Notes0619 - CH 3 O O NH NH NMe 2 O O O CHO CF 3 CF 3 O CN...

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Experiment 5: Diels-Alder Reaction The Diels-Alder reaction is a [4+2] cycloaddition between a conjugated diene, and a dienophile. General Diels-Alder Cycloaddition: Ew Ew Ew Ew or Ew = electron-withdrawing group such as: CR O CH O COR O C N Diene Dienophile Adduct Adduct Dienophile Diene O O O O O O anthracene maleic anhydride 9,10-dyhydoanthracene- 9,10- α , β -succinic acid anhydride dry xylenes heat + The conjugated diene must be able to adopt a s-cis (sigma cis) conformation so that the ends of the conjugated diene are close enough to react with the alkene. A diene that is locked in the s -cis form will react faster than one that is in equilibrium between the two forms. A diene that is locked in the s -trans conformation will not react. 28
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s-trans s-cis locked in s-cis 1,3-butadiene 1,3-cyclopentadiene locked in s-trans 3-vinylcyclohexene Electron-donating groups on the diene and electron-withdrawing groups on the dienophile will speed up the reaction.
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Unformatted text preview: CH 3 O O NH NH NMe 2 O O O CHO CF 3 CF 3 O CN CN CO 2 Et EtO 2 C O O Cis-dienophiles only form cis-adducts while trans-dienophiles only form trans-adducts, therefore, the reaction is stereospecific. CN CN CN CN (mesocompound) + + (racemic mixture) CN CN CN NC + CN CN trans-adduct cis-adduct cis-dienophile cis-dienophile Cyclic dienes react with certain alkene-dienophiles in such a way that the endo product is formed rather than the exo one. 29 CO 2 Me CO 2 Me CO 2 Me CO 2 Me CO 2 Me CO 2 Me endo exo + major product + Draw the structure of the missing reagent(s), or major organic product(s) for each of the following reactions. If there is no reaction write N. R. Show the correct stereochemistry when needed! + O O 2 + CF 3 CF 3 + CN CN O + diene dienophile 30 + diene dienophile O CHO CHO 31...
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Notes0619 - CH 3 O O NH NH NMe 2 O O O CHO CF 3 CF 3 O CN...

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