4328Midtermexam2007 - 1 MIDTERM EXAM - CHM 4328B Please...

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1 MIDTERM EXAM - CHM 4328B Professor: Dr. André Beauchemin Date: Wednesday, February 28, 2007 Time: 90 minutes Name: Student #: QUESTION POINTS RESULT 1 20 2 12 3 10 4 10 5 5 6 22 7 10 8 6 TOTAL 95 / 95 Please check that your exam contains 9 pages Manage your time: browse the exam first!
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2 1. Predict the stereochemical outcome of the following transformations. (20 points/ 2 pts each) N O [Ir(pyr)PCy 3 ] + H 2 OTBS HO Me Me H 2 (1000 psi) [Rh(DIPHOS)] + O H O H Et Me OBn THF Me MgBr Me Me Me Me O OH Me AcOH, –20 °C NaBH(OAc) 3 Me H Br 2 , H 2 O O OH OBn OBn OBn BnO Et 3 Si-H BF 3 •OEt 2
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3 THF, –10 °C Me Me O Me OSiPh 2 ( t -Bu) LiAlH 4 CO 2 Me TBSOH 2 C Me H MeI LiNR 2 -Bu O LiAlH 4 n -Bu Me OH I 2 , AcOH
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4 2. The following question was taken from Kishi's classic synthesis of monensin ( JACS, 1979 , 260). Part A. Predict the product of the following transformation. Provide a mechanism, including an accurate depiction of the transition state, for this reaction. Specifically point out each factor that contributes to the observed selectivity. (10 points) O Ar OH Me 1 equiv. ArCO 3 H 0 °C Part B. The authors report observation of only one isomer Assuming a 98:2 ratio of major to minor isomers, estimate the difference in transition state energies (in kcal/mol). (2 points)
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4328Midtermexam2007 - 1 MIDTERM EXAM - CHM 4328B Please...

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