Highly soluble and green indigo dyes: 4,4′,7,7′-tetraalkoxy-5,5′diaminoindigotins

Article abstract of DOI:10.1002/hlca.200390156

Two new types of 4,4′,7,7′-tetraalkoxyindigotins, 1a-f and 2a-f along with the new N-substituted indigotins 4e-f, were synthesized from dinitrobenzaldehydes 5a-f, which were prepared from 2-hydroxy-5-methoxybenzaldehyde (7) via dialkoxybenzaldehydes 6a-f(

Full text of DOI:10.1002/hlca.200390156

1982
Helvetica Chimica Acta Vol. 86 (2003)
Highly Soluble and Green Indigo Dyes: 4,4',7,7'-Tetraalkoxy-5,5'-
diaminoindigotins
by Gundula Vossa)*, Michael Gradzielskib), J¸rgen Heinzec), Helmut Reinked), and Carlo Unverzagta)
a) Department of Bioorganic Chemistry, University of Bayreuth, D-95440 Bayreuth
b) Department of Physical Chemistry II, University of Bayreuth, D-95440 Bayreuth
c) Department of Physical Chemistry, University of Freiburg, D-79104 Freiburg
d) Department of Inorganic Chemistry, University of Rostock, D-18051 Rostock
Dedicated to the 70th birthday of Prof. Dr. emeritus Hans Gerlach
Two new types of 4,4',7,7'-tetraalkoxyindigotins, 1a f and 2a f along with the new N-substituted indigotins
4e f, were synthesized from dinitrobenzaldehydes 5a f, which were prepared from 2-hydroxy-5-methox-
ybenzaldehyde (7) via dialkoxybenzaldehydes 6a f (Scheme). The new dialkoxyindigotin 3g was obtained from
dialkoxybenzaldehyde 6g via nitrobenzaldehyde 8g. The 1,4-dialkoxy-2,3-dinitrobenzenes 9 were isolated as by-
products. The 4,4',7,7'-tetraalkoxy-5,5'-diaminoindigotins 1 are soluble in organic solvents, and their solutions
are green, which is highly uncommon for indigotins and is primarily caused by electronic effects of substituents,
steric effects playing a minor role. The indigotins 1 produce a strong red shift of the longest-wavelength
absorption and negative solvatochromism indicating the predominance of polar resonance structures in the
ground state. Tautomeric structures were excluded. These indigotins are valuable compounds for technical
applications, for synthetic purposes, and for analytical studies. SANS (Small-angle neutron scattering)
experiments showed that certain 4,4',7,7'-tetraalkoxy-5,5'-diaminoindigotins 1 form rod-like aggregates in
solution. The similarly substituted 4,4',7,7'-tetraalkoxy-5,5'-dinitroindigotins 2 are far less soluble. They produce
red monoanions (preferably dimers) and bluish-purple dianions in organic solvents.
1. Introduction. Indigotin (ˆ2-(1,3-dihydro-3-oxo-2H-indol-2-ylidene)-1,2-dihy-
dro-2H-indol-3-one) is the oldest known natural dye and has been used for more than
5000 years. In the last century, many derivatives have been synthesized and technically
evaluated as dyes. Today the utilization of dyestuffs is not limited to textile applications,
dyes have gained importance in completely new industries [1]. Indigo dyes have some
valuable, unique properties. However, potential applications are rather restricted by
their low solubility. The indigo chromophore limits the absorption range of VIS light to
ca. 570 645 nm [2a,b]. Thus, indigo dyes are associated with poor solubility and blue
color. These investigations probably will challenge both assumptions.
We present a new group of 4,4',7,7'-tetraalkoxy-5,5'-diaminoindigotins 1 (Scheme, a)
that are highly soluble in organic solvents and of green color in solution. Previous
attempts to increase the solubility of indigotins took advantage of steric effects by bulky
substituents [3a,b]. In contrast, the solubility of indigotins 1 is preferentially enhanced
by electronic effects of the substituents in the 5,5'- and 7,7'-positions. Steric effects of
the alkoxy groups in the 4,4'- and 7,7'-positions (as would be expected) contribute only
little to the increased solubility. The uncommon properties of 1 draw parallels to those
of 5,5'-bis(dimethylamino)indigotin [4], which is described as well-soluble in CHCl3,
acetone, benzene, nitrobenzene, and AcOEt with a green color.

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The high solubility of the indigotins 1 allows the utilization of valuable indigo-
inherent properties. For example, oxidation to yellow isatines was used for sensitive and
selective detection of ozone in gaseous mixtures [5]. Similarly to natural N-
glycosylated 5,5'-dichloroindigotins (akashines A, B, and C) [6], derivatives of 1 are
active against human-tumor cell lines [7]. Further research is in progress to obtain
H2O-soluble indigotins. Uncommon for indigotins, spectroscopic investigations even in
nonpolar solvents could be performed. Differently colored anions recommend 5,5'-
dinitroindigotins 2 as indicator dyes in dipolar aprotic solvents. The 1,4-dialkoxy-2,3-
dinitrobenzenes 9, obtained as by-products, have been used in preparing liquid-crystal
mixtures [8a,b]. Compounds of type 1, 2, and 4 have not been described previously.
Only 4,4',7,7'-tetramethoxyindigotin [9][10] and 4,4',7,7'-tetrabutoxyindigotin [10] of
type 3 have been reported.
2. Results and Discussion. 2.1. Syntheses. The 5,5'-diaminoindigotins 1a f were
prepared by reaction of 5,5'-dinitroindigotins 2a f with sodium dithionite [11]
(Scheme,b). The primarily formed leuco compounds of the dinitroindigotins 2a f are
not stable [12]. They were transformed immediately into the leuco forms of
diaminoindigotins 1a f (pale gray precipitates), which were converted into indigotins
1a f by exposure to air oxygen. The 5,5'-dinitroindigotins 2a f and indigotin 3g were
synthesized from 3,6-dinitrobenzaldehydes 5a f and 2-nitrobenzaldehyde 8g, respec-
tively, by reaction with KOH in acetone/H2O [13a,b]. The nitrobenzaldehydes 5a f
and 8g were accessible from dialkoxybenzaldehydes 6a g by nitration with 65% HNO3
solution at elevated temperatures [14]. As by-products, 1,4-dialkoxy-2,3-dinitroben-
zenes 9 were formed. Above an optimum temperature of 35 458, the yield of
dinitrobenzaldehydes 5 decreased in favor of these deformylated compounds 9.
Generally, reaction at lower temperatures gives rise to mononitration yielding
nitrobenzaldehydes of type 8 [9][15]. However, increasing length of the 2-alkoxychain
of 6 favored products of type 8 even at elevated temperatures. Thus, nitration of 2-
(nonyloxy)benzaldehyde 6g at 458 gave 2-nitro-6-(nonyloxy)benzaldehyde 8g. The
dialkoxybenzaldehydes 6a g were prepared by alkylation of 2-hydroxy-5-methoxy-
benzaldehyde (7) [16] which was accessible by formylation of commercially available 4-
methoxyphenol [17]. Traces of 4,4',7,7'-tetraalkoxy-5-nitroindigotins, 4,4',7,7'-tetraal-
koxy-5-aminoindigotins, and of substituted indirubins were isolated in the reactions
leading to 2 and 1, respectively.
Both 2-nitrobenzaldehydes 8 and 3-nitrobenzaldehydes 10 are primary nitration
products of dialkoxybenzaldehydes 6 [9][15]. Surprisingly, not the 2-nitrobenzalde-
hydes 8 (main products), but the 3-nitrobenzaldehydes 10 (minor products) are
precursors of the dinitrobenzaldehydes 5 (Scheme,c). This was concluded from
reactions reported: nitration of 2,5-dimethoxy-3-nitrobenzaldehyde (type 10) yielded
2,5-dimethoxy-3,6-dinitrobenzaldehyde (type 5) [18], whereas further nitration of 3,6-
dimethoxy-2-nitrobenzaldehyde (type 8) gave 2,3-dinitro-1,4-dimethoxybenzene (type
9) [19]. The structure of 2,5-dialkoxy-3,6-dinitrobenzaldehydes 5a f was established
by an X-ray crystal-structure determination of the 2-(heptyloxy) derivative 5f (Fig. 1).
The 5,5'-positions of the amino groups in indigotins 1 were verified by H,C HMBC
(heteronuclear multiple-bond correlation) experiments of the 4,4'-bis(hexyloxy)
derivative 1e.

