Solid state photochemistry of isocoumarins and isothiocoumarins

Article abstract of DOI:10.1016/S0040-4020(00)00498-1

1H-2-Benzothiopyran-1-ones (isothiocoumarins) and 1H-2-benzopyran-1-ones (isocoumarins) behave dissimilarly on solid state irradiation at room temperature as the former photocyclodimerize efficiently while the latter only undergo slow photodecomposition. Both 4H-naphtho[2,1-c]pyran-4-one and thiopyran-4-one turn out to be photostable under these same reaction conditions. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00498-1

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 6763±6767
Solid State Photochemistry of Isocoumarins and Isothiocoumarins
a
Michael A. Kinder, Jurgen Kopf and Paul Margaretha
b
a,
*
È
aInstitute of Organic Chemistry, University of Hamburg, D-20146 Hamburg, Germany
bInstitute of Inorganic Chemistry, University of Hamburg, D-20146 Hamburg, Germany
Received 15 December 1999; accepted 21 February 2000
AbstractÐ1H-2-Benzothiopyran-1-ones (isothiocoumarins) and 1H-2-benzopyran-1-ones (isocoumarins) behave dissimilarly on solid state
irradiation at room temperature as the former photocyclodimerize ef®ciently while the latter only undergo slow photodecomposition. Both
4H-naphtho[2,1-c]pyran-4-one and thiopyran-4-one turn out to be photostable under these same reaction conditions. q 2000 Elsevier
Science Ltd. All rights reserved.
Introduction
shown (Scheme 1). X-Ray structure analyses for naphtho-
pyranone 1d and naphthothiopyranone 2d (Scheme 2) were
performed.
Despite the fact that the isocoumarin skeleton is found in a
variety of natural products,1 the photodimerization of
isocoumarin (1a) itself and of derivatives with an unsubsti-
tuted ole®nic double bond has not been investigated. The
only relevant example in the literature2 reports the photo-
dimerization of 3-phenylisocoumarinÐa molecule contain-
ing a ®xed stilbene moietyÐon sunlight irradiation. The
parent isothiocoumarin (2a) has been found3 to photo-
dimerize ef®ciently on solid state irradiation. Here we
report on the synthesis of novel isocoumarins and isothio-
coumarins and on their comparative behaviour on solid state
irradiations.
Irradiation (350 nm) of 2b as homogeneous solid ®lm leads
to the selective (94%) formation of the HH-cis-cisoid-cis
photocyclodimer 10b and traces (6%) of the HT-cis-
1
cisoid-cis dimer 11b (monitoring by H NMR). Dimer 10b
was isolated and puri®ed by chromatography. Similarly,
irradiation of 2c affords a 4:5 mixture of dimers 10c and
11c (Scheme 3) which were not separated. The structure
1
assignment for these dimers stems from H NMR analysis
of the AA0XX0 signals of the cyclobutane protons.9 Irradia-
tion (300 nm) of either 1b or 1c as solid ®lm leads to photo-
degradation of the starting material, only traces of dimers
being detectable by 1H NMR analysis. Finally, both
naphtho-derivatives 1d and 2d turn out to be photostable
under these conditions.
