Evidence of transannular bonding interaction between two sulfur atoms on photolysis of naphtho[1,8-ef][1,4]dithiepins

Article abstract of DOI:10.1021/jo960517m

Naphtho[1,8-ef][1,4]dithiepins 5 were prepared by the reaction of naphtho[1,8-de]-1,3-dithiins 3 with diethyl diazomalonate in the presence of copper acetylacetonate. The X-ray crystallographic analysis of 2,3-dihydro-2,2-bis(ethoxycarbonyl)-3-phenylnaphtho[1,8-ef][1,4]dithie pin (5a) revealed that the S···S distance is shorter than the sum of their van der Waals radii, indicating that compounds 5 have a strong through-space interaction between the two sulfur atoms. Direct irradiation of 5 with a 500 W high-pressure mercury lamp (313 nm) at room temperature gave the corresponding olefins 6 and naphtho[1,8-cd]-1,2-dithiole (1) quantitatively. The quantum yields of the consumption of 5a and the formation of 6a and 1 were 0.34. The mechanism of this reaction was investigated by examining the effect of sensitization and light intensity. The results indicate that the reaction may proceed by a one-photon process from an excited singlet state. Ab initio calculations were carried out on model compound 7, and it was shown that the excitation to the S₁ state causes a bonding interaction between the two sulfur atoms, making the reaction possible.

Full text of DOI:10.1021/jo960517m

J . Org. Chem. 1996, 61, 6233-6239
6233
Evid en ce of Tr a n sa n n u la r Bon d in g In ter a ction betw een Tw o
Su lfu r Atom s on P h otolysis of Na p h th o[1,8-ef][1,4]d ith iep in s
Takayoshi Fujii, Ohgi Takahashi, and Naomichi Furukawa*
Tsukuba Advanced Research Alliance Center, Department of Chemistry, University of Tsukuba, Tsukuba,
Ibaraki 305, J apan
Received March 18, 1996X
Naphtho[1,8-ef][1,4]dithiepins 5 were prepared by the reaction of naphtho[1,8-de]-1,3-dithiins 3
with diethyl diazomalonate in the presence of copper acetylacetonate. The X-ray crystallographic
analysis of 2,3-dihydro-2,2-bis(ethoxycarbonyl)-3-phenylnaphtho[1,8-ef][1,4]dithiepin (5a ) revealed
that the S‚‚‚S distance is shorter than the sum of their van der Waals radii, indicating that
compounds 5 have a strong through-space interaction between the two sulfur atoms. Direct
irradiation of 5 with a 500 W high-pressure mercury lamp (313 nm) at room temperature gave the
corresponding olefins 6 and naphtho[1,8-cd]-1,2-dithiole (1) quantitatively. The quantum yields
of the consumption of 5a and the formation of 6a and 1 were 0.34. The mechanism of this reaction
was investigated by examining the effect of sensitization and light intensity. The results indicate
that the reaction may proceed by a one-photon process from an excited singlet state. Ab initio
calculations were carried out on model compound 7, and it was shown that the excitation to the S1
state causes a bonding interaction between the two sulfur atoms, making the reaction possible.
In tr od u ction
Ag/AgNO3 in CH3CN as a reference electrode.3,4i When
these sulfur or selenium compounds and their corre-
sponding monooxides were treated with strong acids or
acid anhydrides such as concentrated sulfuric acid or
trifluoromethanesulfonic anhydride [(CF3SO2)2O], they
gave the corresponding dithia and diselena dications via
probably the initial formation of cation radicals, and the
dithia or diselena dications were treated with water to
give the corresponding sulfoxides or selenoxides in high
yields.3,4f,g,i
Transannular interaction or through-space interaction
has often been observed between two or more heteroat-
oms that are arranged appropriately in one molecule.1-5
Such an interaction manifests itself in a low ionization
potential (in gas phase), a low anodic peak potential (in
solution), or reactivities. Considerable lone-pair-lone-
pair interactions between sulfur atoms in mesocyclic
bissulfides such as 1,5-dithiocane (1,5-dithiacyclooctane)
were elucidated by photoelectron spectroscopy (PES).2,3
The existence of the proximity effect between the two
sulfur and selenium atoms in 1,8-dichalcogen-substituted
naphthalenes is indicated by their unusually low oxida-
tion potentials as compared with those of normal sulfides
and selenides, i.e., 1,8-bis(methylthio)naphthalene 0.70
V, 1-(methylthio)naphthalene 0.97 V, 1,8-bis(methylse-
leno)naphthalene 0.48 V, and 1-(methylseleno)naphtha-
lene 0.82 V, by cyclic voltammetry measurement using
Recently, we have reported that photochemical reac-
tions using cyclic 1,8-bis(alkylthio)- and 1,8-bis(alkylse-
leno)naphthalenes provide reactive species by releasing
thermodynamically stable naphtho[1,8-cd]-1,2-dithiole
and naphtho[1,8-cd]-1,2-diselenole. For example, pho-
todecomposition of naphtho[1,8-de]-1,3-dithiin 1-oxides,
1-N-tosyl-sulfilimines, and 1-bis(ethoxycarbonyl)meth-
ylides provided quantitatively the corresponding carbonyl
compounds, N-tosylaldimines, and olefins, respectively,
together with naphtho[1,8-cd]-1,2-dithiole.6 Further-
more, o-quinodimethane is readily generated from pho-
tolysis of 8,13-dihydrobenzo[g]naphtho[1,8-bc][1,5]di-
selenonin.7 We suggested that the photodecomposition
of these compounds proceeded by the interaction between
the two sulfur or selenium atoms at the 1,8-positions of
naphthalene. However, only limited, direct experimental
evidence of the S‚‚‚S interaction has been presented so
far. In further extension of these studies, we prepared
and photolyzed naphtho[1,8-ef][1,4]dithiepins 5 and car-
ried out ab initio calculations of 7 as a model compound.
We now report the evidence of the through-space bonding
interaction between the two sulfur atoms on photolysis
of 5.
X Abstract published in Advance ACS Abstracts, August 1, 1996.
(1) Martin, H.-D.; Mayer, B. Angew. Chem., Int. Ed. Engl. 1983, 22,
283-314.
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Tetrahedron 1981, 37, 2743-2747.
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Steffen, L. K.; Wilson, G. S. J . Am. Chem. Soc. 1989, 111, 4036-4045.
(4) (a) Musker, W. K. Acc. Chem. Res. 1980, 13, 200-206. (b) Asmus,
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R.; Furukawa, N. J . Chem. Soc., Chem. Commun. 1987, 930-931.
Fujihara, H.; Furukawa, N. J . Mol. Struct. (Theochem) 1989, 186, 261-
272. (d) Fujihara, H.; Akaishi, R.; Erata, T.; Furukawa, N. J . Chem.
