Synthesis of spiropyrans and merocyanine dyes based on 1-benzothieno[3,2-b] pyrrole

Article abstract of DOI:10.1007/s11172-010-0019-1

A convenient method was developed for the synthesis of photochromic spiropyrans and merocyanine dyes of the 1-benzothieno[3,2-b]pyrroline series based on the conventional condensation of the analog of Fischer's salt, viz., 1,2,3,3-tetramethyl-3H-[1]benzot

Full text of DOI:10.1007/s11172-010-0019-1

Russian Chemical Bulletin, International Edition, Vol. 58, No. 2, pp. 380—386, February, 2009
380
Synthesis of spiropyrans and merocyanine dyes based on
1ꢀbenzothieno[3,2ꢀb]pyrrole*
A. A. Shimkin, V. Z. Shirinian, A. K. Mailyan, and M. M. Krayushkin
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: shir@ioc.ac.ru
A convenient method was developed for the synthesis of photochromic spiropyrans and
merocyanine dyes of the 1ꢀbenzothieno[3,2ꢀb]pyrroline series based on the conventional
condensation of the analog of Fischer’s salt, viz., 1,2,3,3ꢀtetramethylꢀ3Hꢀ[1]benzothienoꢀ
[3,2ꢀb]pyrrolium triflate, with aromatic 2ꢀhydroxyaldehydes. Unlike Fischer’s salt, benzothienoꢀ
pyrrolium salts readily undergo the [1,5]ꢀsigmatropic rearrangement giving rise to 2Hꢀ[1]benzoꢀ
thieno[3,2ꢀb]pyrrole derivatives. The latter compounds were used for the synthesis of the first
representatives of the previously unknown spiro compounds and merocyanine dyes. The
longꢀwavelength maxima of merocyanines of the 2Hꢀbenzothienopyrrole series are bathoꢀ
chromically shifted by more than 100 nm with respect to the absorption maxima of the
“classical” 3Hꢀbenzothienopyrrole analogs.
Key words: spiropyrans, merocyanine dyes, benzothienopyrroles, Fischer’s salt.
Photochromic spiropyrans have attracted interest as
Scheme 1
materials suitable for the use in optical memory devices
and as molecular switches.1 In addition, spiropyrans can
be used for the extraction of ions from solutions,2 in moꢀ
lecular optoelectronics,3 and as sensors for metal ions.4
Previously, we have developed an approach to the
synthesis of a new class of photochromic spiro comꢀ
pounds5,6 and merocyanine dyes7 based on the thienoꢀ
pyrrole moiety and studied the spectroscopic properties
of the first representatives.8,9 The aim of the present study
was to synthesize new spiropyrans and merocyanine
dyes based on 3Hꢀ and 2Hꢀ[1]benzothieno[3,2ꢀb]pyrrole
derivatives in four steps starting from readily available
1ꢀbenzothiophenꢀ3(2H)ꢀone (1). The synthesis of
3Hꢀ[1]benzothieno[3,2ꢀb]pyrrole derivatives involving the
preparation of hydrazone 2 and its Fischer reaction with
various ketones has been described in detail.10 In the
present study, we investigated the alkylation of benzoꢀ
thienopyrrolenine 3 and examined the possibility of using
salts 4 for the synthesis of spiropyrans 5 and merocyanine
dyes 6 (Scheme 1).
Results and Discussion
Recently, we have shown7 that the reaction of benzoꢀ
thienopyrrolenine 3 with alkylating agents can afford both
X = I, TsO, TfO
* On the occasion of the 75th anniversary of the foundation
of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.
salts 4 and their 2Hꢀisomers 7 (Scheme 2). The latter are
generated from compounds 4 via the [1,5]ꢀsigmatropic
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 376—381, February, 2009.
1066ꢀ5285/09/5802ꢀ0380 © 2009 Springer Science+Business Media, Inc.

Synthesis of spiropyrans and merocyanine dyes
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
381
Scheme 2
Scheme 3
rearrangement. It was found that the most active alkylating
agents, such as triflates, are reagents of choice for the synꢀ
thesis of salts 4. The reactions of benzothienopyrrolenine
3 with less active alkyl tosylates and alkyl iodides require
prolonged heating, resulting in the formation of a mixture
of 3Hꢀ and 2Hꢀbenzothienopyrroles 4 and 7. Compounds
7 can be prepared in the pure form by heating salts 4 in a
highꢀboiling point solvent (pꢀxylene). In this case, triflates
are also reagents of choice, because they are easier to
isolate.
