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The reaction of benzophenone triplets with norbornadiene and quadricyclene
Tetrahedron
Letter8
No. 52, PP 5345 - 5348,
THE REACTION
OF BENZOPHENONE
NORBORNADIENE A.A.
AND
in UK 23 October
in Great Britain.
TRIPLETS WITH
QUADRICYCLENE
Garman and R. L. Leyland
Department of Chemistry, University of Manchester, (Received
Printed
Pergamon Frese.
1972.
1972;
accepted
for
Manchester Ml3
publication
9PL.
30 November 1972)
One of the best documented reactions of organic photochemistry involves the conversion of a norbornadiene to the corresponding quadricyclene
system.
’ Sensitisatian of the reaction is Possible and
Hammond has shown that with aromatic ketone and aldehyde triplet sensitisers a photostationary state between norbarnadiene (1) and quadricyclene the dcnor.*r3
(2) is established, the position of which depends an the triplet energy of
This was interpreted in terms of a non-spectroscopic excitation
triplet of 1 ar a biradical
2;
of 2 to either the Fran&Candan
the different internal energies of r and 2 thus accounted for the importance of the
donor triplet energy on the position of the photostationary state. 1) Kubota,
Shima and Sakurai4 have recently
rep&ted that the 1: 1 adducts of benzophenone and ncrbornadiene -4,5 and 6 are farmed in 32%, yields respectively.
15% and 3%
These workers proposed that the adducts are formed via the intermediacy of interconverting
biradicais of types --7,8 and -9 which are formed by attack of benzaphenone triplet an ground state narbarnadiene. An interest in the mechanism of energy transfer in ketone sensitised reactions5 had led us to investigate the reaction of the norbarnadiene/quadricyclene
system with benzophenone.
The work by the Japanese graup
prampts us to describe cur own results which show that the adducts are -not farmed by addition of benzaphenane triplet to norbarnadiene. Deoxygenated benzene solutions containing norbornadiene (0.82M)
and benzaphenone (0.014M)
were
irradiated in Pyrex with a 1ooW medium pressure mercury arc and the reaction monitored by g. I. c. and t. I. c. After 28 minutes the formation of quadricyclene
1)Substantial
(2) and two unknown products could be detected and after 18
amounts of the starting material were consumed in side reactions.3
534.5
5546
No.
hours all the benzophenone on alumina, A similar
were isolated
reaction
essentially
in 61% and 26% yields
with quadricyclene
the same isolated
were also obtained Clearly
The two unknowns,
had been cansumed.
yields,
(0.02M)
and identified
using ether Q isapentone
respectively.
as solvent
(0.014M)
2)
quadricyclene
the reactions
ond not to norbamadiene
in neat norbarnadiene
were irradiated
The changes in concentration
approximately
100 minutes,
‘Our
assignments
7,8 --
were not as clean.
on norbornadiene
Evidence as follows:
on a conventional
and the quadricyclene
are in cunplete
that in fact benzaphenone degassed O.OllM
*merry-go-round’
and quadricyclene
decay of benzaphenone
and/or
9
and 2.
was obtained
of benzophenme
no deaoy of benzophenone
sttubwal
triplet
and mass spectra)
8
leading to the set of biradicals
to quodricyclene
in benzene gave only 4 and 2 in
The same praducts (nmr.
_4 and _S are the products of exo attack of benzophenone
7
initially
although
separated by dry column chramatagraphy
as the axetans 4 and the ether 2 respectively.
and benzophenane
55% and 26%
52
with
production
solutions
apparatus
order.
and a decrease in the rate of quadricyclene
agreement with
those of Kubota
et al.4
adds only
of benzaphenone
in sealed pyrex tubes.
time are shown in Fig. was pseudo-zero
triplet
1.
3)
There was
After farmation
We did not isolate
the
minor odduct 6. 3) n-Nonone standards.
and P-naphthaldehyde,
added befare and after
irradiation
respectively,
were employed as g. 1. C.
No.
5347
52
became
apparedThis
Therefwe,
indicates that the loss of benzophenone as adduct daes not involve ncrbcrandiene.
since the biradical adducts -7,8 and 2, which experiment shows are derived from quackicyclene, lead
to adducts, they cannot be formed from norbamadiene.
rlj x lo3 ml
-1
0 Fig.
1.
50
100
150
t (mins)
Change in concentration with time of benzophenone (2~ curve 1) and quadricyclene (Q; curve 2) on irradiation of -one (0.6il M) in neat narbornadiene.
Thus, we ccnclude that a) the benzcphenane sensitised conversion of 1 to 2 involves collisianal transfer a complex formation which does -not lead to biradicol and b) -one least in part, to farm a Schenck-like
bfradical,
perhaps via complex fcrmatian.
energy
triplet reacts with 2, at This is to our knowledge the
first example of attack af a ketane triplet on a strained saturated hydroaarbon. A possible alternative mechanism for the process resulting in the conversion of qwdricyclene nabomadlene via aanatic
to
ketone ond aldehyde sensitisation would appear to be one involving the
fragmentation of intermediate adduct birodiwls
of type?.