Soc., Chem. Commun. 1989, 1789-1790. Fujihara, H.; Akaishi, R.;
Furukawa, N. Tetrahedron 1993, 49, 1605-1618. (e) Fujihara, H.;
Ninoi, T.; Akaishi, R.; Erata, T.; Furukawa, N. Tetrahedron Lett. 1991,
32, 4537-4540. Fujihara, H.; Ishitani, H.; Takaguchi, Y.; Furukawa,
N. Chem. Lett. 1995, 571-572. Takaguchi, Y.; Fujihara, H.; Furukawa,
N. Organometallics 1996, 15, 1913-1919. (f) Fujihara, H.; Chiu, J .-J .;
Furukawa, N. Chem. Lett. 1990, 2217-2220. (g) Glass, R. S.; Broeker,
J . L.; Firouzabadi, H. J . Org. Chem. 1990, 55, 5739-5746. (h) Kimura,
T.; Ishikawa, Y.; Ueki, K.; Horie, Y.; Furukawa, N. J . Org. Chem. 1994,
59, 7117-7124. (i) Fujihara, H.; Yabe, M.; Chiu, J .-J .; Furukawa, N.
Tetrahedron Lett. 1991, 32, 4345-4348. (j) Fujihara, H.; Nakahodo,
T.; Furukawa, N. Tetrahedron Lett. 1995, 36, 6275-6278.
(5) Fujihara, H.; Chiu, J .-J .; Furukawa, N. J . Am. Chem. Soc. 1988,
110, 1280-1284. Fujihara, H.; Mima, H.; Erata, T.; Furukawa, N. J .
Am. Chem. Soc. 1992, 114, 3117-3118. Fujihara, H.; Mima, H.;
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311-312.
Resu lts a n d Discu ssion
P r ep a r a tion of Na p h th o[1,8-ef][1,4]d ith iep in s 5.
Naphtho[1,8-ef][1,4]dithiepins 5 were prepared according
(6) Furukawa, N.; Fujii, T.; Kimura, T.; Fujihara, H. Chem. Lett.
1994, 1007-1010. Fujii, T.; Kimura, T.; Furukawa, N. Tetrahedron
Lett. 1995, 36, 1075-1078. Fujii, T.; Sakuragi, H.; Furukawa, N.
Tetrahedron Lett. 1995, 36, 8039-8042.
(7) Fujihara, H.; Yabe, M.; Furukawa, N. J . Org. Chem. 1993, 58,
5291-5292.
S0022-3263(96)00517-8 CCC: $12.00 © 1996 American Chemical Society

6234 J . Org. Chem., Vol. 61, No. 18, 1996
Fujii et al.
Ta ble 1. Selected Bon d Dista n ces (Å) for Com p ou n d 5a a
Sch em e 1
S(1)-C(1)
S(1)-C(11)
S(2)-C(9)
S(2)-C(12)
C(1)-C(2)
C(1)-C(10)
C(2)-C(3)
C(3)-C(4)
1.774(4)
1.830(4)
1.782(4)
1.819(3)
1.382(5)
1.420(6)
1.378(7)
1.328(8)
C(4)-C(5)
C(5)-C(6)
C(5)-C(10)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
C(11)-C(12)
1.435(6)
1.393(7)
1.434(6)
1.321(9)
1.419(8)
1.365(6)
1.434(6)
1.562(5)
a
Numbers in parentheses are estimated standard deviations
in the least significant digits. The atom-labeling scheme is shown
in Figure 1.
Ta ble 2. Selected Bon d An gles (d eg) for Com p ou n d 5a a
C(1)-S(1)-C(11)
C(9)-S(2)-C(12)
S(1)-C(1)-C(2)
S(1)-C(1)-C(10)
C(2)-C(1)-C(10)
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(4)-C(5)-C(6)
C(4)-C(5)-C(10)
C(6)-C(5)-C(10)
103.0(2)
108.0(2)
112.8(3)
126.3(3)
120.9(4)
121.6(4)
119.9(4)
122.0(4)
121.4(5)
118.8(4)
119.8(4)
C(5)-C(6)-C(7)
C(6)-C(7)-C(8)
C(7)-C(8)-C(9)
S(2)-C(9)-C(8)
S(2)-C(9)-C(10)
C(8)-C(9)-C(10)
C(1)-C(10)-C(5)
C(1)-C(10)-C(9)
C(5)-C(10)-C(9)
S(1)-C(11)-C(12)
S(2)-C(12)-C(11)
122.1(5)
120.3(5)
120.5(5)
114.8(3)
124.0(3)
120.3(4)
116.6(4)
126.5(4)
117.0(4)
111.8(2)
112.8(2)
a
Numbers in parentheses are estimated standard deviations
in the least significant digits. The atom-labeling scheme is shown
in Figure 1.
to the following procedures shown in Scheme 1. Naph-
tho[1,8-cd]-1,2-dithiole (1) and 1,8-naphthalenedithiol (2)
were prepared according to the method reported in the
literature.8,9 2-Substituted naphtho[1,8-de]-1,3-dithiins
3a -d were prepared by the reactions of 2 and aldehydes
in the presence of SiCl4 in CH2Cl2 in high yields.10
However, 2,2-disubstituted naphtho[1,8-de]-1,3-dithiins
3e,f were obtained in poor yields on analogous treatment
of ketones and 2. Therefore, compounds 3e,f were
prepared from the reaction of 2-lithiated 3a with elec-
trophiles such as methyl iodide or benzyl bromide.
Treatment of naphtho[1,8-de]dithiins 3 with diethyl
diazomalonate in the presence of copper acetylacetonate
in benzene under reflux conditions gave the correspond-
ing naphtho[1,8-ef][1,4]dithiepins 5, which may be formed
from the corresponding sulfonium ylides by the Stevens-
type rearrangement.11 In fact, 2-substituted naphtho-
[1,8-de]-1,3-dithiin-1-bis(ethoxycarbonyl)methylides 4a
and 4b could be isolated by the reaction of 3a or 3b with
diethyl diazomalonate in the presence of copper acety-
lacetonate6 and these sulfonium ylides underwent the
Stevens-type rearrangement to give the corresponding
ring-expanded compounds 5a and 5b. However, com-
pounds 5c-f were not obtained under similar reaction
conditions. Interestingly, similar treatment of 3d with
diethyl diazomalonate did not yield the allylic rearrange-
ment compounds12 but gave the Stevens-type rearrange-
ment compound 5d .
Ta ble 3. Selected Tor sion a l An gles (d eg) for
Com p ou n d 5a a
S(1)-C(1)-C(10)-C(9)
C(1)-C(10)-C(9)-S(2)
C(10)-C(9)-S(2)-C(12)
C(9)-S(2)-C(12)-C(11)
S(1)-C(11)-C(12)-S(2)
C(1)-S(1)-C(11)-C(12)
C(11)-S(1)-C(1)-C(10)
2.2 C(2)-C(3)-C(4)-C(5)
17.1 C(3)-C(4)-C(5)-C(6)
-73.8 C(4)-C(5)-C(6)-C(7)
47.4 C(5)-C(6)-C(7)-C(8)
36.5 C(6)-C(7)-C(8)-C(9)
-92.0 C(7)-C(8)-C(9)-C(10)
0.2
-177.7
-178.1
1.5
-0.22
-2.9
48.8 C(8)-C(9)-C(10)-C(1) -174.8
C(2)-C(1)-C(10)-C(9) -177.1 C(1)-C(10)-C(5)-C(4)
-5.4
175.2
C(10)-C(1)-C(2)-C(3)
C(1)-C(2)-C(3)-C(4)
0.3 C(9)-C(10)-C(5)-C(4)
-2.3
a
The atom-labeling scheme is shown in Figure 1.
