Intramolecular hydrogen bonding in a triangular dithiazolyl-azaindole for efficient photoreactivity in polar and nonpolar solvents

Article abstract of DOI:10.1002/ejoc.201100676

A triangular dithiazolyl-azaindole derivative has been synthesized as a highly sensitive photochromic molecule. 2,4-Dimethyl-5-phenylthiazol derivative 1a, and a reference compound, 5-methyl-2-phenylthiophene derivative 2a, both showed photochromism with

Full text of DOI:10.1002/ejoc.201100676

FULL PAPER
DOI: 10.1002/ejoc.201100676
Intramolecular Hydrogen Bonding in a Triangular Dithiazolyl-Azaindole for
Efficient Photoreactivity in Polar and Nonpolar Solvents
Sayo Fukumoto,[a] Takuya Nakashima,[a] and Tsuyoshi Kawai*[a]
Keywords: Photochromism / Hydrogen bonds / Cyclization / Conformation analysis / Quantum yield
A triangular dithiazolyl-azaindole derivative has been syn-
thesized as a highly sensitive photochromic molecule. 2,4-
Dimethyl-5-phenylthiazol derivative 1a, and a reference
compound, 5-methyl-2-phenylthiophene derivative 2a, both
showed photochromism with quantum yields of 90 and 45%,
respectively, in hexane, and 90 and 35%, respectively, in
methanol. In the single-crystal state, 1a revealed photochro-
mic coloration. Its conformation was assigned to a photoreac-
tive state with C2-symmetry around the hexatriene reaction
center. Temperature-dependent NMR studies and quantum
chemical calculations indicated the contribution of intramo-
lecular hydrogen-bonding between the central azaindole
unit and the side thiazole units, which stabilizes the photore-
active C2-symmetric conformation and elevates the photore-
activity in both non-polar and polar solvents.
100% photochromic quantum yield. This has stimulated a
number of synthetic works on hexatriene-type photochro-
mic molecules with high sensitivity in solution phase. Re-
cently, we have been exploring photochromic terarylenes in
which three aromatic units are connected in a triangular
manner, forming a hexatriene backbone.[12a,18] Some het-
eroaromatic units possessing hydrogen-bonding activity
have been introduced as a component of the terarylene
structure. The authors recently reported that a dithiazolyl-
benzothiophene derivative shows a photon-quantitative re-
action with almost 100% photocyclization quantum
yield.[19] This extremely high photochromic reactivity of the
molecule was explained in terms of specific intramolecular
S/N and CH/N non-covalent interactions, which were
thought to stabilize the C2-symmetric conformation in non-
polar solvents. In the field of supramolecular chemistry, in-
tramolecular and inter-arylene unit interactions have been
developed to regulate the rotational configuration of oli-
goarylene molecules forming specific foldamers.[20]
We herein expand our study and introduce an N-methyl-
azaindole unit as a central bridging unit in the terarylene
structure. Although the photocyclization quantum yield of
diarylethene derivatives is usually suppressed in polar sol-
vents because of specific twisted intramolecular charge
transfer (TICT)[21] in the excited state, the present molecule
exhibits photocyclization quantum yield as high as 90% in
methanol.
Introduction
Photoresponsive molecules have been developed to ma-
nipulate the chemical and physical properties of various
molecules and polymers and are widely used in many prac-
tical applications.[1] Recently, particular interest has focused
on photochromic molecules as an active unit for photo-re-
versible control of various molecular properties such as
color,[2–4] fluorescence,[5–9] electrochemistry,[10,11] chemical
reactivity,[12] and magnetism.[13] Among a number of pho-
tochromic molecules, those based on a hexatriene back-
bone, such as diarylethenes[14] and fluguides,[15] have at-
tracted broad attention because of their persistent photo-
chromic nature; such molecules do not undergo spontane-
ous isomerization reaction under dark conditions. A wide
range of possible chemical modifications of diarylethene, in
particular, have been demonstrated, which has stimulated
further synthetic chemistry on this class of molecules. The
photochemical reactivity of various photochromic diaryl-
ethenes and their derivatives has been studied to elaborate
structure–reactivity relationships.[14a] Because the photo-
chromic reaction leading from the hexatriene structure to
the cyclohexadiene structure proceeds with contra-rota-
tional motion of the reactive carbons, a C2-symmetric ge-
ometry around the hexatriene reaction center is required for
high sensitivity.[16,17] Complete control of molecular confor-
mation has been achieved in some crystalline samples of
diarylethenes, which have been reported to show almost
Results and Discussion
[a] Graduate School of Materials Science, Nara Institute of Science
and Technology, NAIST,
2,3-Dithiazolylazaindole 1a (Scheme 1) was designed as
a representative photochromic molecule in which the molec-
ular conformation was expected to be stabilized in the
photo-reactive conformation through intramolecular hy-
8916-5 Takayama, Ikoma, Nara 630-0192, Japan
Fax: +81-743-72-6179
E-mail: tkawai@ms.naist.jp
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201100676.
