Final Examination 5 December, 2001
D. J. Burnell 9:00 AM - 12 noon (3 hours)
Instructions: Read the questions completely and carefully. Only Question 1A provides a choice. Full marks will require correct answers for all other questions. Answer Question 5 on the examination sheet. Answer all other questions in an examination booklet. The examination will be marked out of 100.
Question 1. [22 marks]
A. Answer three of the four parts.
i. Give an example of the Skraup synthesis.
ii. Outline the biosynthesis of lanosterol from squalene. (A full rationalization of the
stereochemistry is not required in the cyclization.)
iii. Outline the biosynthesis of shikimic acid from D-erythrose.
iv. Give an example of the Kiliani-Fischer synthesis.
B. Show how the compound above might be synthesized by the Fischer indole synthesis. Start by showing the starting compounds. Outline a mechanism for this synthesis, although a detailed mechanism for the formation of the first intermediate (the part that was Chemistry 2401 material) is not required.
Question 2. [24 marks]
A. Provide a starting compound with no rings that might give the compound T in a single synthetic operation. Give the conditions that you think would be needed (reagents, temperature, etc.) to make this transformation take place. Hint: the same reaction conditions might also do something after the cyclizations...
B. In a biosynthetic study, acetate labeled with a radioactive marker was fed to a flowering plant from Mauritius. Two C10H8O4 natural products, X and Y, were later isolated with the radiolabel. What are the biosynthetic similarities and differences between X and Y?
C. i. What sort of natural product is compound Q? ii. What is the structure and the name of the acyclic (i.e., no ring) biogenetic precursor for Q? iii. Show two patterns of isoprene incorpora-tion in Q, and, for one of these, propose a reasonable biosynthetic sequence from this precursor to Q. iv. Could incorporation of doubly 13C-labeled acetate, along with 13C NMR spectroscopy, tell which of the two isoprene isoprene patterns is the correct one? Explain briefly.
D. i. What structural features allow you to distinguish between addition and condensation polymers? ii. How does pyrrole polymerize in the presence of strong acid? (mechanism) iii. What is the difference between "isotactic" and "syndiotactic" PVC (polyvinyl chloride)? iv. Draw an example of a condensation polymer.
Question 3. [20 marks]
A. Explain what has happened to produce the major product in this attempt to eliminate water.
B. Explain why the major compound in this equilibrium has more axial substituents.
C. Explain why the major product of nitration of thiophene is 2-nitro- rather than 3-nitro-thiophene.
D. Explain why acetal formation with acetone works better with a 1,2-diol rather than a 1,3-diol, and why reaction with a 1,3-diol is favored in acetal formation with benzaldehyde.
Question 4. [11 marks]
A. In just a few words, state what diagnostic features you would look for in i. a shikimic acid derivative, ii. a terpene, iii. an aminoglycoside antibiotic, and iv. an androgen.
B. What is i. an alkaloid, ii. a pheromone, iii. an antifeedant?
C. Identify these compounds (E – H):
Question 5. [24 marks] Fill in the missing structures.