X-r a y Cr ysta llogr a p h ic An a lysis of 2,3-Dih yd r o-
2,2-bis(eth oxycar bon yl)-3-ph en yln aph th o[1,8-ef][1,4]-
d ith iep in (5a ). The detailed structural analysis of 5a
was performed by X-ray crystallographic analysis. Se-
lected bond distances, bond angles, and torsional angles
of 5a are collected in Tables 1-3. The ORTEP drawing
of 5a is depicted in Figure 1. The naphthalene ring in
F igu r e 1. ORTEP drawing of 5a .
compound 5a is appreciably twisted about the C(5)-C(10)
axis. The exocyclic bonds of S(1)-C(1) and S(2)-C(9) are
splayed outward, and the sulfur atoms in the 1,8-
positions of naphthalene are displaced above and below
the average plane of the naphthalene ring. More sub-
stantial twisting of the naphthalene ring has been
observed in 1,8-disubstituted derivatives with bulky
substituents.13 The S(1)‚‚‚S(2) distance of 5a is 3.132 Å,
(8) Zweig, A.; Hoffman, A. K. J . Org. Chem. 1965, 30, 3997-4001.
(9) Yui, K.; Aso, Y.; Otubo, T.; Ogura, F. Bull. Chem. Soc. J pn. 1988,
61, 953-959.
(10) Ku, B.; Oh, D.-Y. Synth. Commun. 1989, 19, 433-438.
(11) (a) Trost, B. M. J . Am. Chem. Soc. 1966, 88, 1587-1588. Trost,
B. M. J . Am. Chem. Soc. 1967, 89, 138-142. (b) Zhang, J .-J .; Schuster,
G. B. J . Org. Chem. 1988, 53, 716-719.
(12) Ando, W.; Kondo, S.; Nakayama, K.; Ichibori, K.; Kohoda, H.;
Yamamoto, H.; Imai, I.; Nakaido, S.; Migita, T. J . Am. Chem. Soc. 1972,
94, 3870-3876.
(13) (a) Robert, J .-B.; Sherfinks, J . S.; Marsh, R. E.; Roberts, J . D.
J . Org. Chem. 1974, 39, 1152-1156. (b) Schweizer, W. B.; Proctor, G.;
Kaftory, M.; Dunitz, J . D. Helv. Chim. Acta 1978, 61, 2783-2808.

Photolysis of Naphtho[1,8-ef][1,4]dithiepins
J . Org. Chem., Vol. 61, No. 18, 1996 6235
F igu r e 2. Light intensity dependence on the consumption of 5a (a) and the formation of 6a (b) (4.61 × 10-3 M 5a in CH2Cl2).
a
Ta ble 4. Ir r a d ia tion of Com p ou n d 5 in CH2Cl2
The effect of light intensity on photolysis of compound
5a was studied in order to understand whether the
reaction proceeds by a one-, two-, or multi-photon process.
The loss of 5a and the formation of 6a were proportional
to the first power of the 313 nm light as shown in Figure
2. These results imply that the reaction proceeds by a
one-photon process.
Ab In itio Ca lcu la tion s of 2,3-Dih yd r on a p h th o[1,8-
ef][1,4]d ith iep in (7). As it was suggested that the
photodecomposition of 5 proceeds via the S1 state, we
carried out ab initio calculations of model compound 7
in the S1 state as well as in the ground state (S0). The
RHF method was applied to the S0 state with the STO-
3G*,15 3-21G(*),16 and 6-31G* 17 basis sets and the CIS
method to the S1 state with the STO-3G* basis set.
R
R′
yield of 6/%b
yield of 1/%b
5a
5b
5c
5d
5e
5f
Ph
H
H
H
H
>99 (92)c
>99 (91)c
>99 (91)c
>99 (96)c
>99 (96)c
>99 (97)c
>99 (100)c
>99 (97)c
>99 (99)c
>99 (98)c
>99 (99)c
>99 (98)c
p-Tol
PhCHdCH
2-furyl
Ph
CH3
C6H5CH2
Selected structural parameters of the optimized S0 and
S1 structures are shown in Table 5, and three-dimen-
sional views of the STO-3G* optimized structures are
shown in Figure 3 in order to visualize the structural
relaxation after the excitation. All basis sets gave similar
structures for S0. The S‚‚‚S distance was calculated to
be 3.060, 3.149, and 3.202 Å by the STO-3G*, 3-21G(*),
and 6-31G* calculations, respectively. These values are
close to the corresponding value (3.132 Å) in Figure 1.
Moreover, the above-mentioned structural features ob-
served for 5a are reasonably reproduced. As shown in
Figure 4, the HOMO of 7 is essentially an out-of-phase
combination of the so-called σ*S-S orbital and the HOMO
of naphthalene, and the LUMO of 7 is essentially the
LUMO of naphthalene. As expected, the S1 state calcu-
lated at the S0 geometry is mainly (72%) composed of the
HOMO f LUMO single excitation. We calculated four
low-lying singlet excited states at the S0 geometry; the
oscillator strength for S1 was the largest among these
states, and it is plausible that the photodecomposition
proceeds via the S1 state. Since the σ*S-S orbital is
Ph
a
500 W high-pressure Hg lamp, λ ) 313 nm, substrates (0.23
b
mmol), CH2Cl2 (5 mL). Yields were determined by HPLC and
1H NMR spectroscopy. c Isolated yields.
which is significantly shorter than the sum of their van
der Waals radii (3.70 Å), being indicative of the existence
of the through-space interaction between the two sulfur
atoms at the 1,8-positions of naphthalene.
P h otolysis of Na p h th o[1,8-ef][1,4]d ith iep in s 5.
Direct irradiation of compounds 5 in deoxygenated CH2-
Cl2 was carried out in a cylindrical quartz tube using a
high-pressure mercury lamp (500 W, 313 nm) at room
temperature to give the corresponding olefins 6 and
naphtho[1,8-cd]-1,2-dithiole (1) quantitatively (Table 4).
Polar and nonpolar solvents including ethanol, acetoni-
trile, THF, CH2Cl2, CHCl3, and hexane were examined
on photoreaction of 5a ; photodecomposition reactions
gave 6a and 1 quantitatively regardless of the solvents
used.
The consumption of 5a and the formation of products
6a and 1 were unaffected by the addition of benzophe-
none as a triplet sensitizer and isoprene as a triplet
quencher, indicating that the reaction may proceed via
an excited singlet state, perhaps the lowest excited
singlet (S1) state. The quantum yields of the consump-
tion of 5a and the formation of 6a and 1 at room
temperature under similar photolysis conditions were
measured by comparison with fulgide actinometry to be
0.34, respectively.14
(14) Heller, H. G.; Langan, J . R. J . Chem. Soc., Perkin Trans. 2 1981,
341-343.
(15) Collins, J . B.; Schleyer, P. v. R.; Binkley, J . S.; Pople, J . A. J .