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T. Kawai et al.
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drogen-bonding, as depicted by dotted lines in Scheme 1. The colored solution of compound 2 after UV light irradia-
The weak CH/N hydrogen-bonding[22] could tether the side tion showed spontaneous bleaching under ambient condi-
thiazolyl rings to the bridging azaindole unit. These interac- tions, probably due to steric repulsion between the N-
tions are expected to stabilize co-planar structures whereas methyl group at the central azaindole and the proton at the
steric hindrance operating between the methyl groups on side thiophene in the ring-closed form. The colored com-
both thiazole units twist the thiazolyl rings. The methyl pound derived from 2a therefore could not be separated
groups are able to interact with the thiazole rings on the from the colored solution. Nevertheless, the colored form is
opposite site through CH–π interactions. A molecular con- regarded as the cyclohexadiene form 2b, illustrated in
formation with C2-symmetry around the hexatriene moiety Scheme 1, because (1) clear isosbestic points were observed,
was thus expected to be stable. 2,3-Dithienylazaindole 2a (2) the colored solution showed a specific absorption band
was also designed as a reference compound in which the at 680 nm typical for the ring-closed form of isomers of
nitrogen atoms in the thiazole rings were replaced by CH terarylene and diarylethenes, and (3) TD-DFT calculations
units.
for 2b are in agreement with the observed absorption bands
at 400 and 710 nm.[23]
Scheme 1. Photochemical and thermal interconversions of teraryl-
enes 1–3.
2,3-Diarylazaindoles 1a and 2a were synthesized by con-
ventional cross-coupling reactions from the corresponding
arylene units. Their chemical structures were confirmed
1
with high-resolution mass spectroscopy, H NMR, and 13C
NMR analyses as well as by X-ray single-crystal analysis.
Detailed procedures and characterization data are pre-
sented in the experimental section.
As shown in Figure 1, compounds 1a and 2a showed
photochromic profiles similar to those of previously re-
ported terarylenes and diarylethenes. Because isosbestic
points were clearly observed, these spectral changes can be
Figure 1. Absorption spectral changes of 1 (a) and 2 (b) in hexane.
Open-form a (bold lines), closed-form b (dotted line for 1), and
photo-stationary state under irradiation with 313 nm light (gray
lines). The concentrations of 1 and 2 were 4.2ϫ 10–5 and 2.0ϫ
10–5 m, respectively.
The thermal stability of the closed-ring isomers 1b and
attributed to a two-component photochromic reaction. The 2b was then investigated. Compound 1b showed negligible
colored solutions were bleached upon visible light irradia- thermal cycloreversion reaction under dark conditions at
tion with a wavelength longer than 400 nm. The colored room temperature, and exhibited spontaneous bleaching
component 1b, formed after UV light irradiation of a hex- with a half-life time of about one month at 333 K. In con-
ane solution of 1a, was isolated by reversed-phase HPLC trast, 2b showed single exponential bleach kinetics under
purification. The closed-ring isomer 1b was confirmed by ambient conditions, and the half-life time in hexane was
1
MS and H NMR spectroscopy in CDCl3 solution. Visible about 5 h at room temperature.
light irradiation of a solution of 1b progressively decreased
We successfully obtained a macroscopic crystal of com-
the absorption band at 650 nm, finally giving the absorp- pound 1a from a hexane solution, and its photochromic
tion spectrum of 1a (Figure 1, a, bold line). The absorption properties in the single-crystal state were studied.[24] The
band in the visible range again increased upon UV irradia- single-crystal of 1a became green upon UV light irradiation
tion (λ = 313 nm) to reach a photostationary state (PSS, and was bleached under visible light irradiation. This color-
gray line). The conversion ratio between the colorless and ation and bleaching cycle could be repeated more than 20
colored isomers at PSS was estimated to be more than 95%. times with no obvious degradation; the observed color
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Intramolecular Hydrogen Bonding in Dithiazolyl-azaindole
change, is shown in Figure 2 (a and b). Part c of Figure 2
shows the polarized absorption spectra of the crystal in the
colored state. The reversible appearance and disappearance
of an absorption band at approximately 650 nm indicated
photochromic reactions between 1a and 1b in the crystal
state. The specific polarization in this absorption band, and
its sustention upon coloration–bleaching cycles suggest that
the molecular alignment in the crystal lattice is maintained
during the photo-isomerization reactions.[25]
Figure 3. ORTEP drawing of the open-ring isomer in crystal 1a,
showing 50% probability displacement ellipsoids.
