Diels-Alder reaction

What is the purpose?

Purpose is to provide a diels-alder cycloaddition rxn.

→An e- rich diene reacts with an e- poor alkene to from a cyclohexene ring

Explain the reaction

-The reaction is between a diene with an electron-
deficient alkene (dienophile) that produces a cyclohexene ring

-Known as a [4+2] cycloaddition bc a ring is formed by the interaction of 4 π e^- of the alkene with 2 π e^- of the alkene/alkyne

What are the stereochemical requirements?

-Diene must be in s-cis conformation.

-Diene’s C1 and C4 p orbitals must overlap with dienophile’s p orbitals to form new sigma bonds.

-Both sigma bonds are on same face of the diene: syn stereochemistry.

Explain the S-Cis Conformation of the Diene

→s-cis conformation: Can rotate around the C-C single bond to get the more STABLE s-trans conformation.

→s-trans conformation: Its more stable (12 kJ/mol) than the s-cis

Explain the Diels–Alder Rate for Dienes

→The cyclopentadiene undergoes Diels-Alder rxn bc of its fixed s-cis conformation.

→When the diene is sterically hindered, the reaction
slows down even though if it has s-cis conformation.

→S-trans dienes do NOT undergo the Diels–Alder reaction

What is the Endo rule?

The p orbitals of the EWG on the dienophile have a secondary overlap with the p orbitals of C2 and C3 in the diene.

Draw mechanism of a 1,4 product

→A 1,4 product can form but a 1,3 product CANNOT

Draw mechanism of a 1,2 product

→A 1,2 product can form but a 1,3 product CANNOT

Draw the products of these of diels-alder reactions

Draw the mechanism of Diels-Alder reaction

-state which is the diene and dienophile

→one-step, concerted mechanism

→A diene reacts with an electron-poor alkene (dienophile) to give cyclohexene or cyclohexadiene rings.

Draw the flow chart of Diels-Alder reaction

What are the 3 steps in this reaction

1. Add 0.5g of anthracene, 0.26g of maleic anhydride, 6mL of xylene and boiling chips into a round bottom flask for a 30min reflux.

2. Cool solution to room temp. Place solution & 10mL of xylene in ice-bath.

3. Vacuum filter & rinse with xylene. Check mp of dry crystals.