Results
Our synthetic approach (Scheme 1) to isocoumarins 1b±d
and isothiocoumarins 2b±d includes pyranones 3 as
common intermediate; compounds 3 are easily accessible
from 2-arylethanols 4 via their MEM-derivatives 5,4 cycliza-
tion5 to isochromans 6 and subsequent oxidation.6 Conver-
sion of 3 to isocoumarins 1 is achieved by a bromination/
dehydrobromination sequence7 without puri®cation of the
intermediate 4-bromoisochromanone. Treatment of 3 with
the anion of a-mercaptotoluene8 affords carboxylic acids 7
which on treatment with tri¯uoroacetic acid anhydride
cyclize to thiopyranones 8. Finally, bromination of 8 with
NBS in boiling CCl4 gives bromothiopyranones 9, which
after puri®cation are then treated with triethylamine to
give isothiocoumarins 2. For comparative purpose the
UV-absorption spectra of 1b and 2b in solution are also
Discussion
To a certain extent the behaviour of isothiocoumarins 2a±c
on solid state photodimerization parallels that of both
coumarins10 and thiocoumarins.9 For 2a we have shown3
that the selective formation of the HH-cis-cisoid-cis photo-
cyclodimer proceeds according to well-established topo-
chemical principles.11 The fact that this same selectivity is
observed for 2b (with the methyl substituent located far
away from the reactive C±C double bond) but not for 2c
(with the tri¯uoromethyl group in proximity of the reactive
centre), might indicate that in addition to the role of packing
in the crystalÐa favourable arrangement of the ole®n
moieties allowing both photochemical dimerization
modesÐthere is also a pronounced effect of the site of
the substituent on the benzene ring on product formation.
For 2d X-ray structural data indicate that the distance
Keywords: isocoumarins; isothiocoumarins; photodimerization; cyclo-
butanes.
* Corresponding author. E-mail: margpaul@chemie.uni-hamburg.de
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00498-1

6764
M. A. Kinder et al. / Tetrahedron 56 (2000) 6763±6767
Scheme 1. Synthesis of isocoumarins 1 and isothiocoumarins 2 [(a) TiCl4; (b) PCC; (c) NBS/Et3N; (d) C6H5CH3S2; (e) TFAA; (f) NBS; (g) Et3N] and UV-
spectrum of 1b and 2b (0.1 mmol l21 in CH3CN)
Ê
between two C±C double bonds (.4.81 A) is too large, thus
preventing dimerization.
In contrast, the reluctance of isocoumarins 1a±c to photo-
dimerize is surprising. A comparison of X-ray structural
parameters for 1 and 2 shows the expected longer bond
lengths for the C±S (174 ppm) vs C±O (136 ppm) bonds
and smaller bond angles for the C±S±C (1048) vs C±O±C
(1218) group, but the bond length for the ole®nic double
bond (133.3 pm) is identical for both heterocycles. It is
well known12 that the structural parameters mentioned
above have important effects on intramolecular photo-
chemical reactions and therefore the different tendencies
of undergoing photodimerization of 1a±c and 2a±c could
be due to a more ef®cient monomolecular side reaction of
Scheme 2. Numbering of isocoumarins, isothiocoumarins, and naphtho-
compounds 1d and 2d.
excited 1. One such possibility would be aÐreversibleÐ
electrocyclic ring opening/closure (Scheme 4), wherein the
Scheme 3. Photodimerization of 2b and 2c.

M. A. Kinder et al. / Tetrahedron 56 (2000) 6763±6767
6765
(d, Jˆ8.65 Hz), 7.63 (m, 2H), 4.66 and 3.43 (AA0XX0, 4H).
13C NMR: dˆ165.5, 138.5, 135.6, 129.8, 128.9, 128.7,
127.7, 127.2, 125.2, 124.4, 122.4, 66.7, 24.2.
Procedure for the preparation of isocoumarins 1
Scheme 4. Electrocyclic ring opening of isocoumarins and isothiocoumar-
ins.
A mixture of 0.01 mol 3, 0.12 mol N-bromosuccinimide and
20 mg AIBN in 25 ml CCl4 was re¯uxed for 2 h, then cooled
to rt and ®ltered. After evaporation of the solvent, triethyl-
amine (25 ml) was added, the mixture re¯uxed for 1 h and
the excess triethylamine evaporated. Ether (25 ml) and 2N
HCl (5 ml) were added, the ethereal layer then separated,
washed with saturated aq. NaCl and dried over MgSO4.
Puri®cation was achieved by ¯ash chromatography using
ether/pentane 1:1 as eluent.
relative stability of the ring open product should be greater
for XˆO due to the much higher bond energy of a CvO
bond as compared to a CvS double bond. The fact that
isocoumarins also undergo slow photodegradation in solu-
tion while, again in solutionÐisothiocoumarins undergo
bimolecular photoreactions ef®ciently tends to support this
interpretation. Further studies aimed at trapping the
proposed ketene intermediates are in progress.