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Scheme
a) New indigotins 1 4. b) Synthesis of indigotins 1 4. c) Synthesis of 3,6-dinitrobenzaldehydes 5 and of 2-
nitrobenzaldehydes 8 (precursors of 2 and 3).
The reaction sequence 6 ! 10 (not 8) ! 5 ! 2 explains a) the absence of any
isomeric 4,4',7,7'-tetraalkoxy-6,6'-dinitroindigotins and b) the low yield of 2 with
respect to 6 (7 15%, two steps). The reactions can be scaled up without problems
because column chromatography was avoided. Probably, the synthesis of 2 could be
improved by use of independently synthesized 2,5-dialkoxy-3-nitrobenzaldehydes 10.

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1985
Fig. 1. ORTEP Representation of 2-(heptyloxy)-5-methoxy-3,6-dinitrobenzaldehyde (5f)
Compounds 10 should be accessible from 7 in two steps analogously to 2,5-dimethoxy-
3-nitrobenzaldehyde [18].
The 4,4',7,7'-tetraalkoxy-5,5'-dinitro-1-pentylindigotins 4e,f were prepared by
alkylation of dinitroindigotins 2e,f with 1-bromopentane in DMSO in the presence of
KOH/H2O. They were isolated as mixtures with some starting material 2e,f. The
reactions were not optimized; their objective was preferentially the characterization of
the anions of 2. No traces of N,N'-dialkylated 4,4',7,7'-tetraalkoxy-5,5'-dinitroindigotins
were found. Kuhn and Trischmann have described the N,N'-dimethylation of indigotin
in DMF/H2O with BaO as base [20]. Both N-monoalkylation and N,N'-dialkylation are
reported for pyrrol-indigotin [21a,b].
2.2. Properties of Indigotins 1 4. Solubility and Color. The 4,4',7,7'-tetraalkoxy-5,5-
diaminoindigotins 1a f display highly unusual properties for indigo dyes. They are well
soluble in organic solvents such as CHCl3 (Fig. 2), acetone, DMF, and DMSO, yielding
green solutions. The indigotins 1 dye cotton green by means of these solutions, no
reduced form (leuco form) is required for dyeing. As solids, they are dark blue (lmax
745 nm, KBr). The solubility of 1a c1) (ca. 30 mg/ml CHCl3) surpasses the solubility
of indigo derivatives described (see [3a,b] for examples) and of dinitroindigotins 2a f
by far. The steric effects of the alkoxy substituents in the 4,4',7,7'-positions contribute to
the enhanced solubility only to a minor degree, as established by direct comparison
with the similarly substituted 4,4',7,7'-tetraalkoxy-5,5'-dinitroindigotins 2a f.
Surprisingly, the green color provides the key to understanding the increased
solubility of indigotins 1 and of 5,5'-bis(dimethylamino)indigotin. All of them carry
strong electron-donating groups in the 5,5'-positions, and 1 additionally in the 7,7'-
positions. These substituents polarize the p-electron system to such a degree that polar
resonance structures dominate in the ground-state (Fig. 3) and less-polar resonance
structures in the first exited state. The polar structure of 1 causes the strong red shift of
the longest-wavelength absorption (lmax 736 nm in CHCl3, see Fig. 4) and negative
1
)
The indigations 1d f with longer 4,4'-dialkoxy chains are still more soluble due to formation of rod-like
aggregates; uncertainties of measured values are possible due to increased viscosity of some solutions.

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Fig. 2. Solubility of 5,5'-diaminoindigotins 1a f in CHCl3 (208)
solvatochromism (lmax 715 nm in MeOH; 703 nm in acetone). It lowers the indigo-
typical intermolecular interactions resulting in enhanced solubility and decreased
melting points. Protonation of 1 results in blue salts in which the indigo chromophore is
re-established (1e, hydrochloride: lmax 648 nm in MeOH). Blue salts are reported for
5,5'-bis(dimethylamino)indigotin too [4].
Fig. 3. Representation of the polar ground state of 5,5'-diaminoindigotins 1
The green color is rare among indigo dyes. The anions of indigotin [21b][22], the
anions of indigo-5,5'-disulfonic acid [21b][22][23], and anionic metal complexes of
substituted indigotins [22][24a,b] exhibit green solutions (lmax ꢀ 700 nm); the anions of
5,5'-dinitroindigotins 2 absorb light of similar frequencies. The bathochromic absorp-
tion of these compounds was explained by an increased electron-donating ability of the
deprotonated N-atom of the anions and by an increased electron-donating ability of the
negatively charged indoxylate (ˆ1H-indol-3-olate) unit of the anionic metal com-
plexes, respectively [21b][22]. Obviously, strong electron-donating substituents in the
5,5'- and 7,7'-positions of indigotin have a similar effect. Other reasons for the red shift
of the longest-wavelenth absorption2) of diaminoindigotins 1 could be excluded. Both
2
)
For instance, lacking planarity [25][26], intermolecular H-bonding [27][28], or formation of dimers [29].

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Fig. 4. UV/VIS spectra of indigotins 1e, 2e, and 3g in CHCl3
lacking planarity and intermolecular H-bonding could be ruled out by the structural
similarity of 1 with the 4,4',7,7'-tetraalkoxy-5,5'-dinitroindigotins 2, which show
properties typical for indigotins. LambertÀBeer×s law was found to be obeyed for 1
in a concentration range of 5 ¥ 10À4 to 5 ¥ 10À7 m (in CHCl3), excluding absorption
changes by aggregation.
The 4,4',7,7'-tetraalkoxy-5,5'-dinitroindigotins 2a f and 4,4',7,7'-tetraalkoxyindigo-
tin 3g are blue as solids and in solvents such as chlorinated hydrocarbons, alkanols, and
acetone. Compounds 2a f show a strong bathochromic shift of the longest-wavelength
absorption (lmax 622 nm in CHCl3) in comparison to red 5,5'-dinitroindigotin [25]. This
indicates a considerable contribution of ionic structures to the resonance system3). The
solubility of 4,4',7,7'-tetraalkoxyindigotins 2a f (ꢁ2 mg/ml of CHCl3) is enhanced as
expected by steric effects of the alkoxy groups in the 4,4'- and 7,7'-positions. The
bathochromic absorption of tetraalkoxyindigotin 3g (lmax 645 nm in CHCl3) is
preferentially due to the electron-donating effect of the MeO groups in the 7,7'-
positions. The solubility of 3g is remarkably high (ca. 40 mg/ml of CHCl3).
The N-monoalkylated indigotins 4e,f are well-soluble in CHCl3 and less-soluble in
DMSO and DMF. As a representative for N-pentylindigotins 4e,f, the bis(heptyloxy)
derivative 4f was characterized spectroscopically. The electronic spectrum of 4f shows
a red shift of the longest-wavelength absorption as expected [26].
1
NMR Spectra. The number of H-NMR signals of indigotins 1 3 and of 13C-NMR
signals of 1 and 3 is reduced by half caused by their symmetric structure. The 1H-NMR
spectra of 1 display significantly broadened NH resonances. Tautomeric structures of 1
1
were excluded by a distinct H,15N-coupling. Compounds 2a f and 3g show sharper
NH signals. The 15N-NMR resonance of 3g appears at À210 ppm, the 1H,15N-coupling
is similar to that of 1e (J ˆ 102.0 Æ 0.5 Hz). The 1H-NMR spectrum of 4f exhibits the
entire number of expected signals.
IR Spectra. The alkoxy substituents in the 4,4'- and 7,7'-positions of indigotins 1 4
prevent intermolecular H-bonding as confirmed by the high-wavenumber NH
3
)
For effects of substituents on color of indigotins, see [30].

