Diels Alder
Read pages 412-417.
Run the Diels Alder condensation reaction between alpha-phellandrene and maleic
anhydride according to the directions below. Obtain IR (KBr pellet) spectrum of the
product.
Write up a pre-lab for the condensation of α-phellandrene (2-methyl-5-isopropyl1,3-cyclohexadiene) and maleic anhydride.
You won't find the product in the CRC.
The α-phellandrene that we have is not pure, it only contains 70% α-phellandrene
by weight. You will need to figure how much of the impure compound to weigh out that
will contain 0.050 mole of the α-phellandrene.
In a 100-mL round-bottom flask put 0.050 mole of maleic anhydride and the
weight of impure α-phellandrene that contains 0.050 mole. Add 25 mL of ethyl acetate,
attach a reflux condenser, and heat on a hot water wath for one hour. Cool in an icewater bath and then suction filter. Recrystallize the product from ethyl acetate, vacuum
filter, let air dry, weigh, package, and obtain the IR spectrum (KBr method).
answer the following questions:
1) Why is the endo product usually preferred in Diels-Alder condensations?
2) In your product, which way is the isopropyl group pointed? Explain.
3) The product of your synthesis has three chiral centers. Draw the product and label
each chiral center with and asterisk (*). How many stereosiomers are theoretically
possible? Only one stereoisomer is actually formed in this reaction, explain.
4) Predict the products of the following:
a)
b)
c)
d)
e)
1,3-butadiene + 2-butyne
1,3-cyclopentadiene + cis-2-butene
1,3-butadiene + dimethyl maleate(methyl ester of maleic acid)
(2 mol)1,3-cyclopentadiene + p-benzoquinone
dicylopentadiene + heat (retro Diels-Alder)
5) Explain why the diene must be in the sigma-cis conformation in order to undergo a
Diels-Alder reaction.