Reduction reactions

Organic chemistry

1. ReductionReduction ReactionsReactions

2. Classification of reduction
reactions
Catalytic hyrdogenation (H
2
with metals)
Hydride transfer reactions, using
hydride sources such as LiAlH
4
,
NaBH
4
,..
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 H
2
to unsat. bond (double ,
triple bonds, NO
2
, CN,..
Without catalysts ,it needs 480
o
c
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 PdCl
2
with H
2
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. PtO
2
( Adams catalyst)
PtO
2 reduced to Pt with H
2

11. Lindlar`s catalyst
Pd supported with CaCO
3
instead of
charcoal,then treated with Pb to deactivate.
Selective reduction of alkynes to Z-alkenes
only via syn addition

12. NaBH
4
Selective (chemoselectivity) reagent
White crystals, safe and easy to handle
Reduces aldehydes, ketones.
Can`t reduce esters ,acids, amides

13. NaBH
4
Generally
Still reducing agent

14. NaBH
4
Luche reduction

15. LiAlH
4
Powerful reducing agent compared to
NaBH
4
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. LiAlH
4

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

18. Borane
BH
3
gas dissolved in THF or Et
2
O 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 NH
3
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 H
2
.

30. Asymmetric hydrogenation

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