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absorption (nÄ (NH) ꢀ 3400 cmÀ1). Under this assumption, the carbonyl absorption
allows conclusions regarding the electronic effects of the substituents in the 5,5'-
positions. A low-wavenumber absorption (nÄ (CO) 1620 1630 cmÀ1) verifies the
presence of polarized mesomeric structures with partial CÀO single bonds (1 and 2).
The indigotins 3g, 4f, and the hydrochloride of 1e exhibit CO absorptions at ca.
1640 cmÀ1 [25][31]. For the 5,5'-diaminoindigotins 1, two additional NÀH absorptions
must be taken into consideration (nÄs (NH2) and nÄas (NH2). Highly uncommon for
indigotins, the IR spectra of 1 could be measured in CCl4 solutions. As expected, they
show three weak but distinct bands in the range of 3375 to 3460 cmÀ1.
Mass Spectra. All new compounds were characterized by low-resolution MS. The
molecular compositions were confirmed by high-resolution MS of the molecular-ion
‡
peaks M . Representative for diaminoindigotins 1a f and dinitroindigotins 2a f,
typical fragment ions of the propoxy derivatives 1b and 2b were analyzed by high-
resolution MS (see Exper. Part).
Anions of Dinitroindigotins 2. The blue color of solutions of 5,5'-dinitroindigotins 2
in common organic solvents changes to red by addition of bases (e.g., KOH/H2O or
NaOMe/MeOH); deprotonation yields red monoanions. However, dissolving of 2 in
dipolar aprotic solvents such as DMSO or DMF also results in red −solutions×, but in the
absence of classical bases. Color and electronic spectra of these −solutions× are similar to
those of the monoanions of 2 created by classical bases in other solvents (lmax ca.
785 nm), i.e., dipolar aprotic solvents are able by themselves to abstract an NH proton
of dinitroindigos 2.
The red monoanions of 2 preferably exist as dimers: the electronic spectrum of the
anion of 2c develops a new maximum at 710 nm in addition to the original absorption
at 785 nm upon dilution up to concentrations of < 10À6 m (in DMSO). Since the
spectral evolution shows isosbestic points, it is likely a conversion of dimers to
monomers (Fig. 5). The UV spectrum of pure monomer 2cÀ could be taken of a diluted
sample only after several hours. Obviously, additional processes play a role in the
process of de-aggregation (e.g., kinetic effects or solvatation).
The addition of strong bases (KOH/H2O or NaH) to the red monoanions of 5,5'-
dinitroindigotins 2 in dipolar aprotic solvents changes the color again, now to bluish-
purple (dianions of 2, lmax ca. 810 nm). Both color changes are reversible. The bluish-
purple solutions of the dianions turn red again by addition of protic acids. An excess of
acid gives turquoise-blue solutions, i.e., the color of neutral indigotins 2 in acidified
dipolar aprotic solvents (see Fig. 6 and Fig. 7,a and b)4).
The anions of 2 were characterized by 1H-NMR spectra5) as saturated solutions in
(D6)DMSO. The monoanion of the 4,4'-dipropoxyindigotin 2b shows the whole
number of sharp signals and only one proton attached to an N-atom (Fig. 8,a).
However, the monoanions of the higher homologues 2c f exhibit only half the number
of broader signals. It could be shown that the signal reduction is caused by aggregation:
4
)
For 4,4',7,7'-tetramethoxy-5,5'-dinitroindigotin (simplified equivalent of 2), absorption maxima were
predicted by PPP calculations in vacuum (l, strength of oscillation): 4,4',7,7'-tetramethoxy-5,5'-
dinitroindigotin, 449 nm (0.68); 4,4',7,7'-tetramethoxy-5,5'-dinitroindigotin monoanion, 559 (0.66) and
403 nm (0.27); 4,4',7,7'-tetramethoxy-5,5'-dinitroindigotin dianion, 479 (1.18) and 409 nm (0.42).
The solubilities of 2aÀ, 2a2À, and 2b2À were too low for measuring 1H-NMR spectra.
5
)

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Fig. 5. UV/VIS Spectra in DMSO: dissociation of dimer 2cÀ into monomer 2cÀ by dilution. Arrows indicate
associated spectral changes.
Fig. 6. Colors of 2c (blue in CHCl3), of 2cÀ (red dimer in DMSO), and of 2c2À (bluish-purple in DMSO/H2O/
KOH)
At ca. 100-fold dilution, the monoanion of 4,4'-dibutoxyindigotin 2c exhibits a
spectrum similar to that of 2bÀ with the whole number of expected signals (Fig. 8,b).
This confirms the result of dilution experiments of the monoanion of 2c (dimer!
monomer, in DMSO) which were followed by electronic spectra (see Fig. 5). 1H-NMR
Spectra of the dianions of 2c f exhibit the expected reduction of signals.

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Fig. 7. UV/VIS spectra of 2cÀ (red dimer in DMSO): a) Gradual addition of AcOH/H2O gives neutral blue 2c
(arrows indicate change of spectra with increasing acidity); b) gradual addition of KOH/H2O gives bluish-purple
2c2À (arrows indicate change of spectra with decreasing acidity).
The monoanions of 2 are comparatively stable in DMF or DMSO (as dimers).
Highly diluted solutions (ꢁ10À5 m) show changes of the electronic spectra due to
dissociation after several hours (see Fig. 5). The solutions of the dianions of 2 are less
stable, they exhibit color change to yellow.
It is reported that dipolar aprotic solvents may dissociate protons [32a c], they
solvate preferentially large planar anions [32a,b]. These properties explain the ability
of DMSO or DMF to abstract an NH proton of 5,5'-dinitroindigotins 2. Other
examples are −neutral× haloform reactions in DMSO or DMF [33], and the

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Fig. 8. 1H-NMR Spectrum of a) monomer 2bÀ in (D6)DMSO and b) of monomer 2cÀ (top) and of dimer 2cÀ
(bottom) in (D6)DMSO

