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634-F11_Midterm_Key - Inwas Chemistry 634 Fall 2011 Midterm...

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Unformatted text preview: Inwas Chemistry 634, Fall 2011 Midterm Exam Prof. Donald Watson 300 points (2 hours) a Closed note, ciosed book. No calculators allowed. You may use a molecular model set. 0 Answers should be written in boxes provided. Other markings will not be considered. Scratch paper can be found at the back of the exam packet. . Please initial each page at the top. 0 Points will only be awarded for clearly communicated answers. . Please make sure you have all pages of the exam packet (18 pages). Na... K E”, Question 1: [30 Question 2: I30 Question 3: 121 Question 4: 128 Question 5: 138 Question 6: 130 Question 7: [25 Question 8: 20 Question 9: [20 Question 10: [20 Question ‘11: I38 Total: I300 Page 1/ 18 Initials 1) (30 points, 6 points each) Predict the expected major product for each reaction sequence after aqueous work-up, drawing your answer in box provided. Denote stereochemistry where needed. If no reaction is expected, state so. OMe C5H11/QOMe BuLi, THF: than EtCHO 10 mol% Cul 20 mol'Ki 1 K3PO4. tel. 110 “c —-————-——h- MBxNAJN,m H 1 out. Pr‘N‘ R004‘ (3 N ‘0’ 'Me TM! I‘M“ BuMgCl 'Bucoct Eran cat. DMAF' :30 points Page 22'18 Initials 2) (30 points, 6 points each) Predict the expected major product for each reaction sequence after aqueous work-up, drawing your answer in box provided. Denote stereochemistry where needed. If no reaction is expected. state so. Me 01 ‘ 1 )zhgeLzAtit'lLi [I l I ————————u- Me ii 002m 1) MOMCI. Nagmxcess of both} 3 PDC 4}T H. MeOH HO OH w :30 points H roast ”M37 aflfixmf Page 3f18 Initials 3) (21 points) In the spaces below, provide the missing reagents needed to complete the synthesis. 21 points 4) (28 points) In the spaces below, provide the missing reagents needed to complete the synthesis- NHBI'I I28 points Page 4/18 Initials 5) (38 points) Shown below is a synthetic sequence from taken from Feldman’s synthesis of (1)—Dragmecidin E (Org. Lett, 2011, 5704). In the boxes below. please provide the missing reagents and intermediates required for making this process viable. Each box corresponds to one required step or intermediate. Hint: This is hell a reaction we have diswssed. but it is closely related to ones that we have. 5: Tips ‘5 " f38point5 13».- ’f’ ’f‘ 6' M} 546:»:0 h” 1"?" ' :53. I 0" PageSflS Initials 6) (30 points. 3 points each) Using your knowledge of pka's, predict the product(s) and equilibrium constant for each proton transfer reaction illustrated below- o NaI-l MEJLOH My ? N." 1' F7, 3 (Nada Iva-V bet-um ”1. be"; a.) [30 points Page 6H 8 Initials 7) (25 points) The next question will consider the “Fmoc” protecting group and the following reaction. O Meek/NMFmoc) 1 0 MeoJk, NH? 2 A) Draw the complete structure of compound 1 (shown below)- C) In the space below, provide a compete mechanism for the conversion of 1 to 2 using the reagent(s) you selected in question B. :25 points Page 7/ 18 Initials 8) (20 points) Please provide a complete and detailed mechanism for the following transformation. MezS, NCS. 01-12012; 0 then EigN MONO” ——'————'—* MEMO NCS = "‘5' o I20 points Page 8118 Initials 9) (20 points) Using a maximum of 5 steps, propose a synthesis of 4 using the given starting material (3) and any other commercial or readily accessible reagents. sue SHE f a swim H2N CO2” . 4 :20 points Page 9f18 Initials 10) (20 points) Using a maximum of 10 steps, propose a synthesis of 6 using the given starting material (5) and any other commercial or readily accessible reagents. IIESoc PMBO _/ ‘Me Me TBSO line E / 7 N NMO/V 20' points Page 10f18 Initials 11) (38 points) As you read in Overman’s 1994 Pure and Applied Chemistry paper. the vinyl iodide shown below cyclizes to give the fused tricycle in 83% yield, after deprotection. Only a single stereoisomer was formed. Me 10 mom PleAc) Me 20 mom Ppha, 15.920203 U (9’3 \ THF. 65 ”C; then TBAF I Fl I n {“th I» +. A-: I H 33% H ‘0 no 0Tes OH +0924.» ‘3 “FOLLV‘A A) Although not observed, how many possible stereoisomers theoretically could have been formed in this reaction? Assume that the starting material is enantiopure and ignore ring strain issues. Briefly (ca. 10 words or less) explain your reasoning. 3P4— For ‘f Zpl- 'Faf' Cry/“bid”: Page ”/18 Inwab C) Please predict the stereochemistry of the product. Justify your answer with clear and concise transition state drawings that iilustrate why you believe this predicted isomer is formed. You {tau +0 look-— .2" W046}. 7‘0 fatiguin- +16. .. ti?" I'S til-,osgaié W/D- .70" s‘i‘JYafwhrLQBo/fi d/‘(A‘ ”‘17;- Page 12:18 ...
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