CEM 852 Exam-2 April 11, 2015

Transcription

1 CEM 852 Exam-2 April 11, 2015 This exam consists of 6 pages. Please make certain that your exam has all of the necessary pages. Total points possible for this exam are 100. In answering your questions, please write legibly and draw all structures clearly. Write all your answers in the exam booklets. Good luck. I. Illustrate examples of 1,2-allylic strain, 1,3-allylic strain and a syn-pentane interaction. Rank their strain energies from highest to lowest. (5 pts) II. Illustrate the following name reactions: A ook rearrangement, a ef reaction, a akurai reaction, the hapiro reaction, and a 2,3-Wittig rearrangement (5 pts) III. how how compound I can be viewed as a homoenolate equivalent: (2 pts) C Et 2 I IV. The allene oxide is not stable enough to serve as a dienophile in Diels-Alder cycloadditions. owever 2-bromoacrylaldehyde can be used as an allene oxide equivalent. Explain. (5 pts) + allene oxide C 2-bromoacrylaldehyde V. 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, be sure to indicate the major and minor species. (30 pts) TMCl, Et 3, DMF 2. 2 C Ph, heat C 2 3. TiCl 4, PhC; 10% aq Cl workup A 2. TP Bu C CrCl 2, TF B

2 CEM exam 2 3. (i-pr) 3 i i(i-pr) 3 1. n-buli, TF, 74 C to rt, 8 h; then BuC , TF, rt 3. TBAF, TF, 0 C, 1.5 h 4. Ph, cat. CuI, cat. Pd 2 dba 3 Bu 2, TF C 4. C 1. CrCl 2, icl 2, DMF 2. PivCl, DMAP, Et 3, C 2 Cl 2, 0 C D 3. B Cr B 3, TF 2. 2 Cl, basic workup 3. 4-chlorobenzaldehyde; ab(c) 3 4. cat. Pd 2 dba 3, dppf, atbu, Ph, toluene E 6. Et TE 1. DIBAL; then 2 Cl 2. Ph 2 Cu(C)Li 2, Et 2 78 C, 2 h; then Tf 2 3. Mg, cat. i(acac) 2 MTBE, 40 C F cat Mo(C) 3 (C-tBu) 3, Bu 3 n, hydroquinone, TF, 60 C 2. I 2, C 2 Cl 2, 0 C 3. cat. (Ph 3 P) 2 PdCl 2, TF 4. C toluene, heat nbu 3 G 8. TM Et 1. TiCl 4, C C 2 Cl 2, 78 C 3 Cbz 2. 2, Pd/C 3. a, ai, BnCl 4. B 2 6 2

3 CEM exam KMD, DME, 55 C; then Ph TB C 2. TBAF 3. wern 4. allyl bromide, In(0) 2 I C 3 C 2 C 2 2. Et Mg BEt 2 3. TECl, i-pr 2 Et 4. cat. PCy 3 Pg Cl Cl Ru PCy 3 J VI. Provide conditions that will effect the transformations outlined below. ome of these conversions will require more than one reaction, so be sure to show all intermediate compounds. (18 pts) 1. Ph TB C Et 2. C 2 Bn C 2 Bn 3. Ph C 2 C 2 3

4 CEM exam 2 4. Ac eph C 2 nbu 3 eph 5. i 3 Bn 6. PMB Et Et i PMB VII. Provide a complete arrow (electron) pushing mechanism for the following transformation, being sure to offer an explanation of the relative stereochemical outcome. (ote: You may assume the insitu formation of Pd(0) has already occured.) (8 pts) I 1 mol % Pd(Ac) 2 4 mol % Ph 3 P 13:1 1 equiv AgC 3 C, rt VIII. In class, we discussed the bezoin condensation as involving an acyl anion equivalent. Miyashita and co-workers developed a synthetically useful retro-benzoin reaction. Provide a complete arrow (electron) pushing mechanism for all steps of the synthesis shown below. (8 pts) Cl 1. a, reflux 1.6 h equiv MgI, TF equiv KC, DMF, 80 C + 4

5 CEM exam 2 IX. The triene shown undergoes a Diels Alder reaction with 2-bromoacrylaldehyde to afford a 9:1 mixture of diastereomers. Predict the major and minor products and provide a written and/or illustrated explanation for your predicted regio- and stereoselectivity. Also offer an explanation for your diene choice. (8 pts) + C [4+2] 9:1 mixture of diastereomers X. Provide a complete arrow (electron) pushing mechanism for the following transformation. (5 pts) C 2 Ph DABC 2 Ph Et CCl 3, 2, rt Et XI. Alkene II undergoes hydroboration to give III as the major product. In these reactions the bulkier the boran reagent the higher the selectivity. In an attempt to understand the stereochemical outcome of these hydroborations, ketone IV was reduced with metal hydrides. LA and superhydride selectively gave Felkin product V and once again the bulkier the metal hydride the higher the selectivity. In contrast, when IV was reduced with Cy 2 B the sterochemistry switched and the anti-felkin product predominated. Using these data and your knowledge of the hydroboration mechanism provide a transition state model that explans the relative stereoselectivity observed during the hydroboration of II and the formation of the anti-felkin product during the reduction of IV with Cy 2 B. (6 pts) boran reagent; 4:1 with thexylb 2 26:1 with Cy 2 B Ac II a, 2 2 Ac III 3:1 with LiAl 4 20:1 with LiEt 3 B 1:9 with Cy 2 B reducing agent; Ac IV 3 + Ac V 5

6 CEM exam 2 Bonus Question: (2 pts) In late January, tanford chemistry professor Carl Djerassi died at the age of 91. Djerassi was perhaps best known for his work on steroid hormones and alkaloids, including the development of oral contraceptive pills. Djerassi published over 1,200 scientific papers, but also wrote novels. is portrait on the 5th floor was taken after publication of his second novel, The Bourbaki Gambit. Published in late 1994, The Bourbaki Gambit is a fictitious account of the discovery of the polymerase chain reaction. (In fact Kary Mullis invented PCR, for which he was awarded the 1993 obel Prize in Chemistry.) Djerassi was also a playwright and and his play xygen was actually performed at MU's Wharton center. xygen is a fictional account on the awarding of the 100th obel Prize in Chemistry. In the play, the obel Prize committee decides to make the first posthumous award and that it should go to the discoverer of oxygen. Who receives that obel Prize? (a) Antoine Laurent Lavoisier (b) Joseph Priestley (c) Carl Wilhelm cheele (d) All of the above (e) one of the above 6