DIELS-ALDER REACTIONS1 Background

IntroductionThe Diels-Alder reaction is a very synthetically useful cycloaddition that results in high yields of cyclohexene products with high stereo- and regioselectivity. In a typi-cal reaction, the substrates consist of an electron rich diene in the s-cis configuration and an alkene substituted by one or more electron withdrawing groups (the dieno-phile). One example is shown below in Figure 1.

s-trans s-cisDIENE

O

H

O

H

DIENOPHILE SUBSTITUTEDCYCLOHEXENEPRODUCT

In todays experiment we will perform two Diels-Alder reactions. First, you will react the diene furan 1 with the common dienophile, maleic anhydride 2 (Fig. 2). The melting point of your product will be used to determine whether the exo or endo stereoisomer is the major product with further characterization via IR spectroscopy.

O O

O

O

THFRT+

O

O

O

O

OO

O

O

1 2 3a 3b

In the second part of this experiment, anthracene 4 and maleic anhydride 2 react to give Diels-Alder Adduct 5 (Fig. 3). You will use NMR as well as melting point data to characterize this second product.

+ HH OO

OO

O

O524

Safety IssuesAnhydrides react quickly with water to form acids, if you spill any anhydride on yourself wash it off immediately.

Standard uses of gloves, safety glasses, and pipettes are to be observed. See Lab 1 or consult your TA for details.

C H E M I S T R Y 2 0 2Duke University - Organic Chemistry Laboratory

A m a n d a K a s p e r, P h . D . O r g a n i c L a b o r a t o r y M a n a g e r 1 2 2 5 F r e n c h F a m i l y S c i e n c e C e n t e r

3LabReading Assignments

Techniques: Filtration: Fessenden2, p. 29-32 Reflux: Fessenden, p. 154-156Chemistry: Diels-Alder: Loudon3, p. 690-700 Aromaticity: Loudon, p. 721-727 Kinetic vs. Thermodynamic control of reactions:

Loudon, Sec. 15.4C, p. 705-707

Figure 1. An example of a Diels-Alder reaction.

Figure 2. The formation of 7-oxobicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride.

Figure 3. The formation of dihydroanthracene succinic anhydride.

Procedure

PART 1. Preparation of a 7-Oxanorbornene Derivative SHOULD HAVE BEEN COMPLETED DURING LAB 1.Step one Synthesis of 7-oxobicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride via the reaction of furan and maleic anhydride.

1. Charge a 50 mL round bottom flask (RBF) with 5g of maleic anhydride. The maleic anhydride may have to be ground into a powder with a mortar and pestle. If so, two groups may want to join together in grinding a larger briquette and share the resulting ground maleic anhydride. Please be sure to clean the mortars and pestles with acetone when you are finished.

2. To the 50 mL RBF containing the maleic anhydride add 15 mL of tetrahydrofuran and swirl until the maleic an-hydride dissolves completely.

3. Add 3.3 mL of furan, swirl to mix thoroughly, and stopper the RBF with a rubber septum.

4. Clearly label your flask with the following information:a. Both lab partners namesb. Lab section numberc. Maleic anhydride + furan + THF

5. Place the RBF in a beaker in your sections box and allow the reaction mixture to stand in until the following lab period.

Stop the rest of the procedure will be performed at the next lab meeting.

!Hint: To maximize efficiency, set up the 20 minute reflux right away then work up your product from last week.

PART 2. Preparation of Dihydroanthracene succinic anhydride.1. Charge a 50 mL round bottom flask with 2g of anthracene, 1.1g of maleic anhydride, 25 mL of dry xylene, a mag-

netic stir bar and a few boiling stones. Fit a reflux condensor into the flask.

2. Place the round bottom flask in the metal heating tray on a hotplate, cover the RB with aluminum foil and heat to reflux with stirring for 20 minutes. What does reflux mean?

Now is a good time to work up the furan/maleic anhydride adduct.

3. Allow the solution to cool completely and collect the crystalline product using vacuum filtration. Allow the vac-uum to pull air through the product for 5-10 minutes to facilitate drying.

4. Dry the product further by pressing the solid between dry filter paper.

5. Weigh your product, calculate a percent yield, and measure the melting point range. Obtain an IR spectrum of your product.

ONLY ONCE YOU HAVE GATHERED ALL OF THE REQUIRED DATA dispose of the product in the waste con-tainer labeled Solid Waste in the common hood.

D u k e U n i v e r s i t y! L a b 3 : D i e l s - A l d e r R e a c t i o n s

2

PART 1. (**Continued from last week**)

Step two Isolation of 7-oxobicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride.

