Module4: Photochemistry of Enones and dienones …nptel.ac.in/courses/104105071/Mod4l12.pdf · 1 |...
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1 | Page Module4: Photochemistry of Enones and dienones Lecture12: Photochemistry of Enones and dienones (Contd.)
Transcript of Module4: Photochemistry of Enones and dienones …nptel.ac.in/courses/104105071/Mod4l12.pdf · 1 |...
1 | P a g e
Module4: Photochemistry of Enones and dienones
Lecture12: Photochemistry of Enones and dienones (Contd.)
2 | P a g e
4.3) Di – π methane Rearrangement (DPM)
Zimmermann Di – π methane Rearrangement
Mechanism
Ionic pathway
h
Radical pathway
h
1,4 diradical
(1)
h
3 | P a g e
hHH HH
H
H
1, 2 H shift
(2)
h
1,4 diradical
Ph Ph Ph Ph
h
Ph Ph
free rotor chemmistry
Ph Ph
Ph Ph
h
1,4 diradical
Ph Ph PhPh PhPh PhPh PhPh Ph Ph
(3)
4 | P a g e
h
Ph PhPh PhC2H5
C2H5 Ph PhC2H5 Ph PhC2H5
a bb
a
Ph PhC2H5 Ph PhC2H5
A
B
(4)
(5)
1
23
45
bond formation
between C2and C4
h
1
23
45
bond breaking between C2 and C3
bond fromation between C3 and C5
Barrelene
(6)
Ph
h
Ph
a b
Ph Ph
(7)
5 | P a g e
h 1, 2 [ H ] shift
H Ph H Ph H Ph
H H
HH
Ph
(8)
h
H Ph H Ph
Ph Ph
Ph
Ph Ph
H Ph
Ph PhPh Ph
4.3.1) Oxa di – pi methane rearrangement (ODPM)
(1)
O
h
O OO
Ha b
(2)
O
h
O O
O
(3)
O
h
O1
2
3
4
O O
(4)
6 | P a g e
OAc
O O
h
O O
O O
O O
4.3.2) Aza di – pi methane rearrangement
(1)
N
Ph Ph Ph
Ph Ph
h N
Ph Ph Ph
Ph Ph
a b N
Ph Ph Ph
Ph
Ph
N
Ph Ph Ph
Ph
Ph
a
b
N
Ph Ph Ph
Ph
Ph
N
Ph Ph PhPh
Ph
(2)
7 | P a g e
N
h a ba
OAcN
OAc
1
2 3
4
b
NOAc
Ph
Ph
NOAc
PhPh
(3)
N
h
OAcN
OAc
NOAcPh
Ph
4.4 ) Photo Fries rearrangement
(1)
h
O
O
R OH
R
OOH
+
RO
+
OH
Mechanism
8 | P a g e
+h
O
O
R O
O
R
solvent cage
escape
O OH
O
R
OO
ROH
H
OH
R
OOH
RO
