Endo-Norbornene-5 6-Dicarboxylic Anhydride
Diels-Alder Synthesis of Exo-Norbornene-cis-5,6-Dicarboxylic Anhydride for Organic Chemistry Laboratory Instruction Kyle Myers and Dr. James Roark University of Nebraska at Kearney, Department of Chemistry, Kearney, NE 68849
Abstract A technique for the Diels-Alder synthesis of endo-norbornene-cis-5,6dicarboxylic anhydride and its stereoisomer, exo-norbornene-cis-5,6-dicarboxylic anhydride, is explained. To prove that each stereoisomer was made in the experiment and to distinguish between the two molecules, the characteristic long range coupling affects seen in the H1-NMR spectra of bridged six member ring molecules are used. A method for the separation of the two molecules is also explained. This technique can be used as a tool to instruct organic chemistry students in the Diels-Alder reaction and how to use NMR techniques to prove the stereochemistry of the products involved in such reactions. Introduction The Diels-Alder reaction has long been an important tool for the organic chemist in that it not only creates new carbon-carbon bonds, but it also creates six-membered rings1. This attribute of the Diels-Alder reaction is especially valuable, because there are few synthetic methods of creating six-membered ring structures. The process of a DielsAlder reaction involves a substituted alkene reacting with a conjugated diene in the cis conformation to create two new carbon-carbon σ bonds which results in the formation of a six-membered ring, as shown below: Figure 1: Example Diels-Alder reaction
+
1,3-butadiene
ethene
cyclohexene
In the case of the reaction outlined in this report, the substituted alkene is maleic anhydride, and the conjugated diene is cyclopentadiene. The two undergo a Diels-Alder reaction to produce norbornene-cis-5,6-dicarboxylic anhydride, as shown:
Figure 2: Diels-Alder reaction between cyclopentadiene and maleic anhydride
H O H H H H O
+
O
H O
+
H
O
O O O O H
cyclopentadiene
maleic anhydride
Abstract A technique for the Diels-Alder synthesis of endo-norbornene-cis-5,6dicarboxylic anhydride and its stereoisomer, exo-norbornene-cis-5,6-dicarboxylic anhydride, is explained. To prove that each stereoisomer was made in the experiment and to distinguish between the two molecules, the characteristic long range coupling affects seen in the H1-NMR spectra of bridged six member ring molecules are used. A method for the separation of the two molecules is also explained. This technique can be used as a tool to instruct organic chemistry students in the Diels-Alder reaction and how to use NMR techniques to prove the stereochemistry of the products involved in such reactions. Introduction The Diels-Alder reaction has long been an important tool for the organic chemist in that it not only creates new carbon-carbon bonds, but it also creates six-membered rings1. This attribute of the Diels-Alder reaction is especially valuable, because there are few synthetic methods of creating six-membered ring structures. The process of a DielsAlder reaction involves a substituted alkene reacting with a conjugated diene in the cis conformation to create two new carbon-carbon σ bonds which results in the formation of a six-membered ring, as shown below: Figure 1: Example Diels-Alder reaction
+
1,3-butadiene
ethene
cyclohexene
In the case of the reaction outlined in this report, the substituted alkene is maleic anhydride, and the conjugated diene is cyclopentadiene. The two undergo a Diels-Alder reaction to produce norbornene-cis-5,6-dicarboxylic anhydride, as shown:
Figure 2: Diels-Alder reaction between cyclopentadiene and maleic anhydride
H O H H H H O
+
O
H O
+
H
O
O O O O H
cyclopentadiene
maleic anhydride
Cited: 1) 2) 3) Durst, H.D., Gokel, G.W., Experimental Organic Chemistry, 2nd ed., McGraw-Hill Inc., New York: 1987, pp 259-265. Bruice, P.Y., Organic Chemistry, 4th ed., Pearson Education, Inc., Upper Saddle River, New Jersey: 2004, pp 320. Silverstein, R.M., Bassler, G.C., Morrill, T.C., Spectrometric Identification of Organic Compounds, 4th ed., John Wiley & Sons, Inc., New York: 1963, pp 209-210.