Photo-Fries rearrangement of carbazol-2-yl sulfonates: Efficient tool for the introduction of sulfonyl groups into polycyclic aromatic compounds

Article abstract of DOI:10.1002/hlca.200690112

Systematic studies on the photo-Fries rearrangement of different 9H-carbazol-2-yl sulfonates 2 have shown that this type of conversion can be readily used for the preparative-scale introduction of alkyl- or arylsulfonyl groups into polycyclic aromatic compounds under very mild conditions. A series of new 1-sulfonyl- (3) or 3-sulfonyl-9H-carbazoles (4) were prepared in medium-to-good yields, and characterized by UV/VIS, ¹H-NMR, and ¹³C-NMR spectroscopy, as well as by elemental analysis. Effects of irradiation wavelength, solvent polarity, presence or absence of O₂, and photosensitizers were studied in detail.

Full text of DOI:10.1002/hlca.200690112

Helvetica Chimica Acta – Vol. 89 (2006)
1147
Photo-Fries Rearrangement of Carbazol-2-yl Sulfonates: Efficient Tool for the
Introduction of Sulfonyl Groups into Polycyclic Aromatic Compounds
by Laura K. Crevatín, Sergio M. Bonesi*, and Rosa Erra-Balsells
CIHIDECAR-CONICET, Departamento de Química Orgánica, Facultad de Ciencias Exactas y Natu-
rales, Universidad de Buenos Aires, Pabellón II, 3er Piso, Ciudad Universitaria, 1428-Buenos Aires,
Argentina
(phone: +54-11-4576-3346; fax: +54-11-4576-3346; e-mail: smbonesi@qo.fcen.uba.ar)
Systematic studies on the photo-Fries rearrangement of different 9H-carbazol-2-yl sulfonates 2 have
shown that this type of conversion can be readily used for the preparative-scale introduction of alkyl- or
arylsulfonyl groups into polycyclic aromatic compounds under very mild conditions. A series of new 1-
sulfonyl- (3) or 3-sulfonyl-9H-carbazoles (4) were prepared in medium-to-good yields, and characterized
by UV/VIS, 1H-NMR, and 13C-NMR spectroscopy, as well as by elemental analysis. Effects of irradiation
wavelength, solvent polarity, presence or absence of O2, and photosensitizers were studied in detail.
1. Introduction. – The introduction of S-atoms into single, polynuclear, or heteropo-
lynuclear aromatic rings has received much attention during the last years [1]. Sulfuri-
zation of aromatic rings can be carried out with S2Cl2 or elemtal S in the presence of
Lewis acids such as, e.g., AlCl3 [2]. This reaction has been used for ring closure. Also,
SOCl2 in the presence of AlCl3 has been used as a reagent, but affords in a straightfor-
ward way diaryl sulfoxides. Unsymmetrical diaryl sulfides can be obtained by treatment
of an aromatic compound with an arenesulfenyl chloride (ArSCl) in the presence of Fe
powder [3]. However, unfortunately, the corresponding diphenyl disulfide is obtained
in high yield as a major side product. Treatment of aromatic amines and phenols with
dialkyl disulfides in the presence of Lewis acid catalysts such as CuI, AlCl3, TiCl4, or
ZrCl4 produces alkyl aryl sulfides, mostly as the ortho products [4]; also, elevated reac-
tion temperatures (150–1708) are needed to accomplish the reaction. Finally, the Herz
reaction can be used for the introduction of an S-atom into aromatic rings [5]. This
reaction is carried out with an aniline and S2Cl2 in the presence of a base, generally
NaOH. After acidic workup, 2-aminothiophenols are obtained. Nevertheless, this reac-
tion is not suited as a general sulfurization method because good yields are obtained
only when 4-chloroanilines are used as starting materials.
To circumvent these problems, we decided to explore the photo-Fries rearrange-
ment of sulfonic ester derivatives as a suitable and general method for the introduction
of S-atoms into aromatic moieties. In Scheme 1, a retrosynthetic, regioselective
approach towards the new heterocyclic compounds I and II is shown, photo-Fries rear-
rangement being the key step. For example, to access Ia, synthon IVa can be prepared
in one step by photo-Fries rearrangement of an adequate substrate such as Va. Cycli-
zation of the resulting synthon IVa could be carried out with KOH in DMSO at
room temperature to afford IIIa in good yield [6]. Finally, reduction with sulfur and
© 2006 Verlag Helvetica Chimica Acta AG, Zürich

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Helvetica Chimica Acta – Vol. 89 (2006)
Scheme 1
heat [7], DIBAL in Et2ACHTREUOGN [8], or LiAlH4 in THF at low temperature [9] affords Ia. Like-
wise, the isomeric carbazole derivatives IIa,b can also be prepared from Va via this
route.
