Answers to PS6

Answers to PS6 - Chem 432 Answers to Problem Set #6 Spring...

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Chem 432 Spring 2009 Answers to Problem Set #6 Question 1. Frequently, the limiting factor in the widespread use of chiral catalysts is the efficiency of the chiral ligand synthesis. Shown below is the synthesis of a ligand for rhodium used by Knochel and co-workers( Angew. Chem. Int. Ed. 2001 , 40 , 1235) for asymmetric hydroboration reactions. OH OH P P O O Ph reflux Ph (1) ClPPh 2 A toluene Ph Ph * * * * Provide a mechanism for this reaction sequence. Identify all stereochemical control elements and identify A . Note the position of the labeled carbon atoms “moves”! OH OH O PPh 2 PPh 2 O P Ph 2 H OPPh 2 O P O Ph 2 Via: P Cl Ph Ph [2,3]-sigmatropic shift (suprafacial) [2,3]-sigmatropic shift (suprafacial) P O O Ph 2 Ph 2 PPh 2 A * * * * * * * *
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Chem 432 Spring 2009 Question 2. Shown below is part of the total synthesis of (+)-methyl epijasmonate ( 1 ) by Fehr and co-workers ( Angew. Chem Int. Ed. 2000 , 39 , 569-573). O C 4 H 9 N B O Me Ph Ph H 5 mol% BH 3 •SMe 2 , THF HO C 4 H 9 2 3 O C 4 H 9 O MeO 2 C 4 C 4 H 9 CO 2 Me 5 O CO 2 Me C 4 H 9 H H esterification 1 1. NaH, TMSCl 2. ! A a) Provide a clear 3-dimensional drawing that clearly illustrates the control elements for the reduction of 2 to 3 .
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This note was uploaded on 02/09/2010 for the course CH CH242 taught by Professor Katz during the Spring '10 term at Colby.

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Answers to PS6 - Chem 432 Answers to Problem Set #6 Spring...

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