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deprotonation of Methylene azure B (protonated trimethylthionine) by HMPA6)
[34a,b]. Similarly to the indigotins 2, indigo-5,5'-disulfonic acid disodium salt (Indigo
Carmine) shows a color change at pH 11 13 due to deprotonation [23]. Indigo
Carmine is commercially used as acid-base indicator dye in aqueous solutions.
2.3. Electrochemistry of Indigotins 2. The electrochemistry of indigotin and its
derivatives is not well-understood. The only certainty is that unsubstituted indigo
undergoes a one-electron reduction forming a radical anion. However, already the next
tip is unclear. Voltammetric data reveal that a dianion is formed [35]. But the height of
the second reduction wave is considerably smaller than that of the first redox step,
indicating some reversible follow-up process such as aggregation after the first charge
transfer.
The electrochemistry of the newly synthesized indigotins 2 resembles that of indigo.
Thus, 2c can be reduced in CH2Cl2 (blue solution) at a potential of À 0.625 V to its
radical anion. The process is chemically reversible (Fig. 9). A second reductive
electron-transfer step occurs at a potential of À 1.12 V, showing the formation of a
dianionic species, and a third redox step is observed in the reverse sweep at a potential
of À 0.8 V. The decreasing heights of the reduction waves during the successive
reduction steps give evidence that, between these different redox states, reversible
dimerization or aggregation must take place. Cyclic voltammetry also shows that the
indigotins can be oxidized to their monocations at potentials of ca. 1.2 V. Again, these
redox reactions are chemically reversible.
Fig. 9. Cyclic voltammograms of 2c in CH2Cl2 and of 2cÀ in DMF (containing 0.1m (Bu4N)PF6)
6
)
The blue dye Methylene azure B instantaneously turns pink when treated with HMPA (hexamethylpho-
sphoric triamide), i.e., to the color of the free base; the pink solution changes to blue again by addition of
an acid.

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A drastic change of the cyclic voltammetric response occurs when the electro-
chemical experiments are carried out in DMF (red solution, 2cÀ). The first small wave
at a peak potential of À 0.540 V indicates a chemical reaction preceding the first redox
step (Fig. 9). Subsequently, the system can be reduced within three additional redox
steps to a tetraanion (E02 ˆ À0.950 V, E30 ˆ À1.3 V, E04 ˆ À1.750 V). This very complex
behavior will be analyzed in the future.
2.4. Small Angle Neutron Scattering (SANS) Experiments of Indigotins 1. To obtain
further information regarding the solution structure of the indigo derivatives, small-
angle neutron-scattering (SANS) experiments were performed. SANS Spectra were
taken at 258 from saturated solutions in (D6)acetone of 1d f. The obtained SANS
spectra are shown in Fig. 10, where the scattering intensity is given as a function of the
magnitude q of the scattering vector.
Fig. 10. SANS Spectra of indigotins 1d f in (D6)acetone
For the compounds with short alkyl chains, basically flat SANS spectra are
observed, indicating that here only an unstructured molecular solution is present.
However, the scattering pattern changes significantly for the compounds with longer
alkoxy chains, which also possess a much higher solubility. Here, a marked increase in
scattering intensity is observed for the lower q-range, which indicates that, in these
solutions, larger particles must be present.
The shape of the increase of the scattering curves can be well-described by rod-like
aggregates. Fitting a model of rods to the solutions of compound 1e and 1f in acetone
yields a radius of 12.7 and 13.6 ä, respectively. These values are in good agreement
with the molecular dimension of the compounds, i.e., they correspond to half the
longest dimension of the molecules. Therefore, the analysis of the scattering pattern
indicates that, in these solutions, rod-like aggregates are present where the individual

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molecules are stacked on top of each other, and where the diameter of these rod-like
aggregates is simply given by the length of the molecule.
A more-detailed description of the present particles may be obtained if one
assumes an isodesmic model for the aggregation of the dye molecules, i.e., a model
where the equilibrium constants Kn for the association process are equal (as it is to be
expected for such an aggregation process of dye molecules; K ˆ xn/(x1xnÀ1)). Here xn
and x1 are the mole fractions of the n-mer and the monomer, respectively. With such a
model, one obtains the number distribution Nl ˆ (Kx1)l/LÀ1 for the length of aggregates,
where L is the effective thickness of one dye molecule in the aggregate, i.e., its effective
extension along the rod axis. With such a model, the absolute intensities are well
accounted for, and they yield a good fit to the experimental data with the same radii of
12.7 and 13.6 ä mentioned above.
In conclusion, one can state that the SANS experiments rationalize the increase of
solubility with increasing length of the alkyl chain. Evidently, for the longer-chain
compounds, aggregation in solvents such as (D6)acetone takes place. This aggregate
formation is responsible for a significant increase in solubility to a much higher value
than the monomer solubility. In an analogous way, micelle formation increases the
solubility of amphiphiles [36]. Presumably, the driving force for aggregation is the
ability of the longer alkyl chains to interact more favorably with the solvent. There is
less interaction in the solid state of the pure compound. At the same time, alkoxy chains
present a steric hindrance for edge-to-edge association. Therefore, only aggregates of
stacked single dye molecules are observed.
3. Conclusions. The new 4,4',7,7'-tetraalkoxy-5,5'-diaminoindigotins 1 are highly
soluble in organic solvents, and their solutions are green a combination of properties
remarkable for indigotins. Both properties are primarily caused by the electron-
donating groups in the 5,5'- and 7,7'-positions; steric effects of the substituents in the
4,4'- and 7,7'-positions play a minor role. A strong red shift of the longest-wavelength
absorption and negative solvatochromism indicate a predominance of polar resonance
structures in the ground state; tautomeric structures were excluded. SANS Experi-
ments showed that homologues with long alkoxy chains in the 4,4'-positions form rod-
like aggregates of molecular diameter in (D6)acetone. The high solubility of 1 is
important for technical applications, for spectroscopic investigations in solution, and
for synthetic purposes (e.g., for the preparation of biologically active substances). The
5,5'-diaminoindigotins 1 were compared to similarly substituted 5,5'-dinitroindigotins 2
which are blue and by far less soluble. They form red monoanions and bluish-purple
dianions in some organic solvents. Alkylation yields N-monosubstituted indigotins 4.
This paper would not have been possible without the preparative work done by several student classes of
future chemistry teachers (University of Bayreuth, 1999 2001). Moreover, the authors are grateful to M.
Blomenhofer, B. Burghardt, I. Immig, Dr. W. L¸ttke, Dr. G. Ludwar-Ene, Dr. P. Morys, Dr. G. Platz, and Dr. B.
Wrackmeyer.

