Ionic Pathways in the Photochemistry of Cyclic Sulfite Esters

Article abstract of DOI:10.1002/jhet.2687

The photochemistry of cyclic carbonate esters proceeds by the photochemical extrusion of carbon dioxide to give 1, 3-diradicals which produce oxiranes as well as other radical derived species. The corresponding cyclic sulfite esters, upon irradiation, give intermediates that are trapped by alcohols yet generate no oxiranes. These results are consistent with ionic intermediates.

Full text of DOI:10.1002/jhet.2687

Month 2016
Ionic Pathways in the Photochemistry of Cyclic Sulfite Esters
a
a
a
a
b
b
*
Rick C. White, Benny E. Arney Jr, Jacob Perry, Nathan Thompson, Philip Pithan, Sebastian von Gradowski, and
Heiko Ihmelsb
aDepartment of Chemistry, Sam Houston State University, Huntsville, TX, 77341, USA
bDepartment of Chemistry, Universität Siegen, Adolf-Reichwein-Str. 2, 57068 Siegen, Germany
*
E-mail: chmrcw@shsdu.edu
Received February 10, 2016
DOI 10.1002/jhet.2687
Published online 00 Month 2016 in Wiley Online Library (wileyonlinelibrary.com).
The photochemistry of cyclic carbonate esters proceeds by the photochemical extrusion of carbon dioxide
to give 1, 3-diradicals which produce oxiranes as well as other radical derived species. The corresponding
cyclic sulfite esters, upon irradiation, give intermediates that are trapped by alcohols yet generate no
oxiranes. These results are consistent with ionic intermediates.
J. Heterocyclic Chem., 00, 00 (2016).
INTRODUCTION
An early report on the photochemistry of aryl sulfones
(e.g., 7) showed the initial generation of radicals [5], while
a report on the photochemistry of benzyl sulfite [6] postu-
lated radical and/or ionic intermediates. Another report on
the photolytic decomposition of dibenzylic sulfites showed
radical intermediates [7]. Because the range of products
of the photolysis of cyclic sulfite esters was not the same
as in the photoreactions of cyclic carbonate esters, we
surmised that because the products were ketone 6, the
photochemical reaction of cyclic sulfite esters may involve
ionic rather than radical intermediates (Scheme 3).
Some time ago, Griffin proposed that both cyclic
carbonate esters and the corresponding cyclic sulfite esters
were carbene precursors, but shorter irradiation times
showed that these results were ambiguous [3].
Some results on the conical intersection of cyclic sulfite
esters showed that on the first excited state, the benzylic
carbon is shown to be more positive in the excited state,
showing the direct formation of benzylic ions.
The photochemistry of cyclic carbonate esters such as 1
has been shown to generate 1-3-diradical intermediates
which undergo (a) ring closure to oxiranes [1] (e.g., 2),
(b) hydrogen migration to form ketones [2] (e.g., 3), and
(c) alkyl or aryl migrations to generate aldehydes or
ketones [3] (e.g., 4) as shown in Scheme 1.
In an earlier manuscript on the photochemistry of
cyclic sulfite esters, we reported that although both
hydrogen and aryl groups migrate, oxirane formation is
not observed [4].
Our initial assumption was that extrusion of sulfur diox-
ide was slow so that a more stable conformation would be
achieved precluding oxirane formation. In an attempt to
circumvent this, we prepared cis1, 2-dihydroxyindane
sulfite (5) which would not form a more stable conforma-
tion and found that upon irradiation in acetonitrile, only
ketone 6 was formed as shown in Scheme 2.
© 2016 Wiley Periodicals, Inc.

R. C. White, B. E. Arney Jr, J. Perry, N. Thompson, P. Pithan, S. v. Gradowski, and H. Ihmels
Vol 000
Scheme 1
Scheme 2
maintained later such that oxirane formation is not
observed.
These results are not unexpected. The photochemistry of
meso-hydrobenzoin carbonate (1) involves a 1, 3-diradical
intermediate which gives the products shown in Scheme 1
The photochemistry of lactones gives rise to predomi-
nately radical intermediates [8] as shown in Scheme 5
along with 19, a secondary product of 18.
RESULTS AND DISCUSSION
We irradiated sulfite esters 5, 11. 14, and 18 in methanol
to examine the photolysates for solvolysis products. These
are summarized in Scheme 4.
The observation that the photoreaction of the sulfite
esters in methanol gave ethers 7, 11–13 as the major prod-
ucts shows the ionic intermediates of the photochemical
reaction of sulfite esters (Scheme 4). In the case of 9, in
addition to 12, the photolysate also includes 21–24, which
was also observed in acetonitrile [4].
Therefore, it appears that the photochemistry of cyclic
sulfite esters differs from the photochemistry of cyclic car-
bonate esters in two ways. First, the cyclic carbonate esters
undergo photolysis to generate radical intermediates, and
secondly, the loss of SO2 from cyclic sulfite esters is such
that ionic intermediates are formed and the sulfite moiety is
However, the photolysis of benzyl phosphate esters in-
volves ionic intermediates [9,10]. Photolysis of phosphate
ester 19 produces alcohol 20 in 60–80% yield (Scheme 6).
From the observation that the corresponding cyclic sufite
ester does not form the oxirane, we propose that the 1,3-
intermediate is not operative here, but that the sulfite
portion remains once the ground state is reached and the
results noted earlier show that the loss of sulfur dioxide
from the ground state species is ionic in nature. Thus, for
irradiation of sulfite 5 in acetonitrile and methanol, we
can write the reaction pathway in Scheme 7
Conical intersection studies of 11 revealed an increasing
positive charge over the aromatic ring upon excitation
further verifying the role of carbocation formation during
the photochemical process.
Scheme 3
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DOI 10.1002/jhet

