Final Exam /340 ( CHEM 6352 Fall %) Name

Transcription

1 Final Exam /340 ( CEM 6352 Fall 2012 %) Name Dec. 15 th, :30-13:45 You may NT use any references or aids to complete the following with the exception of a chemical model set and the scrap paper that I provide at the end of the test. Note that showing proper stereochemistry and the rational for that stereochemistry will be graded. ALWAYS show a rationale for new stereochemistry (including substituted olefins) if a reaction would be selective. Also note that chiral structures with designated stereochemistry (i.e. hashes and wedges) are assumed to be enantiopure unless a racemic mixture is explicitly stated. You may use existing structures in the problems for your rational if appropriate. <<BNUS items are optional but worth additional points.>> (30 bonus points) Note that the following compounds can be used for any problem on the test. All other reagents you use may incorporate only 4 carbons or less into the reaction product of a given reaction. C 6 13 BnBr CEM 6352 Library Si Cl N B Bu N Cl Br Grubb's Catalyst Bu4 NF TMS Li B C 2 i-pr C 2 i-pr MPU N I Me i-pr 2 C i-pr 2 C B TMS ClB TMS Et 3 N Et Cp C Me Ti Al Cp Cl Me B Bu TMS 2 N TMS 9-BBN N Ac Ac I Ac (Et) 2 P()CC 2 Et Bu 2 BTf B BCl

2 1. Predict the major products and any new stereochemistry found therein. A. (10 points) 1) L-Selectride (±) 2) C 2 I 2, Zn(Cu) B. (10 points) C 2 I 2, Zn(Cu) ne enantiomer

3 2. Provide reagents for these transformations. A. (10 points) Me ne Enantiomer B. (10 points) Me Me 99% ee 99% ee C. (10 points) <<BNUS (5 points): provide the name of the precursor to the starting material.>> BocN BocN Me ne Enantiomer ne Enantiomer

4 D. (10 points) BocN ne Enantiomer BocN Me ne Enantiomer E. (5 points) <<BNUS (5 points): provide the name of the named reaction.>> N 2 N N N (±) 3. Pick your favorite name reaction! Provide the name of the reaction and an example of the overall transformation. Also, state why you think it is useful. (15 points)

5 4. Describe a synthesis of the compounds on the left from the starting materials on the right. Use reagents from the CEM 6352 library or that add 4 carbons or less. A. (15 points) ne enantiomer B. (10 points)

6 C. (15 points) (±)

7 5. Draw a mechanism for the following idea that Woodward had for prostaglandin synthesis. Provide a detailed explanation of the chemoselectivity, regioselectivity, and diastereoselectivity involved. (20 points) 1) 3, DMS 2) heat C

8 6. Define the stereochemical relationship between the following pairs of compounds. A. (5 points) vs. B. (5 points) vs. C. (5 points) vs. t-bu t-bu D. (5 points) vs.

9 7. Provide a mechanism for the Favorskii reaction shown below. (15 points) INT: Remember Baldwin s rules! Use them to justify your mechanism. Br NaMe, Me Me (±)

10 8. The following reactions would NT give the indicated product. State WY NT. Predict the actual outcome of the reaction(s). A. (15 points) Me Piv Piv N excess EtAlCl 2 Me Piv Piv N Me NaMe Me Piv Piv Me B. (10 points) 1) MeMgBr 2) 3 + (±) (±)

11 C. (10 points) 3 P I (±) KMDS (±) D. (5 points) 3 PCC 3, -78 C; then Li then Me, warm to r.t. (±) (±)

12 9. Tom oye presented the following sequence from his thesis work with R. B. Woodward. Woodward had a key insight into the transformation of A to B that was decades ahead of its time. Based on your knowledge, you should be able to provide reagents for the transformation of B to C. Propose a set of conditions to do so. Show intermediates for partial credit. (15 points) <<BNUS (10 points): provide the reagents to transform A to B via Woodward s strategy.>> N C C 2 Me C 2 Me A B (±) C A to B <<BNUS (10 points)>> B to C (15 points)

13 10. In Baldwin s studies the following transformation was attempted. (±) Base: no reaction Acid: product observed A. The reaction DID NT proceed under basic (alkaline) conditions. Explain why. (10 points) B. The reaction DID proceed under acidic conditions. Explain why. (10 points)

14 C. Provide a synthesis of the starting material above (see instructions at beginning of exam). (10 points)

15 11. Propose a stereoselective synthesis for each of the following molecules. A. ne enantiomer! (30 points) P 2 P 1 NAc ne Enantiomer

16 B. ne enantiomer! (25 points) C 2 C 2 ne Enantiomer

17 C. (25 points) (±)

18 <<12. BNUS (10 points): Give an example of a new discovery that has appeared in the chemical literature during this semester. For full points you should include the name of the author and journal in which it appeared.>>