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The photochemical rearrangement of 2,5-diphenyloxazole
TetrahedronLettersNo.28, PP. 2379-2381,1969. PergamonPress. Printed in Great Britain.
THE PHOTOCHEMICALREARRANGEMENTOF 2,5-DIPHENYLOXAZOLE(1) Masaharu Kojima and Minor-uMaeda Faculty of PharmaceuticalSciences,Kyushu University,Fukuoka (JAPAN)
(Receivedin Japan 5 April 1969; received in IJKfor publication12 May 1969) Recently,it has been reportedthat the five-memberedheterocycliccompoundscontaining two vicinal hetero-atomsinterchangedtheir positionsto 1,3-systemsas a common mode of reaction when irradiatedwith ultravioletlight.
Examplesincludethe photo-inducedrearrangementof
indazolesto benzimidazoles(Z), pyrazole to imidazole(2),3,5-diphenylisoxazole to 2,5-diphenyloxazole(3),benzisoxazolesto benzoxazoles(4), and 1,3,5-trimethylpyrazole to 1,2,4-trimethylimidazole(5).
On the other hand, there is no record of the rearrangementof 1,3- to 1,2-
system.
n-7.
\’ X'
n---if
hv
-
fxP
Here we wish to report the new photo-inducedrearrangementof 2,5-diphenyloxazole(1). A 2.3 x 1O-2 M ethanol solutionof I was irradiatedfor 50 hr. at 80' under a nitrogen atmosphere using 100 w. high pressure mercury-vapourlamp with a Pyrex filter. by UV spectroscopy.
The reactionwas followed
Chromatographyon silica gel of the evaporatedreactionmixture gave 3,5-
diphenylisoxazole(II)(3%), m.p. 14l'[authenticsample(6),m.p. 140-141'1,4,5-diphenyloxazole (III)(ZO%),m.p. 44'[authenticsample(7),m.p. 44'1, phenanthr(9,lO)oxazole(IV)(l.S%), m.p. 152153'[authenticsample(g),m.p. 152-153'1,and benzoic acid(l%),and approximately5% of the startingmaterial was recovered.
All the isolatedcompoundswere identifiedin comparison
with those of authenticsamplesby mixed m.p. and I.R. spectra.
Irradiationof a 1.4 x 10s3
M ethanol solutionof III in the presence of air led to the formationof IV(42%).
The result
showed that IV was not derived directlyfrom I, but the photo-oxidationproduct of III. Further,when a 2.3 x 10m2 M benzene solutionof I was irradiatedfor 72 hr. under similar conditions,11(7%),benzoic acid(2%),dibenzamide(0.4%), and a new product, 2,4-diphenyloxazole
2379
No.28
2300 (V) (4.5%)) together
m.p.
103-104°,
with unchanged
identified
by direct
1(17%).
comparison
In benzene
with
solution,
authentic
sample(g),
I was not converted
to
+
were isolated
III.
+
$H$OOH
I
II
+
CH + 6 5
C6H5COOH
+
( C6H5C0‘2NH
V
On the basis the protic
nature
reversible.
light,
as a true
efforts
ethanol
of the medium, and the In the rearrangement
was isolated although
of the above experiments,
to
or benzene and the
induced
breaking
imidazole,
giving
to V(eq
In a pathway of IX and X, similar
II(eq
should
I are affected
be photochemically
the azirine
derivertive(VI1)
On the rearrangement mixture
be the azirine(VII),
of
were unsuccessful,
upon irradiation
by
I to
II,
I in
with ultraviolet
which undergoes
a further
photo-
A).
a supposed
intermediate,
of
I in benzene
solution
to V, involves
l-benzoyl-2-phenyl-azirine(VIII),
the
which is
B).
I in ethanol
solution
by P. Beak et al.(S)(eq
The investigations
of
I and II should
to oxazole(I),
O-C2 bond cleavage
to the photo-rearrangement
suggested
between
from the reaction
the mechanism of the rearrangement
of O-C5 bond,
then transformed
isoxazole(II)
reactions
by Ullman and Singh(3).
undergoes
photoproduct to
isomerization
the azirine(VI1)
solutions
rearrangement Similarly,
intermediate,
isolate
initial
of
the photochemical
on the detailed
to
III,
we consider
four-membered
of
1,2,5-trimethylpyrazole
to
ring
intermediates
1,2,4_trimethyl-
6). mechanisms
of these
reactions
are in progress.
No.28
2381
CsH55;.\ 0
N
c6H5 (Al
VII
II
>
C’sH5N
-b C6H5
(8)
0
V
REFERENCES
1. Photochemistryof HeterocyclicCompounds.I. 2.
(a) H. Tiefethaler,W. Dorschelen,H. G&h and H. Schmid,TetrahedronLetters,2999(1964). (b) H. GUth, H. Tiefethalerand W. Dtlrschelen, Chimia, 19, 596(1965). __
3.
(a) E. F. Ullman and B. Singh, J. Am. Chem. Sot., 80, 1844(1966). (b) B. Singh and E. F. Ullman, -ibid, __ 83, 6911(1967). (c) D. W. Kurz and H. Shechter,Chem. Comm., 689(1966).
4.
(a) H. Goth and H. Schmid, Chimia, z??,148(1966). (b) M. Ogata, H. Matsumotoand H. Kano, Abstractsof the Symposiumon the Chemistryof HeterocyclicCompounds(Osaka, JAPAN, Oct., 1968), P. 157.
5.
P. Beak, J. L. Miesel and W. R. Messer, TetrahedronLetters,53X(1967).
6.
T. Posner,s,
22, 3985(1901).
7. H. Bredereckand R. Gompper, Chem. Ber., iz, 700(1954). a. A. Schonbergand W. I. Awad, J. Chem. Sot., 651(1947). 9. F. 0. Bltlmlein, K,
V, 2578(1884).