1
7-Methyl-1H-2-benzopyran-1-one (1b). 48%, mp 958. H
NMR: dˆ8.10 (d, Jˆ1.0 Hz), 7.53 (dd, Jˆ7.63 and
1.02 Hz), 7.33 (d, Jˆ7.63 Hz), 7.23 (d, Jˆ5.60 Hz), 6.47
(d, Jˆ5.60 Hz), 2.47 (s, 3H). 13C NMR: dˆ162.4, 143.9,
138.1, 136.0, 134.0, 129.4, 125.5, 121.8, 106.9, 21.4. MS:
160 (M1., 80), 132 (100). UV: 324 (3.59), 273 (3.93), 263
(4.02), 254 (4.94), 241 (4.19), 229 (4.51), 208 (4.26). Anal.
Calcd for C10H8O2: C, 75.00; H, 5.03. Found: C, 74.98; H,
5.01.
Experimental
General
Photolyses were performed in a Rayonet RPR-100 photo-
reactor equipped with either 300 or 350-nm lamps.
Chromatographic puri®cation was accomplished with
230±400 mesh silica gel. Melting points are uncorrected.
1H and 13C NMR spectra were recorded in CDCl3 at 500
and 125.8 MHz, resp.; chemical shifts in ppm rel. to TMS
(ˆ0 ppm), coupling constants J in Hz. UV spectra (nm,
log e) were obtained on a Perkin±Elmer Lambda20 spectro-
meter in CH3CN as solvent. Mass spectra (m/z) were
measured at 70 eV. X-Ray analyses were run on a Enraf-
Nonius-CAD-4 four circle diffractometer at 293 K with
5-Tri¯uoromethyl-1H-2-benzopyran-1-one (1c). 42%,
mp 538. 1H NMR: dˆ8.52 (d, Jˆ7.88 Hz), 8.05 (d,
Jˆ7.88 Hz), 7.62 (dd, Jˆ7.88 and 7.88 Hz), 7.38 (d,
Jˆ5.99 Hz), 6.80 (d, Jˆ5.99 Hz). 13C NMR: dˆ160.9,
146.2, 134.1, 133.7, 132.1 (q, Jˆ5 Hz), 127.9, 125.5 (q,
Jˆ31 Hz), 123.3 (q, Jˆ274 Hz), 123.2, 103.0 (q,
Jˆ2.5 Hz). MS: 214 (M1., 70), 186 (100). UV: 317
(3.79), 279 (4.14), 270 (4.26), 260 (4.14), 238 (4.51), 230
(4.60), 225 (4.60), 200 (4.80). Anal. Calcd for C10H5O2F3:
C, 56.09; H, 2.35. Found: C, 56.04; H, 2.34.
Ê
CuKa radiation (lˆ1.54178 A).
Procedure for the preparation of benzopyranones 3
4H-Naphtho[2,1-c]pyran-4-one (1d). 90%, mp 1H and 13
C
NMR, MS, cf.14 UV: 360 (3.68), 344 (3.70), 313 (3.93), 299
(3.87), 288 (3.69), 250 (4.65), 247 (4.68), 244 (4.65), 242
(4.63), 239 (4.62), 203 (4.26). Anal. Calcd for C13H8O2: C,
79.58; H, 4.11. Found: C, 79.61; H, 4.04.
The respective 2-arylethanols 4 are converted to their
MEM-ethers 5 by treatment with MEM-Cl and ethyldiiso-
propylamine in dichloromethane for 24 h at rt;4 cyclization
to isochromanes 6 is achieved by reacting 5 with TiCl4 in
dichloromethane at 2408 for 6 h5 and oxidation to 3 with
PCC in boiling dichloromethane6 followed by puri®cation
by chromatography using dichloromethane as eluent.
