Oxidation and Reduction

Reduction

• gain of electrons/protons

• Increase in H-bonds

• decrease in C-Z bonds

**electrons follow protons

Oxidation

• loss of electrons/protons

• decrease in H-bonds

• increase in C-Z bonds

**electrons follow protons

Regioselective Reaction

one constitutional isomer is formed almost exclusively (major vs minor product)

Stereoselective Reaction

one stereoisomer is almost exclusively (trans major product vs cis minor product)

Enantioselective Reaction

one enantiomer is almost exclusively formed

Reduction of Alkenes

H2 with Pd, Pt, or Ni

• Syn addition H2 occurs

• increasing alkyl substitution on C=C, decreases rate of reaction

Reduction of Alkynes

• H2 (2 equiv) and Pd, Pt, or Ni

• reduces alkyne to alkane

• 4 new C-H bonds are added

Reduction of Alkynes

• H2 w/ lindlar’s catalyst

• lindlar’s catalyst produces cis alkene via syn addition

Reduction of alkyl halides

Na with NH3

• Anti-addition of H2

• trans-alkene formed

Reduction of alkyl halides

LiAlH4 with H2O

• forms alkane (?)

• SN2 mechanism

• less substituted react faster

Reduction of Epoxides

LiAlH4 and H2O

• forms alcohol

• SN2

• Unsymmetrical epoxides: H- (LiAlH4) attacks LESS substituted carbon

Oxidation of Alkenes: Epoxidation

going from alkene → epoxide

• Reaction with RCO2-OH

• one step

• Syn addition

• stereospecific

Oxidation of alkenes: Anti Dihydoxylation

alkene → 1,2-diol

• reaction with RCO3H and H2O

• Epoxide intermediate with -OH/H2O

• Add in ANTI fashion

• makes enantiomer

Oxidation of Alkenes: Syn dihydroxylation

alkene → 1,2 diol

• 1) OsO4

• 2) NaHSO3, H2O

• 1) OsO4, NMO

• 2) NaHSO3, H2O

or

• 2) KMnO4, H2O, HO-

• makes enantiomer

Oxidation of alkenes: Oxidative Cleavage (Ozonolysis)

alkene → ketone and aldehyde

• 1) O3

• 2) Zn, H2O or CH3SCH3

alkene double bond cleaved to make two carbonyl groups

Oxidative Cleavage of Alkynes: internal alkyne

R—R → (1. O3, 2. H2O)→ two carboxylic acids

• ozonolysis

Oxidative Cleavage of Alkynes: terminal alkyne

R—H → (1. O3, 2. H2O)→ carboxylic acid and CO2

• ozonolysis

Oxidation of Alcohols

R—OH → (PCC or HCrO4-) → ALDEHYDE

• primary alcohol

• stops at aldehyde stage where only one C-H bond is replaced by C-O bond

Oxidation of Alcohols

R—OH → (CrO3, H2SO4 + H2O) → carboxylic acid

• harsher conditions

• replaces two C-H bonds with C=O

• primary alcohol

Oxidation of Alcohols

2 alcohol → (PCC or CrO3 or HCrO4-)

• oxidize secondary alcohol to ketone

Asymmetric epoxidation of allylic alcohols

allylic alcohol → (CH3)3C-OOH and Ti[OCH(CH3)2]4 → epoxide

• (+)-DET : epoxide faces downwards

• (-)-DET : epoxide faces upwards