Further work concerning this possibility
is in
progress.
We thank the Science Research Council fa financial support.
‘)The experiment was repeated using a different agparatus and 313 nm light. The decay of benzcphenme c~mnenced much later (100 hours) but at the same quadricyclene ccncentraticn (1.8 x 10m2M).
No. 52
5348 References
Dauben and 1. (a) S. J. Cristol and R. L. Snell, J. Amer. Chem. Sot., 1958, gj, 1950; (b) W.G. R.L. Cargill, Tetrahedron, 1961, 15, 197; (c) J.R. Edman and H.E. Simmons, J. 0 7; Chem.,.196B, 33, 3808; (d) P.R. Starey and S.R. FaEenholr, J. Amer. Chem. Sot., 1964,%, 527; a H.G. Rrchey and N.C. Budcley, ibid., 1963, as, 3057; (t) P.G. Gassmann, D.S. Patton and D.H. Aue, ib&, 1964, 86, 4211; (g) P.G.xumann, D.H. Aue, andD.S. Patton, ibid., 1968, 90, 7271; (h) A.A. Gorman and J.B. Sheridan, Tetrahedron Letters, 1969, 2569; (i) H. P%&ch and J. Rivier, Helv. Chem. Acta, 1970, 53, 2201; (i) H. Prinzbach, J. Rivier and G. Englert, ibid., 1970, 53, 2219; (k) G. Kaupp and H. Prinzbach, Annalen, 1969, 725, 52. 2.
G.S.
Hmnmond, N.J.
Two,
and A. Fischer, J. Amer. Chem. Sot.,
3.
G.S.
Hammond, P. Wyatt,
4.
T. Kubota, K. Shima, and H. Sdwai,
C.D.
DeBoer, and N.J.
1961, 83, 4674.
Turro, J. Amer. Chem. Sot.,
1964, 86, 2532.
Chemistry Letters, 1972, 343.
5. N.C. Yang, J.I. Cohen and A. Shani, J. Amer. Chem. Sot., 1968, 90, 3264. J. Saltiel, K.R. Neuberger and M. Wrighton, ib&, 1969, E, 3658. N. J. Two and P.A. Wriede, 5, 1970, 92, 320; I.E. Kochevar and P. J. Wagner, ibid., 1972,E, 3859.
Letter8
No. 52, PP 5345 - 5348,
THE REACTION
OF BENZOPHENONE
NORBORNADIENE A.A.
AND
in UK 23 October
in Great Britain.
TRIPLETS WITH
QUADRICYCLENE
Garman and R. L. Leyland
Department of Chemistry, University of Manchester, (Received
Printed
Pergamon Frese.
1972.
1972;
accepted
for
Manchester Ml3
publication
9PL.
30 November 1972)
One of the best documented reactions of organic photochemistry involves the conversion of a norbornadiene to the corresponding quadricyclene
system.
’ Sensitisatian of the reaction is Possible and
Hammond has shown that with aromatic ketone and aldehyde triplet sensitisers a photostationary state between norbarnadiene (1) and quadricyclene the dcnor.*r3
(2) is established, the position of which depends an the triplet energy of
This was interpreted in terms of a non-spectroscopic excitation
triplet of 1 ar a biradical
2;
of 2 to either the Fran&Candan
the different internal energies of r and 2 thus accounted for the importance of the
donor triplet energy on the position of the photostationary state. 1) Kubota,
Shima and Sakurai4 have recently
rep&ted that the 1: 1 adducts of benzophenone and ncrbornadiene -4,5 and 6 are farmed in 32%, yields respectively.
15% and 3%
These workers proposed that the adducts are formed via the intermediacy of interconverting
biradicais of types --7,8 and -9 which are formed by attack of benzaphenone triplet an ground state narbarnadiene. An interest in the mechanism of energy transfer in ketone sensitised reactions5 had led us to investigate the reaction of the norbarnadiene/quadricyclene
system with benzophenone.
The work by the Japanese graup
prampts us to describe cur own results which show that the adducts are -not farmed by addition of benzaphenane triplet to norbarnadiene. Deoxygenated benzene solutions containing norbornadiene (0.82M)
and benzaphenone (0.014M)
were
irradiated in Pyrex with a 1ooW medium pressure mercury arc and the reaction monitored by g. I. c. and t. I. c. After 28 minutes the formation of quadricyclene
1)Substantial
(2) and two unknown products could be detected and after 18
amounts of the starting material were consumed in side reactions.3
534.5
5546
No.
hours all the benzophenone on alumina, A similar
were isolated
reaction
essentially
in 61% and 26% yields
with quadricyclene
the same isolated
were also obtained Clearly
The two unknowns,
had been cansumed.