Procedure for the preparation of arenecarboxylic acids 7
Ring opening of pyranones 3 (0.03 mol) with the anion of
a-mercaptotoluene and subsequent work-up according to8
afforded the crude carboxylic acids 7 which were then
recrystallized from ether.
7-Methyl-3,4-dihydro-1H-2-benzopyran-1-one (3b). 61%,
mp cf.13 1H NMR: dˆ7.87 (d, Jˆ1.02 Hz), 7.34 (dd, Jˆ1.02
and 7.63 Hz), 7.15 (d, Jˆ7.63 Hz), 4.49 and 3.00 (AA0XX0,
4H), 2.37 (s, 3H). 13C NMR: dˆ165.3, 137.4, 136.7, 134.5,
130.4, 125.0, 127.5, 67.5, 27.4, 21.0.
2-(20-Benzylthioethyl)-5-methylbenzenecarboxylic acid
(7b). 99%, mp 988. 1H NMR: dˆ7.87 (d, Jˆ1.5 Hz),
7.35±7.18 (m, 6H), 7.14 (d, Jˆ7.63 Hz), 3.73 (s, 2H),
3.25 and 2.72 (AA0XX0, 4H), 2.36 (s, 3H). 13C NMR:
dˆ172.8, 140.3, 138.7, 136.4, 133.9, 132.3, 131.7, 128.9,
128.5, 127.7, 126.9, 36.4, 34.6, 32.9, 20.6.
5-Tri¯uoromethyl-3,4-dihydro-1H-2-benzopyran-1-one
(3c). 34%, mp 588. 1H NMR: dˆ8.33 (d, Jˆ8.10 Hz), 7.88
(d, Jˆ7.63 Hz), 7.54 (dd, Jˆ7.63 and 8.10 Hz), 4.57 and
3.25 (AA0XX0, 4H). 13C NMR: dˆ163.8, 138.2, 130.7 (q,
Jˆ5.1 Hz), 128.0 (q, Jˆ31.5 Hz), 127.6, 127.2, 123.7 (q,
Jˆ273.7 Hz), 66.5, 25.0 (q, Jˆ2.0 Hz).
2-(20-Benzylthioethyl)-3-tri¯uoromethylbenzenecarboxylic
1
acid (7c). 91%, mp 1128. H NMR: dˆ11.42 (s), 8.17 (d,
1,2-Dihydro-4H-naphtho[2,1-c]pyran-4-one (3d). 74%,
mp cf.13 1H NMR: dˆ8.11 (d, Jˆ8.65 Hz), 8.02 (dd,
Jˆ6.61 and 2.80 Hz), 7.90 (dd, Jˆ6.61 and 2.80 Hz), 7.83
Jˆ8.1 Hz), 7.85 (d, Jˆ8.1 Hz), 7.42 (dd, Jˆ8.0 and 8.1 Hz),
7.37±7.23 (m, 5H), 3.80 (s, 2H), 3.49 and 2.72 (AA0XX0,
4H). 13C NMR: dˆ172.4, 141.7, 138.6, 135.1, 131.2, 130.7

6766
M. A. Kinder et al. / Tetrahedron 56 (2000) 6763±6767
(q, Jˆ6.1 Hz), 128.8, 128.5, 128.4 (q, Jˆ32.6 Hz), 126.9,
126.7, 124.2 (q, Jˆ274.0 Hz), 36.5, 33.0, 30.7.
Jˆ2.54 and 3.56 Hz), 4.05 (dd, Jˆ2.54 and 14.75 Hz), 3.60
(dd, Jˆ3.56 and 14.75 Hz). 13C NMR: dˆ189.3, 137.7,
135.8, 130.2, 129.0, 128.9, 128.1, 128.0, 127.9, 124.1,
122.7, 40.5, 37.1.
1-(20-Benzylthioethyl)-napthalene-2-carboxylic acid (7d).