The condensation of salts 4a,b with various oꢀhydroxyꢀ
aldehydes 8a—d in ethanol in the presence of piperidine
afforded a broad range of spiropyrans of the benzothienoꢀ
pyrrole series 5a—g containing both the methyl and
octadecyl groups at the nitrogen atom of the benzothienoꢀ
pyrrole moiety (Scheme 3). The latter compounds are of
interest for studying the aggregation in solution and at the
air—water interface.11 The yields of spiropyrans vary from
moderate to high.
Reagents and conditions: i, piperidine, EtOH, Δ.
Comꢀ
pound
5a
5b
5c
5d
5e
5f
5g
R1
R2
R3
R4
Me
C18H37
Me
C18H37
Me
C18H37
Me
H
H
NO2
NO2
H
H
H
H
H
H
MeO
H
(CH)4
(CH)4
H
H
H
H
H
4ꢀHOC6H4
4ꢀHOC6H4
H
H
5h
8a
C18H37
NO2
H
8b
(CH)4
H
8c
8d
H
H
H
H
4ꢀHOC6H4
MeO
when synthesizing spiropyran 5e, we also isolated bisꢀ
spiropyran 5i in low yield (Scheme 4). After the recrystalꢀ
lization from ethanol, this compound contains an ethanol
molecule. Even the drying over P2O5 with heating
(50—55 °C) for a long time did not allow us to completely
The formylation of 4,4´ꢀdihydroxybiphenyl (biphenol)
affords both monoꢀ and diformylation products (comꢀ
pounds 8c and 8e), which were not separated. Hence,
Scheme 4

382
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
Shimkin et al.
Scheme 5
piperidine
remove the ethanol. There are four bisꢀspiropyran
compound 13, which is the first representative of the preꢀ
viously unknown spiropyrans of the 2Hꢀ[1]benzothienoꢀ
[3,2ꢀb]pyrrole series.
molecules 5i per ethanol molecule. This is clearly seen in
1
the H NMR spectrum and is confirmed by elemental
analysis.
In spite of the fact that this compound is intensely
colored in the solid state, it exists in the spiro form in
chloroform solutions, as evidenced by the spinꢀspin
coupling constants (J ≈ 10 Hz) of the signals for the
Merocyanine dyes of the benzothienopyrrole series 6
were synthesized by the condensation of salt 4a with
heterocyclic analogs of salicylic aldehyde 9 or, if these
compounds are difficult to synthesize, with dimethylꢀ
aminomethylidene derivatives 10 (Scheme 5). The latter
compounds were synthesized by the reactions of
methyleneꢀactive heterocyclic compounds with dimethylꢀ
formamide dimethylacetal12 and have not been previously
used for the synthesis of merocyanines. However, these
compounds proved to be very convenient synthons due
both to the ease of preparation and high activity. Meroꢀ
cyanine dyes 6 were synthesized by refluxing the reagents
in ethanol in the presence of piperidine. The reactions
of compounds 10 do not require the addition of bases
because dimethylamine that is eliminated in the course of
the reaction acts as the base.
The analogous reactions of 2Hꢀbenzothienopyrrolium
salt 7 with 2ꢀhydroxyaldehydes 9 or dimethylaminoꢀ
methylidene derivatives of heterocycles 10 give isomeric
merocyanines 11 (Scheme 6). Under the analogous
conditions, the reaction of salt 7 with salicylic aldehyde
produces triflate 12, which is stable in the presence of a
weak base, such as piperidine. The treatment of salt 12
with an aqueous sodium carbonate solution affords
1
methine protons in the H NMR spectrum. Therefore,
compound 13 is the first example of spiropyrans containꢀ
ing the 2Hꢀpyrrole fragment. However, this spiropyran
appeared to be very unstable and it was characterized only
1
by H NMR spectroscopy. This compound can be stored
only as the salt.
The structures of the resulting compounds were estabꢀ
lished by 1H NMR spectroscopy, mass spectrometry, and
elemental analysis. The absorption bands of solutions of
merocyanines 6 in acetonitrile are in the 503—540 nm
range and are shifted to longer wavelengths by ~20 nm
compared to indoline analogs. The absorption bands of
isomeric dyes 11 are redꢀshifted by more than 110 nm.