Month 2016
Photochemistry of Cyclic Sulfites
Scheme 4
Scheme 5
EXPERIMENTAL
procedure as trans-4, 6-diphenyl trimethylene sulfite [12].
Cis-1, 2-dihydroxyindane (0.50g) was stirred with 75mL
benzene and 4mL pyridine. A solution of thionyl chloride
1.01 g in 4 mL benzene was added dropwise, and the mix-
ture was allowed to stir for 3 h. After filtering, the benzene
layer was washed with water (2 × 25mL), dried (MgSO4),
Styrene glycol and benzene-1, 2-dimethanol, and indan-2-
one were purchased commercially. Cis-1, 2-dihydroxy-
indane [11], and meso-hydrobenzoin [12] were prepared as
described. The cyclic sulfite esters were prepared in the
following manner:
1
and the solvent removed to give a pale yellow solid. H
The diol (10 mmol) and triethylamine (20 mmol) were
dissolved in 50mL anhydrous ether. Using a dropping fun-
nel, thionyl chloride (10 mmol) in 30 mL anhydrous ether
was added dropwise over an hour. After stirring for an ad-
ditional hour, the mixture was poured into water (100mL
to dissolve the triethyl ammonium chloride. The ether layer
was washed once more with water (50 mL), dried (MgSO4)
and the ether removed via rotary evaporation to give the
cyclic sulfite ester which was either distilled or recrystal-
lized. Cyclic sulfite 5 was prepared using the same
NMR: 6.28 (d), 6.05 (d), 5.72 (ddd), 5.49 (ddd) 3.25–
3.58 (multiplet) and was a 3:1 mixture of syn/anti isomers.
13CNMR: 139, 84, 1128.15, 128.01, 126.25, 126.02,
125.95, 125.75, 125.54, 87.95, 86.91, 83.35, 39.55, 37.10
as a mixture of syn/anti isomers.
Photochemical Reactions. An example is described for
the photochemical reaction of styrene glycol sulfite (11). A
solution of 11 in 5 mL acetonitrile (~6× 10À2M) was
placed in a 13× 100mm quartz tube fitted with a septum
and outgassed with Argon for 30min prior to irradiation.
Photochemical reactions were carried out in a Rayonet
Photochemical Reactor fitted with 8 RPR 2548 lamps for
2 h. When 11 was irradiated in methanol, the photolysate
displayed a singlet at δ 3.4, which was the same signal
observed when 2-methoxy-2-phenylethanol was prepared
from styrene oxide in methanol with HCl, and the same
signal when 5 was treated with HCl in methanol at reflux
temperature for 1h.
Scheme 6
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R. C. White, B. E. Arney Jr, J. Perry, N. Thompson, P. Pithan, S. v. Gradowski, and H. Ihmels
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Scheme 7
[2] White, R. C.; Drew, P.; Moorman, R. J Heterocyclic Chem
1988, 25, 1781.
After removal of the solvent, the reaction products were
analysed by GC/MS and by 300MHz NMR.
[3] White, R. C.; Rix, T. J Org Chem 1987, 52, 2309.
[4] White, R. C.; Arney, B. E. Jr.; Ihmels, H. Beilstein J Org Chem
2012, 8, 1208.
CONCLUSIONS
[5] Gould, I. R.; Tung, C.; Turro, N. J.; Givens, R. S.;
Matuszewski, B. J Am Chem Soc 1984, 106, 1789.
[6] Olsen, R. J.; Maxwell, B.; Ridgeway, C. J Org Chem 1984, 48,
3847.
[7] (a) Grenga, P.; Stoutenburg, E.; Priefer, R. Tetrahrdron Lett
2012, 53, 4933; (b) Griffin, G. W.; Manmade, A. J Org Chem 1972, 37,
2589.
[8] Givens, R. S.; Oettle, W. F. J Org Chem 1972, 37, 4325.
[9] Clark, V. M.; Hobbs, J. E.; Hutchinson, D. W. J Chem Soc
1970, 25, 1781.
The results of the photochemistry of the cyclic carbonate
esters and the cyclic sulfite esters show that although the
carbonates undergo loss of CO2 through a diradical
species, Aryl sulphite esters undergo loss of SO2 by means
of ionic intermediates.
[10] Givens, R. S.; Matuszewski, B.; Athey, P. S.; Stoner, M. R. J
Am Chem Soc 1990, 112, 6016.
[11] Horan, J. E.; Schiessler, R. W. Organic Syntheses. Collective
V, 647, 1973.
Acknowledgments. Support of this research by the Welch Foundation
(X-0011) is gratefully acknowledged.
[12] (a) Fieser, L. F.; Williamson, K. L. Organic Experiments, “Or-
ganic Experiments”, 3rd ed.; D. C. Heath: Lexington, MA, 1975, pp 266;
(b) Buchanan, G.; Cousineau, M.; Mundell, T. Can J Chem 1978, 15,
2019.
REFERENCES AND NOTES
[1] White, R. C. Tetrahedron Lett 1980, 1021.
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