Chemistry 251/253

Answer Key

Homework 11

Draw the structure of the diene used in the Diels-Alder reaction that produces each of the cyclohexene derivatives shown in Questions 1 and 2.

1.COC=CC(=C)C

2.ClC1C=CC=C1

Draw the structure of the dieneophile used in the Diels-Alder reaction that produces each of the cyclohexene derivatives shown in Questions 3 and 4.

3.O=C1CC(=O)C=C1

4.COC(=O)C#C

5.CC1=C(C)CC(CC1)C#N

6.COC1=CCC2C(C1)C(=O)OC2=O

7.CC(=O)C1CC2CCCC12

8.ClC1=CCCC(=CCC1)Cl

9.CC1(C)OC2CCCC21

10. CC1=CCC23CC=CCC3(C1)C(=O)OC2=O This is a good example of electronic complementarity. The diene is electron rich. It reacts preferentially with the electron poor double bond of the other reactant.

11. Draw the structure of the starting material you photochemical p2s+p2s cycloaddition.

12. How many diastereomers would be produced in the following reaction? 4 The relative stereochemistry of the methyl group and the chlorine atom has to be maintained in this reaction.

13. The following scheme suggests a strategy for trapping cyclobutadiene, an antiaromatic compound which is too unstable to be isolated as a pure material. Draw the structure of the product that is formed in this trapping experiment.

O=C1C=CC(=O)C2C3C=CC3C21

14.The reaction shown below produces an intermediate that decomposes under the reaction conditions to produce the compound that gives the attached 1H-NMR spectrum and a side product. Draw the structure of the side product.

O=C=O

Questions 15-24 involve structures a-h.

15. Enter the letter of the most electron rich diene. g

16. Enter the letter of the most electron rich dienophile. d

17. One of the dienophile/diene pairs will undergo a Diels-Alder reaction faster than any other. Enter the 2-letter combination for this pair, putting the letter for the dienophile before that of the diene. Do not leave any spaces between the letters. cg

18. One of the dienophile/diene pairs will undergo a Diels-Alder reaction slower than any other. Enter the 2-letter combination for this pair, putting the letter for the dienophile before that of the diene. Do not leave any spaces between the letters. ch

19. Rank the dienophiles in order of increasing reactivity towards diene g in a ¼2s + ¼4s cycloaddition. d<b<a<c

20. Which diene will react fastest with dienophile a in a Diels-Alder reaction? g

21. Which diene will undergo a Diels-Alder reaction faster with dienophile b, diene e or diene f ? Enter the just the letter.f

22. How many isomeric cyclohexenes could be produced by the Diels-Alder reaction of d and h? Do not include enantiomers?4

23. Draw the structure of the major cycloaddition product that you might reasonably expect to be formed by irradiation of compound d.C[Si](C)(C)OC1CC(C1)O[Si](C)(C)C

24. Draw the structure of the product that would be formed by a [1,3]-sigmatropic rearrangement of one of the C-H bonds in compound b.COC=CC

25. Al Kane needed a sample of for a research project he was conducting. He proposed to make this compound by the following scheme:. Draw the structure of compound X. Hint-Using curved arrows to show the movement of electrons will help.C1CC=CCCC=C1 or C1CC=C1
Using the notation [x,y] classify each of the following sigmatropic rearrangements. For example, if you think a reaction is a [1,3] sigmatropic rearrangement, enter [1,3]. Be careful about typos.

26.[3,3]

27. [3,3]

28.[1,7]

29. If a Diels-Alder reaction is classified as a p2s+ p4s process, how would you classify the following orbital symmetry allowed reaction? Note-Hold down the option key while pressing the lower case p key to enter the Greek letter p. Do not leave any spaces between the characters in your answer. p2s+ p14a or p2a+ p4s One of the two reactants must undergo an antarafcial addition.

30. Using Frontier Orbital theory, enter the letter of the orbital correlation diagram that applies to the allowed reactionC