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