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Jacobsen Catalyst

Jacobsen Catalyst. C344. Overview. Asymmetric catalysis Lab overview Organometallic reactions Chiral GC analysis Optical Activity. Asymmetric Catalysis. Asymmetric Synthesis. Stereoselectivity Diastereomeric excess Enantiomeric excess From JOC , 2013 , 78 , 4762-4778. 91% ee.

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Jacobsen Catalyst

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  1. Jacobsen Catalyst C344

  2. Overview • Asymmetric catalysis • Lab overview • Organometallic reactions • Chiral GC analysis • Optical Activity

  3. Asymmetric Catalysis

  4. Asymmetric Synthesis • Stereoselectivity • Diastereomeric excess • Enantiomeric excess • From JOC, 2013, 78, 4762-4778. 91% ee

  5. Lab Overview

  6. Lab 1 • Formylation reaction • Isolate chiral salt during reflux • May not get to silica column of aldehyde

  7. Lab 2 • Imine formation • Lowest yielding reaction • Optical activity

  8. Lab 3 • Jacobsen’s catalyst • Air, moisture stable! • You do not need optical activity data

  9. Lab 4 • Finally getting to the point! • Bleach: a green, stoichiometric catalyst • Full characterization, with optical activity • Submit sample for chiral GC • Lab 5 can be used to catch up, finish characterization data

  10. Organometallic Chemistry • Mechanism: Wikipedia

  11. Enantiomeric Excess • Maybe due to radical mechanism • Calculations of ee

  12. Chiral GC • Basics of separation • Cyclodextrin column • Calculating ee • But which peak is which?

  13. Optical Activity • Chiral compounds bend plane polarized light • Angle depends on concentration, path length, solvent, temperature, wavelength of light, which enantiomer • Specific rotation The specific rotation of sucrose is reported: [a]20D = +66.4o (H2O) D = sodium D-line = 589 nm

  14. Calculation • Specific rotation is calculated from observed rotation by [a] = a / (c . l) • C (concentration) is in grams/mL • L (pathlength) is in decimeters • Most samples are determined at more dilute concentrations (g/ 100mL) • Dilution does affect rotation, so to compare to literature, you must obtain data at same concentration they did

  15. Example • Reported data: Compound A has a reported specific activity [a]23D = 93o (c = 1.9, CH2Cl2) • To repeat the experiment, you mixed 190 mg of compound in 10mL of methylene chloride at 23o C and used a sodium lampand standard tube. • You obtained a rotation of 1.6o • What is the ee of your compound? • Answer: 90% ee (Mixture is 95% to 5%)

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