1
81%, mp 1488. H NMR: dˆ8.04 (d, Jˆ8.6 Hz), 8.00 (d,
Jˆ8.6 Hz), 7.87 (dd, Jˆ1.0 and 8.1 Hz), 7.78 (d, Jˆ8.6 Hz),
7.56 (m, 2H), 7.39 (d, Jˆ7.1 Hz), 7.32 (m, 2H), 3.86 (s, 2H),
3.78 and 2.86 (AA0XX0, 4H).
Procedure for the preparation of isothiocoumarins 2
A solution of bromothiolactone 9 (0.003 mol) in triethyl-
amine (5 ml) was re¯uxed for 1 h and the excess triethyl-
amine evaporated. Ether (10 ml) and 2N HCl (2 ml) were
added, the ethereal layer then separated, washed with satu-
rated aq. NaCl and dried over MgSO4. Puri®cation was
achieved by ¯ash chromatography using ether/pentane 1:1
as eluent.
Procedure for the preparation of benzothiopyranones 8
Treatment of carboxylic acids 7 with tri¯uoroacetic acid
anhydride and work-up according to8 gave crude thio-
lactones 8 which were then puri®ed by ¯ash-chromato-
graphy using ether/pentane 1:1 as eluent.
7-Methyl-1H-2-benzothiopyran-1-one (2b). 78%, mp 548.
1H NMR: dˆ8.12 (d, Jˆ1.52 Hz), 7.54 (dd, Jˆ7.89 and
1.52 Hz), 7.47 (d, Jˆ7.89 Hz), 7.14 (d, Jˆ9.92 Hz), 7.03
(d, Jˆ9.92 Hz), 2.49 (s, 3H). 13C NMR: dˆ186.7, 139.3,
135.6, 135.0, 130.1, 128.9, 125.5, 124.0, 121.7, 21.5. MS:
176.2 (M1., 100), 147.2 (90). UV: 349 (3.63), 296 (3.83),
284 (3.84), 274 (3.72), 245 (4.49), 238 (443), 223 (4.46).
Anal. Calcd for C10H8OS: C, 68.15; H, 4.58; S, 18.19.
Found: C, 68.12; H, 4.58; S, 18.21.
7-Methyl-3,4-dihydro-1H-2-benzothiopyran-1-one (8b).
1
61%, mp 578. H NMR: dˆ7.75 (d, Jˆ1.40 Hz), 7.29 (dd,
Jˆ7.60 and 1.40 Hz), 7.13 (d, Jˆ7.60 Hz), 3.25 and 3.18
(AA0XX0, 4H), 3.37 (s, 3H). 13C NMR: dˆ191.3, 138.1,
137.4, 134.0, 132.0, 129.9, 126.9, 30.0, 28.9, 20.9.
5-Tri¯uoromethyl-3,4-dihydro-1H-2-benzothiopyran-1-
1
one (8c). 34%, mp 388. H NMR: dˆ8.16 (d, Jˆ7.90 Hz),
7.85 (d, Jˆ7.50 Hz), 7.50 (dd, Jˆ7.90 and 7.50 Hz), 3.41
and 3.30 (AA0XX0, 4H). 13C NMR: dˆ190.0, 139.6, 134.0,
130.5, 130.3 (q, Jˆ6.1 Hz), 128.7 (q, Jˆ30.0 Hz), 127.3,
123.8 (q, Jˆ274.2 Hz), 27.7, 26.2 (q, Jˆ2.0 Hz).
5-Tri¯uoromethyl-1H-2-benzothiopyran-1-one (2c). 87%,
mp 828. 1H NMR: dˆ8.56 (d, Jˆ8.14 Hz), 8.08 (d,
Jˆ7.63 Hz), 7.65 (dd, Jˆ8.14 and 7.63 Hz), 7.54 (d,
Jˆ10.17 Hz), 7.30 (d, Jˆ10.17 Hz). 13C NMR: dˆ185.2,
135.0, 131.4 (q, Jˆ5 Hz), 130.1, 130.0, 127.9, 127.8, 127.7
(q, Jˆ31 Hz), 123.8 (q, Jˆ275 Hz), 117.0 (q, Jˆ3 Hz). MS:
230 (M1., 99), 202 (100). UV: 343 (3.52), 306 (3.81), 2.95
(3.83), 264 (3.68), 256 (3.65), 242 (4.22), 236 (4.20), 219
(4.55). Anal. Calcd for C10H5OF3S: C, 52.17; H, 2.19; S,
13.93. Found: C, 52.16; H, 2.18; S, 13.86.
1,2-Dihydro-4H-naphtho[2,1-c]thiopyran-4-one (8d). 74%,
1
mp 1428. H NMR: dˆ8.16 (m, 1H), 8.06 (d, Jˆ8.50 Hz),
7.89 (m, 1H), 7.82 (d, Jˆ8.50 Hz), 7.62 (m, 2H), 3.70 and
3.40 (AA0XX0, 4H). 13C NMR: dˆ191.4, 139.6, 135.5,
130.8, 129.8, 128.9, 128.4, 127.5, 127.1, 124.6, 122.8,
27.9, 25.1.
Procedure for preparation of bromothiopyranones 9
4H-Naphtho[2,1-c]thiopyran-4-one (2d). 92%, mp 1488.
1H NMR: dˆ8.49 (m, 1H), 8.34 (d, Jˆ9.16 Hz), 8.13 (d,
Jˆ10.17 Hz), 7.94 (m, 2H), 7.70 (m, 2H), 7.43 (d,
Jˆ10.17 Hz). 13C NMR: dˆ186.2, 136.0, 135.5, 130.0,
129.4, 129.1, 129.0, 127.5, 127.4, 123.0, 124.2, 121.5,
116.4. MS: 212.1 (M1., 85), 184 (100). UV: 385 (3.67),
367 (3.72), 325 (3.82), 311 (3.80), 298 (3.73), 265 (4.78),
261 (4.64), 257 (4.69), 254 (4.78), 222 (4.13), 213 (4.30),
208 (4.30). Anal. Calcd for C13H8OS: C, 73.56; H, 3.79; S,
15.11. Found: C, 73.63; H, 3.78; S, 15.04.
A mixture of thiopyranone 8 (0.01 mol), NBS (0.015 mol)
and 20 mg AIBN in CCl4 (20 ml) was re¯uxed for 2 h, then
cooled to rt and ®ltered. After evaporation of the solvent the
residue was puri®ed by ¯ash-chromatography using ether/
pentane 1:1 as eluent.
4-Bromo-7-methyl-3,4-dihydro-1H-2-benzothiopyran-1-
one (9b). 36%, mp 458 (dec.). 1H NMR: dˆ7.82 (d,
Jˆ0.95 Hz), 7.37 (d, Jˆ7.88 and 0.95 Hz), 7.32 (d,
Jˆ7.88 Hz), 4.57 (dd, Jˆ2.84 and 4.41 Hz), 3.93 (dd,
Jˆ2.84 and 14.03 Hz), 3.47 (dd, Jˆ4.41 and 14.03 Hz),
2.39 (s, 3H).
Crystal structure determination of 1d. Pale yellow trans-
parent blocks (0.40£0.60£0.70 mm3) from dichloro-
methane, C13H8O2, Mˆ196.20, monoclinic, P21/n, Zˆ4,
Ê
aˆ7.1881(17), bˆ7.8160(16), cˆ16.183(4) A, bˆ
4-Bromo-5-tri¯uoromethyl-3,4-dihydro-1H-2-benzo-
thiopyran-1-one (9c). 34%, mp 528(dec.). 1H NMR:
dˆ8.21 (d, Jˆ7.35 Hz), 7.91 (d, Jˆ8.4 Hz), 7.63 (dd,
Jˆ8.4 and 7.35 Hz), 5.99 (dd, Jˆ3.06 and 4.06), 3.93 (dd,
Jˆ3.06 and 14.25 Hz), 3.54 (dd, Jˆ4.06 and 14.25 Hz). 13C
NMR: dˆ188.2, 139.0, 132.5, 131.4, 130.8 (q, Jˆ5.6 Hz),
129.8, 127.1 (q, Jˆ30.5 Hz), 123.4 (q, Jˆ274.7 Hz), 39.1
(q, Jˆ2.5 Hz), 36.8.