This is a consequence of the presence of an additional
double bond between the nitrogen atom and the carbonyl
group in these compounds.
To sum up, we developed a convenient method for the
synthesis of photochromic spiropyrans and merocyanine
dyes of the 1ꢀbenzothieno[3,2ꢀb]pyrroline series based on
the condensation of quaternary benzothienopyrrolium
salts with aromatic 2ꢀhydroxyaldehydes. Unlike Fischer’s

Synthesis of spiropyrans and merocyanine dyes
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
383
Scheme 6
piperidine,
were used. Aldehydes 8c,e based on 4,4´ꢀbiphenol were syntheꢀ
sized according to a known procedure.13
salt, benzothienopyrrolium salts readily undergo the [1,5]ꢀ
sigmatropic rearrangement to give 2Hꢀ[1]benzothienoꢀ
[3,2ꢀb]pyrrole derivatives. The condensation of the latter
compounds with various hydroxyaldehydes afforded first
representatives of the previously unknown spiro comꢀ
pounds and merocyanine dyes containing the 2Hꢀpyrrole
fragment.
Synthesis of spiropyrans 5 (general procedure). Methyl
or octadecyl triflate (1.1 mmol) was added to a solution of
3Hꢀbenzothienopyrrole 3 (0.22 g, 1.0 mmol) in anhydrous
acetonitrile (5 mL). The reaction solution was refluxed until
compound 3 was consumed (0.5—3 h) and then cooled and
concentrated. Anhydrous ethanol (5 mL), the corresponding
oꢀhydroxyaldehyde 8 (1.0 mmol), and piperidine (0.1 mL,
1 mmol) were added to the residue. The reaction mixture was
refluxed for 3—12 h. The course of the reactions was monitored
by TLC (petroleum ether—ethyl acetate, 5 : 1, as the eluent).
The product was isolated by column chromatography or recrysꢀ
tallization from an appropriate solvent.
1,3,3ꢀTrimethylꢀ6´ꢀnitrospiro[2,3ꢀdihydroꢀ1Hꢀ[1]benzoꢀ
thieno[3,2ꢀb]pyrroleꢀ2,2´ꢀ2Hꢀchromene] (5a). The yield was
47%, m.p. 184—186 °C (hexane). 1H NMR (CDCl3), δ: 1.28 (s,
3 H, 0.5 CMe2); 1.35 (s, 3 H, 0.5 CMe2); 3.06 (s, 3 H, NMe);
5.95 (d, 1 H, CH, J = 10.5 Hz); 6.86 (d, 1 H, Harom, J = 8.5 Hz);
6.93 (d, 1 H, CH, J = 10.5 Hz); 7.21—7.37 (m, 2 H, 2 Harom);
7.76—7.85 (m, 2 H, 2 Harom); 8.01—8.11 (m, 2 H, 2 Harom).
MS (EI, 70 eV), m/z (Irel (%)): 378 [M]+ (88), 363 [M – Me]+
Experimental
The 1H and 13C NMR spectra were recorded on Bruker
AMꢀ300, Bruker WMꢀ250, and Bruker ACꢀ200 spectrometers.
The mass spectra were obtained on a Kratos instrument (70 eV)
using a direct inlet system. The melting points were determined
on a Boetius hotꢀstage apparatus and are uncorrected. The elecꢀ
tronic spectra were measured on a LOMO SFꢀ256U spectroꢀ
photometer. The completion of the reactions was controlled by
TLC (Silufol UVꢀ254). The column chromatography was
carried out with the use of Merck silica gel (0.060—0.200).
Commercially available (Acros, Merck) reagents and solvents

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Shimkin et al.
(100). Found (%): C, 66.45; H, 4.84; N, 7.34. C21H18N2O3S.
Calculated (%): C, 66.65; H, 4.79; N, 7.40.