The photo Fries-rearrangement has received considerable attention since its discov-
ery in 1960 [10]. However, studies have been devoted mainly to elucidate the underly-
ing reaction mechanism, rather than to explore the synthetic potential of the reaction
[11]. Nevertheless, this photochemical reaction has been successfully used in the syn-
thesis of natural products such as griseofulvin [12], daunomycine [13], and flavonoids
[14].
The photo-Fries rearrangement of aryl sulfonic esters has been scarcely investigated
[15]; and, according to our knowledge, no attention has been paid to the photochemical
behavior of aza-type heteroaromatic sulfonic esters such as carbazol-2-yl alkanesulfo-
nates. The photo-Fries rearrangement is a mild and clean reaction, where no hazardous
solvents or Lewis acids are needed. Also, the photoproducts are formed in good yields,
with predictable regioselectivity.
In continuation of our research on photo-Fries reactions [16], we herein report a
protocol for the efficient synthesis of various sulfonates of 9H-carbazol-2-ol (1), as
well as their isolation and full characterization by means of physical and spectroscopic
methods.
2. Results and Discussion. – 2.1. Preparation and Characterization of Starting Mate-
rials. Starting from 9H-carbazol-2-ol (1), compounds 2a–2c required for photo-Fries
rearrangement were prepared by acylation (Scheme 2). For the synthesis of 2a and
2b, we used methanesulfonyl chloride (MsCl) and benzenesulfonyl chloride, respec-
tively, in the minimum volume of anhydrous pyridine at room temperature. Com-
pounds 2a and 2b were obtained in excellent yields (>95%) as colorless crystalline sol-
ids. For compound 2c, trifluoromethanesulfonic anhydride, (CF3SO2)2ACHTREUONG , was used as
acylating agent, which gave rise to a yield of 85%. In all these experiments, the
molar ratio of acylating reagent to 1 was 1.1 to 1.0.
When the above acylations of 1 were performed in anhydrous benzene or CH2Cl2 in
the presence of pyridine, the yields dropped substantially, and the reaction time was

Helvetica Chimica Acta – Vol. 89 (2006)
1149
Scheme 2
longer. This was particularly noteworthy for compound 2c, where the chemical yield
dropped from 85% (pyridine) to 45% (benzene/pyridine 3 :1 (v/v)).
1
The sulfonates 2 were characterized by H- and 13C-NMR spectroscopy, including
1
2D-NMR experiments. Their H-NMR spectra invariably showed the signals of Hꢀ
C(4) and HꢀC(5) at d(H) 7.90–8.20, which corresponds to a downfield shift (relative
to those of 1) due to inductive effects exerted by the sulfonyloxy groups attached to the
carbazole moiety [17]. HꢀC(3) and HꢀC(1) of 2a–2c resonated at d(H) 7.04–7.46, and
experienced a noticeable deshielding compared to the corresponding signals in 1. The
other H-atoms, HꢀC(6), HꢀC(7), and HꢀC(8), appeared at d(H) 7.20–7.70, which is
quite similar as in 1.
In the 13C-NMR spectra of compounds 2, C(2) was observed at d(C) 147.2–150.7,
slightly upfield-shifted in comparison to C(2) of 1. The signals for C(3) and C(1)
were shifted downfield to d(C) 99.9–114.7 due to inductive effects of the sulfonyloxy
groups. Finally, while the signal for C(4) was shifted upfield by 4 ppm relative to that
in 1, the other resonances were hardly affected by acylation.
2.2. Photoelectronic Properties of Starting Materials. The UV-spectroscopic data of
compounds 2a–c are collected in Table 1 for different organic media at 298 K. Gener-
ally, three bands centered at lmax 245, 298, and 310 nm were observed. Comparison of
previous spectroscopic data and theoretical calculations of carbazoles [18] with those of
compound 2a allowed us to assign the lowest-lying excited electronic states of the bands
1
1
located at 298 and 310 nm as La (S2 ! S0) and Lb (S1 ! S0) electronic transitions,
respectively. On changing the solvent polarity, a bathochromic shift of 2–6 nm was
observed, which suggests that the nature of the lowest singlet-excited state most likely
corresponds to a p ! p* transition [19].
Excitation at 310 nm induced a fluorescence emission at 320–370 nm. The high-
energy edge of the emission spectrum overlapped well with the 0–0 absorption
band. The nearly negligible amount of Stokes’ shift reflects a high structural similarity
between the ground and the excited states. Similar spectroscopic features were also
observed for the analogs 2b and 2c.
The phosphorescence emission spectra of compounds 2a–2c were recorded in a fro-
zen matrix of i-PrOH/Et
2ACHTREOUNG 1:1 at 77 K. Excitation at 310 nm induced phosphorescence
at 400–600 nm, with lmax values at 407, 410, and 407 nm, respectively, for 2a, 2b, and 2c.