Chem. Phys. 1976, 64, 5142-5151.
(16) Pietro, W. J .; Francl, M. M.; Hehre, W. J .; DeFrees, D. J .; Pople,
J . A.; Binkley, J . S. J . Am. Chem. Soc. 1982, 104, 5039-5048.
(17) Hariharan, P. C.; Pople, J . A. Theor. Chim. Acta 1973, 28, 213-
222. Francl, M. M.; Pietro, W. J .; Hehre, W. J .; Binkley, J . S.; Gordon,
M. S.; DeFrees, D. J .; Pople, J . A. J . Chem. Phys. 1982, 77, 3654-
3665.

6236 J . Org. Chem., Vol. 61, No. 18, 1996
Fujii et al.
Ta ble 5. Op tim ized Geom etr ies for th e S0 a n d S1 Sta tes
of 7a
As to the photodecomposition reactivity, we note the
following four points. (1) Upon the S0 f S1 excitation,
the repulsive interaction between the two sulfur atoms
becomes a bonding one, and a “four-membered ring” is
formed. Disappearance of the S‚‚‚S repulsion is the first
requisite for the reaction to occur. In the S0 state, not
only is the reaction symmetry-forbidden as shown in
Figure 5 but the two sulfur atoms cannot approach each
other due to the lone-pair-lone-pair repulsion. (2) The
S1 state is not essentially concerned with the S-C bonds
to be broken but mainly with the S‚‚‚S moiety and the
naphthalene ring, and the reaction is symmetry-forbid-
den also in the S1 state (σ*S-S and the naphthalene
LUMO have the same symmetry). The energy of the S1
state is raised on the initial stage of the concerted
S0
S1
STO-3G* 3-21G(*)
6-31G* STO-3G*
Interatomic Distances (Å)
S(1)-C(1)
S(1)-C(11)
S(2)-C(9)
S(2)-C(12)
C(1)-C(2)
C(1)-C(10)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(5)-C(10)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
C(11)-C(12)
S(1)...S(2)
1.759
1.789
1.761
1.784
1.366
1.453
1.418
1.350
1.430
1.432
1.412
1.349
1.420
1.365
1.455
1.558
3.060
1.784
1.815
1.784
1.813
1.365
1.437
1.405
1.352
1.416
1.419
1.420
1.350
1.408
1.364
1.443
1.543
3.149
1.788
1.812
1.788
1.812
1.367
1.439
1.407
1.354
1.417
1.421
1.419
1.351
1.411
1.365
1.445
1.528
3.202
1.721
1.806
1.696
1.815
1.409
1.419
1.386
1.378
1.420
1.413
1.434
1.387
1.376
1.423
1.431
1.566
2.516
elongation of the two S-C bonds. However, the energy
+
of a higher excited state (“Sn”) which has a σS-C- f σ*
S-C
doubly excited character is lowered. Avoided crossings
occur between excited states along the reaction coordi-
nate, and as may be seen from Figure 6, the barrier on
the S1 surface is expected to be much lower than that in
S0. The photoreaction pathway shown in Figure 6 is
consistent with the observed quantum yield, 0.34. The
naphthalene ring is of significance in that it gives rise
to the excited state of a relatively low energy. (3) The
stabilization of the S1 state due to the structural relax-
ation amounts to 20.6 kcal mol-1. A part of the resulting
high excess energy can be used to override the reaction
barrier. (4) The shortening of the S‚‚‚S distance raises
Interatomic Angles (deg)
C(1)-S(1)-C(11)
C(9)-S(2)-C(12)
S(1)-C(1)-C(2)
S(1)-C(1)-C(10)
C(2)-C(1)-C(10)
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(4)-C(5)-C(6)
C(4)-C(5)-C(10)
C(6)-C(5)-C(10)
C(5)-C(6)-C(7)
C(6)-C(7)-C(8)
C(7)-C(8)-C(9)
S(2)-C(9)-C(8)
S(2)-C(9)-C(10)
C(8)-C(9)-C(10)
C(1)-C(10)-C(5)
C(1)-C(10)-C(9)
C(5)-C(10)-C(9)
S(1)-C(11)-C(12)
S(2)-C(12)-C(11)
99.7
101.7
115.5
125.3
119.2
122.4
119.5
120.7
119.1
120.5
120.4
120.8
119.4
122.5
115.5
124.9
119.1
117.7
124.5
117.8
113.3
113.6
100.5
103.6
114.5
125.5
120.0
122.1
119.4
120.7
118.8
120.7
120.6
120.9
119.3
122.2
114.8
124.7
119.9
116.8
126.3
116.9
113.1
113.6
101.6
103.0
104.9
113.9
126.0
120.1
122.2
119.2
120.7
118.5
120.9
120.7
121.0
119.1
122.3
114.3
124.9
120.0
116.7
126.6
116.7
113.9
114.4
104.2
119.8
119.4
120.8
119.3
121.3
121.5
123.4
118.0
118.6
121.0
121.6
119.7
120.5
119.7
119.8
119.1
121.6
119.2
105.3
104.8
-
the energy levels of σS-C and σ*S-S and lowers that of
σ*S-C+. This may favor the reaction.
The relaxed S1 state can be regarded as an S‚‚‚S radical
cation plus a naphthalene radical anion, and our pro-
posed mechanism of the photodecomposition may remind
one of the fragmentation of the radical cation of 1,5-
dithiocane (1,5-dithiacyclooctane) generated under mass
spectroscopic conditions into the 1,2-dithiolane radical
cation and cyclopropane and similar reactions of other
mesocyclic bissulfides.18 These reactions are also sym-
metry-forbidden, but they were observed under mass
spectroscopic conditions where the parent radical cation
has a high excess energy. The 1,5-dithiocane radical
cation is an unusually stable, long-lived species.19
Our photoreaction may also be related to the loss of
ethylene from the thiirane dimer radical cation.20 While
our reaction and the above-mentioned fragmentation of
mesocyclic bissulfide radical cations are symmetry-
forbidden, the decomposition of the thiirane dimer radical
cation is symmetry-allowed. This difference originates
from the relative orientation of the S‚‚‚S bond and the
forming C-C single or double bond. In the case of the
thiirane dimer radical cation, they are perpendicular to
each other, while in our case and in the case of the
mesocyclic bissulfide radical cations, they are parallel
with each other.
