Module I Oxidation Reactions - NPTel

NPTEL – Chemistry – Reagents and Organic reactions
Me
Mechanism
Me
H
Me
Me
O
O
OMe
SeO 2, reflux
SeO 2, AcOH (cat)
H 2O-dioxane, reflux
Scheme 3
Joint initiative of IITs and IISc – Funded by MHRD Page 38 of 122
O
Me
O
Me
H
Me
O
Me
O
OMe
The proposed mechanism is similar to that of allylic oxidation i.e. ene reaction
followed by [2,3]-sigmatropic rearrangement and then elimination gives the
desired 1,2-dicarbonyl compounds (Scheme 4). 1
R
O
O SeO
R'
H
H
Ene
reaction R
HO
Se
O O
H
1.4.1.3 Oxidation of Alkynes
R'
[2,3] sigmatropic
rearrangement R
Scheme 4
O
O
R' H
Se OH
In the presence of acid, SeO2 oxidizes alkynes to give 1,2-dicarbonyl
compounds. Internal alkynes can be converted into 1,2-diketones, where as
terminal alkynes are transformed into glyoxylic acid (Scheme 5).
Ph
Ph
Ph
H
SeO 2
H 2SO 4
SeO 2
H 2SO 4
Scheme 5
O
Ph
Ph
O
O
OH
Ph
O
R
O
O
R'
+ H 2O + Se