Organic chemistry

1. Reduction Reactions

2. Classification of reduction
reactions
 Catalytic hyrdogenation (H2 with metals)
 Hydride transfer reactions, using
hydride sources such as LiAlH4,
NaBH4,..
 Dissolving metal reductions (Na, Li in
ammonia solution) (Birch reduction)

3. Classification of reduction
reactions
 Replacement of oxygen by hydrogen
 Removing oxygen from the substrate
 Reduction with cleavage
 Reductive coupling

4. Catalytic Hydrogenation
 Addition of H2 to unsat. bond (double ,
triple bonds, NO2 , CN,..
 Without catalysts ,it needs 480 co
 Pt group metals (Pd, Ni ,Ru and Rh)
used as catalysts
 Can be selective reduction, depends
on conditions

5. Catalytic Hydrogenation

6. Catalytic Hydrogenation

7. Pd/C reduction
 Pd powder spread on charcoal after
reduction of PdCl2 with H2
 Homogenous catalyst, can be recovered by
filtration

8. Raney Nickel
 Treatment of Al-Ni alloy with NaOH
 To reduce alkenes, alkynes, nitriles aromatics
and carbonyl compounds
 Syn addition product

9. Raney Nickel
 Hydrogenolysis: removal of sulphur (C-S
to C-H) in desulphurization reaction
 Use after open immediately????

10. PtO2( Adams catalyst)
 PtO2 reduced to Pt with H2

11. Lindlar`s catalyst
 Pd supported with CaCO3 instead of
charcoal,then treated with Pb to deactivate.
 Selective reduction of alkynes to Z-alkenes
only via syn addition

12. NaBH4
 Selective (chemoselectivity) reagent
 White crystals, safe and easy to handle
 Reduces aldehydes, ketones.
 Can`t reduce esters ,acids, amides

13. NaBH4
Generally
Still reducing agent

14. NaBH4
Luche reduction

15. LiAlH4
 Powerful reducing agent compared to
NaBH4 due to weaker Al-H bond.
 Pure sample is white but commercially
is grey????
 Dangerous, reacts violently with water
 Reduce aldehyde, ketones, esters,
amides and nitro compounds.

16. LiAlH4

17. DIBAL
 Selective reagent (alkyne to alkene, ester
or ketone to aldehyde).
 Specialist reductant of nitrile to aldehyde

18. Borane
 BH3 gas dissolved in THF or Et2O or DMS
 Selective reducing agent
 Hydroboration is syn addition, highly
regioselective

19. Borane Regioselectivity

20. Borane chemoselectivity

21. Borane
Amide to amine
Dialkyl borane

22. CBS ???
 Borane complexed with oxazoborolidine
 Enantioselective reduction of ketones
 So, CBS is a catalyst, not reagent

23. CBS ???
 R,R` difference is very important
 High ee, high yield
 Easy recovered

24. Wolff-Kishner reduction
 Reduction of aldehydes, ketones to alkane
 Using hydrazine in basic media

25. Metal dissolving reduction
 Dissolving Li or Na in NH3 solution
 Birch reduction in case of aromatics
 Good access to cyclohexadienes

26. Metal dissolving reduction
+I, -I effect

27. Metal dissolving reduction
Why 1,4 not 1,3 ???

28. Clemmensen reduction
 Kind of electron reduction reactions
 Zinc metal in Conc. HCl
 Carbonyl to alkane (CH )
2
Carbenoid mechanism

29. Asymmetric hydrogenation
 Using catalytic amounts of chiral ligands
with H2.

30. Asymmetric hydrogenation

31. Staudinger reduction
 Azide to amide (possible via hydrogenation)
 Mild conditions