Dihedral Angles (deg)
S(1)-C(1)-C(10)-C(9)
C(1)-C(10)-C(9)-S(2)
4.5
10.3
6.0
14.8
-74.4
50.5
35.5
-93.0
46.8
-176.1
-0.8
-3.1
2.6
-178.8
-179.0
2.2
-1.3
-2.3
6.1
16.4
-73.2
46.6
38.7
-92.2
44.0
-175.9
-0.8
-3.3
2.8
-178.9
-178.8
2.3
-1.5
-2.1
-3.6
7.5
-80.0
80.7
7.0
-90.7
73.6
C(10)-C(9)-S(2)-C(12) -73.4
C(9)-S(2)-C(12)-C(11)
S(1)-C(11)-C(12)-S(2)
C(1)-S(1)-C(11)-C(12) -90.1
C(11)-S(1)-C(1)-C(10) 53.1
C(2)-C(1)-C(10)-C(9) -175.2
C(10)-C(1)-C(2)-C(3)
C(1)-C(2)-C(3)-C(4)
C(2)-C(3)-C(4)-C(5)
C(3)-C(4)-C(5)-C(6)
C(4)-C(5)-C(6)-C(7)
C(5)-C(6)-C(7)-C(8)
C(6)-C(7)-C(8)-C(9)
C(7)-C(8)-C(9)-C(10)
60.6
24.5
177.6
0.1
-1.5
-1.7
2.4
178.9
-177.7
1.0
-0.6
-0.6
-177.1
177.3
1.6
-1.5
-0.3
0.1
-1.5
-174.9
-2.5
-178.8
C(8)-C(9)-C(10)-C(1) -178.4
C(1)-C(10)-C(5)-C(4)
C(9)-C(10)-C(5)-C(4)
-174.3
-5.3
175.6
-174.2
-5.6
175.3
-3.3
176.0
a
The atom-labeling scheme is shown in Figure 3.
antibonding between the two sulfur atoms, the excitation
to S1 causes a bonding character between them. Indeed,
the geometry optimization for S1 resulted in a shortening
of the S‚‚‚S distance by ca. 0.5 Å. Moreover, the
naphthalene moiety is not so distorted in the optimized
S1 structure compared with the S0 structure, since the
repulsive interaction between the two sulfur atoms in S0
is changed to a bonding interaction. At the optimized
S1 structure, the HOMO is largely localized between the
two sulfur atoms, and the contribution of the HOMO f
LUMO single excitation to the S1 state is 91%.
Con clu sion
Compounds 5 were photolyzed by a 500 W high-
pressure mercury lamp to give 6 and 1 quantitatively.
These reactions proceeded via an excited singlet state as
(18) Musker, W. K.; Gorewit, B. V.; Roush, P. B.; Wolford, T. L. J .
Org. Chem. 1978, 43, 3235-3236.
(19) Brown, T. G.; Hirschon, A. S.; Musker, W. K.; J . Phys. Chem.
1981, 85, 3767-3771.
(20) Qin, X.-Z.; Meng, Q.-c.; Williams, F. J . Am. Chem. Soc. 1987,
109, 6778-6788.

Photolysis of Naphtho[1,8-ef][1,4]dithiepins
J . Org. Chem., Vol. 61, No. 18, 1996 6237
F igu r e 3. Three-dimensional view for RHF/STO-3G* optimized S0 structure (left) and CIS/STO-3G* optimized S1 structure (right)
of 7.
F igu r e 4. Schematic representation of HOMO and LUMO of
7. The orbital energies of HOMO are -5.34, -7.68, and -7.56
eV, and those of LUMO are 5.57, 2.22, and 2.32 eV by STO-
3G*, 3-21G(*), and 6-31G* calculations, respectively.
F igu r e 6. A schematic state correlation diagram between 7
and 1 + ethylene. The proposed photodecomposition pathway
is also shown. The ground state S0 of the reactant is described
+
0
by (σS-C+)2(σS-C-)2(σ*S-S)2(π*Np)0(σ*S-C
) where π*Np is the
LUMO of naphthalene (see also Figure 5). The lowest excited
singlet state S1 is approximately described by (σS-C+)2(σS-C-)2-
(σ*S-S)1(π*Np
)
(σ*S-C+)0. “Sn” represents an excited state to
1
which the electronic configuration (σS-C+)2(σS-C-)0(σ*S-S)2(π*Np)0-
(σ*S-C+)2 largely contributes.
is also expected to play an important role in the related
photochemical reactions.6,7
Exp er im en ta l Section
Photolysis, quantum yield, sensitization, and intensity effect
experiments were performed by irradiation with a 500 W
ultrahigh-pressure mercury lamp equipped with a glass filter
and monochromator. All photoreactions were monitored and
quantified by HPLC or 1H NMR. X-ray data collection was
performed on an Enraf-Nonius CAD4 computer-controlled κ
axis diffractometer (23 ( 1 °C), and calculations for structure
solution and refinement were perfomed on
a VAX 3100
F igu r e 5. An MO correlation diagram which explains that
the thermal decomposition of a -S-CH2-CH2-S- moiety to
give -S-S- and ethylene is symmetry-forbidden (a Cs sym-
metry is assumed). The lone-pair orbitals other than σ*S-S and
π*S-S are not included for clarity.
computer using SDP/VAX. Elemental analyses were carried
out by Chemical Analysis Center at this University.
Naphtho[1,8-cd]-1,2-dithiole (1) was prepared according to
the method reported in the literature.8 1,8-Naphthalenedithi-
ole was prepared by reduction of 1 with NaBH4 in ethanol-
THF.9
Syn th esis of Na p h th o[1,8-d e]-1,3-d ith iin s 3a -d . Gen -
er a l P r oced u r e.10 To a well-stirred solution of 5 mmol of
carbonyl compound and 5 mmol of 1,8-naphthalenedithiol (1)
in 20 mL of CH2Cl2 at -20 °C was added dropwise 5 mmol of
a one-photon process. Ab initio calculations of model
compound 7 showed that the excitation to the S1 state
causes the S‚‚‚S bonding interaction, and this is related
to the clean photodecomposition of 5. Such an interaction

6238 J . Org. Chem., Vol. 61, No. 18, 1996
Fujii et al.
tetrachlorosilane. The solution was warmed up to room
temperature and monitored by TLC. When the reaction was
complete (within 2 h), the solution was quenched with 10 mL
of 5% sodium bicarbonate solution and extracted with CH2Cl2
(3 × 100 mL). After the solution was dried with magnesium
sulfate and the solvent removed, the residue was separated
by silica-gel column chromatography (eluent, tetrachlo-
romethane) and then recrystallization from ethyl acetate-
hexane gave the pure product.
2-P h en yln a p h th o[1,8-d e]-1,3-d ith iin (3a ): yield 98%; mp
124-125 °C; 1H NMR (270 MHz, CDCl3) δ 5.42 (s, 1H), 7.36-
7.49 (m, 7H), 7.55-7.58 (m, 2H), 7.70-7.73 (m, 2H); 13C NMR
(67.8 MHz, CDCl3) δ 46.83, 125.27, 125.48, 125.91, 127.71,
128.84, 129.02, 129.06, 132.04, 135.06, 136.51; MS (m/z) 280
(M+). Anal. Calcd for C17H12S2: C, 72.82, H, 4.31. Found:
C, 72.71, H, 4.21.
presence of 15 mg of copper acetylacetonate. After cooling,
the solvent was evaporated. The residues were purified by
silica-gel column chromatography (eluent, ethyl acetate-
hexane) and recrystallization from dichloromethane-hexane
to give the pure products 5.