ture was similar to the ORTEP structure obtained from the
X-ray analysis and appears to be suitable for the photocycli-
zation reaction. The atomic contacts between H1 and N4,
and between H6 and N3 (estimated distance; H1/N4: 2.9 Å
and H6/N3: 2.6 Å) were well-reproduced in the DFT calcu-
lation. The CH/N intramolecular interactions were also
supported by the calculation. The distance between the
methyl protons on the thiazole units and the molecular pla-
nes of the opposite thiazole units were evaluated to be ap-
proximately 3.2 and 3.3 Å for each of the molecule sides,
which are also short enough to allow CH/π interactions.
Figure 2. Photographs of a crystal of 1 (a) before and (b) after irra-
diation with UV light. (c) Polarized absorption spectra of the
photo-generated green crystal of 1.
The ORTEP drawing of 1a shown in Figure 3 displays
the conformation of C2-symmetry around the central hexa-
triene moiety. Regarding the contra-rotational motion in
the hexatriene moiety upon photocyclization, the C2-sym-
metric structure seems to be suitable for the photochromic
reaction, which is typically recognized as an anti-parallel
conformation of the diarylethene. The distance between the
reaction center carbon atoms, C11 and C21, in the thiazole
units was about 3.5 Å, which is short enough for the photo-
cyclization reaction to take place in the hexatriene unit.[26]
The X-ray structural data also provides information on the
intramolecular atomic contact interactions. Interatomic dis-
tances between the N4/H1 atoms and the N3/H6 atoms
were estimated to be 2.70 Å and 2.7 Å, respectively, which
are similar to, or a little less than, the sum of the van der
Waals radii of the H (1.2 Å) and N (1.55 Å) atoms. These
atomic contacts clearly indicate dual intramolecular hydro-
gen-bonding interactions between the nitrogen atoms and
Figure 4. Optimized structures at the B3LYP/6-31G* level; (a) 1a
and (b) 1b. Left side: overall view; Right side: side-view of the area
associated with hydrogen-bonding interactions.
To evaluate the conformation of 1a in solution, the tem-
1
the CH units. Similar multiple hydrogen-bonding interac- perature dependence of H NMR spectra were studied in
tions have been reported to control rotational isomerization [D8]toluene and [D4]methanol. The H NMR signal of H1
1
of polyarylene molecules that form specific foldamer struc- on the 1-methyl-7-azaindole unit of 1a (see Figure 3) was
tures.[27]
observed at δ = 8.25 ppm at 293 K as a double-doublet sig-
Quantum chemical calculations based on the density nal (J = 7.5, 1.3 Hz) in [D8]toluene, as shown in Figure 5.
functional theory (DFT)[28] at the B3LYP/6-31G* level were The chemical shift was far downfield compared to that of
performed to evaluate an optimized structure of 1a, as the corresponding proton in compound 2a (δ
=
shown in Figure 4. The coplanar optimized molecular 7.72 ppm).[23] Such a downfield shift has been reported as
structure was evaluated with the C2-symmetric hexatriene a typical feature of intramolecular weak CH/N hydrogen-
reaction center, in which the distance between the reactive bonding.[29] As summarized in Figure 6, the chemical shift
carbon atoms was as short as 3.69 Å. This evaluated struc- of H1 showed a systematic upfield shift of 0.095 ppm upon
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T. Kawai et al.
FULL PAPER
heating from 293 to 353 K. Furthermore, the signal corre-
sponding to the N-methyl protons of 1-methyl-7-azaindole
in compound 1a showed an upfield shift upon heating from
293 to 353 K, which also suggests specific hydrogen-bond-
ing at room temperature. No other signal from the 1-
methyl-7-azaindole group revealed such a significant tem-
perature dependence. In contrast, signals of the H1 and N-
methyl protons on the 1-methyl-7-azaindole group in com-
pound 2a showed a slight downfield shift upon heating to
353 K. These results indicate that the CH/N interactions in
compound 1a are attenuated at higher temperatures and
that the molecular conformation changes upon heating.
