Diels-Alder reaction between butadiene and maleic anhydride

Objective

The objective of this practice is the realization of a Diels-Alder cycloaddition between a diene and an alkene to obtain a highly functionalized cyclohexene derivative.

Background

Diels-Alder reaction is one of the most remarkable chemical reactions discovered in the 20th century. The authors of this reaction won the Nobel Prize in 1950. It is a powerful tool for constructing 6-membered rings and has been used for the synthesis of many complex molecules.

A [4+2] cycloaddition is usually carried out at moderate to high temperatures and even under pressure. It is a stereospecific reaction with respect to both the diene and the dienophile. In this experiment, two examples of Diels-Alder reactions are described, in the first case the diene is prepared "in situ" from 3-sulfolene, and in the second case a functionalized diene is used.

Experimental procedure

[4+2] Cycloaddition between maleic anhydride and buta-1,3-diene

In a 100 ml round flask 10 g of 3-sulfolene (buta-1,3-diene sulfone) and 5 g of maleic anhydride powder are introduced. Subsequently, 10 ml of xylene are added and the flask is refluxed with magnetic stirring for 45 min. Since SO2 is released during the reaction, a gas trap containing a 5 % NaOH solution is placed at the end of the condenser.

Cool the solution to room temperature and add 50 ml of toluene and activated carbon to decolorize the solution. Filter by gravity. To the filtrate add 25-30 ml of hexane, heat to 80 ºC. Cool the solution first to room temperature and then in an ice bath. Filter the formed crystals under vacuum.

[4+2] Cycloaddition between maleic anhydride and E,E-2,4-hexadien-1-ol

A mixture of 0.40 g maleic anhydride and 0.40 g E,E-2,4-hexadien-1-ol in 5 ml toluene is heated to reflux for 5 min. The solution is allowed to cool slowly to room temperature, whereupon a solid will begin to appear on the walls of the flask.

To assure the total precipitation of the product, (3aR,4S,5S,7aR)-5-methyl-3-oxo-1,3,3a,4,5,7a-hexahydro-2-benzofuran-4-carboxylic acid, we cool in an ice bath for 10 min. It is filtered under vacuum and dried in the air. It can be recrystallized from toluene. (melting point 156-159 ºC).

International Chemical Identifier

The IUPAC InChI key identifiers for the main compounds used in this experiment are provided to facilitate the nomenclature and formulation of chemical compounds and the search for information on the Internet for these compounds.

1,3-butadieneKAKZBPTYRLMSJV-UHFFFAOYSA-N
3-sulfoleneMBDNRNMVTZADMQ-UHFFFAOYSA-N
(3aR,4S,5S,7aR)-5-methyl-3-oxo-1,3,3a,4,5,7a-hexahydro-2-benzofuran-4-carboxylic acidRWDXHRNUDNBBLT-DKXJUACHSA-N
cis-1,2,3,6-tetrahydrophthalic anhydrideKMOUUZVZFBCRAM-OLQVQODUSA-N
maleic anhydrideFPYJFEHAWHCUMM-UHFFFAOYSA-N
E,E-2,4-hexadien-1-olMEIRRNXMZYDVDW-MQQKCMAXSA-N
n-hexaneVLKZOEOYAKHREP-UHFFFAOYSA-N
NaOHHEMHJVSKTPXQMS-UHFFFAOYSA-M
SO2RAHZWNYVWXNFOC-UHFFFAOYSA-N
tolueneYXFVVABEGXRONW-UHFFFAOYSA-N
1,2-xyleneCTQNGGLPUBDAKN-UHFFFAOYSA-N
1,3-xyleneIVSZLXZYQVIEFR-UHFFFAOYSA-N
1,4-xyleneURLKBWYHVLBVBO-UHFFFAOYSA-N
HClVEXZGXHMUGYJMC-UHFFFAOYSA-N

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