2,3-Dih ydr o-2,2-bis(eth oxycar bon yl)-3-ph en yln aph th o-
[1,8-ef][1,4]d ith iep in (5a ): yield 66%; mp 139-140 °C; 1H
NMR (400 MHz, CDCl3) δ 0.87-0.92 (m, 6H), 3.56-3.67 (m,
1H), 3.82-3.91 (m, 3H), 5.72 (s, 1H), 7.25-7.33 (m, 5H), 7.44-
7.47 (m, 2H), 7.70-7.79 (m, 4H); 13C NMR (100 MHz, CDCl3)
δ 13.29, 13.65, 59.43, 62.25, 74.56, 125.63, 125.81, 128.11,
128.20, 128.89, 129.58, 129.95, 131.27, 133.67, 133.82, 134.08,
135.67, 135.83, 137.25, 165.68, 167.65; IR (KBr) 1742, 1721,
1241, 1218 cm-1 (CO2); MS (m/z) 438 (M+). Anal. Calcd for
C24H22O4S2: C, 65.73, H, 5.06. Found: C, 65.63, H, 5.03.
2,3-Dih yd r o-2,2-bis(eth oxyca r bon yl)-3-p-tolyln a p h th o-
[1,8-ef][1,4]d ith iep in (5b): yield 72%; mp 144-145 °C; 1H
NMR (400 MHz, CDCl3) δ 0.88-0.95 (m, 6H), 3.21 (s, 3H),
3.65-3.69 (m, 1H), 3.83-3.91 (m, 3H), 5.69 (s, 1H), 7.10 (d, J
) 8.0 Hz, 2H), 7.26-7.32 (m, 2H), 7.35 (d, J ) 8.0 Hz, 2H),
7.71-7.86 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 13.40, 13.71,
21.12, 59.14, 62.30, 62.33, 74.65, 125.67, 125.90, 127.75,
128.85, 129.78, 129.97, 131.27, 133.74, 133.92, 134.19, 134.26,
135.67, 135.90, 138.10, 165.80, 167.77; IR (KBr) 1738, 1301,
2-p-Tolyln a p h th o[1,8-d e]-1,3-d ith iin (3b): yield 97%; mp
1
135-136 °C; H NMR (270 MHz, CDCl3) δ 2.37 (s, 3H), 5.37
(s, 1H), 7.21 (d, J ) 7.8 Hz, 2H), 7.36 (d, J ) 7.8 Hz, 2H),
7.42-7.46 (m, 4H), 7.68 (d, J ) 7.8 Hz, 2H); 13C NMR (67.8
MHz, CDCl3) δ 21.26, 46.58, 125.25, 125.45, 125.84, 127.60,
128.12, 129.69, 132.22, 133.42, 135.02, 138.99; MS (m/z) 294
(M+). Anal. Calcd for C18H14S2: C, 73.43, H, 4.79. Found:
C, 73.48, H, 4.70.
2-(3-P h en yl-2-pr open yl)n aph th o[1,8-de]-1,3-dith iin (3c):
yield 88%; mp 148-149 °C; 1H NMR (270 MHz, CDCl3) δ 5.07
(dd, J 1 ) 8.4 Hz, J 2 ) 1.1 Hz, 1H), 6.39 (dd, J 1 ) 15.4 Hz, J 2
) 8.4 Hz, 1H), 6.85 (dd, J 1 ) 15.4 Hz, J 2 ) 1.1 Hz, 1H), 7.26-
7.41 (m, 9H), 7.47 (dd, J 1 ) 8.1 Hz, J 2 ) 1.4 Hz, 2H), 7.69 (dd,
J 1 ) 8.1 Hz, J 2 ) 1.4 Hz, 2H); 13C NMR (67.8 MHz, CDCl3) δ
43.76, 124.21, 125.61, 126.36, 126.41, 126.76, 127.66, 128.36,
128.61, 129.81, 134.38, 134.91, 135.71; MS (m/z) 306 (M+).
Anal. Calcd for C19H14S2: C, 74.47, H, 4.60. Found: C, 74.25,
H, 4.57.
2-(2-F u r yl)n a p h th o[1,8-d e]-1,3-d ith iin (3d ): yield 87%;
mp 67-68 °C; 1H NMR (270 MHz, CDCl3) δ 5.33 (s, 1H), 6.31
(dd, J 1 ) 3.2 Hz, J 2 ) 1.9 Hz, 1H), 6.35 (d, J ) 3.2 Hz, 1H),
7.36-7.40 (m, 2H), 7.47 (dd, J 1 ) 8.1 Hz, J 2 ) 1.1 Hz, 2H),
7.70 (dd, J 1 ) 8.1 Hz, J 2 ) 1.1 Hz, 2H); 13C NMR (67.8 MHz,
CDCl3) δ 38.60, 109.04, 110.82, 125.46, 125.61, 126.34, 127.84,
129.76, 134.91, 142.73, 150,08; MS (m/z) 270 (M+). Anal.
Calcd for C15H10O1S2: C, 66.64, H, 3.73. Found: C, 66.50, H,
3.67.
1238, 1195 cm-1 (CO2); MS (m/z) 452 (M+). Anal. Calcd for
C25H24O4S2: C, 66.35, H, 5.34. Found: C, 66.38, H, 5.30.
2,3-Dih ydr o-2,2-bis(eth oxyca r bon yl)-3-(3-ph en yl-2-p r o-
p en yl)n a p h th o[1,8-ef][1,4]d ith iep in (5c): yield 72%; oil; 1H
NMR (400 MHz, CDCl3) δ 1.12 (t, J ) 7.1 Hz, 3H), 1.31 (t, J
) 7.1 Hz, 3H), 4.09-4.16 (m, 2H), 4.29-4.37 (m, 2H), 4.76 (d,
J ) 8.7 Hz, 1H), 6.43 (d, J ) 15.6 Hz, 1H), 6.50 (dd, J 1 ) 15.6
Hz, J 2 ) 8.7 Hz, 1H), 7.18-7.38 (m, 7H), 7.69-7.71 (m, 2H),
7.83-7.86 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 13.94, 14.00,
59.01, 62.30, 62.57, 70.06, 124.51, 125.45, 125.96, 126.58,
127.89, 128.39, 128.44, 128.62, 131.67, 132.24, 133.48, 133.91,
135.42, 136.19, 136.31, 137.48, 166.29, 168.53; IR (KBr) 1735,
1272, 1241, 1218 cm-1 (CO2); MS (m/z) 464 (M+). Anal. Calcd
for C26H24O4S2: C, 67.22, H, 5.21. Found: C, 67.34, H, 5.33.
2,3-Dih yd r o-2,2-b is(et h oxyca r bon yl)-3-(2-fu r yl)n a p h -
1
th o[1,8-ef][1,4]d ith iep in (5d ): yield 68%; mp 91-92 °C; H
NMR (400 MHz, CDCl3) δ 1.16 (t, J ) 7.2 Hz, 3H), 1.17 (t, J
) 7.2 Hz, 3H), 4.05-4.09 (m, 1H), 4.13-4.23 (m, 3H), 5.47 (s,
1H), 6.28-6.30 (m, 2H), 7.30-7.37 (m, 3H), 7.71-7.77 (m, 3H),
7.85 (d, J ) 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 13.71,
13.96, 53.80, 62.41, 62.76, 70.64, 108.94, 110.58, 125.51,
125.97, 128.04, 129.06, 132.23, 132.31, 133.63, 135.19, 132.26,
137.43, 141.97, 150.00, 165.80, 167.96; IR (KBr) 1742, 1721,
1255, 1195 cm-1 (CO2); MS (m/z) 428 (M+). Anal. Calcd for
C22H20O4S2: C, 61.66, H, 4.70. Found: C, 61.65, H, 4.61.
