Chem 332, Exam 4. Spring Provide reagents for the following transformations (2 pts each) NaOH , KOH. 4) H2/Pd NO 2. 1) AlCl 3 O 2) H 2 NNH 2

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1 AME 1. Provide reagents for the following transformations (2 pts each) 2 a 2 1) Al 3 2) 2 2, K h! 1) 3, 2) LDA 3) + 4) 2/Pd C 2

2 AME 2a Circle the correct product (no mechanisms or partial credit). 3 pts 1) Li (2 equiv) 2) C 3) + D 2b Circle the correct product (no mechanisms or partial credit). 3 pts + 2c Circle the aromatic molecules. o partial credit. 3 pts each (points are also given for uncircled answers) S +

3 AME 3 The reaction of anionic compound A to form B is fast, and the equilibrium lies strongly in the direction of B. C 2 A a. Explain why the equilibrium lies in the direction of B. You do T need to provide an arrow pushing mechanism, but do provide a clear picture that helps explain your answer. (3 points) B + B Anion B is delocalized over both carbonyls, and is therefore more stable than A, in which there is obviously only one carbonyl that can stabilize the anion. As a result of this special stability, the conjugate acid of B is acidic enough (pka ~ 10) to be deprotonated by, and therefore drives the equilibrium to the right.

4 AME 3 The reaction of anionic compound A to form B is fast, and the equilibrium lies strongly in the direction of B. C 2 A b. In contrast to the above observation, it is found that the equilibrium of C and D lies in the opposite direction, and favors the formation of C. Explain in detail. Again, it is essential to provide a clear picture that helps explain your answer. (9 points) B + 2 C C D + if we draw an orbital picture of anion D, we see that there is very poor overlap between the anion and the neighboring carbonyls. Thus, there can be no conjugation with those carbonyls. Therefore, there is no special stability for this anion, as was the case with C. therefore, the anion D deprotonates ethanol, and drives the equilibrium back toward the starting materials this anion is in an orbital that is ~ perpendicular to the plane of the carbonyls x x not a significant resonance form D not a significant resonance form

5 AME 4 Consider the thermal reaction of trans,trans-1,4-dimethylbutadiene with allylcation: 3 C! + 9 pts 3 C C 3 C 3 Would you expect this to be a concerted process under thermal conditions? Explain in detail using an argument based in molecular orbital theory. For this to be a concerted process under thermal conditions, the orbital symmetry of the M of one reactant must match the LUM of the other reactant. For the case here, we will identify the LUM of the butadiene and the M of the allylcation. (this analysis still works if we were to choose the LUM of allyl cation and the M of butadiene). We treat the allyl cation as a two electron, 3-carbon system of pi-orbitals. Like any other system, we remember that the ends of the allyl system have like symmetry for the lowest energy orbital, unlike symmetry for the next orbital, etc.. Butadiene allyl cation LUM M ote: is was Required to Show that there Are three carbons In the Pi system M bonding bonding For the reaction to be concerted, we need to have bonding interactions at both termini of the reacting system. This is the case for the current reaction. The thermal reaction does take place by a concerted mechanism. LUM

6 AME 5 Provide a synthesis of A using benzene and any other materials that contain 4 carbons or less. 12 pts Br A Br 1) ac 2) a/ 2 Br Br 2 /FeBr 3 Br Al 3 S 2 Br + a(c)b C a(c)b ) Sn/ 2) / C LiAl S 4 3) CuC

7 AME 6 Provide a detailed arrow pushing mechanism. int: this reaction is sometimes classified as an Aza-Cope-Mannich reaction (Aza means contains nitrogen ) (12 points). C 3 catalytic + C 3 + C 3 catalytic + C 3 C 3 + transfer 2 C 3 C 3 Aza-Cope C 3 C 3 Mannich C 3

8 AME 7 Provide a detailed arrow pushing mechanism.! 12 pts + aisen rearrangment Cope rearrangment proton transfer

9 AME 8 Circle the structures of the D-aldohexoses (shown below) that give meso compounds upon oxidation with 3. 1 point each (points are also given for uncircled answers): 8 points total 9 Identify the following pairs as identical, anomers, enantiomers, or (non-anomeric) diastereomers. Write your answers on the line below the structures. (3 points each) C C 2 C 2 C anomers enantiomers C C C 2 C 2 on-anomeric diastereomers

10 AME 10 Using Solid phase synthesis, show how to synthesize the tripeptide Val-e-Ala. As starting materials,you should use any of the naturally occuring amino acids, rrifield resin, and any other materials. (10 points) Val-e-Ala rrifield Resin Your final product should be cleaved from the rrifield resin and free of any protecting groups. Be sure to draw the chemical structures of your product and intermediates (i.e., do not use the three letter abbreviations.) ASWER EXT PAGE

11 + Val-e-Ala 3 This is the amino acid that we are building. n solid support, we begin building at the C-terminus and we end at the -terminus terminus C terminus BC protection of amino acids + 3 R Boc 2 3 R Boc R R = ipr;; C 2 Synthesis Cs 2 C 3 Boc C 3 3 C Boc TFA Boc 3 C 2 DCC pyridine Boc 3 C 2 TFA 3 C Boc 3 C DCC pyridine Boc TFA 3 C 2 3 C + 3