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Helvetica Chimica Acta – Vol. 89 (2006)
Table 1. Spectroscopic Data of 2a–c in Different Media. Unless stated otherwise, the experiments were
performed at ambient temperature under Ar atmosphere.
Compound
Solvent
lmax [nm]
ET [kcal/mol]
Absorption
Fluorescence
Phosphorescence
2a
Cyclohexane
MeCN
334
334
336
355
351
351
MeOH
Solid matrixa)
Cyclohexane
MeCN
407
410
409
69.8
69.5
69.7
2b
2c
336
335
336
355
355
357
MeOH
Solid matrix
Benzene
MeCN
MeOH
335
334
335
346
346
355
Solid matrix
a) In i-PrOH/Et
2ACHTREOUNG 1:1 frozen at 77 K.
The energy of the lowest triplet-excited state (ET) of these compounds was readily esti-
mated at 69.5–69.8 kcal/mol (Table 1).
2.3. Photo-Fries Rearrangement in Solution. Irradiation of a 6 mM solution of 9H-
carbazol-2-yl methanesulfonate (2a) in benzene, cyclohexane, MeCN, or MeOH at
313 nm under Ar atmosphere at room temperature afforded the ortho-migrated prod-
ucts 3a and 4a, together with 1 and methanesulfonic acid (Scheme 2). The reaction was
followed both spectrophotometrically and by HPLC analysis. After irradiation, the
products were separated by column chromatography (SiO2), and were identified and
characterized (see Exper. Part). Irradiation of compounds 2b and 2c under similar con-
ditions yielded the corresponding ortho-rearrangement products 3b and 4b, and 3c and
4c, respectively, along with 1. The yields of these transformations are collected in Table
2 for different solvents.
The pairs of ortho-rearranged products, i.e., 3a/4a, 3b/4b, and 3c/4c, were all
obtained in a molar ratio of ca. 2 :1. As shown in Table 2, the C(1)-rearrangement prod-
ucts 3a–3c were the main products formed in yields of ca. 60%. The C(3)-rearrange-
ment products 4a–4c were side products (ca. 25% yield). In all experiments, compound
1 was observed, resulting from acyl cleavage rather than rearrangement. These results
are similar to those obtained previously for the irradiation of 2-acetyloxy- and 2-(ben-
zoyloxy)carbazoles [16c].
To rationalize the observed regioselectivity in the above transformations, we per-
formed semi-empirical and abinitio optimizations of the 2-hydroxy-9H-carbazole rad-
ical. The charge density at C(1) was found to be slightly higher than at C(3). Addition-
ally, the carbazole NH might assist the acyl rearrangement through H-bonding, a pro-
cess that, for geometric reasons, is possible only for the rearrangement to C(1), not to
C(3). Therefore, both factors, a slightly higher charge density at C(1) and the possibility
of a H-bridge assisting in the rearrangement may account for the observed regioselec-
tivity in favor of the 1-substituted product.

Helvetica Chimica Acta – Vol. 89 (2006)
1151
Table 2. Product Distribution upon Irradiation of 2a–c in Different Media. Conditions: substrates 2,
6 mM; excitation at 313 nm; T=298 K; Ar atmosphere; conversion >90%.
Substrate
Solvent
Yield [%]a)
3
4
1
2a
MeCN
MeOH
Benzene
Cyclohexane
MeCN
MeOH
Benzene
MeCN
MeOH
Benzene
61.5
65.7
60.0
58.1
57.6
67.3
54.5
64.8
68.4
55.6
27.0
23.3
24.5
23.5
26.2
22.5
22.6
24.3
23.8
21.6
9.5
11.0
10.5
11.4
10.5
10.3
9.9
10.8
10.8
16.8
2b
2c
a) Determined by HPLC analysis.
The rearranged products 3 and 4 are described and characterized herein for the first
time. They can be synthesized under very mild conditions at room temperature by
means of the photo-Fries rearrangement in moderate-to-good yields. The present
experimental conditions are advantageous over the thermal Fries rearrangement,
where higher temperatures (80–1208) and Lewis acid catalysts such as AlCl3 or
FeCl3 ACHTREaUGN re required [20].
2.4. NMR Properties of Rearrangement Products. The 1H-NMR spectra of the 1-sub-
stituted products 3 invariably showed the signal of HꢀC(4) at d(H) ca. 8 due to the
known deshielding at the peri-positions in the carbazole moiety. The signals of Hꢀ
C(3) appeared at d(H) 6.84–6.94. The signals of HꢀC(5), HꢀC(6), HꢀC(7), and Hꢀ
C(8) appeared in the range d(H) 7.20–8.10, which is quite similar to the corresponding
chemical shifts in the starting materials. The 13C-NMR spectra of 3a–3c showed the sig-
nals for C(2) and C(1) at d(C) ca. 163 and 105, respectively. The other C-atoms showed
chemical shifts in the same range as those of the respective starting materials.