8´ꢀMethoxyꢀ1,3,3ꢀtrimethylspiro[2,3ꢀdihydroꢀ1Hꢀ[1]benzoꢀ
thieno[3,2ꢀb]pyrroleꢀ2,2´ꢀ2Hꢀchromene] (5g). The yield was
41%, m.p. 173—175 °C (petroleum ether—benzene). H NMR
1
3,3ꢀDimethylꢀ6´ꢀnitroꢀ1ꢀoctadecylspiro[2,3ꢀdihydroꢀ1Hꢀ
[1]benzothieno[3,2ꢀb]pyrroleꢀ2,2´ꢀ2Hꢀchromene] (5b). The
(CDCl3), δ: 1.27 (s, 3 H, 0.5 CMe2); 1.38 (s, 3 H, 0.5 CMe2);
3.07 (s, 3 H, NMe); 3.74 (s, 3 H, OMe); 5.79 (d, 1 H, CH,
J = 10.5 Hz); 6.68—6.76 (m, 1 H, Harom); 6.77—6.86 (m, 3 H,
CH + 2 Harom); 7.23 (t, 1 H, Harom, J = 7.2 Hz, J = 7.9 Hz); 7.31
(t, 1 H, Harom, J = 7.2 Hz, J = 7.9 Hz); 7.75—7.85 (m, 2 H,
2 Harom). MS (EI, 70 eV), m/z (Irel (%)): 363 [M]+ (100), 348
[M – Me]+ (38). Found (%): C, 72.25; H, 6.56; N, 3.48.
C22H21NO2S. Calculated (%): C, 72.70; H, 5.82; N, 3.85.
8´ꢀMethoxyꢀ3,3ꢀdimethylꢀ1ꢀoctadecylspiro[2,3ꢀdihydroꢀ1Hꢀ
[1]benzothieno[3,2ꢀb]pyrroleꢀ2,2´ꢀ2Hꢀchromene] (5h). The
1
yield was 20%, amorphous powder. H NMR (CDCl3), δ: 0.89
(t, 3 H, Me, J = 6.6 Hz); 1.20—1.31 (m, 33 H, 0.5 CMe2 + (CH2)15);
1.34 (s, 3 H, 0.5 CMe2); 1.69—1.83 (m, 2 H, CH2); 3.23—3.59
(m, 2 H, NCH2); 5.95 (d, 1 H, CH, J = 10.5 Hz); 6.83 (d, 1 H,
Harom, J = 8.5 Hz); 6.90 (d, 1 H, CH, J = 10.5 Hz); 7.20—7.40
(m, 2 H, 2 Harom); 7.69 (d, 1 H, Harom, J = 7.8 Hz); 7.80 (d, 1 H,
Harom, J = 7.8 Hz); 8.00—8.10 (m, 2 H, 2 Harom). MS (EI,
70 eV), m/z (Irel (%)): 616 [M]+ (18), 600 [M – Me]+ (20), 570
+
[M – NO2]+ (52), 364 [M – C18H36
]
(100). Found (%):
1
yield was 47%, amorphous powder. H NMR (CDCl3), δ: 0.90
C, 73.44; H, 8.80; N, 4.45. C38H52N2O3S. Calculated (%):
C, 73.98; H, 8.50; N, 4.54.
(t, 3 H, Me, J = 6.6 Hz); 1.21—1.31 (m, 33 H, 0.5 CMe2 + (CH2)15);
1.36 (s, 3 H, 0.5 CMe2); 1.68—1.84 (m, 2 H, CH2); 3.36—3.50
(m, 2 H, NCH2); 3.73 (s, 3 H, OMe); 5.77 (d, 1 H, CH,
J = 10.3); 6.68—6.73 (m, 1 H, Harom); 6.75—6.82 (m, 3 H,
CH + 2 Harom); 7.22 (t, 1 H, Harom, J = 7.3 Hz, J = 7.7 Hz);
1,3,3ꢀTrimethylspiro[2,3ꢀdihydroꢀ1Hꢀ[1]benzothienoꢀ
[3,2ꢀb]pyrroleꢀ2,3´ꢀ3Hꢀbenzo[f]chromene] (5c). The yield was
68%, m.p. 243—245 °C (petroleum ether—benzene). 1H NMR
(CDCl3), δ: 1.32 (s, 3 H, 0.5 CMe2); 1.40 (s, 3 H, 0.5 CMe2);
3.07 (s, 3 H, NMe); 5.90 (d, 1 H, CH, J = 10.5 Hz); 7.08 (d,
1 H, Harom, J = 9.2 Hz); 7.20—7.40 (m, 3 H, Harom); 7.53 (t,
1 H, Harom, J = 7.2 Hz, J = 7.9 Hz); 7.62 (d, 1 H, CH, J = 10.5 Hz);
7.67 (d, 1 H, Harom, J = 9.2 Hz); 7.72—7.87 (m, 3 H, 3Harom);
8.06 (d, 1 H, Harom, J = 8.5 Hz). MS (EI, 70 eV), m/z (Irel (%)):
383 [M]+ (100), 368 [M – Me]+ (85), 215 (41). Found (%):
C, 77.68; H, 5.37; N, 3.79. C25H21NOS. Calculated (%):
C, 78.30; H, 5.52; N, 3.65.