95.87(2)8, Vˆ904.4(4) A , Dxˆ1.4410(6) g cm23, F(000)ˆ
Ê 3
408, mˆ0.79 mm21. The cell parameters were determined
by least-square re®nement against the setting angles of 25
re¯ections, Qˆ22.6±42.88. Of the 1899 independent
re¯ections (Qmaxˆ76.48), 1851 were considered to be
observed [I.2((I)]. Final R value for all re¯ections
Rˆ0.0818 (vR2ˆ0.2395).²
1-Bromo-1,2-dihydro-4H-naphtho[2,1-c]thiopyran-4-one
(9d). 32%, mp 708 (dec.). 1H NMR: dˆ8.25 (d, Jˆ8.70 Hz),
8.09 (d, Jˆ8.70 Hz), 7.94 (m, 2H), 7.71 (m, 2H), 6.36 (dd,
²
Crystallographic data were deposited (CCDC 139670 for 1d/CCDC
139671 for 2d) with the Cambridge Crystallographic Data Center, Univer-
sity Chemical Laboratory, 12 Union Road, Cambridge CB2 1EZ, UK.

M. A. Kinder et al. / Tetrahedron 56 (2000) 6763±6767
6767
0
Crystal structure determination of 2d. Pale yellow trans-
parent blocks (0.35£0.70£0.80 mm3) from dichloro-
methane, C13H8OS, Mˆ212.26, monoclinic, P21/c, Zˆ4,
JXX ˆ25.5 Hz, 4H) and of 6aa,6ba,12aa,12ba-1,7-
(bis)tri¯uoromethyl-tetrahydrocyclobuta[1,2-c;3,4-c0]bis-
([2]benzothiopyran)-5,11-dione (11c), 1H NMR dˆ8.09 (d,
Jˆ7.9 Hz, 2H), 7.65 (d, Jˆ7.9 Hz, 2H), 7.44 (dd, Jˆ7.8 and
Ê
aˆ10.3305(15), bˆ8.590(2), cˆ11.757(3) A, bˆ
Ê 3
Dxˆ1.429 g cm23
,
7.9 Hz, 2H), 5.10 and 4.90 (AA0XX0, JAXˆJAX ˆ7.8 Hz,
0
109.016(17)8,
Vˆ986.4(4) A ,
F(000)ˆ440, mˆ2.61 mm21. The cell parameters were
determined by least-square re®nement against the setting
angles of 25 re¯ections, Qˆ23.4±43.18. Of the 2067 inde-
pendent re¯ections (Qmaxˆ76.48), 1869 were considered to
be observed[I.2((I)]. Final R value for all re¯ections
Rˆ0.0853 (vR2ˆ0.2288).²
JAA ˆJXX ˆ0 Hz, 4H).
0
0
Acknowledgements
Financial support by Fonds der Chemischen Industrie and
Deutsche Forschungsgemeinschaft is gratefully acknowl-
edged.
Photodimerization experiments. Solutions of 0.1 mmol of
1 or 2 in dichloromethane (1 ml) in a 5 ml tapered ¯ask were
slowly evaporated to produce a homogeneous solid ®lm.
The ¯ask was then purged with Ar and irradiated (1 with
lˆ300 nm, 2 with lˆ350 nm) for 12 h, the progress of the
reaction being monitored by 1H NMR spectroscopy. In this
period isocoumarins 1b and 1c underwent slow degradation
to non-dimeric material and the naphtho-derivatives 1d and
2d remained unaltered. For 2b and 2c the solid residue was
separated by preparative thin layer chromatography using
References
1. Hill, R. A. Naturally Occuring Isocoumarins. In Progress in the
Chemistry of Natural Compounds; 1986; Vol. 49, p 1.
2. Schoenberg, A.; Latif, N.; Moubasher, R.; Awad, W. I. J. Chem.
Soc. 1950, 374.