In the 1H-NMR spectra of the 3-substituted carbazoles 4a–4c, HꢀC(4) was
observed as d(H) 8.4 (s) due to the deshielding effect at the peri-positions. The signal
of HꢀC(1) appeared at d(H) ca. 6.85 (s). HꢀC(5), HꢀC(6), HꢀC(7), and HꢀC(8) res-
onated in the range d(H) 7.20–8.10. The 13C-NMR spectra of these compounds invar-
iably showed the signals for C(2) and C(3) at d(C) ca. 164 and 119, respectively. The
other C-atoms showed chemical shifts in the same range as those of the respective start-
ing materials.
2.5. Photophysical Considerations. To characterize the multiplicity of the reactive
excited states of compounds 2, we carried out additional experiments. Irradiation of
the starting materials in MeOH in the presence of air or O2 did not show any change
in the distribution of the rearrangement products, although both rate of conversion
and yield were slightly lower under these conditions. This minor effect suggests that
O2 does not quench the reactive excited state. Also, no significant difference in the
product ratio was observed when compounds 2a, 2b, or 2c were irradiated in MeOH
or benzene at 254 and 313 nm (Table 3). These results suggests that the lowest excited

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Helvetica Chimica Acta – Vol. 89 (2006)
Table 3. Product Distribution upon Irradiation of 2a–c in MeOH vs. Benzene. Conditions: substrates 2,
6 mM; excitation at 254 nm; T=298 K; Ar atmosphere; conversion >90%.
Substrate
Solvent
Yield [%]a)
3
4
1
2a
2b
2c
MeOH
Benzene
MeOH
Benzene
MeOH
Benzene
63.5
61.0
66.0
55.2
67.4
55.6
24.3
20.5
21.2
21.6
21.3
21.6
11.0
10.5
10.5
10.1
9.5
16.8
a) Determined by HPLC analysis.
state is the chemically reactive state involved in the photorearrangement, which, prob-
ably, is a singlet state.
Next, we carried out photosensitized reactions of 6 mM solutions of 2a–2c in MeCN
under Ar atmosphere by exciting at 366 nm in the presence of 10 mM xanthone as a trip-
let-energy donor [21]. The results are shown in Table 4. In solution, xanthone was the
only substrate capable of absorbing light, and of populating the triplet-excited state of
the carbazole substrates through a triplet-energy-transfer process. This process is exer-
gonic because the ET value of xanthone (74 kcal/mol) is higher than those of com-
pounds 2 (69.5 kcal/mol; see above). However, the photo-Fries rearrangement of 2
did not take place upon photosensitization with xanthone. Therefore, we concluded
that the triplet-excited state of these substrates did not provide the observed rearrange-
ment products.
Next, 50 mM solutions of 2 in MeCN were irradiated separately at 310 nm under Ar
gas in the presence of 1 mM ‘tetramethyl-1,2-diazetine dioxide’ (TMDD), a triplet-
energy quencher (ET 54 kcal/mol) [21], under Ar gas. In these experiments, only the
substrates 2 absorbed light at 310 nm. Now, in the presence of TMDD, a regular
photo-Fries rearrangement was observed (Table 4). Thus, the photoreactive lowest-
excited state of these compounds is the singlet-excited state. These results clearly
show i) that compounds 2 populate efficiently the S1 state by direct absorption of
light; ii) that the photoreactive excited state affording the ortho-rearrangement prod-
ucts is the S1 state (p ! p*); and iii) that the photosensitized formation of the trip-
let-excited state does not yield any stable photoproduct; indeed, this triplet-excited
state should be deactivated efficiently at room temperature through radiationless path-
ways.
It is interesting to point out that the photoreactive excited states of compounds
2a–2c are similar to those of excited N-acetyl- and N-benzoyl-9H-carbazole [16a,b],
as well as of the corresponding 2-substituted congeners [16c]. This means that the pop-
ulation of the singlet-excited state, which is the photoreactive excited state, is indepen-
dent of the position where the Ac or SO2 groups are attached to the carbazole moiety.
Finally, the quantum yields (f) for the photo-Fries rearrangement of 2a–2c were
determined in different organic media using ‘potassium ferrioxalate’ (=potassium tris-
(oxalato)ferrate(III)) as actinometer [22–24]. These measurements were conducted

Helvetica Chimica Acta – Vol. 89 (2006)
1153
Table 4. Photosensitization and Quenching of Substrates 2 in MeCN. Conditions: substrate concentration,
6.0 mM; T=298 K; Ar atmosphere; conversion >90%.
