Pinacol pinacolone rearrangement involves conversion of 1,2 - diols to carbonyl compounds in presence of acid catalyst with change in carbon skeleton. It is an example of whitmore shift.

1. PINACOL PINACOLONE
REARRANGEMENT
SAVITA K.

2. Introduction:
• Conversion of 1,2- diol ( vicinal diols) into
carbonyl compounds in presence of acid
catalyst with change in carbon skeleton.
• Example of 1,2- shift ( Whitmore shift)

3. General reaction:
OH
R
R
1
R
2
R
3
OH
1,2- Diol ( Vicinal diol)
H+ O
R
R
2
R
3
R
1
Carbonyl comp. ( Pinacolone)

4. Mechanism:
OH
R
R
1
R
2
R
3
OH
H+ OH
R
R
1
R
2
R
3
OH2
+
- H2O
C
+
OH
R
R
1
R
2
R
3
Carbocation
1, 2 - shift
C
+
O
R
R
2
R
3
R
1H O
R
R
2
R
3
R
1
- H+

5. Migratory Aptitude:
• The most electron-rich alkyl group (more
substituted carbon) migrates first. The
general migration order:
Tertiary alkyl > cyclohexyl > secondary alkyl > benzyl >
phenyl > primary alkyl > methyl >> H
• For substituted aryls:
p-MeO-Ar > p-Me-Ar > p-Cl-Ar > p-Br-Ar > p-MeOAr > p-O2N-Ar

6. Migratory Aptitude:
• The OH group lost should be the one that leaves behind the
more stable carbocation
Order of migratory aptitude :
Ar > H > CH3
• In case of alkyl group : tert. Alkyl > sec. > pri. > CH3
• In case of aryl group:
Eg. p- Cl Phenyl< Phenyl < p- tolyl < p- methoxy phenyl
EDG EWG
> >

7. Migratory Aptitude:
• In case of electron rich aryl ring, the position of EDG will
decide the migratory aptitude.
para > meta > ortho
• In case of electron deficient ring, the position of EWG will
decide migratory aptitude.
meta preferred
• Reaction occurs in anti manner i.e. migrating group should
be anti to leaving group.

8. Example 1.
OH
H5C6 C6H5
OH
O2N OCH3
1,2- Diol ( Vicinal diol)
H+
O
C6H5
C6H5
O2N OCH3

9. Example 1. mechanism
OH
H5C6 C6H5
OH
O2N OCH3
OH
H5C6 C6H5
OH2
+
O2N OCH3
H+
- H2O
C
+
OH
H5C6 C6H5
O2N OCH3
1. Migration of C6H5
2. Deprotonation
O
C6H5
C6H5
O2N OCH3

10. Example 2.
OHOH
O2N OCH3
NO2O2N
H+ O
O2N OCH3
NO2
O2N

11. Example 2. mechanism
OHOH
O2N OCH3
NO2O2N
H+
OH2
+
OH
O2N OCH3
NO2O2N
C
+
OH
O2N OCH3
NO2O2N
migration of m-
NO2 C6 H4
-H+
O
O2N OCH3
NO2
O2N

12. Example 3.
OHOH
H3CO OCH3
H3CO OCH3
H+ O
OCH3
OCH3
H3CO
OCH3

13. Example 3. mechanism
OHOH
H3CO OCH3
H3CO OCH3
H+
OH2
+
OH
H3CO OCH3
H3CO OCH3
C
+
OH
H3CO OCH3
H3CO OCH3
O
OCH3
OCH3
H3CO
OCH3
migration of
p - methoxy phenyl
- H+

14. Example 4.
Of the two OH groups that one departs which leaves behind more stable carbocation.
This factor takes precedence over migratory aptitude.
OH
Me
MePh
Ph
OH
H+
O
Me
Ph
Ph
Me Ph
Me
Me
Ph
O
Formed Not formed

15. Example 4. mechanism
C
+
OH
Me
MePh
Ph
C
+
Me
MePh
Ph
OH
Me migrates
- H+
O
Me
Ph
Ph
Me
More stable carbocation
Less stable carbocation

16. Example 5.
OH
OH
H+
OH2
+
OH
Me shift
- H2O
- H+
CH3
O

17. Example 6.
ring contraction
OH
CH3
OH
H+
OH2
+
OH
1 , 2 - shift
- H2O
- H+
O

18. Example 7.
spiro ketone formation
OH
OH
H2SO4
OH2
+
OH
- H2O
C
+
OH
- H+
O
OH
OH
H2SO4
OH2
+
OH
- H2O
C
+
OH
O
- H+

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