Transformation Chromium reagent

CH-‐423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan

Chromium based oxidation

1

R OH R CHO

OH

R R'

O

R R'

R OH R COOH

Transformation Chromium reagent PCC, Collins reagent, PDC in DCM

PCC, Collins reagent, PDC, Jones reagent

Jones reagent, PDC in DMF

CHO

Etard reaction


Manganese based oxidation KMnO4 MnO2 Mn(OAc)3

Potassium permanganate (KMnO4)

R'

RKMnO4+

R'

R OMnO O

O-K+

R'

R OH

OH

HOMn

HO O

O-K++

R'

R OMnO O

O-K+H

R'

R O

OH R'

R O

O

Under mild condition KMnO4 can effect conversion of alkenes to glycol

KmnO4 is such a powerful oxidant that it can cleave the glycol further. So, careful control is required

2


R R'KMnO4, H2O

Manganese based oxidation

R R'

HO OH

R

R'O

O

R R'

O OH

ArKMnO4, H2O ArCO2H

CH3Ar KMnO4, H2OArCO2H

Potassium permanganate (KMnO4)

In water medium:

3


Manganese based oxidation Potassium permanganate (KMnO4)

In Organic Solvents:

3.3 mol KMnO4

Benzene polyether

1.0 mol KMnO4

R4NCl

OH

OH

O

O

Oxidation of acetylenes:

Ph CH2CH2CH3

KMnO4

R4N+, DCM HO

CH2CH2CH3

OH

Ph

O

CH2CH2CH3

OH

Ph

O

CH2CH2CH3

O

Ph

4



Oxidation of aromatic side chain:

Ar R Ar CO2HKMnO4

R3C NH2 R3C NO2KMnO4

Oxidation of amino compounds:

Tertiary alkylamines can be oxidized to nitro compounds

Oxidation of sulphides:

S

NO2

O2N S

NO2

O2NO

O

KMnO4

5



Application in the synthesis of Saccharin: Me

SO2NH2

KMnO4

OH-

CO2

SO2NH2

Na

SO2

NH

O

Saccharin

Oxidation of terminal alkynes:

CO2H

6

Me

SO2Cl

(NH4)2CO3

KMnO4


Manganese based oxidation Manganese dioxide (MnO2)

Excess of MnO2 is required

O

MnO2, KCNOH

EtOH

OH

CN

Uses: Selective oxidation of allylic & benzylic alcohols

O

CN

MnO2

CH2Cl2

OH

7

O

OEtEtOH


Manganese based oxidation Manganese dioxide (MnO2)

8

OH

MnO2ROH

NaCNCO2R

OH MnO2

O

H

CN OH

CN

MnO2

O

CN

O

OR R OH



CH2OH CHO

MnO2 OHCHO

MnO2

DCM

OHCHO

MnO2 MnO2, CH2Cl2

HO

OH

O

OH

Manganese dioxide (MnO2)

9

OH

HO

MnO2

CHCl3

OH OH

O

OH


Manganese based oxidation Manganese(lll) acetate Mn(OAc)3

O

Mn(OAc)3

OOAc

OOAcOMn(OAc)3

10

OHO OMn(OAc)2

Mn(OAc)3

Mn(OAc)2

OMn(OAc)3

O

Mn(OAc)2

OOAc



OH

Manganese(lll) acetate Mn(OAc)3

11

Mn(OAc)3

NMe

O

OH

NMe

O

O

NMe

O

O OH

NMe

O

O OHMn(OAc)3

Mn(OAc)2

NMe

O

OH OH

NMe

O

OOH


Silver-based oxidation

R

O

H

Ag2OR

O

OH+ 2 Ag

Ag2CO3 on Celite (Fetizon’s reagent)

OHOH

Fetizon's reagent

O

O

Fetizon's reagent

O

OH

OH O

OH

O

Ag2O Mild oxidant to oxidize aldehyde to carboxylic acid

CHO Ag2O

NaOH

CO2H

Conversion of diols to lactones

12



Ag2CO3 on Celite (Fetizon’s reagent) Highly selective:

Mono-oxidation:

Mechanism:

OH OH OH

Fetizon's reagent

OH O OH

OHOH

Fetizon's reagent

OHO

Fetizon's reagent

OH

OH

O

OH

HO H

R R

Ag+ Ag+

O

O--O

O

O O

HH

R R

Ag

O

Ag+O

R RH2O + CO2 + 2Ag

13


R

R'

I2Ag(OAc)2 or Ag(O2CPh)2

R

R'I

O

OR

R'CH3

O

OR

R'CH3

R

R'

OAc

OAc

-OAc

H2O

R

R'

OH

OHcis product

R

R'

OH

OHtrans product

In absence of water, Prevost Hydroxylation, trans-product

In presence of water, Woodwards hydroxylation,

cis-product

Silver acetate


14

R

R'

I

O CH3

O

Transformation Chromium reagent

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