4328FinalExam2008 - 1 FINAL EXAM CHM 4328B Please check...

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1 FINAL EXAM - CHM 4328B Professor: Dr. André Beauchemin Date: Monday, April 28, 2008 Time: 3 hours Name: Student #: QUESTION POINTS RESULT 1 24 2 10 3 10 4 10 5 16 6 30 Bonus 10 TOTAL 110 / 110 Please check that your exam contains 13 pages Manage your time: browse the exam first!
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2 1. (24 points) Predict the stereochemical outcome of the following transformations. (18 points: 2 pts each) When requested, please also provide a clear 3-D representation of the transition state leading to the observed product. (6 points: 2 pts each) Me Me Me Me O OH OBn AcOH, –40 °C NaBH(OAc) 3 Provide major TS here: Provide major TS here: Provide major TS here: N B O Ph Ph R H Me O (0.1 equiv) 1 equiv BH 3 •THF N O B Ph Ph + O H Me Me O H Me N H CO 2 H (10 mol%) O N Me O O 1. n -Bu 2 BOTf, i -Pr 2 NEt 2. R O H
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3 O N Bn O R + Me 2 AlCl (2 equiv) O O N Me O O Bn 1. KHMDS 2. i -Pr i -Pr Pr- i S N 3 O O 3. AcOH LiO Me H H Et-I BF 4 Rh Ph 2 P PPh 2 (CH 2 ) 4 H 2 (1000 psi) HO Me Me OTBS O H OSiMe 2 t -Bu SnBu 3 BF 3 •OEt 2
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4 2. DAE Problem 111: 10 points. The Zimmerman-Traxler transition state nicely correlates starting enolate geometry and product aldol stereochemistry. This point is illustrated in equation 1 below in the correlation of the (Z) enolate geometry with the syn aldol product stereochemistry. The intent of this question is to have you ponder the related addition to the illustrated imine (eq 2). Me O Metal H Ph O H Ph N R i -Pr O Me Ph O M i -Pr O Me Ph N M R (1) (2) Me Me In the space below, draw the Zimmerman-Traxler transition state for the "imine-aldol" process (eq 2) and illustrate the predicted stereochemical outcome of the addition reaction. Assume that the imine geometry cannot isomerize under the reaction conditions. Note : Partial points can be obtained by illustrating the transition state accounting for the selectivity presented in eq 1. (but the transition state is not necessary if you are sure of your answer for eq 2 !)
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5 3. DAE problem 864 : Tetrahedron Lett. 2002 , 43 , 3777-3780.
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