Substrate
Additive
lexc [nm]
Yield [%]a)
3
4
1
2a
2b
2c
None
313
313
366
313
313
366
313
313
366
61.5
61.3
no reaction
57.6
56.2
no reaction
64.8
62.1
27.0
27.4
9.5
10.5
TMDDb)
Xanthonec)
None
26.2
25.8
10.5
9.5
TMDD
Xanthone
None
TMDD
Xanthone
24.3
22.5
10.8
9.8
no reaction
a) Determined by HPLC analysis. b) ‘Tetramethyl-1,2-diazetine dioxide’, used as triplet quencher. c) Used
as triplet photosensitizer.
Table 5. Quantum Yields for the Photo-Fries Conversion of Compounds 2. The experiments were con-
ducted both in the absence and presence of O2.
Substrate
Solvent
Quantum yielda)
Anaerobicb)
Aerobic
2a
2b
2c
MeCN
0.13
0.09
0.13
0.22
0.18
0.17
0.18
0.21
0.12
0.12
0.09
0.13
0.21
0.19
0.17
0.18
0.21
0.12
MeOH
Benzene
MeCN
MeOH
Benzene
MeCN
MeOH
Benzene
a) Determined at low conversion (<10%) of starting material at lexc 313 nm. For details, see Exper. Part.
b) Ar Atmosphere.
both under aerobic and anaerobic conditions. The conversions of the starting materials
were monitored by HPLC analysis, and the quantum yields determined are listed in
Table 5. As can be seen, the f values did not depend significantly on the presence or
absence of O2. This means that dissolved O2 did not quench efficiently the singlet-
excited states of the substrates, which is in agreement with the results presented in
Tables 2 and 3. However, the f values of 2a–2c were moderately dependent on solvent
polarity, which suggests that the reaction intermediates are, to some extent, stabilized
preferentially in polar solvents.
3. Conclusions. – We have shown that ortho-rearranged products of type 3 and 4 can
be obtained in good yield and under very mild conditions from the corresponding 9H-
carbazol-2-yl sulfonates 2 through photo-Fries rearrangement on preparative scale, and

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Helvetica Chimica Acta – Vol. 89 (2006)
with significant regioselectivity. The rearrangement involves an ‘in-cage’ 1,3-type
migration of the RO2ASO or ArO2SO moiety, 9H-carbazol-2-ol (1) being formed as an
CTHREUNG
‘out-of-cage’ side product. From a synthetic point of view, photo-Fries rearrangement
provides interesting ortho-rearranged products as potential synthons for the prepara-
tion of 1,3-thioxolane and 1,4-thioxolane rings fused to the carbazole moiety. This syn-
thetic approach, thus, represents a convenient tool for the introduction of sulfur func-
tional groups in polycyclic aromatic compounds. We have also shown that, mechanisti-
cally, the lowest singlet-excited state of the carbazole substrates is the photoreactive
excited state yielding the ortho-rearranged products.
We thank the Universidad de Buenos Aires (X022), CONICET (PIP05/5443) and ANPCyT (PICT 6-
12312) for partial financial support. Dr. F. Quina, Federal University of Sao Paulo, Brazil, is kindly
acknowledged for providing access to the spectrofluorometer, and for generous hospitality. R. E.-B.
and S. M. B are research members of CONICET.
Experimental Part
General. Xanthone, ‘tetramethyldiazetine dioxide’ (TMDD), benzenesulfonyl chloride, methanesul-
fonyl anhydride, and trifluoromethanesulfonyl anhydride were purchased from Aldrich, and were used
without further purification. Compound 1 was purchased from Aldrich, and purified by column chroma-
tography (CC). Spectrograde solvents were obtained from J. T. Baker, and used as received. Column
chromatography (CC): Merck silica gel 60 (0.040–0.063 mm). TLC: Merck silica gel 60 F254 on Al sheets
(0.2 mm thickness). Melting points (m.p.): Fisher-Jones apparatus; uncorrected. 1H- and 13C-NMR Spec-
tra: Bruker AC-200 spectrometer; chemical shifts d in ppm rel. to Me4ACHTRESUGN i, J in Hz. UV/VIS Spectra: Shi-
madzu UV-1203 spectrophotometer; in 1-cm stoppered quartz cells, at 298 K; lmax in nm. Fluorescence
and phosphorescence spectra: Hitachi F-500 spectrofluorometer; at r.t. in 1-cm stoppered quartz cells,
and in the 908 mode. Measurement at 77 K were made in transparent matrices prepared by freezing i-
PrOH/Et2ACHTREOUNG 1:1 with liquid N2 in a 2-mm cylindrical cell.