yields,
(0.02M)
and identified
using ether Q isapentone
respectively.
as solvent
(0.014M)
2)
quadricyclene
the reactions
ond not to norbamadiene
in neat norbarnadiene
were irradiated
The changes in concentration
approximately
100 minutes,
‘Our
assignments
7,8 --
were not as clean.
on norbornadiene
Evidence as follows:
on a conventional
and the quadricyclene
are in cunplete
that in fact benzaphenone degassed O.OllM
*merry-go-round’
and quadricyclene
decay of benzaphenone
and/or
9
and 2.
was obtained
of benzophenme
no deaoy of benzophenone
sttubwal
triplet
and mass spectra)
8
leading to the set of biradicals
to quodricyclene
in benzene gave only 4 and 2 in
The same praducts (nmr.
_4 and _S are the products of exo attack of benzophenone
7
initially
although
separated by dry column chramatagraphy
as the axetans 4 and the ether 2 respectively.
and benzophenane
55% and 26%
52
with
production
solutions
apparatus
order.
and a decrease in the rate of quadricyclene
agreement with
those of Kubota
et al.4
adds only
of benzaphenone
in sealed pyrex tubes.
time are shown in Fig. was pseudo-zero
triplet
1.
3)
There was
After farmation
We did not isolate
the
minor odduct 6. 3) n-Nonone standards.
and P-naphthaldehyde,
added befare and after
irradiation
respectively,
were employed as g. 1. C.
No.
5347
52
became
apparedThis
Therefwe,
indicates that the loss of benzophenone as adduct daes not involve ncrbcrandiene.
since the biradical adducts -7,8 and 2, which experiment shows are derived from quackicyclene, lead
to adducts, they cannot be formed from norbamadiene.
rlj x lo3 ml
-1
0 Fig.
1.
50
100
150
t (mins)
Change in concentration with time of benzophenone (2~ curve 1) and quadricyclene (Q; curve 2) on irradiation of -one (0.6il M) in neat narbornadiene.
Thus, we ccnclude that a) the benzcphenane sensitised conversion of 1 to 2 involves collisianal transfer a complex formation which does -not lead to biradicol and b) -one least in part, to farm a Schenck-like
bfradical,
perhaps via complex fcrmatian.
energy
triplet reacts with 2, at This is to our knowledge the
first example of attack af a ketane triplet on a strained saturated hydroaarbon. A possible alternative mechanism for the process resulting in the conversion of qwdricyclene nabomadlene via aanatic
to
ketone ond aldehyde sensitisation would appear to be one involving the
fragmentation of intermediate adduct birodiwls
of type?.
Further work concerning this possibility
is in
progress.
We thank the Science Research Council fa financial support.
‘)The experiment was repeated using a different agparatus and 313 nm light. The decay of benzcphenme c~mnenced much later (100 hours) but at the same quadricyclene ccncentraticn (1.8 x 10m2M).
No. 52
5348 References
Dauben and 1. (a) S. J. Cristol and R. L. Snell, J. Amer. Chem. Sot., 1958, gj, 1950; (b) W.G. R.L. Cargill, Tetrahedron, 1961, 15, 197; (c) J.R. Edman and H.E. Simmons, J. 0 7; Chem.,.196B, 33, 3808; (d) P.R. Starey and S.R. FaEenholr, J. Amer. Chem. Sot., 1964,%, 527; a H.G. Rrchey and N.C. Budcley, ibid., 1963, as, 3057; (t) P.G. Gassmann, D.S. Patton and D.H. Aue, ib&, 1964, 86, 4211; (g) P.G.xumann, D.H. Aue, andD.S. Patton, ibid., 1968, 90, 7271; (h) A.A. Gorman and J.B. Sheridan, Tetrahedron Letters, 1969, 2569; (i) H. P%&ch and J. Rivier, Helv. Chem. Acta, 1970, 53, 2201; (i) H. Prinzbach, J. Rivier and G. Englert, ibid., 1970, 53, 2219; (k) G. Kaupp and H. Prinzbach, Annalen, 1969, 725, 52. 2.
G.S.
Hmnmond, N.J.
Two,
and A. Fischer, J. Amer. Chem. Sot.,
3.
G.S.
Hammond, P. Wyatt,
4.
T. Kubota, K. Shima, and H. Sdwai,
C.D.
DeBoer, and N.J.
1961, 83, 4674.
Turro, J. Amer. Chem. Sot.,
1964, 86, 2532.
Chemistry Letters, 1972, 343.
5. N.C. Yang, J.I. Cohen and A. Shani, J. Amer. Chem. Sot., 1968, 90, 3264. J. Saltiel, K.R. Neuberger and M. Wrighton, ib&, 1969, E, 3658. N. J. Two and P.A. Wriede, 5, 1970, 92, 320; I.E. Kochevar and P. J. Wagner, ibid., 1972,E, 3859.