Lab # 1 The Diels-Alder Reaction.doc

Lab # 1 The Diels-Alder Reaction.doc - CH2630 Lab 1 The...

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CH2630: Lab # 1 - The Diels-Alder Reaction Name: Megan Hopkins Date: September 18, 2017 Objective: The Diels Alder Reaction: Synthesis of cis-4-cyclohexene-1,2-dicarboxylic anhydride from 2,5-dihydrothiophene-1,2-dioxide and maleic anhydride in a Diels- Alder Cycloaddition Reaction. References: 1. T.W.G. Solomons, C.B. Fryhle and S.A. Snyder, Organic Chemistry, 12 th Edition, Wiley, 2016, pages 599-616. 2. T.W.G. Solomons, C.B. Fryhle and S.A. Snyder, Organic Chemistry, 11 th Edition, Wiley, 2014, pages 608 – 625. 3. T.W.G. Solomons and C.B. Fryhle, Organic Chemistry, 10 th Edition, Wiley, 2011, pages 616 – 628. 4. http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch10/ch10-5.html Introduction In 1928 two German chemists, Otto Diels and Kurt Alder, developed a 1,4-cycloaddition reaction of dienes that is now known by their names as the Diels-Alder Reaction. In recognition of the synthetic usefulness of the reaction Diels and Alder were awarded the Nobel Prize in 1950. Notes on the Diels-Alder reaction include: 1. The Diels-Alder reaction is a conjugate addition reaction of a conjugated diene to an alkene (the dienophile ) to produce a cyclohexene. 2. The simplest example is the reaction of 1,3-butadiene with ethene to form cyclohexene: 3. The analogous reaction of 1,3-butadiene with ethyne to form 1,4-cyclohexadiene is also known: © Dr. John Purdie Sloan; CH2610 & CH 2630 Organic Chemistry Experiments, Fall 2017 & Winter 2018. Page 1 of 13
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4. Since the reaction forms a cyclic product, via a cyclic transition state, it is also described as a, " Cycloaddition ", reaction. 5. The reaction is a concerted process: 6. Due to the high degree of regio- and stereo-selectivity (due to the concerted mechanism), the Diels-Alder reaction is a very powerful reaction and is widely used in synthetic organic chemistry. 7. The reaction is usually thermodynamically favourable due to the conversion of 2 π- bonds into 2 new stronger σ-bonds. In the reaction 3 relatively weak π-bonds break, and 2 new stronger σ-bonds and one new π-bond form. 8. The two reactions shown above require harsh reaction conditions, but the normal Diels-Alder reaction is favoured by electron withdrawing groups on the electrophilic dienophile and by electron donating groups on the nucleophilic diene. 9. Some common examples of the components are shown below: Dienes Dienophiles © Dr. John Purdie Sloan; CH2610 & CH 2630 Organic Chemistry Experiments, Fall 2017 & Winter 2018. Page 2 of 13
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10.Stereoselectivity: 10.1 The Diels-Alder reaction is stereospecific with respect to both the diene and the dienophile. 10.2 Addition is syn on both components (bonds form from same species at the same time). 10.3This is illustrated by the examples below: A cis -dienophile gives cis -substituents in the product. A trans -dienophile gives trans -substituents in the product. If the diene substituents have the same stereochemistry (here they are both E), then both end up on the same face of the product If the diene substituents have opposite stereochemistry (here one is E and one Z), then they end up on opposite faces of the product © Dr. John Purdie Sloan; CH2610 & CH 2630 Organic Chemistry Experiments, Fall 2017 & Winter 2018.
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