General Procedure for the Synthesis of Compounds 2. To a soln. of 1 (1 g, 5.46 mmol) in anh. pyridine
(10 ml), a soln. of the appropriate alkane- or benzenesulfonyl chloride (6.05 mmol) in pyridine (5 ml) was
added dropwise over 15 min, while the mixture was gently stirred at 08. The mixture was then stirred for
3 h at r.t. (TLC and HPLC control). After completion of the reaction, the mixture was poured into H2O
(50 ml). The resulting brownish solid was separated, and extracted with CHCl3 (2×20 ml). The combined
org. layers were washed with 10% aq. HCl, dried (MgSO4), and concentrated in vacuo. The solid residue
was purified by filtration over a short pad of SiO2 (hexane/AcOEt 7:3) to afford the corresponding prod-
uct.
9H-Carbazol-2-yl Methanesulfonate (2a). Yield: 1.40 g (98.2%). Colorless solid. M.p. 968. 1H-NMR
(200 MHz, (D6)DMSO): 11.50 (s, NH); 8.20 (d, J=8.0, HꢀC(5)); 8.15 (d, J=8.4, HꢀC(4)); 7.53 (d,
J=8.0, HꢀC(6)); 7.46 (d, J=1.8, HꢀC(1)); 7.40 (d, J=7.6, HꢀC(7)); 7.22 (d, J=7.6, HꢀC(8)); 7.14
(dd, J=1.8, 8.4, HꢀC(3)); 3.38 (s, Me). 13C-NMR (50 MHz, (D6)DMSO): 150.7 (C(2)); 144.0 (C(9a));
143.3 (C(8a)); 129.4 (C(7)); 124.6 (C(4)); 123.8 (C(5)); 122.6 (C(6)); 122.3 (C(4b)); 121.8 (C(4a));
116.3 (C(8)); 114.7 (C(3)); 99.9 (C(1)); 40.7 (Me). Anal. calc. for C13H11NO3S (261.30): C 59.76, H
4.24, N 5.36, S 12.27; found: C 59.72, H 4.23, N 5.45, S 12.25.
9H-Carbazol-2-yl Benzenesulfonate (2b). Yield: 1.68 g (95.2%). Colorless solid. M.p. 1248. 1H-NMR
(200 MHz, (D6)DMSO): 8.14 (s, NH); 8.01 (d, J=7.7, HꢀC(5)); 7.89 (d, J=8.4, HꢀC(4)); 7.86 (d, J=8.0,
2 arom. H); 7.76 (t, J=7.3, HꢀC(6)); 7.51 (t, J=7.3, HꢀC(7)); 7.46–7.39 (m, 3 arom. H); 7.27 (d, J=7.3,
HꢀC(8)); 7.18 (d, J=1.8, HꢀC(1)); 7.64 (dd, J=1.8, 8.4, HꢀC(3)). 13C-NMR (50 MHz, (D6)DMSO):
147.2 (C(2)); 140.5 (C(9a)); 139.9 (C(8a)); 135.2 (C(10)); 134.2 (C(13)); 129.1 (C(12,14)); 128.5 (C(11,
15)); 126.0 (C(7)); 122.3 (C(4a)); 122.1 (C(4b)); 120.6 (C(4)); 120.1 (C(5)); 119.5 (C(6)); 113.0 (C(8));
110.9 (C(3)); 104.9 (C(1)). Anal. calc. for C18H13NO3S (323.37): C 66.86, H 4.05, N 4.33, S 9.92; found:
C 66.75, H 4.00, N 4.35, S 9.96.

Helvetica Chimica Acta – Vol. 89 (2006)
1155
9H-Carbazol-2-yl Trifluoromethanesulfonate (2c). Yield: 1.46 g (84.8%). Colorless solid. M.p. 928.
1H-NMR (200 MHz, (D6)DMSO): 11.50 (s, NH); 8.20 (d, J=8.0, HꢀC(5)); 8.15 (d, J=8.4, HꢀC(4));
7.53 (d, J=8.0, HꢀC(6)); 7.46 (d, J=1.8, HꢀC(1)); 7.40 (d, J=7.6, HꢀC(7)); 7.22 (d, J=7.6, Hꢀ
C(8)); 7.14 (dd, J=1.8, 8.4, HꢀC(3)). 13C-NMR (50 MHz, (D6)DMSO): 147.6 (C(2)); 140.4 (C(9a));
139.3 (C(8a)); 126.8 (C(7)); 120.4 (C(4)); 121.3 (C(5)); 120.4 (C(6)); 123.3 (C(4b)); 122.3 (C(4a));
115.8 (F3C); 112.5 (C(8)); 111.0 (C(3)); 103.8 (C(1)). Anal. calc. for C13H8F3NO3S (315.27): C 49.53, H
2.56, F 18.08, N 4.44, S 10.17; found: C 49.73, H 2.58, F 18.02, N 4.43, S 10.13.