That is, at higher temperature, the distance between the hy-
drogen and nitrogen atoms and the twisting angle between
the 1-methyl-7-azaindole group and the thiazole unit be-
come larger. As also shown in Figure 5, signals of the
methyl groups at the reactive carbon atoms of the thiazole
rings of 1a were observed at δ = 1.89 and 1.82 ppm at
293 K. Systematic downfield shifts of these peaks upon
heating indicates a suppressed reverse ring-current effect at
higher temperature. Thus, the temperature dependence of
these signals is also consistent with a planar geometry at
room temperature and a larger twisting angle at higher tem-
1
peratures. In [D4]methanol solution, H NMR signals of
H1 and N-methyl protons in compound 1a also showed
similar upfield shifts upon heating (shown in Figure 6).
Thus, intramolecular hydrogen-bonding seems to be effec-
tive even in methanolic solutions of compound 1a. It
should be noted that the N-methyl signal in [D4]methanol
indicated almost the same temperature dependence as that
in toluene, whereas the H1 signal showed suppressed tem-
perature dependence in methanol.
Figure 6. Temperature-dependent chemical shifts of (a) H1 and (b)
N-methyl protons of 1a in [D8]toluene and in [D4]methanol and 2a
in toluene.
tion of UV irradiation time due to the spontaneous thermal
bleaching.[23] Because this procedure also needed an esti-
mate of the absorption coefficient, the calculated values ap-
pear to include significant probable error for 2b as com-
pared to those estimated from the standard procedure. The
photocyclization quantum yield, Φa–b, of 1a was 90% in
hexane and also in methanol, whereas those of 2a were less
than one half of those of 1a. Because the dynamics of the
photocyclization reaction of diarylethene proceeds within
less than 200 fs, its photochromic quantum yield is mainly
affected by the thermal equilibrium in the ground state and
not in the excited state. That is, the extremely high quantum
yield of 1a should require a significantly high population
ratio of the reactive C2-symmetric conformation in the solu-
tion phase, which would be promoted by the tight dual CH/
N interactions in both hexane and methanol.
1
Figure 5. Temperature-dependent H NMR spectra of 1a in [D8]-
toluene.
Finally, we report on the photochromic properties of
compounds 1 and 2, which are summarized in Table 1. The
photochromic reaction quantum yields of 1 were measured
with the standard procedure using 1,2-bis(2-methylbenzo-
[b]thiophen-3-yl)perfluorocyclopentene[30] and 1,2-bis(2,3-
Table 1. Absorption maxima and coefficients of the open- and
closed-ring isomers of 1–3, together with the quantum yields in
solution.
λmax [nm]
Φa–b
Φb–a
(ε [104 m–1 cm–1])
dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene[31]
as
1a
1b
2a
2b
3a
297 (3.0)
654 (1.0)
294 (3.5)
680 (1.0[c])
307 (2.9)
0.90,[a] 0.90[b]
–
reference compounds for photocyclization and cyclorever-
sion reactions, respectively. On the other hand, the photo-
chromic reaction quantum yields of 2 were evaluated by
numerical fitting of the progression curve of the absorption
–
0.007[a]
–
0.45,[a][c] 0.35[b][c]
–
0.086[a][c]
0.008[a]
0.98,[a] 0.54[b]
band corresponding to the ring-closed isomer 2b as a func- [a] In hexane. [b] In methanol. [c] Calculated.
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Intramolecular Hydrogen Bonding in Dithiazolyl-azaindole
We herein briefly comment on a comparison between the compound 1 in hexane and in methanol were 0.90, whereas
photochromic quantum yields of 1a and 3a, the photocycli- those of compound 2 in hexane and in methanol were esti-
zation quantum yields of which have recently been reported mated to be 0.45 and 0.35, respectively. Compound 1a is
to be 98% in hexane and 54% in methanol.[19] Because both stabilized in the reactive conformation with C2-symmetry
molecules are composed of similar molecular units and dis- through dual intramolecular hydrogen-bonding, as revealed
play dual non-covalent intramolecular interactions, one by both X-ray crystal structure analysis and DFT calcula-
may expect similar photochromic reactivity. Indeed, the tions. Intramolecular hydrogen-bonding in the solution
photochromic quantum yield of 1a was similar to that of phase was also supported by the results of temperature-de-
1
3a in hexane (90% for 1a and 98% for 3a), whereas that of pendent H NMR spectroscopic studies.