Helvetica Chimica Acta Vol. 86 (2003)
1995
Experimental Part
General. All solvents were distilled before use. Column filtration: Merck silica gel 60 (0.04 0.063 mm).
TLC: Merck silica gel 60 F254 (precoated silica gel plates). Solubility: determined by evaporation of sat. solns. at
208. M.p.: B¸chi 510, uncorrected. Differential scanning calorimetry (DSC): Netzsch DSC 200, heating rate 108/
min (in parentheses temp. of phase change). GC: Carlo-Erba Fractovap 41060 with FID, CS-FS-OV-1-CB-0.5
column (0.32 mm  25 m), 120 2508, 58/min, carrier gas H2, 0.3 kg/cm2; tR in min.
UV/VIS: lmax in nm, e in mÀ1 cmÀ1; Specord 200 (Analytik Jena AG); 1 ¥ 10À5 m to 5 ¥ 10À5 m solns. if not
mentioned otherwise; calc. electronic spectra by semi-empirical PM3 calculations in vacuum (Hyper-Chem 5.01,
HyperCube). IR Spectra: in cmÀ1; Perkin-Elmer Paragon 1000 FT. NMR Spectra: d in ppm, J in Hz; Jeol. JNM-
EX 270 (1H 270 MHz, 13C 67.9 MHz), Bruker AM 360 (1H 360 MHz, 13C 90.6 MHz), Bruker DRX 500 (1H
500 MHz, 15N 50.7 MHz); d(H) and d(C) rel. to SiMe4 and d(N) rel. to MeNO2; for (non-systematic) atom
numbering, see Scheme 1,a. EI-MS: in m/z (rel. %); Varian MAT 312 at 70 eV. SANS Spectra: Paxe instrument,
¬
Laboratoire Leon Brillouin, Saclay, France; at 258 with sat. solns. in (D6)acetone; the wavelength l chosen was
6 ä, and the sample-detector distances were 1.07 m and 3.87 m, respectively, thereby covering an effective q
range of 0.011 to 0.34 äÀ1, where q is the magnitude of the scattering vector q, as defined by q ˆ 4 p lÀ1 sinq/2
(l: wavelength; q: scattering angle).
General Procedure A (GP A). Under vigorous stiring, ca. 1.8 equiv. of 1-bromoalkane (or 1-iodoalkane)
was added within 10 min at r.t. to a suspension of 1.0 equiv. of 7 [17] and 1.8 equiv. of K2CO3 in EtOH (ca. 1.2 ml/
mmol of 7). The mixture was heated to reflux for 16 h. After cooling, the mixture was filtered and the solid
carefully washed with EtOH. The filtrate was evaporated and the residue dissolved in toluene/Et2O 1:4 and
extracted twice with 1m KOH. The aq. phases were re-extracted with toluene/Et2O 1:4. The combined org.
phase was dried (Na2SO4) and evaporated, and the crude product was purified by destillation in vacuo: 6a
g
(75 86% ).
General Procedure B (GP B). Under vigorous stirring, 6a g was added dropwise without external cooling
to 65% HNO3 soln. (d ˆ 1.41; ca. 2.7 ml/mmol of 6) within ca. 1.5 h at 35 458. After stirring for additional 4 h at
r.t., the mixture was poured into ice water (ca. 20 g/mmol of 6). The resulting yellow precipitate was filtered off,
washed with H2O until neutral, and then dissolved in toluene/Et2O 1 :4. The soln. was extracted with H2O until
neutral, dried (Na2SO4), and evaporated. The residue was filtered over a ca. 40-fold amount of silica gel with
toluene/AcOEt 19 :1 to give 5a f or 8g (impure; < 48% yield), which was used in the next step without further
purification. For analysis, a sample was purified by crystallization. Compounds 9 were isolated from polar
fractions and purified by crystallization.
General Procedure C (GP C). A soln. of 5a f or 8g (from 6a g) in acetone at r.t. (ca. 15 ml/g of impure 5
or 8) was cooled to À108, and 0.2m KOH (ca. 2 ml/g of 5 or 8) was added dropwise within 10 min under vigorous
stirring. After 15 min, 0.4m KOH (ca. 15 ml/g of crude 5 or 8) was added at 58 within 20 min under stirring. The
resulting dark-colored suspension was stirred at r.t. for additional 16 h and then centrifuged (30 min;
10000 rpm). The precipitate was washed several times with H2O (until neutral and almost colorless), EtOH, and
Et2O, and air-dried: 7 15% (rel. to 6a f) of 2a f; 24% (rel. to 6g) of 3g.
Monoanions of 2. Dissolution of 2 in DMF or DMSO gave red solns. of monoanions, preferentially dimers.
Monoanions 2bÀ and 2cÀ were also characterized as monomers (1H-NMR in (D6)DMSO) and 2cÀ (UV/VIS in
DMSO).
Dianions of 2. Addition of 2m KOH (ca.1% (w/w) to solns. of monoanions of 2 in DMF or DMSO gave
bluish-purple solns. of dianions.
General Procedure D (GP D). To a stirred suspension of powdered 2 in 1m NaOH (ca. 40 ml/mmol of 2),
Na2S2O4 (85%; ꢁ10 mmol/mmol of 2) was added at 508. The mixture was heated, and suddenly the dark blue
solid was converted into a gray precipitate (at ca. 808). After 10 min stirring, the hot suspension was filtrated; on
contact with air, the color of the precipitate changed to blue. After careful washing (H2O and some EtOH), the
solid was dissolved in CHCl3, the soln. filtered through a pad of silica gel rinsing with CHCl3, and the filtrate
evaporated: dark-colored 1 (79% 88%7).
General Procedure E (GP E). To a soln. of ca. 1 2 mg of 2 in 1.0 ml of DMSO containing two drops of 2n
KOH, two drops of 1-bromopentane were added (color change from bluish-purple to green). After ca. 4 h, the
resulting dark-colored precipitate of 4 (1-2 mg, containing some 2) was filtered off, washed with EtOH, and air-
dried. The reaction was not optimized.
7
)
The yield of 1a (11%) is not representative.