General Procedure for the Preparative-Scale Photo-Fries Rearrangement of 2. Through a soln. of the
substrate (1.5 mmol) in the appropriate solvent (250 ml) in a quartz immersion well was bubbled Ar gas
for 20 min. The soln. was irradiated at 313 nm under gentle stirring with a medium-pressure Hg lamp
(Hereaus TQ150) for 2–3 h. Alternatively, irradiation at 254 nm was carried out with a low-pressure
Hg lamp (Hanau TNQ 15), and the progress of the reaction was monitored by TLC (SiO2; hexane/
AcOEt 4 :1) and HPLC (RP-18; MeCN/H2O 7:3, 1.0 ml/min; detection at 310 nm). The photolysis
soln. was concentrated in vacuo, and the resulting yellowish oily residue was purified by CC (SiO2; hex-
ane/AcOEt) to afford the corresponding photoproducts.
1-(Methylsulfonyl)-9H-carbazol-2-ol (3a). Yield: 254 mg (64.8%). Colorless solid. M.p. 170–1718.
1H-NMR (200 MHz, CDCl3): 11.99 (s, NH); 8.55 (s, OH); 8.10 (d, J=8.8, HꢀC(4)); 8.01 (dd, J=1.9,
8.8, HꢀC(5)); 7.40–7.20 (m, HꢀC(6,7,8)); 6.84 (d, J=8.8, HꢀC(3)); 2.91 (s, Me). 13C-NMR (50 MHz,
CDCl3)): 163.0 (C(2)); 140.1 (C(9a)); 139.8 (C(8a)); 124.9 (C(7)); 124.6 (C(4)); 123.2 (C(4b)); 120.9
(C(5)); 119.1 (C(6)); 113.3 (C(4a)); 110.9 (C(8)); 103.8 (C(3)); 103.1 (C(1)); 39.8 (Me). Anal. calc. for
C13H11NO3S (261.30): C 59.76, H 4.24, N 5.36, S 12.27; found: C 59.71, H 4.23, N 5.42, S 12.29.
3-(Methylsulfonyl)-9H-carbazol-2-ol (4a). Yield: 91.2 mg (23.3%). Colorless solid. M.p. 216–2188.
1H-NMR (200 MHz, CDCl3): 12.7 (s, NH); 8.41 (s, HꢀC(4)); 8.15 (br. s, OH); 7.99 (d, J=7.8, Hꢀ
C(5)); 7.4–7.2 (m, HꢀC(6,7,8)); 6.86 (s, HꢀC(1)); 2.77 (s, Me). 13C-NMR (200 MHz, CDCl3)1): 162.3
(C(2)); 145.4 (C(9a)); 140.3 (C(8a)); 125.9 (C(7)); 123.6 (C(4b)); 120.7 (C(5)); 120.6 (C(4)); 119.6
(C(6)); 119.1 (C(3)); 116.8 (C(4a)); 110.7 (C(8)); 97.3 (C(1)); 41.9 (Me). Anal. calc. for C13H11NO3S
(261.30): C 59.76, H 4.24, N 5.36, S 12.27; found: C 59.73, H 4.22, N 5.40, S 12.31.
1-(Phenylsulfonyl)-9H-carbazol-2-ol (3b). Yield: 362 mg (74.6%). Colorless solid. M.p. 2058. 1H-
NMR (200 MHz, CDCl3): 12.20 (s, NH); 8.16 (d, J=8.4, HꢀC(4)); 7.92 (dd, J=1.5, 7.0, HꢀC(5));
7.73 (dd, J=7.5, 2 arom. H); 7.67–7.58 (m, 3 arom. H); 7.37 (br. s, OH); 7.30 (dd, J=1.5, 7.3, Hꢀ
C(6)); 7.24 (dt, J=1.8, 7.3, HꢀC(7)); 7.08 (dt, J=1.8, 8.04, HꢀC(8)); 6.94 (d, J=8.4, HꢀC(3)). 13C-
NMR (50 MHz, CDCl3): 163.3 (C(2)); 140.0 (C(9a)); 139.1 (C(8a)); 138.1 (C(10)); 132.4 (C(13));
129.5 (C(11,15)); 129.2 (C(7)); 127.6 (C(12,14)); 124.8 (C(4)); 122.7 (C(4b)); 120.5 (C(5)); 119.0
(C(6)); 116.9 (C(4a)); 110.5 (C(3,8)); 105.3 (C(1)). Anal. calc. for C18H13NO3S (323.37): C 66.86, H
4.05, N 4.33, S 9.92; found: C 66.81, H 4.03, N 4.36, S 9.95.
3-(Phenylsulfonyl)-9H-carbazol-2-ol (4b). Yield: 109.0 mg (22.5%). Colorless solid. M.p. 218–2208.