2,2-Bis(et h oxyca r b on yl)-3-m et h yl-3-p h en yln a p h t h o-
[1,8-ef][1,4]d ith iep in (5e): yield 82%; mp 139-140 °C; 1H
Syn th esis of 2,2-Disu bstitu ted Na p h th o[1,8-d e]-1,3-
d ith iin s 3e,f. Gen er a l P r oced u r e. n-Butyllithium (1.3 mL
of 1.67 N solution in hexane, 2.2 mmol) was added dropwise
at -78 °C to a solution of 2-phenylnaphtho[1,8-de]-1,3-dithiin
(5a ) (408 mg, 2.0 mmol) in THF (20 mL) and stirred for 1 h.
To this solution was added electrophiles (2.2 mmol) for 1 h at
-78 °C with stirring, and then the solution was warmed up
to room temperature and monitored by TLC. After the
reaction and usual workup process, the products were sepa-
rated by silica-gel column chromatography using carbon
tetrachloride as eluent and then recrystallization from ethyl
acetate-hexane to give the pure product.
NMR (400 MHz, CDCl3
) δ 0.76 (t, J ) 7.1 Hz, 3H), 0.98 (t, J
) 7.1 Hz, 3H), 2.52 (s, 3H), 3.48-3.67 (m, 4H), 7.295-7.39
(m, 5H), 7.77-7.83 (m, 4H), 7.99-8.01 (m, 2H); 13C NMR (100
MHz, CDCl3) δ 13.41, 13.70, 25.10, 61.50, 62.11, 63.76, 78.95,
125.34, 125.35, 126.01, 127.78, 128.29, 128.73, 130.53, 131.24,
132.10, 134.38, 135.81, 141.38, 165.04, 165.68; IR (KBr) 1729,
1238, 1185 cm-1 (CO2); MS (m/z) 452 (M+). Anal. Calcd for
C25H24O4S2: C, 66.35, H, 5.34. Found: C, 66.23, H, 5.32.
2,2-Bis(et h oxyca r b on yl)-3-b en zyl-3-p h en yln a p h t h o-
[1,8-ef][1,4]d ith iep in (5f): yield 66%; mp 176-177 °C; 1H
NMR (400 MHz, CDCl3) δ 0.70 (t, J ) 6.9 Hz, 3H), 1.03 (t, J
) 6.9 Hz, 3H), 3.39-3.43 (m, 2H), 3.83 (d, J ) 15.0 Hz, 1H),
3.90-4.05 (br s, 2H), 4.54 (d, J ) 15.0 Hz, 1H), 7.13-7.20 (m,
5H), 7.21-7.32 (m, 5H), 7.72-7.78 (m, 4H), 7.90-7.92 (m, 2H);
13C NMR (100 MHz, CDCl3) δ 13.12, 13.75, 42.12, 61.82, 62.27,
69.59, 80.29, 125.37, 126.08, 126.17, 127.17, 127.43, 127.52,
130.24, 130.39, 130.80, 130.93, 131.88, 131.97, 133.84, 135.09,
133.35, 134.55, 137.43, 139.65, 165.40, 165.99; IR (KBr) 1744,
1717, 1241, 1212 cm-1 (CO2); MS (m/z) 528 (M+). Anal. Calcd
for C31H28O4S2: C, 70.43, H, 5.34. Found: C, 70.19, H, 5.25.
Gen er a l P h otolysis P r oced u r e. A solution of naphtho-
[1,8-ef][1,4]dithiepins (0.23 mmol) in solvent (10 mL) was
placed in a cylindrical quartz tube equipped with a stirrer bar
and a silicon septum. The solution was bubbled with Ar for
30 min to remove O2. Irradiation of samples was carried out
2-Meth yl-2-ph en yln aph th o[1,8-de]-1,3-dith iin (3e): yield
1
97%; mp 116-117 °C; H NMR (270 MHz, CDCl3) δ 2.09 (s,
3H), 7.25-7,30 (m, 1H), 7.33-7.39 (m, 4H), 7.47 (dd, J 1 ) 8.0
Hz, J 2 ) 1.1 Hz, 2H), 7.67 (dd, J 1 ) 8.0 Hz, J 2 ) 1.1 Hz, 2H),
7.82-7.84 (m, 2H); 13C NMR (67.8 MHz, CDCl3) δ 30.39, 51.86,
125.23, 125.71, 126.13, 127.48, 127.60, 128.12, 128.50, 131.36,
134.75, 141.90; MS (m/z) 294 (M+). Anal. Calcd for C18H14S2:
C, 73.43, H, 4.79. Found: C, 73.42, H, 4.75.
2-Ben zyl-2-p h en yln a p h th o[1,8-d e]-1,3-d ith iin (3f): yield
1
84%; mp 137-138 °C; H NMR (270 MHz, CDCl3) δ 3.55 (s,
2H), 6.73 (d, J ) 7.1 Hz, 2H), 7.12 (t, J ) 7.1 Hz, 2H), 7.16-
7.22 (m, 4H), 7.34 (t, J ) 7.3 Hz, 2H), 7.48 (dd, J 1 ) 7.3 Hz, J 2
) 1.0 Hz, 2H), 7.61-7.66 (m, 4H); 13C NMR (67.8 MHz, CDCl3)
δ 49.33, 57.32, 125.73, 126.42, 126.52, 126.97, 127.46, 127.55,
127.98, 128.05, 128.46, 130.05, 130.80, 134.61, 134.86, 140.54;
MS (m/z) 370 (M+). Anal. Calcd for C24H18S2: C, 77.80, H,
4.90. Found: C, 77.66, H, 4.78.
Syn th esis of Na p h th o[1,8-ef][1,4]d ith iep in s 5a -f. Gen -
er al P r ocedu r e. A mixture of 2-substituted- or 2,2-substituted-
naphtho[1,8-de]dithiins 3 (1 mmol) and diethyl diazomalonate
(1 mmol) in benzene (5 mL) was refluxed for 48 h in the

Photolysis of Naphtho[1,8-ef][1,4]dithiepins
J . Org. Chem., Vol. 61, No. 18, 1996 6239
using the output of a 500 W high-pressure mercury lamp
filtered through a Toshiba UVD33S filter and a monochroma-
tor set at 313 nm under conditions of complete light absorption.
The reaction progress was monitored by HPLC or 1H NMR
spectroscopy. After irradiation, the solvent was evaporated
and the residue was purified by preparative HPLC, and the
products were characterized by NMR and GC-MS spec-
troscopies.
Quantification was done with HPLC. Maleic anhydride was
used as an external standard for HPLC. Yields were deter-
mined from the solutions that began at concentration 6 mM,
and irradiation times were kept under 1 h. The measurement
of yields was repeated several times by HPLC detection.