1996
Helvetica Chimica Acta Vol. 86 (2003)
2-Ethoxy-5-methoxybenzaldehyde (6a). According to GP A, with 7 (26.05 g, 171 mmol), iodoethane
(24.6 ml, 48.0 g, 308 mmol), K2CO3 (42.5 g, 308 mmol), and EtOH (180 ml): 23.2 g (75%) of 6a. Yellow oil,
which solidified to pale yellow crystals. B.p. 76 818/0.05 Torr ([35]: 508/0.05 Torr). M.p. 47.6 49.58 ([37]: 548).
Rf (toluene/AcOEt 19 :1) 0.46. GC: tR 9.8. IR (CCl4): 3077, 3046, 3001, 2985, 2941, 2908, 2865, 2760, 1687 (CO),
1613, 1587, 1495, 1476, 1423, 1390, 1277, 1220, 1160, 1047. 1H-NMR (270 MHz, (D6)DMSO): 1.36 (t, 3J ˆ 7.0,
3
4
3
MeCH2O); 3.75 (s, MeO); 4.13 (t, J ˆ 6.9, MeCH2O); 7.16 (d, J ˆ 3.1, HÀC(6)); 7.18 (d, J ˆ 8.2, HÀC(3));
7.25 (dd, 3J ˆ 8.2 Hz, 4J ˆ 3.1, HÀC(4)); 10.35 (s, CHO). 13C-NMR (67.9 MHz, (D6)DMSO): 15.0 (q,
MeCH2O); 56.0 (q, MeO); 65.2 (t, MeCH2O); 110.5 (d, C(3)); 116.0 (d, C(6)); 123.6 (d, C(4)); 125.1 (s, C(1));
‡
‡
153.6 (s, C(2)); 156.1 (s, C(5)); 189.4 (d, CHO). EI-MS: 180 (95, M ), 152 (79, [M À C2H4] ), 151 (75, [M À
‡
‡
‡
C2H5] ), 137 (100). HR-MS: 180.0786 (M , C10H12O3 ; calc. 180.0786).
5-Methoxy-2-propoxybenzaldehyde (6b). According to GP A, with 7 (24.0 g, 158 mmol), 1-bromopropane
(26.4 ml, 35.7 g, 290 mmol), K2CO3 (40.2 g, 291 mmol), and EtOH (176 ml): 25.1 g (82%) of 6b. Pale yellow oil.
B.p. 86 908/0.05 Torr. Rf (toluene/AcOEt 19 :1) 0.49. GC: tR 12.2. IR (CCl4): 3077, 3047, 3005, 2968, 2940, 2878,
2758, 1687 (CO), 1613, 1588, 1494, 1467, 1423, 1388, 1277, 1220, 1159, 1042. 1H-NMR (270 MHz, (D6)DMSO):
1.00 (t, 3J ˆ 7.0, MeCH2CH2O); 1.77 (sext., 3J ˆ 7.0, MeCH2CH2O); 3.75 (s, MeO); 4.04 (t, 3J ˆ 6.5,
MeCH2CH2O); 7.16 (d, 4J ˆ 3.0, HÀC(6)); 7.18 (d, 3J ˆ 9.0, HÀC(3)); 7.25 (dd, 3J ˆ 9.0, 4J ˆ 3.0, HÀC(4));
10.37 (s, CHO). 13C-NMR (67.9 MHz, (D6)DMSO): 10.7 (q, Me(3')); 22.6 (t, C(2')), 55.8 (q, MeO), 70.7 (t,
C(1')); 110.4 (d, C(3)); 115.4 (d, C(6)); 123.3 (d, C(4)); 125.1 (s, C(1)); 153.6 (s, C(2)); 156.2 (s, C(5)); 189.0 (d,
‡
‡
‡
‡
CHO). EI-MS: 194 (78, M ), 152 (100, [M À C3H6] ), 137 (78). HR-MS: 194.0941 (M , C11H14O3 ; calc.
194.0942).
2-Butoxy-5-methoxybenzaldehyde (6c). According to GP A, with 7 (23.4 g, 153 mmol), 1-bromobutane
(27.9 ml, 35.6 g, 260 mmol), and K2CO3 (35.9 g, 260 mmol), and EtOH (185 ml): 27.1 g (86%) of 6c. Pale yellow
oil. B.p. 92 988/0.03 Torr. Rf (toluene/AcOEt 19 :1) 0.50. GC: tR 14.6. IR (CCl4): 3078, 3042, 3002, 2962, 2937,
2914, 2874, 2758, 1686 (CO), 1614, 1588, 1495, 1466, 1423, 1388, 1276, 1219, 1160, 1043. 1H-NMR (270 MHz,
(D6)DMSO): 0.93 (t, 3J ˆ 7.0, Me(4')); 1.45 (sext., 3J ˆ 7.0, CH2(3')); 1.74 (quint., 3J ˆ 7.0, CH2(2')); 3.75 (s,
MeO); 4.08 (t, 3J ˆ 6.5, CH2(1')); 7.16 (d, 4J ˆ 3.0, HÀC(6)); 7.18 (d, 3J ˆ 9.0, HÀC(3)); 7.25 (dd, 3J ˆ 9.0, 4J ˆ
3.0, HÀC(4)); 10.35 (s, CHO). 13C-NMR (67.9 MHz, (D6)DMSO): 14.1 (q, Me(4')); 19.3 (t, C(3')); 31.2 (t,
C(2')); 56.0 (q, MeO); 69.1 (t, C(3')); 110.5 (d, C(3)); 115.9 (d, C(6)); 123.6 (d, C(4)); 125.1 (s, C(1)); 153.6 (s,
‡
‡
C(2)); 156.2 (s, C(5)); 189.2 (d, CHO). EI-MS: 208 (20, M ), 152 (100, [M À C4H8] ), 137 (22). HR-MS:
‡
‡
208.1099 (M , C12H16O3 ; calc. 208.1099).
5-Methoxy-2-(pentyloxy)benzaldehyde (6d). According to GP A, with 7 (19.1 g, 126 mmol), 1-bromopen-
tane (28.1 ml, 34.2 g, 226 mmol), K2CO3 (31.2 g, 226 mmol), and EtOH (159 ml): 21.2 g (76%) of 6d. Pale
yellow oil. B.p. 114 1178/0.05 Torr. Rf (toluene/AcOEt 19 :1) 0.51. GC: tR 17.1. IR (CCl4): 3080, 3048, 3003, 2959,
2938, 2863, 2758, 1687 (CO), 1613, 1588, 1495, 1467, 1423, 1388, 1276, 1220, 1160, 1042. 1H-NMR (270 MHz,
(D6)DMSO): 0.85 (t, 3J ˆ 7.0, Me(5')); 1.22 1.46 (CH2(3'), CH2(4')); 1.70 (quint., 3J ˆ 6.5, CH2(2')), 3.72 (s,
MeO), 3.99 (t, 3J ˆ 6.5, CH2(1')), 7.12 (d, 3J ˆ 9.0, HÀC(3)); 7.13 (d, 4J ˆ 3.0, HÀC(6)); 7.18 (dd, 3J ˆ 9.0, 4J ˆ
3.0, HÀC(4)); 10.33 (s, CHO). 13C-NMR (67.9 MHz, (D6)DMSO): 14.3 (q, Me(5')), 22.4 (t, C(4')), 28.2 (t,
C(3')); 28.9 (t, C(2')); 55.9 (q, MeO), 69.3 (t, C(1')); 110.4 (d, C(3)); 115.7 (d, C(6)); 123.5 (d, C(4)); 125.0 (s,
‡
‡
C(1)); 153.6 (s, C(2)); 156.3 (s, C(5)); 189.1 (d, CHO). EI-MS: 222 (52, M ), 152 (100, [M À C5H10] ), 137 (58).
‡
‡
HR-MS: 222.1254 (M , C13H18O3 ; calc. 222.1255).
2-(Hexyloxy)-5-methoxybenzaldehyde (6e). According to GP A, with 7 (16.3 g, 107 mmol), 1-bromohex-
ane (27.8 ml, 32.7 g, 198 mmol), K2CO3 (27.3 g, 198 mmol), and EtOH (136 ml): 21.7 g (86%) of 6e. Yellow oil
which solidified to a pale yellow solid. B.p. 123 1258/0.04 Torr. M.p. 25.5 26.68. Rf (toluene/AcOEt 19 :1) 0.52.
GC: tR 19.4. IR (CCl4): 3077, 3051, 3004, 2958, 2935, 2862, 2758, 1686 (CO), 1614, 1588, 1495, 1467, 1423, 1388,
1276, 1219, 1160, 1043. 1H-NMR (270 MHz, (D6)DMSO): 0.86 (t, 3J ˆ 6.8, Me(6')); 1.22 1.48 (CH2(3'),
CH2(4'), CH2(5')); 1.74 (quint., 3J ˆ 6.5, CH2(2')); 3.72 (s, MeO); 4.06 (t, 3J ˆ 6.5, CH2(1')); 7.15 (d, 4J ˆ 3.0,
HÀC(6)); 7.17 (d, 3J ˆ 9.0, HÀC(3)), 7.23 (dd, 3J ˆ 9.0, 4J ˆ 3.0, HÀC(4)); 10.34 (s, CHO). 13C-NMR
(67.9 MHz, (D6)DMSO): 14.3 (q, Me(6')); 22.6 (t, C(5')); 25.7 (t, C(4')); 29.1 (t, C(3')); 31.5 (t, C(2')); 56.0 (q,
MeO), 69.4 (t, C(1')); 110.4 (d, C(3)); 115.8 (d, C(6)); 123.6 (d, C(4)); 125.0 (s, C(1)); 153.6 (s, C(2)); 156.3 (s,
‡
‡
‡
C(5)); 189.2 (d, CHO). EI-MS: 236 (26, M ), 152 (100, [M À C6H12] ), 137 (29). HR-MS: 236.1410 (M ,
‡
C14H20O3 ; calc. 236.1411).
2-(Heptyloxy)-5-methoxybenzaldehyde (6f). According to GP A, with 7 (23.0 g, 151 mmol), 1-bromohep-
tane (45.0 ml, 51.3 g, 287 mmol), K2CO3 (39.6 g, 287 mmol), and EtOH (200 ml): 30.95 g (82%) of 6f. Pale
yellow oil. B.p. 148 1528/0.05 Torr. Rf (toluene/AcOEt 19 :1) 0.54. GC: tR 21.6. IR (CCl4): 3077, 3041, 3004, 2959,
2937, 2862, 2758, 1687 (CO), 1612, 1588, 1495, 1467, 1423, 1388, 1276, 1220, 1160, 1042. 1H-NMR (270 MHz,
3
(D6)DMSO): 0.86 (t, 3J ˆ 6.5, Me(7')); 1.20 1.50 (CH2(3'), CH2(4'), CH2(5'), CH2(6')); 1.74 (quint., J ˆ 6.5,