1H-NMR (200 MHz, CDCl3): 12.7 (s, NH); 8.41 (s, HꢀC(4)); 8.01 (dd, J=1.5, 7.0, HꢀC(5)); 8.15 (dd,
J=8, HꢀC(11,15)); 7.45–7.55 (m, HꢀC(12,13,14)); 7.54 (dd, J=1.5, 7.3, HꢀC(6)); 7.27 (dt, J=1.5,
7.3, HꢀC(7)); 7.15 (dt, J=1.5, 8.0, HꢀC(8)); 6.90 (s, HꢀC(1)). 13C-NMR (50 MHz, CDCl3): 172.5
(C(2)); 145.2 (C(9a)); 140.1 (C(8a)); 138.1 (C(10)); 132.4 (C(13)); 129.5 (C(11,15)); 128.4 (C(7));
127.6 (C(12,14)); 125.9 (C(4)); 122.2 (C(4b)); 120.7 (C(5)); 119.8 (C(6)); 117.2 (C(3)); 115.3 (C(4a));
110.8 (C(8)); 97.6 (C(1)). Anal. calc. for C18H13NO3S (323.37): C 66.86, H 4.05, N 4.33, S 9.92; found:
C 66.92, H 4.06, N 4.31, S 9.90.
1-[(Trifluoromethyl)sulfonyl]-9H-carbazol-2-ol (3c). Yield: 321 mg (67.9%). Colorless solid. M.p.
1
134–1368. H-NMR (200 MHz, CDCl3): 11.99 (s, NH); 8.55 (s, OH); 8.10 (d, J=8.8, HꢀC(4)); 8.01 (d,
J=1.9, 8.8, HꢀC(5)); 7.40–7.20 (m, HꢀC(6,7,8)); 6.84 (d, J=8.8, HꢀC(3)). 13C-NMR (50 MHz,
CDCl3): 163.0 (C(2)); 140.1 (C(9a)); 139.8 (C(8a)); 124.9 (C(7)); 124.6 (C(4)); 123.2 (C(4b)); 120.9
(C(5)); 119.1 (C(6)); 115.2 (F3C); 113.3 (C(4a)); 110.9 (C(8)); 103.8 (C(3)); 103.1 (C(1)). Anal. calc.
for C13H8F3NO3S (315.27): C 49.53, H 2.56, F 18.08, N 4.44, S 10.17; found: C 49.65, H 2.57, F 18.04; N
4.42, S 10.14.
3-[(Trifluoromethyl)sulfonyl]-9H-carbazol-2-ol (4c). Yield: 110 mg (23.3%). Colorless solid. M.p.
196–1988. 1H-NMR (200 MHz, CDCl3): 12.7 (s, NH); 8.41 (s, HꢀC(4)); 8.15 (br. s, OH); 7.99 (d,
J=7.8, HꢀC(5)); 7.4–7.2 (m, HꢀC(6,7,8)); 6.86 (s, HꢀC(1)). 13C-NMR (200 MHz, CDCl3): 162.3

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Helvetica Chimica Acta – Vol. 89 (2006)
(C(2)); 145.4 (C(9a)); 140.3 (C(8a)); 125.9 (C(7)); 123.6 (C(4b)); 120.7 (C(5)); 120.6 (C(4)); 119.6 (C(6));
119.1 (C(3)); 116.8 (C(4a)); 115.9 (F3C); 110.7 (C(8)); 97.3 (C(1)). Anal. calc. for C13H8F3NO3S (315.27):
C 49.53, H 2.56, F 18.08, N 4.44, S 10.17; found: C 49.62, H 2.58, F 18.03, N 4.41, S 10.18.
Determination of Chemical Quantum Yields for Photo-Fries Rearrangements. Solns. of the appropri-
ate substrate 2 (0.55 mmol) were prepared in different organic solvents (10 ml). An aliquot (2 ml) of each
soln. was placed in a spectrophotometric quartz cell, through which Ar gas was bubbled during 20 min.
Similarly, a 6 mM soln. of ‘potassium ferrioxalate’ (K3Fe(C2O4)3ACHTREUNG·3 H2O) was prepared, an aliquot (2 ml)
was placed in a spectrophotometric quartz cell, and Ar gas was bubbled through the soln. for 20 min. The
cells were then placed in an optical bench, and irradiated simultaneously with a medium-pressure Hg
lamp (Hereaus TQ150), whose radiation was collimated with a Schott quartz lens, and filtered with an
interference Schott filter (5-nm path band) to give a nearly parallel beam at 313 nm. The chemical quan-
tum yields f were then determined with ‘potassium ferrioxalate’ as an actinometer according to the pro-
cedure described in [23]. The conversions of 2a–2c were monitored by HPLC, and were lower than 10%.
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Received February 15, 2006