7.31 (t, 1 H, Harom, J = 7.3 Hz, J = 7.7 Hz); 7.69 (d, 1 H, Harom
,
J = 7.7 Hz); 7.78 (d, 1 H, Harom, J = 7.7 Hz). MS (EI, 70 eV),
m/z (Irel (%)): 601 (100) [M]+, 586 (40) [M – Me]+. Found (%):
C, 77.01; H, 9.24; N, 2.36. C39H55NO2S. Calculated (%):
C, 77.82; H, 9.21; N, 2.33.
8´,8″ꢀBis(1,3,3ꢀtrimethylspiro[2,3ꢀdihydroꢀ1Hꢀ[1]benzoꢀ
thieno[3,2ꢀb]pyrroleꢀ2,2´ꢀ2Hꢀchromene]) (5i). The yield was
1
30 mg (9%), m.p. 261—263 °C (ethanol). H NMR (250 MHz,
CDCl3), δ: 1.26 (t, 0.75 H, CH3, J = 7.2 Hz); 1.28 (s, 6 H,
0.5 CMe2); 1.39 (s, 6 H, 0.5 CMe2); 3.08 (s, 6 H, NMe); 3,74
(m, 0.5 H, CH2); (d, 2 H, CH, J = 10.5 Hz); 6.85 (d, 2 H,
Harom, J = 8.5 Hz); 6.91 (d, 2 H, CH, J = 10.5 Hz); 7.18—7.37
(m, 8 H, Harom); 7.75—7.88 (m, 4 H, Harom). MS (EI, 70 eV),
m/z (Irel (%)): 664 [M]+ (1), 652 (34), 214 (100). Found (%):
C, 74.51; H, 5.94; N, 4.03. C42H36N2O2S2•0.25EtOH. Calcuꢀ
lated (%): C, 74.33; H, 5.95; N, 3.94.
Synthesis of dimethylaminomethylidene derivatives of heteroꢀ
cycles 10 (general procedure). A solution of dimethylformamide
dimethylacetal (1.5 mL, 11 mmol) in petroleum ether (10 mL)
was added with stirring and cooling (10 °C) to a suspension of
the corresponding heterocyclic ketone (10 mmol) in petroleum
ether (20 mL) for 40 min. Then the cooling was stopped, and the
reaction mixture was kept with stirring at room temperature.
After 3 h, the precipitate was filtered off. The mother liquor was
concentrated to 5 mL. The precipitate that formed was filtered
off and combined with the precipitate obtained previously. The
compounds were used without purification.
Methyl 5ꢀ[(dimethylamino)methylidene]ꢀ2ꢀmethylꢀ4ꢀoxoꢀ
3(4H)ꢀthiophenecarboxylate (10a). The yield was 87%,
m.p. 157—160 °C. 1H NMR (CDCl3), δ: 2.60 (s, 3 H, Me); 3.21
(s, 6 H, NMe2); 3.83 (s, 3 H, OMe); 7.76 (s, 1 H, CH). MS (EI,
70 eV), m/z (Irel (%)): 227 [M]+ (76), 167 [M – HCOOMe]+
(100).
2ꢀ(4ꢀChlorophenyl)ꢀ4ꢀ[(dimethylamino)methylidene]ꢀ5ꢀpheꢀ
nylꢀ2,4ꢀdihydroꢀ3Hꢀpyrazolꢀ3ꢀone (10b). The yield was 93%,
m.p. 180—182 °C. 1H NMR (CDCl3), δ: 3.26 (s, 3 H, 0.5 NMe2);
3,3ꢀDimethylꢀ1ꢀoctadecylspiro[2,3ꢀdihydroꢀ1Hꢀ[1]benzoꢀ
thieno[3,2ꢀb]pyrroleꢀ2,3´ꢀ3Hꢀbenzo[f]chromene] (5d). The
yield was 69%, viscous oil. 1H NMR (CDCl3), δ: 0.91 (t, 3 H,
Me, J = 6.6 Hz); 1.17—1.35 (m, 33 H, 0.5 CMe2 + (CH2)15);
1.39 (s, 3 H, 0.5 CMe2); 1.72—1.84 (m, 2 H, CH2); 3.35—3.55
(m, 2 H, NCH2); 5.90 (d, 1 H, CH, J = 10.3); 7.05 (d, 1 H,
Harom, J = 8.8 Hz); 7.20—7.40 (m, 3 H, Harom); 7.49—7.60 (m,
2 H, CH + Harom); 7.66 (d, 1 H, Harom, J = 8.8 Hz); 7.69—7.83
(m, 3 H, 3 Harom); 8.06 (d, 1 H, Harom, J = 8.1 Hz). MS
(EI, 70 eV), m/z (Irel (%)): 621 [M]+ (73), 606 [M – Me]+ (18),
454 (100), 370 (64). Found (%): N, 2.19. C42H55NOS. Calcuꢀ
lated (%): N, 2.25.