Helvetica Chimica Acta Vol. 86 (2003)
1997
CH2(2')); 3.75 (s, MeO); 4.06 (t, 3J ˆ 6.5, CH2(1')); 7.16 (d, 4J ˆ 3.0, HÀC(6)); 7.17 (d, 3J ˆ 9.0, HÀC(3)); 7.23
(dd, J ˆ 9.0, J ˆ 3.0, HÀC(4)); 10.35 (s, CHO). 13C-NMR (67.9 MHz, (D6)DMSO): 14.3 (q, Me(7')), 22.6 (t,
C(6')), 26.0 (t, C(5')); 29.0 (t, C(4')), 29.2 (t, C(3')), 31.9 (t, C(2')), 55.9 (q, MeO), 69.3 (t, C(1')); 110.4 (d, C(3));
115.6 (d, C(6)); 123.5 (d, C(4)); 125.0 (s, C(1)); 153.6 (s, C(2)); 156.3 (s, C(5)); 189.0 (d, CHO). EI-MS: 250 (14,
3
4
‡
‡
‡
‡
M ), 152 (100, [M À C7H14] ), 137 (58). HR-MS: 250.1567 (M , C15H22O3 ; calc. 250.1568).
5-Methoxy-2-(nonyloxy)benzaldehyde (6g). According to GP A, with 7 (28.2 g, 185 mmol), 1-bromono-
nane (55.4 ml, 60.1 g, 290 mmol), K2CO3 (40.1 g, 290 mmol), and EtOH (230 ml): 38.9 g (75%) of 6g. Pale
yellow oil. B.p. 170 1758/0.002 Torr. M.p. 30.9 35.98. Rf (toluene/AcOEt 19 :1) 0.55. GC: tR 25.8. IR (CCl4):
3074, 3047, 3002, 2956, 2930, 2858, 2758, 1687 (CO), 1613, 1588, 1508, 1495, 1467, 1422, 1388, 1276, 1220, 1160,
1043. H-NMR (270 MHz, (D6)DMSO): 0.83 (t, J ˆ 6.5, Me(9')), 1.15 1.50 (12 H, CH2(3') to CH2(8')), 1.72
(quint., 3J ˆ 6.5, CH2(2')); 3.73 (s, MeO); 4.03 (t, 3J ˆ 6.5, CH2(1')); 7.14 (d, 3J ˆ 9.0, HÀC(3)); 7.15 (d, 4J ˆ 3.0,
HÀC(6)); 7.21 (dd, 3J ˆ 9.0, 4J ˆ 3.0, HÀC(4)); 10.34 (s, CHO). 13C-NMR (67.9 MHz, (D6)DMSO): 14.5 (q,
Me(9')); 22.7 (t, C(8')); 26.1 (t, C(7')), 29.18 (t, C(6')); 29.34 (t, C(5')); 29.4 (t, C(4')); 29.5 (t, C(3')); 31.9 (t,
C(2')); 56.0 (q, MeO); 69.4 (t, C(1')); 110.4 (d, C(3)); 115.7 (d, C(6)); 123.6 (d, C(4)); 125.1 (s, C(1)); 153.6 (s,
1
3
‡
‡
‡
C(2)); 156.3 (s, C(5)); 189.1 (d, CHO). EI-MS: 279 (5, M ), 278 (18, M ), 152 (100, [M À C9H18] ), 137 (19).
‡
‡
HR-MS: 278.1880 (M , C17H26O3 ; calc. 278.1881).
2-Ethoxy-5-methoxy-3,6-dinitrobenzaldehyde (5a) and 1-Ethoxy-4-methoxy-2,3-dinitrobenzene (9a). Ac-
cording to GP B, with 6a (18.66 g, 104 mmol) and 65% HNO3 soln. (286 ml) (Tꢁ 538): 8.55 g of 5a (impure,
< 29%). A sample was recrystallized from cyclohexane/toluene 1:3. Pale yellow solid. M.p. 133.3 133.98. Rf
(toluene/AcOEt 19 :1) 0.50. GC: tR 19.4. IR (CCl4): 3039, 2956, 2936, 2874, 2774, 1714 (CO), 1561, 1546, 1495,
1468, 1438, 1420, 1386, 1362, 1310, 1275, 1241, 954, 860. 1H-NMR (270 MHz, (D6)DMSO): 1.34 (t, 3J ˆ 7.0,
MeCH2O); 3.97 (s, MeO); 4.20 (q, 3J ˆ 6.9, MeCH2O); 8.30 (s, HÀC(4)); 10.16 (s, CHO). 13C-NMR (67.9 MHz,
(D6)DMSO): 15.5 (q, MeCH2O); 58.6 (q, MeO); 76.0 (t, MeCH2); 116.5 (d, C(4)); 123.0 (s, C(1)); 139.4, 146.0,
‡
‡
146.8, 147.5 (4s, C(2), C(3), C(5), C(6)); 186.1 (d, CHO). EI-MS: 270 (38, M ), 242 (10, [M À C2H4] ), 224
‡
‡
(100), 194 (22), 179 (35), 164 (39), 136 (35). HR-MS: 270.0488 (M , C10H10N2O7 ; calc. 270.0488).
From polar fractions, a sample was recrystallized from cyclohexane/AcOEt (1:1): 9a. Yellow crystals. M.p.
155 1618. Rf (toluene/AcOEt 19 :1) 0.30. GC: tR 19.0. IR (KBr): 3025, 2989, 2952, 2889, 2849, 1550, 1494, 1366,
1279, 1051, 810. 1H-NMR (270 MHz, (D6)DMSO): 1.30 (t, 3J ˆ 7.0, MeCH2O); 3.95 (s, MeO); 4.25 (q, 3J ˆ 6.9,
MeCH2O); 7.67, 7.70 (2d, J ˆ 9.5, HÀC(5), HÀC(6)). 13C-NMR ((D6) DMSO): 14.8 (q, MeCH2O); 58.4 (q,
3
MeO), 67.1 (t, MeCH2); 119.6, 120.7 (2d, C(5), C(6)); 133.2, 133.7 (2s, C(2), C(3)); 144.6, 145.4 (2s, C(1), C(4)).
‡
‡
‡
‡
EI-MS: 242 (42, M ), 214 (100, [M À C2H4] ), 184 (14), 136 (18). HR-MS: 242.0538 (M , C9H10N2O6 ; calc.
242.0538).
5-Methoxy-3,6-dinitro-2-propoxybenzaldehyde (5b) and 4-Methoxy-2,3-dinitro-1-propoxybenzene (9b).
According to GP B, with 6b (20.0 g, 103 mmol) and 65% HNO3 soln. (280 ml) (Tꢁ 458): 11.4 g of 5b (impure,
<38%). A sample was recrystallized from cyclohexane/AcOEt 9 :1. Pale yellow crystals. M.p. 146.2 147.18. Rf
(toluene/AcOEt 19 :1) 0.53. GC: tR 22.0. IR (KBr): 3023, 2961, 2944, 2877, 1712 (CO), 1558, 1480, 1467, 1438,
1420, 1365, 1310, 1274, 1243, 1101, 1023. 1H-NMR (270 MHz, (D6)DMSO): 0.95 (t,3J ˆ 7.5, MeCH2CH2O); 1.75
(sext., 3J ˆ 7.5, MeCH2CH2O); 3.98 (s, MeO); 4.08 (t, 3J ˆ 6.5, MeCH2CH2O), 8.31 (s, HÀC(4)); 10.14 (s,
CHO). 13C-NMR (67.9 MHz, (D6)DMSO): 10.3 (q, MeCH2CH2O); 23.1 (t, MeCH2CH2O); 58.5 (q, MeO); 81.4
(t, MeCH2CH2O); 116.4 (d, C(4)); 123.0 (s, C(1)); 139.4, 146.0, 146.8, 147.5 (4s, C(2), C(3), C(5), C(6)); 185.9
‡
‡
‡
(d, CHO). EI-MS: 284 (10, M ), 242 (30, [M À C3H6] ), 224 (75), 194 (23), 43 (100, C3H7 ). HR-MS: 284.0643
‡
‡
(M , C11H12N2O7 ; calc. 284.0644).
From polar fractions, a sample was recrystallized from cyclohexane: 9b. Yellow platelets. M.p. 107.4 108.5.
Rf (toluene/AcOEt 19 :1) 0.34. GC: tR 20.8. IR (KBr): 3016, 2976, 2950, 2884, 2848, 1543, 1495, 1352, 1277, 1061,
811. 1H-NMR (270 MHz, (D6)DMSO): 0.92 (t, 3J ˆ 7.3, MeCH2CH2O); 1.68 (m, MeCH2CH2O); 3.94 (s, MeO);
4.14 (t, 3J ˆ 6.5, MeCH2CH2O), 7.63, 7.69 (2d, 3J ˆ 9.6, HÀC(5)), HÀC(6)). 13C-NMR ((D6)DMSO): 10.5 (q,
MeCH2CH2O); 22.3 (t, MeCH2CH2); 58.3 (q, MeO); 72.5 (t, MeCH2CH2O); 119.5, 120.5 (2d, C(5), C(6)); 133.2,
‡
‡
133.7 (2s, C(2), C(3)); 144.7, 145.4 (2s, C(1), C(4)). EI-MS: 256 (15, M ), 214 (100, [M À C3H6] ), 184 (5), 151
‡
‡
(8), 136 (8). HR-MS: 56.0695 (M , C10H12N2O6 ; calc. 256.0695).
2-Butoxy-5-methoxy-3,6-dinitrobenzaldehyde (5c) and 1-Butoxy-4-methoxy-2,3-dinitrobenzene (9c). Ac-
cording to GP B, with 6c (19.1 g, 91.8 mmol) and 65% HNO3 soln. (250 ml) (Tꢁ 428): 10.6 g of 5c (impure,
<38%). A sample was recrystallized from cyclohexane/AcOEt 9 :1. Pale yellow crystals. M.p. 123.8 124.78. Rf
(toluene/AcOEt 19 :1) 0.55. GC: tR 24.6. IR (CCl4): 3023, 2964, 2936, 2877, 2760, 1714 (CO), 1561, 1546, 1479,
1467, 438, 1419, 1380, 1358, 1310, 1241, 1101, 1026. 1H-NMR (270 MHz, (D6)DMSO): 0.91 (t, 3J ˆ 7.3, Me(4'));
3
3
3
1.40 (sext., J ˆ 7.3, CH2(3')); 1.72 (quint., J ˆ 6.5, CH2(2')); 3.97 (s, MeO); 4.14 (t, J ˆ 6.4, CH2(1')); 8.30 (s,
C(4)); 10.14 (s, CHO). 13C-NMR (67.9 MHz, (D6)DMSO): 14.1 (q, Me(4')); 18.9 (t, C(3')); 31.8 (t, C(2')); 58.6

