CHEM 330. Final Exam December 11, 2007 A N S W E R S. This a closed-notes, closed-book exam. The use of molecular models is allowed

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1 CEM 330 Final Exam December 11, 2007 Your name: A S W E R S This a closed-notes, closed-book exam The use of molecular models is allowed This exam contains 12 pages Time: 2h 30 min 1. / 20 / / / / / / / 40 TTAL / 250 = / 100 This exam counts for 45% of your CEM 330 final grade

2 Chem 330 final exam p. 2 of (20 pts.) Write a chemical equation to show an example of the following reactions (do not write mechanisms just the reactions). a. aylis-illman reaction: cat. + b. Prasad Reduction: a 4 Et 2 c. Cannizzaro reaction: 2 C Aq. a C 2 + C (then + ) d. Mukaiyama aldol reaction: Si 3 + F 3 e. Swern oxidation: R C 2 DMS (CCl) 2 then Et 3 R C

3 Chem 330 final exam p. 3 of 12 (20 pts.) A highly stereoselective reaction ensues when compound A below is treated with 1 equivalent of ZnCl 2, followed by cyclopentadiene. The result is product. (i) Draw the structure of in the box; (ii) Sketch an approximate transition state structure that accounts for the observed stereoselectivity. A ZnCl 2, then cyclopentadiene C X c approximate transition state structure: 4!s + 2!s endo secondary orbital interaction Cl 2 Zn

4 Chem 330 final exam p. 4 of (30 pts.) Complete the reaction diagram shown below by indicating all missing reagents / products. Each box corresponds to one reagent / product. ote: aqueous workup steps are understood and are not to be included in your answers. 1. LDA Et C CEt C Et C C DU (together) excess C CEt C 3 SiTf TMS CEt TMS C (together) and (together) A 1. TAF heat TMS C TMS CEt Pr 4 Ru 4 and (together) C CEt final product

5 Chem 330 final exam p. 5 of (40 pts) Check the appropriate box to indicate whether the following statements are or. a. The copper atom undergoes reductive elimination in the following reaction: 2 CuLi + 2 r 2 + Lir + Cu r b. The following transformation may be induced by the use of Mgr: Cl c. Treatment of A with Li and tert-u in liquid 3, followed by allyl bromide, results in formation of : Li, tert-u A liq. 3, then C 2 =C-C 2 r d. The reaction shown below will give compound C as the major product: CEt CEt a,cat. Et then aq. wrkp. C CEt e. The reaction shown below is a retro-diels-alder: C C C C

6 Chem 330 final exam p. 6 of 12 f. Treatment of D with a(ac) 3 followed by aqueous workup yields E as the major product: a(ac) 3 then aq. wrkp. D E g. Reaction of F with a yields compound G: cat. F a G h. Compound may be converted to I as follows: 1. LDA -C 2 r I i. Substrate and reagent in the reaction shown below are stereochemically matched: C + u u Xc j. Compound J forms when 1,3-cyclohexadiene reacts with maleic anhydride: J

7 Chem 330 final exam p. 7 of (30 pts.) Provide a succinct explanation for the following experimental observations: (a) enzoquinone A undergoes Diels-Alder reaction with butadiene selectively at the methyl-substituted double bond, because: A the -substituted double bond is less electron-rich (= more electron-deficient) than the -substituted double bond ( is a more powerful electron-donating substituent than ) (b) The oyori copper reagent shown below adds stereoselectively to enone to form C, Cu(Pu 3 ) 2 because: then aq. workup C the organo-cu reagent tends to add axially to the double bond. The group occupies an equatorial position (A-value 3), and this defines the conformation of the cyclohexenone. (b) Reaction of ketone D with a defect of LDA produces enolate E, 0.9 equiv. of LDA because: D Li E the initially formed kinetic enolate can equilibrate with the thermodynamic one, because leftover ketone can act as a "proton shuttle".

8 Chem 330 final exam p. 8 of (40 pts) Predict the structure of the major product expected from the following reactions. otes: (i) it is not necessary to draw mechanisms; (ii) aqueous workups at appropriate stages are understood. 1. LDA, TF a. TS C TS C b. n 1. LDA C 2 =CC 2 r 3. K 2 C 3 C c 1. Cy 2 Cl Et 3 C 3. a(ac) 3 d. Et 1. LDA, TF - MPA C CEt e. 1. u 2 Tf, Et 3 C X c

9 Chem 330 final exam p. 9 of 12 f Tf Et 3 C 3. a(ac) 3 g. 1. excess tuk, 1 equiv. of EtC-CEt 2 2 CEt 2 h. 1. LDA, then Ser MCPA, then heat 3. 2 CuLi, then Et 3 and r i. CEt 1. a, cat. Et, cat. DU CEt 3. tuk CEt j. 1. C excess C, aq. a

10 Chem 330 final exam p. 10 of (30 pts.) Indicate all the reagents that are necessary to effect the following transformations. Provide your answers as a numbered list of reagents, in the correct order, written over/under the reaction arrows, according to the format of question 6 above. a. cat. a C b LDA 3. nr 4. 3 c. 1. TMS 2 TMS I Li 3. C 2 =C C 2 r d. CEt CEt 1. a, cat. Et I CEt e. CEt 1. LDA, TF-MPA C 3. Mgr (racemic) f. 1. TMSTf, üning base C C (racemic) 3. TAF g. CEt 1. a, then + Conc. 2 S 4 3. LDA, then Ser 4. MCPA, then heat 5. u 2 CuLi

11 Chem 330 final exam p. 11 of (40 pts) Propose a method to achieve the enantioselective synthesis of the molecules shown below starting with the indicated building blocks. e careful about protecting groups and configurations of stereocenters. Assume the availability of all needed reagents, auxiliaries, etc. Present your answer as a flowchart. It is not necessary to draw mechanisms. from: C a. n 1. u 2 Tf, Et 3 C X c 1. TS-Cl Et 3 DIAL 3. Swern TS Cy 2 Cl Cy 2 Et 3 TS a(ac) 3 TS TAF PDT.

12 Chem 330 final exam p. 12 of 12 b. TS -Si(iPr) 3 from: I -Si(iPr) 3 (cf. J. rg. Chem. 2006, 71, 9853) 1. LDA I -Si(iPr) 3 X c -Si(iPr) 3 1. DIAL Swern -Si(iPr) 3 + u u X c -Si(iPr) 3 1. TS Cl Et 3 DIAL 3. Swern u u TS -Si(iPr) 3 TS -Si(iPr) 3 + X c Li then + PDT. appy olidays!