Post on 11-May-2015
description
ReductionReduction ReactionsReactions
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)
Classification of reduction reactions
Replacement of oxygen by hydrogen Removing oxygen from the substrate Reduction with cleavage Reductive coupling
Catalytic Hydrogenation
Addition of H2 to unsat. bond (double , triple bonds, NO2 , CN,..
Without catalysts ,it needs 480oc Pt group metals (Pd, Ni ,Ru and Rh)
used as catalysts Can be selective reduction, depends
on conditions
Catalytic Hydrogenation
Catalytic Hydrogenation
Pd/C reduction
Pd powder spread on charcoal after reduction of PdCl2 with H2
Homogenous catalyst, can be recovered by filtration
Raney Nickel
Treatment of Al-Ni alloy with NaOH To reduce alkenes, alkynes, nitriles aromatics
and carbonyl compounds Syn addition product
Raney Nickel
Hydrogenolysis: removal of sulphur (C-S to C-H) in desulphurization reaction
Use after open immediately????
PtO2( Adams catalyst) PtO2 reduced to Pt with H2
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
NaBH4
Selective (chemoselectivity) reagent White crystals, safe and easy to handle Reduces aldehydes, ketones. Can`t reduce esters ,acids, amides
NaBH4
Generally
Still reducing agent
NaBH4
Luche reduction
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.
LiAlH4
DIBAL
Selective reagent (alkyne to alkene, ester or ketone to aldehyde).
Specialist reductant of nitrile to aldehyde
Borane
BH3 gas dissolved in THF or Et2O or DMS Selective reducing agent Hydroboration is syn addition, highly
regioselective
Borane Regioselectivity
Borane chemoselectivity
Borane
Amide to amine
Dialkyl borane
CBS ??? Borane complexed with oxazoborolidine Enantioselective reduction of ketones So, CBS is a catalyst, not reagent
CBS ??? R,R` difference is very important High ee, high yield Easy recovered
Wolff-Kishner reduction Reduction of aldehydes, ketones to alkane Using hydrazine in basic media
Metal dissolving reduction
Dissolving Li or Na in NH3 solution Birch reduction in case of aromatics Good access to cyclohexadienes
Metal dissolving reduction
+I, -I effect
Metal dissolving reduction
Why 1,4 not 1,3 ???
Clemmensen reduction Kind of electron reduction reactions Zinc metal in Conc. HCl Carbonyl to alkane (CH2)
Carbenoid mechanism
Asymmetric hydrogenation Using catalytic amounts of chiral ligands
with H2.
Asymmetric hydrogenation
Staudinger reduction
Azide to amide (possible via hydrogenation) Mild conditions