1
ether/pentane 1:1 as eluent. Irradiation of 2b. H NMR
3. Bethke, J.; Margaretha, P.; Kopf, J.; Pignon, B.; Dupont, L.;
Christiaens, L. Helv. Chim. Acta 1997, 80, 1865.
4. Corey, E. J.; Gras, J. L.; Ulrich, P. Tetrahedron Lett. 1976, 17,
809.
indicates the formation of two dimers 10b and 11b in a
94:6 ratio, the degree of conversion of 2b reaching a
constant level at 80%. Chromatography afforded 10.5 mg
(75%) of 6aa,6ba,12ba,12ca-3,10-dimethyl-tetrahydro-
cyclobuta[1,2-c;4,3-c0]bis([2]benzothiopyran)-5,8-dione
5. Mohler, D. L.; Thompson, D. W. Tetrahedron Lett. 1987, 28,
2567.
1
(10b). Mp 178±1838, H NMR dˆ7.72 (s, 2H), 7.08 (d,
6. Bonadies, F.; Di Fabio, R. J. Org. Chem. 1984, 49, 1647.
7. Sristava, J. N.; Chaudhury, D. N. J. Org. Chem. 1962, 27, 4337.
8. Lumma, W. C.; Dutra, G. A.; Voeker, C. A. J. Org. Chem. 1970,
35, 3442.
Jˆ7.9 Hz, 2H), 6.62 (d, Jˆ7.9 Hz, 2H), 4.81 and 4.48
(AA0XX0, JAA ˆ8.5 Hz, JAXˆ8.3 Hz, JAX ˆ1.5 Hz, JXX
ˆ
0
0
0
25.5 Hz, 4H), 2.30 (s, 6H). 13C NMR dˆ188, 139, 134,
132, 128, 127, 46.9, 43.0, 20.3. The corresponding 1H
NMR data for the cyclobutane hydrogens of 11b are: 4.82
9. Klaus, C. P.; Thiemann, C.; Kopf, J.; Margaretha, P. Helv.
Chim. Acta 1995, 78, 1079.
and 4.44 (AA0XX0, JAXˆJAXˆ8.05 Hz, JAA ˆJXX ˆ0 Hz, 4H).
10. Gnanaguru, K.; Ramasubbu, N.; Venkatesan, K.;
Ramamurthy, V. J. Org. Chem. 1985, 50, 2337.
11. Venkatesan, K.; Ramamurthy, V. Photochemistry in
Organized and Constrained Media; Ramamurthy, V., Ed.; VCH:
New York, 1991, p 133.
0
0
1
Irradiation of 2c. H NMR indicates the formation of two
dimers 10c and 11c in a 45:55 ratio, the degree of conver-
sion of 2c reaching a constant level at 65%. Chromato-
graphy afforded 11 mg (80%) of a 1:1 mixture of
6aa,6ba,12ba,12ca-1,12-(bis)tri¯uoromethyl-tetrahydro-
cyclobuta[1,2-c;4,3-c0]bis([2]benzothiopyran)-5,8-dione
(10c), 1H NMR dˆ8.37 (d, Jˆ7.9 Hz, 2H), 7.97 (d,
Jˆ7.8 Hz, 2H), 7.60 (dd, Jˆ7.8 and 7.9 Hz, 2H), 5.10 and
12. Margaretha, P. In Molecular and Supramolecular
Photochemistry, Ramamurthy, V., Schanze, K., Eds.; Marcel
Dekker: New York, 1997; Vol. 1, p 85.
13. Colonge, J.; Boisde, P. Bull. Soc. Chim. Fr. 1956, 1337.
14. Stara, I. G.; Stary, I.; Kollarovic, A.; Teply, F.; Saman, D.;
Fiedler, P. Tetrahedron 1998, 54, 11209.
4.90 (AA0XX0, JAA ˆ8.5 Hz, JAXˆ8.3 Hz, JAX ˆ1.5 Hz,
0
0