THE PHOTOCHEMICALREARRANGEMENTOF 2,5-DIPHENYLOXAZOLE(1) Masaharu Kojima and Minor-uMaeda Faculty of PharmaceuticalSciences,Kyushu University,Fukuoka (JAPAN)
(Receivedin Japan 5 April 1969; received in IJKfor publication12 May 1969) Recently,it has been reportedthat the five-memberedheterocycliccompoundscontaining two vicinal hetero-atomsinterchangedtheir positionsto 1,3-systemsas a common mode of reaction when irradiatedwith ultravioletlight.
Examplesincludethe photo-inducedrearrangementof
indazolesto benzimidazoles(Z), pyrazole to imidazole(2),3,5-diphenylisoxazole to 2,5-diphenyloxazole(3),benzisoxazolesto benzoxazoles(4), and 1,3,5-trimethylpyrazole to 1,2,4-trimethylimidazole(5).
On the other hand, there is no record of the rearrangementof 1,3- to 1,2-
system.
n-7.
\’ X'
n---if
hv
-
fxP
Here we wish to report the new photo-inducedrearrangementof 2,5-diphenyloxazole(1). A 2.3 x 1O-2 M ethanol solutionof I was irradiatedfor 50 hr. at 80' under a nitrogen atmosphere using 100 w. high pressure mercury-vapourlamp with a Pyrex filter. by UV spectroscopy.
The reactionwas followed
Chromatographyon silica gel of the evaporatedreactionmixture gave 3,5-
diphenylisoxazole(II)(3%), m.p. 14l'[authenticsample(6),m.p. 140-141'1,4,5-diphenyloxazole (III)(ZO%),m.p. 44'[authenticsample(7),m.p. 44'1, phenanthr(9,lO)oxazole(IV)(l.S%), m.p. 152153'[authenticsample(g),m.p. 152-153'1,and benzoic acid(l%),and approximately5% of the startingmaterial was recovered.
All the isolatedcompoundswere identifiedin comparison
with those of authenticsamplesby mixed m.p. and I.R. spectra.
Irradiationof a 1.4 x 10s3
M ethanol solutionof III in the presence of air led to the formationof IV(42%).
The result
showed that IV was not derived directlyfrom I, but the photo-oxidationproduct of III. Further,when a 2.3 x 10m2 M benzene solutionof I was irradiatedfor 72 hr. under similar conditions,11(7%),benzoic acid(2%),dibenzamide(0.4%), and a new product, 2,4-diphenyloxazole
2379
No.28
2300 (V) (4.5%)) together
m.p.
103-104°,
with unchanged
identified
by direct
1(17%).
comparison
In benzene
with
solution,
authentic
sample(g),
I was not converted
to
+
were isolated
III.
+
$H$OOH
I
II
+
CH + 6 5
C6H5COOH
+
( C6H5C0‘2NH
V
On the basis the protic
nature
reversible.
light,
as a true
efforts
ethanol
of the medium, and the In the rearrangement
was isolated although
of the above experiments,
to
or benzene and the
induced
breaking
imidazole,
giving
to V(eq
In a pathway of IX and X, similar
II(eq
should
I are affected
be photochemically
the azirine
derivertive(VI1)
On the rearrangement mixture
be the azirine(VII),
of
were unsuccessful,
upon irradiation
by
I to
II,
I in
with ultraviolet
which undergoes
a further
photo-
A).
a supposed
intermediate,
of
I in benzene
solution
to V, involves
l-benzoyl-2-phenyl-azirine(VIII),
the
which is
B).
I in ethanol
solution
by P. Beak et al.(S)(eq
The investigations
of
I and II should
to oxazole(I),
O-C2 bond cleavage
to the photo-rearrangement
suggested
between
from the reaction
the mechanism of the rearrangement
of O-C5 bond,
then transformed
isoxazole(II)
reactions
by Ullman and Singh(3).
undergoes
photoproduct to
isomerization
the azirine(VI1)
solutions
rearrangement Similarly,
intermediate,
isolate
initial
of
the photochemical
on the detailed
to
III,
we consider
four-membered
of
1,2,5-trimethylpyrazole
to
ring
intermediates
1,2,4_trimethyl-
6). mechanisms
of these
reactions
are in progress.
No.28
2381
CsH55;.\ 0
N
c6H5 (Al
VII
II
>
C’sH5N
-b C6H5
(8)
0
V
REFERENCES
1. Photochemistryof HeterocyclicCompounds.I. 2.
(a) H. Tiefethaler,W. Dorschelen,H. G&h and H. Schmid,TetrahedronLetters,2999(1964). (b) H. GUth, H. Tiefethalerand W. Dtlrschelen, Chimia, 19, 596(1965). __
3.
(a) E. F. Ullman and B. Singh, J. Am. Chem. Sot., 80, 1844(1966). (b) B. Singh and E. F. Ullman, -ibid, __ 83, 6911(1967). (c) D. W. Kurz and H. Shechter,Chem. Comm., 689(1966).
4.
(a) H. Goth and H. Schmid, Chimia, z??,148(1966). (b) M. Ogata, H. Matsumotoand H. Kano, Abstractsof the Symposiumon the Chemistryof HeterocyclicCompounds(Osaka, JAPAN, Oct., 1968), P. 157.
5.
P. Beak, J. L. Miesel and W. R. Messer, TetrahedronLetters,53X(1967).
6.
T. Posner,s,
22, 3985(1901).
7. H. Bredereckand R. Gompper, Chem. Ber., iz, 700(1954). a. A. Schonbergand W. I. Awad, J. Chem. Sot., 651(1947). 9. F. 0. Bltlmlein, K,
V, 2578(1884).