4328Midtermexam2008 - 1 MIDTERM EXAM CHM 4328B Please check that your exam contains 10 pages Professor Dr Andr Beauchemin Date Tuesday Manage your

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1 MIDTERM EXAM - CHM 4328B Professor: Dr. André Beauchemin Date: Tuesday, February 26, 2008 Time: 80 minutes Name: Student #: QUESTION POINTS RESULT 1 29 2 10 3 15 4 10 5 27 6 15 TOTAL 106 (6 pt bonus!) / 100 Please check that your exam contains 10 pages Manage your time: browse the exam first!
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2 1. (29 points) Predict the stereochemical outcome of the following transformations. (20 points: 2 pts each) When requested, please also provide a clear 3-D representation of the transition state leading to the observed product. (9 points: 3 pts each) m -CPBA Et 2 O, 0 °C Me Me Me Me O OH OBn AcOH, –40 °C NaBH(OAc) 3 Et 3 Si-H BF 3 •OEt 2 OTBS TBS = SiMe 2 t -Bu Br 2 , MeOH H H Me Zn(BH 4 ) 2 Ph O OMe Me HO CO 2 H H I 2 , NaHCO 3 (aq) O RO 2 C OH Me O N Me H Me OSiPh 3 [Ir(pyr)PCy 3 ] + H 2 N H N Me O H O H H
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3 Me OH Me m -CPBA Provide major TS here: Provide major TS here: RMgBr Et 2 O CH 3 O OCH 2 OBn TBSO Provide major TS here: Me Me Me OLi Ph Me H O Note: for these two TS, using Nuc is OK!
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4 2. (DAE Problem 496) (10 points) Many factors influence the reactivity and conformational bias of cyclic systems including steric, electronic, and stereoelectronic effects. For each of the following cases involving a six-membered heterocycle, provide a rationalization for the observed selectivity, including clear 3-dimensional representations when relevant. Part A. Eliel and co-workers disclosed that the successive deprotonation of conformationally locked 1 and trapping with an electrophile occurs with high selectivity at the equatorial position ( J. Am. Chem. Soc. 1974 , 96 , 1807). S S Me Me H H S S Me Me D H 1 1. n -BuLi 2. DCl Part B. Eliel has also reported that the acid-catalyzed equilibrium of dioxane 2 favours the equatorial
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This note was uploaded on 01/11/2012 for the course CHM CHM 4328 taught by Professor Andrébeauchemin during the Spring '11 term at University of Ottawa.

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4328Midtermexam2008 - 1 MIDTERM EXAM CHM 4328B Please check that your exam contains 10 pages Professor Dr Andr Beauchemin Date Tuesday Manage your

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