CEM 852 Exam What is the ratio of (S) / (R) alcohol formed during this reaction? (2 pts) baker's yeast. H 2 O, sucrose 25 C

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1 CEM 852 Exam-1 February 19, 2005 This exam consists of 5 pages. Please write ALL your answers in the answer books. Please write legibly and draw all structures clearly. Good luck. 1. What is the ratio of () / () alcohol formed during this reaction? (2 pts) C 2 Et baker's yeast 2, sucrose 25 C () C 2 Et 93% ee 2. Provide chemical examples of the following terms: (10 pts) a. a prochiral center b. a syn pentane interaction c. a kinetic resolution d. the Cieplak effect e. a synthon 3. The Evans-Tishchenko reaction is a process that selectively reduces β-hydroxy ketones to anti- 1,3 diols. llustrate the stereochemical determining intermediate of this reaction. (3 pts) 4. Early this semester we learned about the Umpolung strategy based on 2-lithio-1,3-dithianes being used as acyl anion equivalents. While this chemistry works quite well, the analogous sequence (4b) shown below fails. Which step of 4b is problematic and why? (4 pts) 4a: this sequence is viable C BF 3 Et 2 BuLi, MPA, TF, 78 C Li ' X ' gcl 2, g, 2 Me ' 4b: this sequence is T viable C BF 3 Et 2 BuLi, MPA, TF, 78 C Li ' X ' gcl 2, g, 2 Me ' 1

2 5. Provide the product or products of the reactions outlined below. how all intermediate compounds and be sure to indicate the product s relative or absolute stereochemistry. For reactions where multiple products are possible, indicate the major and minor species. (28 pts) (a) o-xylene 1. a (2.5 equiv), 3, Et 2, Et 2. 2, cat. (Ph 3 P) 3 hcl toluene 3. B 3, TF; then a, 2 2 (b) Et 2 C Et 2 C Me 1. 9-BB 2. a, cat. Ts, C 2 Cl 2 4. LiCl, DM, 2, Δ (hint: the conditions in step 4 selectively cleave Me & Et esters via an 2 mechanism) (c) 2 C 1. 2, 10% Pd-C, EtAc 2. B 3, TF, 0 C 3. Ac Ac Ac 4. LiAlD 4, Et 2 ; then + (d) TP 1. ab 4 /CeCl 3, Me 2. a, TF, rt C 3 7 C 2 3. cat. Tf, Bn CCl 3 (e) Bn PMB 1. TMC 2 C 2 C 2 Cl, (i-pr) 2 Et, Bu 4, TF, rt 2. (i-bu) 2 Al, C 2 Cl 2, 78 C Ac 3. TPAP, M, 4 Å M, C 2 Cl 2, rt (f) TB 1. L-electride, TF 2. K, TF, PhC 2 Br Bn 3. 5% F, MeC 4. Jones 2

3 (g) benzoic acid 1.DCC, (Me)Me Cl Et 3, C 2 Cl 2, rt 2. MeMgBr; then aq. Cl 3. B 3, TF, rt Ph Ph 5 mol % B 6. Provide the reagents necessary to convert the starting material to the product. Most of these transformations will require more than one step. Be sure to consider the product s relative or absolute stereochemistry. To maximize your chances at partial credit, it is recommended that you show all intermediate compounds. (20 pts) (a) BP Ac BP Et (b) Bz C 2 Bz C 2 Me (c) Me Me Me TB TB TB Me (d) (e) Me 2 C Me Me Me Me 3

4 7. Provide the reagents necessary to convert the starting material to the product. This transformation will require more than one step. Be sure to consider the product s relative or absolute stereochemistry. To maximize your chances at partial credit, it is recommended that you show all intermediate compounds. (8 pts) Me 2 C Boc steps Boc Bn int: -aryl bonds can be made by reacting amines and aryl iodides in the presence of 5 mol % Cu,10 mol %,'-dimethylethylenediamine, and K 3 P 4 in DMF at 60 C 8. Unsaturated carboxylic acid A possesses the requisite structural features for an iodolactonization reaction. A source of electrophilc iodine could conceivably engage either diastereotopic face of the double bond in A, leading to a mixture of B and C. owever this reaction only affords B in 87% yield. Please explain why C is so disfavored relative to B. (6 pts) K 3, ac 3, A 2 B (87%) C (0%) 9. Provide a complete arrow (electron) pushing mechanism for the Corey-Kim oxidation shown below. (6 pts) Cl Me 2, Et 3, C 2 Cl 2 C 10. n class we learned about the reactions of alkylboranes with α-bromocarbonyl compounds. A closely related reaction employs α-diazoesters or α-diazoketones. Provide the product and a detailed arrow pushing mechanism for the following example of such a reaction. (10 pts) BCl CC 2 C 2 5 4

5 11. An example of the vinylogous Mukaiyama Aldol is shown below. Provide an explanation for the observed stereochemical outcome of that reaction. (3 pts) TB TB TB Me Et 2, i-pr, B(C 6 F 5 ) 3 Me Bonus Question: We have heard Classics talks on syntheses accomplished by the groups of both Woodward and Corey. Both of these chemists won obel prizes, Woodward in 1965 for his outstanding achievements in the art of organic synthesis and Corey in 1990 for his development of the theory and methodology of organic synthesis. Woodward might very well have won a second prize for his work with oald offmann on the Woodward offmann ules, but obels are not awarded posthumously and Woodward had already died when offmann (shared with Fukui) won the prize in Decades later these chemists have found themselves embroiled in a public spat. Corey, like offmann before him, was awarded the Priestley Medal in Being the highest award of the American Chemical ociety, winners are invited to address the American Chemical ociety at its national conference. Prof. Corey s acceptance speech last year raised a few eyebrows. For in this, Corey claimed to have had the initial idea that ultimately led to offmann s obel Prize. Corey claimed he had a discussion with Woodward on May 4, 1964, in which he suggested the ideas behind the yet-to-be-formulated Woodward-offmann rules. eedless to say, this has caused considerable controversy in the chemistry world, and offmann has responded by publishing a paper in Angewandte Chemie, outlining his recollections of the time. n this, he reveals that Corey wrote him two letters in 1981, immediately following the announcement of offmann s obel Prize, in which Corey accuses Woodward of being dishonest and pirating his idea, and offmann of unwitting participation in fraud. Prof offmann, in turn, states he asked Woodward in 1964 if Corey had a role in the research, to which Woodward replied o. What brand of cigarettes did Woodward smoke? (2 pts) a. Benson & edges b. Camels c. Lucky trikes d. Winstons e. ewports 5