3a was significantly suppressed in methanol. The difference
between Φa–b of the two compounds in methanol suggests
Experimental Section
that the CH/N interaction in 1a might be stronger than the
S/N interaction in 3a, and that the reactive C2-symmetric
conformation of 1a persists even in methanol. In meth-
anolic solution, 3a showed no marked temperature-depend-
General: 1H NMR spectra were recorded with a JEOL AL-300
spectrometer (300 MHz). Preparative HPLC was performed with a
HITACHI LaChrom ELITE HPLC system and a JASCO LC-2000
Plus Series. Mass spectra were measured with a JEOL JMS-
T100LC AccuTOF mass spectrometer instrument. Absorption
spectra in solution were studied with JASCO V-550 and V-670 spec-
trophotometers with a temperature control unit. Photoirradiation
was carried out using an USHIO 500 W ultra-high-pressure mer-
cury lamp or a Panasonic Aicure UV curing system (LED, λ =
365 nm) as the excitation light source. Monochromic light was ob-
tained by passing the light through a monochromator (Shimazu
SPG-120S, 120 mm, f = 3.5). Absorption spectra in the single-crys-
talline phase were measured by using an Olympus BX-51 polarizing
microscope connected to a Hamamatsu PMA-11 photodetector
through an optical fiber; polarizer and analyzer were set in parallel.
X-ray crystallographic analyses were carried out with a Rigaku R-
AXIS RAPID/s Imaging Plate diffractometer with Mo-Kα radia-
tion at 296 K.
1
ent H NMR shifts, and almost no specific regulation of
conformation with the intramolecular interaction. In hex-
ane, both 1a and 3a are mostly in the reactive conformation
and show high Φa–b. A slight difference in Φa–b of 1a (Φa–b
= 0.90), and of 3a (Φa–b = 0.98), may thus be explained,
not from the viewpoint of population ratio of the reactive
and non-reactive conformations, but by the reactivity of the
reactive conformation. Regarding this minor contradiction,
little attention was paid to the distance between the N1-
CH3 and N3 atoms in 1a and in 1b, which were evaluated
by the DFT calculations to be 0.261 and 0.282 nm, respec-
tively (see Figure 4). The H6/N3 distance in 1b is longer
than the sum of the van der Waals radii of hydrogen and
nitrogen atoms, which suggests that the N1-CH3/N3 inter-
action is not effective in 1b. Collapse of the CH3/N3 interac-
tion upon the photocyclization of 1a to 1b should require
excess heat for the reaction and could be the origin of de-
creased photocyclization reactivity of 1a. Meanwhile, the
distance between the N1–CH3 unit and the N2 atom on the
azaindole unit in 1a and 1b was demonstrated to be 0.246
and 0.247 nm, respectively, indicating a tight interaction be-
tween these moieties both before and after the photocycli-
zation. As a result of this intra-unit tight CH/N interaction,
the H6 atom is out of the molecular plane of the azaindole
unit, and the distance between the H6 and the N3 atoms is
short in the twisted 1a but not in the coplanar 1b. This
specific stabilization of the reactive conformation of 1a with
the intramolecular non-covalent interaction could be the
origin of the slightly suppressed photochromic reactivity of
1a compared with that of 3a for which the S/N interaction
should be effective for both the open and the closed forms.
To gain further understanding, the authors are now explor-
ing X-ray structural analyses of the closed ring isomers 1b
and 3b.
Syntheses of Compounds 1a and 2a: Compounds 1a and 2a were
prepared with cross-coupling reactions as illustrated in Scheme 2.
Scheme 2. Syntheses of compounds 1a and 2a. Reagents and condi-
tions: K2CO3, P(oTol)3, Pd(OAc)2, anhydrous DMF.