X-r a y An a lysis of 5a .24 X-ray diffraction analysis on 5a
was carried out on an Enraf-Nonius CAD4 computer-controlled
κ axis diffractometer. The structure of 5a C24H22O4S2 (formula
weight 438.57) was determined from a monoclinic crystal of
dimension 0.5 × 0.5 × 0.3 mm (space group P21/c), with unit
cell a ) 9.460(2) Å, b ) 15.673(6) Å, c ) 14.933(3) Å, â )
105.05(2)°, V ) 2138.0 Å3. It has four molecules per cell, F )
1.36 g/cm3, µ ) 2.7 cm-1, F(000) ) 920. The cell dimensions
were determined from the setting angles of 25 reflections with
4 < θ < 21° using Mo KR radiation (λ ) 0.710 73 Å). A total
of 4056 reflections were measured (2θ < 50°) using the ω-2θ
step scan technique. All data processing was performed on a
Micro VAX 3100 computer by using the MolEN structure-
solving program obtained from Enraf Nonius Corp., Delft, The
Netherlands. An empirical absorption correction based on
series of ψ scans was also applied to the data. The structure
was refined by full-matrix least-squares where the function
minimized was Σw(|Fo| - |Fc|)2, and the weight w is defined
as 1.0 for all observed reflections. All hydrogen atoms were
located, and their positions were refined in least-squares; their
isotropic thermal parameters were held fixed at 4.0 Å. The
final R and Rw values were 0.056 and 0.053, respectively.
Ab In itio Ca lcu la tion s. Ab initio calculations were carried
out on a HP735/125 workstation. Spartan 3.121 was used for
the RHF calculations of the S0 state and Gaussian 9222 for the
CIS calculations of excited states. The STO-3G*,15 3-21G(*),16
and 6-31G*17 basis sets were used for the S0 state, while only
the STO-3G* basis set was used in the excited-state calcula-
tions. All these basis sets include d polarization functions on
S. The STO-3G* basis set was successfully used for related
molecules.23
1
6a : H NMR (400 MHz, CDCl3) δ 1.29 (t, J ) 7.1 Hz, 3H),
1.34 (t, J ) 7.1 Hz, 3H), 4.28-4.37 (m, 4H), 7.37-7.40 (m, 3H),
7.44-7.47 (m, 2H), 7.74 (s, 1H); MS (m/z) 248 (M+).
1
6b: H NMR (400 MHz, CDCl3) δ 1.31 (t, J ) 7.1 Hz, 3H),
1.33 (t, J ) 7.1 Hz, 3H), 2.37 (s, 3H), 4.30 (q, J ) 7.1 Hz, 2H),
4.35 (q, J ) 7.1 Hz, 2H), 7.18 (d, J ) 8.1 Hz, 2H), 7.35 (d, J )
8.1 Hz, 2H), 7.70 (s, 1H); MS (m/z) 262 (M+).
6c: 1H NMR (400 MHz, CDCl3) δ 1.27-1.41 (m, 12H), 4.23-
4.40 (m, 8H), 6.62-6.67 (m, 1H), 7.00-7.07 (m, 2H), 7.23-
7.42 (m, 8H), 7.49-7.54 (m, 4H), 7.79-7.82 (m, 1H); MS (m/z)
274 (M+).
1
6d : H NMR (400 MHz, CDCl3) δ 1.32 (t, J ) 7.1 Hz, 3H),
1.37 (t, J ) 7.1 Hz, 3H), 4.28 (q, J ) 7.1 Hz, 2H), 4.40 (q, J )
7.1 Hz, 2H), 6.50 (dd, J 1 ) 3.5 Hz, J 2 ) 1.7 Hz, 1H), 6.70 (d,
J ) 3.5 Hz, 1H), 7.45 (s, 1H), 7.52 (d, J ) 1.7 Hz, 1H); MS
(m/z) 238 (M+).
1
6e: H NMR (400 MHz, CDCl3) δ 0.95 (t, J ) 7.1 Hz, 3H),
1.32 (t, J ) 7.1 Hz, 3H), 2.44 (s, 3H), 3.96 (q, J ) 7.1 Hz, 2H),
4.29 (q, J ) 7.1 Hz, 2H), 7.23-7.26 (m, 2H), 7.32-7.37 (m,
3H); MS (m/z) 262 (M+).
1
6f: H NMR (400 MHz, CDCl3) δ 0.93 (t, J ) 7.1 Hz, 3H),
1.32 (t, J ) 7.1 Hz, 3H), 3.94 (q, J ) 7.1 Hz, 2H), 4.16 (s, 2H),
4.32 (q, J ) 7.1 Hz, 2H), 7.10-7.14 (m, 2H), 7.15-7.20 (m,
3H), 7.22-7.26 (m, 3H); MS (m/z) 338 (M+).
Qu a n tu m Yield s. The measurement of the quantum yield
was carried out using the output of a 500 W high-pressure
mercury lamp filtered through a Toshiba UVD33S filter and
a monochromator set at 313 nm under conditions of complete
light absorption. The fulgide, (E)-R-(2,5-dimethyl-3-furyleth-
ylidene)(isopropylidene)succinic anhydride, which has a quan-
tum yield of 0.20 for its photocolouration at 313 nm in toluene
was used as an actinometer.14 Quantification was done with
HPLC. Maleic anhydride was used as an external standard
for HPLC. Sample and actinometer cells were sequentially
irradiated. The actinometer cells were used to determine the
photo flux, which was then used to convert the rate of loss of
the material into a quantum yield. Quantum yield was
determined from the solution that began at concentration of
6 mM, and conversions were kept under 5%. The measure-
ment of quantum yields was repeated several times by HPLC
detection.
Ack n ow led gm en t. This work was supported by a
special grant from University of Tsukuba [TARA project]
and a Grant-in-Aid from the Ministry of Education,
Science, and Culture of J apan (No. 07404035).
J O960517M
(21) Hehre, W. J .; et al. Wavefunction, Inc., Irvine, CA.
(22) Gaussian 92, Revision G4: Frisch, M. J .; Trucks, G. W.; Head-
Gordon, M.; Gill, P. M. W.; Wong, M. W.; Foresman, J . B.; J ohnson, B.
G.; Schlegel, H. B.; Robb, M. A.; Replogle, E. S.; Gomperts, R.; Andres,
J . L.; Raghavachari, K.; Binkley, J . S.; Gonzales, C.; Martin, R. L.;
Fox, D. J .; DeFrees, D. J .; Baker, J .; Stewart, J . J . P.; Pople, J . A.
Gaussian, Inc., Pittsburgh, PA, 1992.
(23) Glass, R. S.; Adamowicz, L.; Broeker, J . L. J . Am. Chem. Soc.
1991, 113, 1065-1072.
(24) The author has deposited atomic coordinates for this structure
with the Cambridge Crystallographic Data Centre. The coordinates
can be obtained, on request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, U.K.
Effect of Ligh t In ten sity. The measurement of the light
intensity effect was carried out using the output of a 500 W
high-pressure mercury lamp filtered through a Toshiba UVD33S
filter and a monochromator set at 313 nm under conditions of
complete light absorption. The light intensity was attenuated
by using a quartz filter (313 nm; 27%, 52%, and 83%).