LECTURE FOUR
    chiral reagents
gareth j rowlands
O




(R)-muscon
          e
J. Chem. Soc., Chem., Commun., 1990, 795 & J.
    Chem. Soc., Perkin Trans. 1, 1991, 1445    ...
how                   O

is the selectivity

     achieved?

                                    NH
                      ...
chiral reagent
    control



substrate
 (achiral)
              chiral
             reagent
                       [ ]
  ...
problem
                it is wasteful


©maol@flickr
H        O
                                 B




            (+)-α-pinene       9-BBN•THF


            of
synthesis
   c...
O

     RL       RS


      H                        B O
              B            H         RL

                        ...
O

     RL       RS


      H                        B O
              B            H         RL

                        ...
O

     RL       RS


      H                        B O
              B            H         RL

                        ...
(R)-fluoxetin
               e
     Prozac
   J. Org. Chem., 1986, 51, 3394 &
J. Am. Chem. Soc., 1988, 110, 1539




     ...
O

                                                                 Cl
                        Cl                         ...
of
synthesis           reagent
             chiral




                              pinene
of
synthesis                 reagent
                   chiral


     (+)-α-pinene

           BH3

                      ...
of
use          boron reagents
      chiral
                   H


                   H       ii. H2O2     H OH
          ...
of
use          boron reagents
      chiral
  Me
                                         Me
                         ii. ...
of
use          boron reagents
      chiral

            i. (–)-Ipc2BOTf
                 iPr2NEt          OH   O
      O ...
©Brittany G@flickr
enolate
geometry

           i. (–)-Ipc2BOTf
  O             iPr2NEt          B
                                     O


 ...
reagent chiral
                        B
                            O
                                   control
        ...
OH
                                              O             H
                                                         ...
chiral reagent control
                                                                           OH
                     ...
organobora
          nes   ©Pierre J.@flickr
allylation with organoboranes
                  O
                                                L       L
             R...
stereospecific
                 O
                                               L       L
            R                  ...
stereospecific
         H               L                  H               L
                 R                           ...
stereospecific
         H               L                  H               L
                 R                           ...
stereospecific
         H                L                  H                    L
                 R                     ...
synthesis
               BH3•SMe2           BOMe
                MeOH


                              2


                ...
chiral reagent control
                                  OH
           B         O
                             Et
       ...
chiral reagent control
                                             OH
               B                O
                 ...
chiral reagent control
               CO2iPr                          OH
                               O
       O
       ...
chiral reagent control
                 CO2iPr                               OH
                                   O
     ...
OH
                                         O
                                                 O       O    OH
           ...
chiral reagent control                                       O
                                                           ...
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Lecture4: 123.702

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Use of stoichiometric amounts of a chiral source. The usual suspects will be discussed, including borane reagents (mostly pinene derivatives) and the Brown allylation.

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Lecture4: 123.702

  1. 1. LECTURE FOUR chiral reagents gareth j rowlands
  2. 2. O (R)-muscon e J. Chem. Soc., Chem., Commun., 1990, 795 & J. Chem. Soc., Perkin Trans. 1, 1991, 1445 ©baboon™@flickr
  3. 3. how O is the selectivity achieved? NH OH N H (2 eq.) MeLi, CuI O 99% ee
  4. 4. chiral reagent control substrate (achiral) chiral reagent [ ] substrate (achiral) chiral reagent chiral product
  5. 5. problem it is wasteful ©maol@flickr
  6. 6. H O B (+)-α-pinene 9-BBN•THF of synthesis chiral H B reagent alpine borane
  7. 7. O RL RS H B O B H RL RS with a reduction H OH chiral RL RS reagent
  8. 8. O RL RS H B O B H RL RS with a reduction H OH chiral RL RS reagent
  9. 9. O RL RS H B O B H RL RS with a reduction H OH chiral RL RS reagent
  10. 10. (R)-fluoxetin e Prozac J. Org. Chem., 1986, 51, 3394 & J. Am. Chem. Soc., 1988, 110, 1539 CF3 O H Me N H•HCl ©Touchstone Pictures
  11. 11. O Cl Cl Ipc B O H Ph H BCl Cl 2 (+)-Ipc2BCl H OH synthesis CF 3 Cl using a chiral O H Me N reagent H•HCl ≥99% ee 1 recrystallisation
  12. 12. of synthesis reagent chiral pinene
  13. 13. of synthesis reagent chiral (+)-α-pinene BH3 H H 1. TMEDA H 2. BF3•OEt2 B BH2 H H H H (–)-Ipc2BH (+)-IpcBH2
  14. 14. of use boron reagents chiral H H ii. H2O2 H OH H NaOH H H H B 98.4% ee H H H
  15. 15. of use boron reagents chiral Me Me ii. H2O2 H H NaOH H HO BH2 H 66% ee H
  16. 16. of use boron reagents chiral i. (–)-Ipc2BOTf iPr2NEt OH O O ii. RCHO R
  17. 17. ©Brittany G@flickr
  18. 18. enolate geometry i. (–)-Ipc2BOTf O iPr2NEt B O 2
  19. 19. reagent chiral B O control 2 H O H OH R H B O or H O OH O R R
  20. 20. OH O H O Me OH O O H H O Me (–)-laulimali de fijianolide B Org. Lett., 2001, 3, 3149 ©luxpacis@flickr
  21. 21. chiral reagent control OH O H O OH O O H H O (+)-Ipc2BO CO2Me OTBS H H H O O O OH OPMB CO2Me H H OTBS O H H O 86% O OPMB 62%de
  22. 22. organobora nes ©Pierre J.@flickr
  23. 23. allylation with organoboranes O L L R B O RZ RZ L R B RE RE L L L OH H2O2 B NaOH O R RZ RE R RZ RE
  24. 24. stereospecific O L L R B O RZ RZ L R B RE RE L L L OH H2O2 B NaOH O R RZ RE R RZ RE
  25. 25. stereospecific H L H L R H B B L vs L RE RE O O H R RZ RZ
  26. 26. stereospecific H L H L R H B B L vs L RE RE O O H R RZ RZ
  27. 27. stereospecific H L H L R H B B L vs L RE RE O O H R RZ RZ H OH H R RE OH RZ RE R RZ
  28. 28. synthesis BH3•SMe2 BOMe MeOH 2 MgBr K BF3•OEt2 B B 2 2
  29. 29. chiral reagent control OH B O Et Et H 2 92% ee
  30. 30. chiral reagent control OH B O Et Et H 2 92% ee H H H B OH Et H O Et
  31. 31. chiral reagent control CO2iPr OH O O t-Bu B CO2iPr t-Bu H O 82% ee
  32. 32. chiral reagent control CO2iPr OH O O t-Bu B CO2iPr t-Bu H O 82% ee H2O2 NaOH CO2iPr CO2iPr O O H CO2iPr H CO2iPr B B O O O O t-Bu t-Bu H H
  33. 33. OH O O O OH CO2H O O NaO2C OH O O O HO (+)-SCH351448 Org. Lett., 2005, 7, 3809 ©Exothermic@flickr
  34. 34. chiral reagent control O O O OH OH CO2H O O NaO2C OH O O O HO OBn O BnO2C O H OBn OH DCM, 0°C Ar BnO2C 80% O N 95% d.e. Si N Cl Ar
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