1-Methyl-2,3-bis(5-methyl-2-phenylthiazol-4-yl)-1H-pyrrolo[2,3-b]-
pyridine (1a): A mixture of 2,3-dibromo-1-methyl-1H-pyrrolo[2,3-b]-
pyridine (4; 0.12 g, 0.4 mmol),[32] 5 (0.31 g, 1.0 mmol), Pd(OAc)2
(9.8 mg, 0.04 mmol), tri(o-Tolyl)phosphane [P(oTol)3; 28 mg,
0.09 mmol], and K2CO3 (0.67 g 4.8 mmol) in a 100-mL four-necked
flask was flushed with nitrogen for 10 min. A solution of DMF
(30 mL) was added by syringe and the mixture was heated at 100 °C
for 15 h under nitrogen. The cooled reaction mixture was extracted
with diethyl ether and the organic layer was dried with anhydrous
Conclusions
We have designed and synthesized diarylazaindole deriv-
atives 1a and 2a. The former was designed as a representa-
tive photochromic molecule with intramolecular hydrogen-
bonding between the central azaiodole unit and the side
thiazole units. The photocyclization quantum yields of magnesium sulfate, filtered, and concentrated. Silica gel column
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T. Kawai et al.
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chromatography (hexane/ethyl acetate, 9:1) and reversed-phase
HPLC (methanol) afforded compound 1a (0.05 g, 0.10 mmol, 25%)
as a white solid. 1H NMR (300 MHz, CDCl3/TMS): δ = 8.46–8.44
(dd, J = 4.8, 1.5 Hz, 1 H), 8.18–8.16 (dd, J = 7.8, 1.5 Hz, 1 H),
7.98–7.96 (m, 4 H), 7.48–7.41 (m, 6 H), 7.18–7.16 (q, J = 4.8 Hz,
1 H), 3.99 (s, 3 H), 2.02 (s, 3 H), 1.95 (s, 3 H) ppm. 13C NMR
(75 MHz, CDCl3/TMS): δ = 164.92, 164.24, 148.58, 146.74, 144.01,
143.48, 134.77, 133.92, 133.50, 131.84, 130.08, 129.56, 129.11,
129.08, 129.02, 128.86, 126.29, 126.25, 126.16, 120.24, 116.45,
108.85, 29.84, 12.08, 11.95 ppm. HRMS (FAB): calcd. for
C28H22N4S2+ [M]+ 478.1286; found 478.1288. C26H22N4S2 (454.61):
calcd. C 70.26, H 4.63, N 11.71; found C 70.00, H 4.53, N 11.53.
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Compound 1b: 1H NMR (300 MHz, CDCl3/TMS): δ = 8.14–8.09
(m, 2 H), 8.01–7.98 (m, 2 H), 7.88–7.85 (m, 2 H), 7.54–7.26 (m, 6
H), 6.84–6.81 (q, J = 4.5 Hz, 1 H), 3.86 (s, 3 H), 2.08 (s, 3 H), 2.02
(s, 3 H) ppm.
1-Methyl-2,3-bis(2-methyl-5-phenylthiophen-3-yl)-1H-pyrrolo[2,3-b]-
pyridine (2a): Prepared by the same procedure as that used for 1a,
except that 5 was replaced by 2-methyl-5-phenyl-4-(4,4,5,5-tet-
ramethyl-1,3,2-dioxaborolan-2-yl)thiophene (6). From 4 (0.15 g,
0.5 mmol) and 6 (0.34 g, 1.0 mmol) with Pd(OAc)2 (8.0 mg,
0.04 mmol), P(oTol)3 (14 mg, 0.05 mmol), and K2CO3 (0.67 g,
4.8 mmol) in DMF (40 mL), 2a (0.018 g, 0.04 mmol, 8.0%) was
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obtained as a white solid. H NMR (300 MHz, CDCl3/TMS): δ =
8.43–8.40 (dd, J = 4.8, 1.5 Hz, 1 H), 7.93–7.89 (dd, J = 7.8, 1.5 Hz,
1 H), 7.60–7.56 (d, J = 7.2 Hz, 2 H), 7.54–7.51 (d, J = 7.2 Hz, 2
H), 7.42–7.22 (m, 7 H), 7.17–7.12 (m, 2 H), 3.86 (s, 3 H), 2.08 (s,
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148.25, 143.14, 140.98, 139.95, 139.39, 134.82, 134.47, 133.94,
133.41, 131.84, 128.96, 128.81, 127.70, 127.51, 127.01, 125.48,
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The authors thank Mr. S. Katao and Mrs. Y. Nishikawa, both tech-
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the Ministry of Education, Culture, Sports, Science and Technol-
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www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 5047–5053

Intramolecular Hydrogen Bonding in Dithiazolyl-azaindole
¯
=
79.614(2)°; triclinic, space group P1;
Z
=
2;
V
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Received: May 13, 2011
Published Online: July 22, 2011
Eur. J. Org. Chem. 2011, 5047–5053
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5053