6´ꢀ(4ꢀHydroxyphenyl)ꢀ1,3,3ꢀtrimethylspiro[2,3ꢀdihydroꢀ1Hꢀ
[1]benzothieno[3,2ꢀb]pyrroleꢀ2,2´ꢀ2Hꢀchromene] (5e). The
1
yield was 67%, m.p. 114—116 °C (hexane). H NMR (CDCl3),
δ: 1.30 (s, 3 H, 0.5 CMe2); 1.41 (s, 3 H, 0.5 CMe2); 3.10 (s, 3 H,
NMe); 4.81 (br.s, 1 H, OH); 5.84 (d, 1 H, CH, J = 10.2 Hz),
6.82—6.97 (m, 4 H, CH + 3 CHarom); 7.22—7.37 (m, 4 H,
4 Harom); 7.43 (d, 2 H, 2 Harom, J = 8.8 Hz); 7.76—7.88 (m, 2 H,
2 Harom). MS (EI, 70 eV), m/z (Irel (%)): 425 [M]+ (100), 410
[M – Me]+ (99). Found (%): C, 76.22; H, 6.50; N, 3.17.
C27H23NO2S. Calculated (%): C, 76.21; H, 6.45; N, 3.29.
6´ꢀ(4ꢀHydroxyphenyl)ꢀ3,3ꢀdimethylꢀ1ꢀoctadecylspiroꢀ
[2,3ꢀdihydroꢀ1Hꢀ[1]benzothieno[3,2ꢀb]pyrroleꢀ2,2´ꢀ2Hꢀchroꢀ
mene] (5f). The yield was 23%, viscous oil. 1H NMR (300 MHz,
CDCl3), δ: 0.92 (t, 3 H, Me, J = 6.6 Hz); 1.24—1.36 (m, 33 H,
0.5 CMe2 + (CH2)15); 1.40 (s, 3 H, 0.5 CMe2); 1.74—1.87 (m,
2 H, CH2); 3.33—3.59 (m, 2 H, NCH2); 5.84 (d, 1 H, CH,
J = 10.3 Hz); 6.81—6.93 (m, 4 H, CH + 3 Harom); 7.23—7.28
(m, 2 H, 2 Harom); 7.30—7.38 (m, 2 H, 2 Harom); 7.43 (d, 2 H,
2 Harom, J = 8.8 Hz); 7.73 (d, 1 H, Harom, J = 8.1 Hz); 7.80 (d,
3.89 (s, 3 H, 0.5 NMe2); 7.16 (s, 1 H, CH); 7.33 (d, 2 H, Harom
,
J = 8.5 Hz); 7.41—7.57 (m, 5 H, Harom); 8.06 (d, 2 H, Harom
,
J = 8.5 Hz). MS (EI, 70 eV), m/z (Irel (%)): 325 [M]+ (100), 281
[M – NMe2]+ (43).
1 H, Harom, J = 8.1 Hz). MS (EI, 70 eV), m/z (Irel (%)): 663
+
[M]+ (100), 453 (56), 410 [M – C18H37
]
(37). A sample suitꢀ
Synthesis of merocyanines (general procedure). Merocyanines
were synthesized analogously to spiropyrans 5. The reactions of
able for elemental analysis was not obtained.

Synthesis of spiropyrans and merocyanine dyes
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
385
dimethylaminomethylidene derivatives 10 were carried out in
the absence of piperidine. The product was isolated by column
chromatography (chloroform—ethyl acetate, 3 : 1, as the
eluent) or recrystallization from ethanol. Merocyanines 6a and
11a have been synthesized and characterized earlier.7
3.3 mmol) was added to a solution of 3Hꢀbenzothienopyrrole 3
(0.65 g, 3.0 mmol) in anhydrous acetonitrile (6 mL). The reacꢀ
tion solution was refluxed for 32 h, cooled, and concentrated.
