Tetrahedron Letters,Vol.25,No.21,pp 2253-2254,1984
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NOVEL PHOTOISOMERIZATION OF SPIRODIENONES
T.R. Kasturi , K.B. Ganesha Prasad, G. J. Raju and Vo Ramamurthy
Indian Institute of Science, Bangalore-560012, India.
Abstract:
Spironaphthalenones of the type cl_)have been demonstrated te
undergo isomerization to (2) upon UV irradiation.
2,4-Cyclohexadienones have been established to undergo l,ó-bond cleavage
upon photolysis 1,2 . On the other hand, 6,6-spiroepoxy-2,4-cyclehexadienone is
reported to result in aromatization via B C-O bond cleavage upon excitation3*
Here, we report a novel photoarrangement of spironaphthalenones [ (&) and <2)]
involving B C-O bond cleavaget rearrangement of such type is not common.
-1
-2
-3
The spironaphthalenones (Ib-li)
and (2b-21)
were prepared4 by the oxidation
--of the corresponding substituted P-naphthols with o-chloranil in benzene, Compounds (la)
and (2a)
were prepared5 by the oxidation of l-(2'-hydroxy-phenoxyl-2naphthol with o-chloranil in benzene.
Photolysis of benzene solution (OoC02-0o004M) of <&) and (2) were carried
out in pyrex tubes under deareated conditions using 450 W medium pressure mercury
lamp.
(&-ti>
Results are presented in the table.
readily photoisomerize to (&-a)
Inspection of the table reveals that
in near quantitative yield.
On the
other hand, spironaphthalenones
(lh)
and(_) photoisomerize to (2) and (2)
respectively in reduced yields. Similar irradiation of (2a+2q)
did not bring
-
about any change whereas
(2)
and (21)
rearranged to (lh)
and(li)
respectively,
The photosiomerization is believed to originate from the lowest excited singlet
state, as triplet quenchers such as naphthalene
(ET=61 Kcal/mole) and cyclohexa-
diene (52 Kcal/mole) failed to quench the photorearrangement in the case of
ll&) and Cls>.
2253
2254
Table
extent of isomerization (X1
Isomeric spirodienones
(&)d
R = R2= R3= R=H
(2)
(2) +
(&)
c-1
and (&):
100
0
(2)
and (2b)r
R:= R2= R3= H: R=Cl
-
100
0
c-1
and (&):
Rl= R2=H; R3=Me; R=Cl
100
0
(0)
and (_)t
Rl= R2=H: R3= pri; R=Cl
90
0
(5)
and (2_e)rRl=R2= but: R3=H1 R=Cl
100
0
(12) and (22): Rl=R3=H; R2= but: R=Cl
90
0
(9)
95
0
(12) and (2h)t
Rl= OMe: R2= R3= H; R=Cl
-
25
75
c-1
75
25
and (_Z): Rl=CN: R2= R3= H: R=Cl
and (2i)r
Rl= Brt R2= R3= H: R=Cl
-
The photorearrangement could be visualized as occurring through the
intennediacy of spirocyclohexadienone of the type (3) formed by initial
8 C-O cleavage.
Further work, to have a deeper insight into its mechanism
is under progress.
Acknowledqement:
We wish to thank Mr. V. Ramesh for helpful discussions.
One of us (K.B.G.) wish to thank the Department of Atomic Energy for financia1
assistance.
Referentes:
1)
G. Quinkert, Anqew, Chem. Internat. edno, 2.
1072 (1972); H. Hart,
D. A. Dickinson and W, Y, Li, Tetrahedronyett.,
2253 (1975)t G. Quinkert,
Pure. Appl. Chem ., -35 285 (1973); G. Quinkert, Fo Cech, Eo Kleiner and
D. Rehm, Anqew. Chem. internat. edn,, 18 557 (1979).
2)
T. Sala and M.V. Sargent, 3. Chem. Soco, Perk, Trans. II 870
(1981).
3)
H.D. Becker, T, Bremholt and E, Adler, Tetrahedron Lett. 4205 (1972).
4)
T. R. Kasturi, T. Arunachalam and G, Subramanyam, J. Chem. SOcc (C)
1257 (1970); ToR. Rasturi and R. Sivaramakrishnan, Indian. J. Chem.
16B 668 (1978).
5)
T. R. Kasturi, K. B. Ganesha Prasad and B, Rajasekhar, Indian Jo Chem.,
21B 813 (1981)o
(Received in UK 29 February 1984)