6. Collect the crystalline product using vacuum filtration. Wash with a small amount (

In-Lab NotebookProcedure and Observations record EXACT amounts of reagents used (use table similar to one shown above), observations, and any changes you have made to the written procedure. This should be written directly in your notebook while you are in the lab.

All information above should be written directly into your lab notebook. The duplicate pages will be turned in to your TA at the end of the lab.

All information below will be included on the Post-Lab Report and does NOT have to be written separately in the notebook. You may choose to work through your calculations or organize your ideas for the discussion, etc. in the notebook, but this information is not required in the notebook.

Post-Laboratory ReportComplete the report as directed below.

References1 Parts of this procedure have been adapted from: Roy, C.P., Sebahar, H.L. Organic Chemistry Laboratory Handout, Duke University, 2005, 2008; France, M., Alty, L. and Earl, T.M., J Chem Ed., 76, 5, 1999, pg. 659; and Campbell, B., and Ali, M., Organic Chemistry Experiments, Brooks/Cole Publishing 1994.2 Fessenden, Fessenden, Feist. Organic Laboratory Techniques, 3rd Edition. Brooks/Cole, Pacific Grove, CA, 2001.3 Loudon, GM. Organic Chemistry. 5th ed. Roberts & Company Publishers; 2008

D u k e U n i v e r s i t y! L a b 3 : D i e l s - A l d e r R e a c t i o n s

4

Chemistry 202L - Post Lab Report for Diels-Alder Reactions (Lab 3)Name:__________________________________! TA name/Section number:______________________________

7-oxanorbornene derivative

Balance the equation used in the reaction:

Calculate amount of furan (in moles) actually used (based on the amount you measured):

Calculate amount of maleic anhydride (in moles) actually used (based on the amount you measured):

The limiting reagent is: ______________________________________

Calculate theoretical yield for the 7-oxanorbornene derivative:

Calculate the percent yield for the 7-oxanorbornene derivative:

D u k e U n i v e r s i t y! L a b 3 : D i e l s - A l d e r R e a c t i o n s

5

O O

O

O

THFRT+

O

O

O

O1 2 3a + 3b

In the space below, draw a curved-arrow mechanism for the reaction performed in Part 1.

Appearance of isolated 7-oxanorbornene derivative:_________________________

Literature appearance:__________________________ Observed mp range:___________! Literature mp range:___________

Show the exo-product in the space below:! ! Show the endo-product in the space below:

Based on what youve learned from consulting your text or in lecture, which is the expected major product (exo/endo)?

_____________________________

Based on the analysis of your experiment, what was the major product you synthesized? (exo/endo)?

_____________________________

D u k e U n i v e r s i t y! L a b 3 : D i e l s - A l d e r R e a c t i o n s

6

Dihydroanthracene succinic anhydride:

Balance the equation used in the reaction:

Calculate amount of anthracene (in moles) actually used (based on the amount you measured):

Calculate amount of maleic anhydride (in moles) actually used (based on the amount you measured):

The limiting reagent is: ______________________________________

Calculate theoretical yield for dihydroanthracene succinic anhydride:

Calculate the percent yield for dihydroanthracene succinic anhydride:

D u k e U n i v e r s i t y! L a b 3 : D i e l s - A l d e r R e a c t i o n s

7

+ HH OO

OO

O

O

524

In the space below, draw a curved-arrow mechanism for the reaction performed in Part 2.

Observed mp range: ________________________! ! Literature mp range: ________________________

Additionally:

Attach a copy of your IR spectrum for the anthracene/maleic anhydride adduct. Indicate the functional group re-sponsible for each important peak. You may ignore the fingerprint region. Attempt to identify at least two impor-tant peaks.

Attach a copy of 1H NMR spectra of the oxanorbornene derivative. Draw the structure of the molecule directly on the spectra and letter (Ha, Hb, Hc, etc.) the unique protons. Does the number of unique protons that you have pre-dicted match the number from the spectra? Identify the peaks that correspond to each labeled proton.

Attach a copy of the 13C NMR spectra of the dihydroanthracene succinic anhydride. Draw the structure of the molecule directly on the spectra and number the unique carbons. Does the number of unique carbons that you have predicted match the number from the spectra? Identify the following four types of carbons on the drawing and the corresponding peaks on the spectra: sp3-hybridized, quaternary aromatic carbons, non-quaternary aro-matic, and carbonyl carbons.

D u k e U n i v e r s i t y! L a b 3 : D i e l s - A l d e r R e a c t i o n s

8