Anhydrous ethanol (6 mL), salicylaldehyde (0.32 mL, 3.0 mmol),
and piperidine (0.33 mL, 3.3 mmol) were added to the residue.
The reaction mixture was refluxed for 1 h. The precipitate that
formed was filtered off and washed with ethanol (2×5 mL). The
mother liquor was concentrated and washed with petroleum
ether. Then ethanol (10 mL) was added, and the precipitate was
again filtered off.
Methyl 2ꢀmethylꢀ4ꢀoxoꢀ5ꢀ[2ꢀ(1,3,3ꢀtrimethylꢀ1,3ꢀdihydroꢀ
2Hꢀ[1]benzothieno[3,2ꢀb]pyrrolꢀ2ꢀylidene)ethylidene]ꢀ3(4H)ꢀ
thiophenecarboxylate (6b). The yield was 57%, m.p. 216—218 °C
(ethanol), λmax = 520 nm (acetonitrile). 1H NMR (DMSOꢀd6 +
CF3COOH), δ: 1.82 (s, 6 H, CMe2); 2.69 (s, 3 H, Me); 3.85
(s, 3 H, NMe); 4.19 (s, 3 H, COOMe); 6.76 (d, 1 H, CH,
J = 15.3 Hz); 7.51 (t, 1 H, Harom, J = 7.3 Hz, J = 7.9 Hz);
7.58 (t, 1 H, Harom, J = 7.3 Hz, J = 7.9 Hz); 8.17 (d, 1 H,
Harom, J = 7.9 Hz); 8.22—8.32 (m, 2 H, 2 Harom). 13C NMR
(DMSOꢀd6 + CF3COOH), δ: 18.00 (Me), 27.49 (CMe2), 35.01
(NMe), 51.11 (COOMe), 51.66 (CMe2), 101.92, 116.18, 120.79,
122.04, 124.95, 125.20, 125.65, 126.14, 137.08, 137.96, 141.49,
142.61, 161.05, 163.00, 169.49, 179.03 (COOMe). MS (EI, 70 eV),
m/z (Irel (%)): 411 [M]+ (100), 396 [M – Me]+ (20), 264 (66),
215 (50). Found (%): C, 63.73; H, 5.33; N, 3.38. C22H21NO3S2.
Calculated (%): C, 64.21; H, 5.14; N, 3.40.
The yield was 0.38 g (26%), red needleꢀlike crystals (triflate
12), m.p. 290—292 °C (ethanol). 1H NMR (DMSOꢀd6
+
CF3COOH), δ: 1.70 (s, 6 H, CMe2); 3.93 (s, 3 H, NMe); 6.92
(t, 1 H, Harom, J = 7.3 Hz, J = 7.9 Hz); 6.99 (d, 1 H, Harom
,
J = 7.9 Hz); 7.31 (t, 1 H, Harom, J = 7.3 Hz, J = 7.9 Hz); 7.45
(d, 1 H, CH, J = 16.5 Hz); 7.63—7.73 (m, 2 H, CH + Harom);
7.91—7.98 (m, 2 H, 2 Harom); 8.19 (d, 1 H, Harom, J = 7.9 Hz);
8.53 (d, 1 H, Harom, J = 7.9 Hz). 13C NMR (DMSOꢀd6
+
CF3COOH), δ: 20.67 (CMe2), 32.20 (NMe), 85.51 (CMe2),
116.18, 116.42, 119.76, 122.15, 122.27, 126.23, 126.48, 127.18,
127.47, 129.60, 132.74, 136.26, 138.74, 153.15, 157.03, 161.72,
170.29. MS (EI, 70 eV), m/z (Irel (%)): 333 [M]+ (36), 318
[M – Me]+ (100), 217 (28). Found (%): C, 54.56; H, 4.17;
N, 2.89. C21H19NOS·CF3SO3H. Calculated (%): C, 54.65;
H, 4.17; N, 2.90.
