H CH 2 -OH (4) H b. H H (5) (6) a. b.

Transcription

1

2 ame 215 F010-Exam o. 2 Page 2 I. (15 points) For each of the following pairs of compounds, predict which compound is more acidic. Compare the two underlined s for each pair and circle the compound that is more acidic for each pair. The more acidic compound for each pair will be (circle one): (1) F a. F C C 2 - b. F C C 2-2 () a. b. (2) a. b. Cl C 2 (5) a. b. C C C () a. S b. S 2 (6) a. b. C II. (a) (9 points) Show the structures of the three possible conjugate acids of benzotriazole and explain, in several words, as to which of the three conjugate acids is most stable and would be expected to form preferentially. Use drawings of pertinent resonance form(s) and several words to explain your answer. benzotriazole explanation: three possible conjugate acid structures: (b) (6 points) The pk a values of indole and benzotriazole are estimated to be 20.1 and 11.9, respectively. Explain this difference in pk a values using resonance structures of the conjugate bases of the two compounds. indole explanation: pk a ~20.1 benzotriazole pk a ~11.9 6

3 ame 215 F10-Exam o. 2 Page III. (28 points) Glycoside 1 is a new steroidal saponins isolated from the rhizomes of Polygonatum kinigianum, one of the original plants commonly known as uang-jing in traditional Chinese medicine [elv. Chhem. Acta 2010, 9, 1086]. Treatment of the glycoside, 1, with the enzyme β glycosidase provides trisaccharide 2. Answer the following questions about this glycoside 1 and trisaccharide 2. C A A B 1 2 enzyme (1) ( points) Label each of the glycosidic bonds in glycoside 1 using a small arrow ( ). C B (2) ( points) Classify each glycosidic linkage in 1 as α or β right next to each of the arrows you have shown. () (2 points) ow many D-sugar units does trisaccharide 2 have? (circle one) () (2 points) Is the hemi-acetal in trisaccharide 2 α or β? (circle one) α β (5) (2 points) Is trisaccharide 2 a reducing sugar? (circle one) Yes o (6) ( points) Describe the linkages between the following sugar units [e.g., α(1 -> 6)]: For A and C: For B and C: (7) (12 points) Draw Fischer projections for the open-chain forms of the three carbohydrates produced when glycoside 1 is hydrolyzed with a warm dilute aqueous acidic solution. Carbohydrate A Carbohydrate B Carbohydrate C

4 ame 215 F10-Exam o. 2 Page IV. (1 points) Treatment of glycosyl trichloroacetimidate 1 with isopropyl alcohol (2) in the presence of a catalytic amount of a strong acid results in the formation of an anomeric mixture of glycosides [Angew. Chem. Int. Ed. 2010, 9, 872]. Propose in the box below a step-by-step, curved-arrow reaction mechanism for this transformation from 1 to. You may use -A and A- for the catalytic acid and its conjugate base, respectively. You do not need to balance each step. PhC 2 PhC 2 Mechansim: PhC 2 CCl 1 acid catalyst (2) C 2 Cl 2 (solvent) PhC 2 PhC 2 PhC 2 anomeric mixture PhC 2 CCl PhC 2 1 PhC 2 A PhC 2 PhC 2 PhC 2 V. (22 points) Treatment of hydroxy ester with a catalytic amount of p-toluenesulfonic acid (Ts; pka -0.51) results in the formation of its lactone derivative, 5, shown below [Angew. Chem. Int. Ed. 2010, 9, 5887]. Provide in the box below a step-by-step, curved-arrow reaction mechanism for this transformation from the hydroxy ester. You may use -A and A- for the acid Ts and its conjugate base, respectively. C Mechanism: Ts (catalytic) 5 + C 1 C A 5 22

5 ame 215 F10-Exam o. 2 Page 5 VI. (18 points) Complete the following reaction schemes by providing in the boxes the structures of the corresponding products. Make sure to indicate the stereochemistry where applicable. (1) [Synthesis 2010, 2512] K 2 C (2 equiv) C I (2 equiv) + 2 KI (2) [Synthesis 2010, 2512] C 2 C 2 C + C 2 C () [J. Med. Chem. 2010, 5, 777] C 2 + () [J. Med. Chem. 2010, 5, 777] ac (1.1 equiv) C (5) [Chem. Eur. J. 2010, 16, 12788] C ac (1.1 equiv) C C C

6 ame 215 F10-Exam o. 2 Page 6 VII. (18 points) Complete the following reaction schemes by providing in the boxes the structures of the corresponding products. Make sure to indicate the stereochemistry where applicable. (1) [J. Med. Chem. 2010, 5, 7296] Br a (1 equiv) abr (2) [J. rg. Chem. 2010, 75, 716] 5% K C C 2 + K + 2 () [Chem. Asian J. 2010, 5, 2192] C BrMg MgBr aq Cl C () [rg. Lett. 2007, 9, 01] C C 2 Ph 1. LDA (1.1 equiv) -78 C 2. I + LiI

7

8

9 Reagent List Page 9 Shown below is a list of key reagents (not always the whole recipe) that may be useful for solving questions on the exam #1. reagent classification or specialized use From Chem 210 s / 2 oxidation KMn oxidation peroxyacid epoxidation (e.g., - or meta-chloroperoxybenzoic acid [MCPBA]*) i. ; ii. (C ) 2 S or Zn ozonolysis i. ; ii. 2 2 ozonolysis a 2 base, nucleophile a base KC(C ) bulky base 2 /Pd hydrogenation 2 /Pd, BaS, quinoline hydrogenation i. B or 9-BB;* ii. 2 2, a hydroboration PBr e.g., R- R-Br SCl 2 e.g., R- R-Cl p-c C 6 S 2 Cl (TsCl) tosylate formation C S 2 Cl (MsCl) mesylate formation -bromosuccinimide (BS)* source of electrophilic Br ========================================================================= Chapter 1 C ClCr - (pyridinium chlorochromate [PCC]* oxidant Cr / 2 S / 2 /acetone oxidant i. ClC(=)-C(=)Cl, (C ) 2 S; ii. (C 2 C ) oxidant Chapter 1 ab nucleophilic hydride LiAl nucleophilic hydride diisobutylaluminum hydride nucleophilic hydride (DIBAL) a(c)b nucleophilic hydride RMgX nucleophilic carbon RLi nucelophilic carbon -C C 6 S (Ts) organic-soluble acid * Cl MCPBA Raney i SC 2 C 2 S BF (C 2 C ) B 9-BB Br Lewis acid BS desulfurization thioacetal/thioketal formation hydrazone formation oxime formation Cr PCC Cl