.0 mL of 1:1 EtOH/H2O and a boiling chip.
  3. Attach a reflux condenser, and heat at reflux for 30 min.
  4. Cool on an ice bath.
  5. Collect the crude product by vacuum filtration.
  6. Save a small sample of the crude product for a mp determination.

Purification:

  1. Recrystallize the product from methanol. (Review chapter 15 in Mohrig).
  2. Get the crystals as dry as possible by sucking air through on the Buchner funnel for approx 15 min or by air drying for one week.

Analysis:

  1. Obtain the IR spectrum using the cast-film method of sample preparation. (see pp 286-287 in Mohrig).
  2. Obtain the mp of both the crude and recrystallized product.
  3. Prepare a sample for NMR spectroscopy (CDCl3) and obtain a proton NMR. The group with the highest quality proton NMR (as judged by the instructor) will also obtain the following spectra: 13C NMR, DEPT-135, HMQC, HMBC, or COSY. The instructor will assist and the other groups will report on their own proton NMR in conjunction with the additional spectra from the chosen group.