Triflate 12 (30 mg) was treated with an aqueous Na2CO3
solution and extracted with chloroform. The greenish soluꢀ
tion was concentrated, and darkꢀblue solid substance 13 was
obtained. 1H NMR (CDCl3), δ: 1.27 (s, 3 H, 0.5 CMe2); 1.42
(s, 3 H, 0.5 CMe2); 3.10 (s, 3 H, NMe); 5.82 (d, 1 H, CH,
J = 9.9 Hz); 6.63 (d, 1 H, CH, J = 9.9 Hz); 6.76—6.89 (m,
2 H, 2 Harom); 7.03 (d, 1 H, Harom,, J = 7.9 Hz); 7.10 (t, 1 H,
Harom, J = 7.2 Hz, J = 7.9 Hz); 7.26—7.33 (m, 2 H, 2 Harom);
7.61—7.75 (m, 1 H, Harom); 7.85—7.94 (m, 1 H, Harom).
1ꢀ(4ꢀChlorophenyl)ꢀ3ꢀphenylꢀ4ꢀ[2ꢀ(1,3,3ꢀtrimethylꢀ1,3ꢀ
dihydroꢀ2Hꢀ[1]benzothieno[3,2ꢀb]pyrrolꢀ2ꢀylidene)ethylidene]ꢀ
1Hꢀpyrazolꢀ5ꢀone (6c). The yield was 49%, m.p. 241—243 °C
(ethanol), λ
= 525 nm (acetonitrile). 1H NMR (CDCl3), δ:
1.71 (s, 6 Hm, aCxMe2); 3.89 (s, 3 H, NMe); 7.29—7.59 (m, 7 H,
7 Harom); 7.60—7.76 (m, 3 H, 3 Harom); 7.85 (d, 1 H, Harom
,
J = 7.9 Hz); 7.90—8.06 (m, 2 H, 2 Harom); 8.15 (d, 2 H, 2 Harom
,
J = 7.9 Hz). MS (EI, 70 eV), m/z (Irel (%)): 509 [M]+ (100), 494
[M – Me]+ (54), 228 (52). Found (%): C, 70.32; H, 5.01;
N, 8.42. C30H24ClN3OS. Calculated (%): C, 70.64; H, 4.74;
N, 8.24.
Methyl 2ꢀmethylꢀ4ꢀoxoꢀ5ꢀ[3ꢀ(1,2,2ꢀtrimethylꢀ1,2ꢀdihydroꢀ
3Hꢀ[1]benzothieno[3,2ꢀb]pyrrolꢀ3ꢀylidene)ethylidene]ꢀ3(4H)ꢀ
thiophenecarboxylate (11b). The yield was 49%, m.p. > 350 °C
(ethanol), λmax = 645 nm (acetonitrile). 1H NMR (DMSOꢀd6 +
CF3COOH), δ: 1.66 (s, 6 H, CMe2); 2.67 (s, 3 H, Me); 3.83—3.93
(m, 6 H, NMe + COOMe); 6.81 (d, 1 H, CH, J = 15.9 Hz);
7.46 (d, 1 H, CH, J = 15.9 Hz); 7.65 (t, 1 H, Harom, J = 7.3 Hz,
J = 7.9 Hz); 7.90 (t, 1 H, Harom, J = 7.3 Hz, J = 7.9 Hz); 8.16
(d, 1 H, Harom, J = 7.9 Hz); 8.49 (d, 1 H, Harom, J = 7.9 Hz).
13C NMR (DMSOꢀd6 + CF3COOH), δ: 17.40 (Me), 21.20
(CMe2), 31.76 (NMe), 52.02 (COOMe), 84.39 (CMe2), 111.70,
114.33, 119.22, 122.06, 124.20, 125.95, 126.80, 128.80, 132.58,
135.40, 152.38, 153.65, 158.93, 161.66, 163.64, 168.71. MS
(EI, 70 eV), m/z (Irel (%)): 411 [M]+ (61), 396 [M – Me]+ (23),
264 (100). Found (%): N, 3.38. C22H21NO3S2. Calculated (%):
N, 3.40.
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 08ꢀ03ꢀ00865).
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1ꢀ(4ꢀChlorophenyl)ꢀ3ꢀphenylꢀ4ꢀ[2ꢀ(1,2,2ꢀtrimethylꢀ1,2ꢀ
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1.56 (s, 6 Hm, CaxMe2); 3.52 (s, 3 H, NMe); 7.36 (d, 2 H, Harom
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Harom); 7.01 (d, 1 H, Harom, J = 7.9 Hz); 8.17 (d, 2 H, Harom
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Received July 16, 2008;
in revised form September 26, 2008