1998
Helvetica Chimica Acta Vol. 86 (2003)
(q, MeO); 79.8 (t, C(1')); 116.5 (d, C(4)); 123.0 (s, C(1)); 139.2, 146.1, 146.8, 147.4 (4s, C(2), C(3), C(5), C(6));
‡
‡
‡
186.0 (d, CHO). EI-MS: 298 (11, M ), 242 (36, [M À C4H8] ), 224 (100), 194 (28), 57 (86, C4H9 ). HR-MS:
‡
‡
298.0801 (M , C12H14N2O7 ; calc. 298.0801).
From polar fractions, a sample was recrystallized from cyclohexane/AcOEt 9 :1: 9c [8a,b]. Yellow needles.
M.p. 119.5 120.88. Rf (toluene/AcOEt 19 :1) 0.35. GC: tR 22.8. IR (KBr): 3039, 2967, 2949, 2880, 2849, 1546,
1498, 1361, 1280, 1057, 809. 1H-NMR (270 MHz, (D6)DMSO): 0.90 (t, 3J ˆ 7.5, Me(4')); 1.38 (sext., 3J ˆ 7.5,
CH2(3')); 1.67 (quint., 3J ˆ 7.5, CH2(2')); 3.94 (s, MeO); 4.19 (t, 3J ˆ 6.1, CH2(1')), 7.68, 7.70 (2d, 3J ˆ 9.9,
HÀC(5), HÀC(6)). 13C-NMR (67.9 MHz, (D6)DMSO): 14.0 (q, Me(4')); 19.0 (t, C(3')); 30.9 (t, C(2')); 58.4 (q,
MeO); 70.8 (t, C(1')); 119.6, 120.6 (2d, C(5), C(6)); 133.2, 133.7 (2s, C(2), C(3)); 144.7, 145.4 (2s, C(1), C(4)).
‡
‡
‡
‡
EI-MS: 270 (8, M ), 214 (100, [M À C4H8] ), 197 (5), 179 (8), 149 (10). HR-MS: 270.0852 (M , C11H14N2O6
;
calc. 270.0852).
5-Methoxy-3,6-dinitro-2-(pentyloxy)benzaldehyde (5d) and 4-Methoxy-2,3-dinitro-1-(pentyloxy)benzene
(9d). According to GP B, with 6d (16.3 g, 73.4 mmol) and 65% HNO3 soln. (200 ml) (Tꢁ 408): 11.1 g of 5d
(impure, <48%). A sample was recrystallized from cyclohexane/AcOEt 9 :1. Pale yellow crystals. M.p. 79.2
80.48. Rf (toluene/AcOEt 19 :1) 0.58. GC: tR 26.6. IR (CCl4): 3026, 2961, 2938, 2876, 2758, 1712 (CO), 1559, 1526,
1480, 1467, 1438, 1420, 1387, 1365, 1310, 1275, 1242, 1101, 1024. 1H-NMR (270 MHz, (D6)DMSO): 0.89 (m,
Me(5')); 1.20 1.42 (CH2(3'), CH2(4')); 1.71 (quint., 3J ˆ 6.5, CH2(2')); 3.98 (s, MeO); 4.14 (t, 3J ˆ 6.5, CH2(1'));
8.31 (s, HÀC(4)); 10.14 (s, CHO). 13C-NMR (67.9 MHz, (D6)DMSO): 14.1 (q, Me(5')); 22.3 (t, C(4')); 27.0 (t,
C(3')); 29.5 (t, C(2')); 58.2 (q, MeO); 80.2 (t, C(1')); 116.4 (d, C(4)); 122.9 (s, C(1)); 139.2, 146.2, 146.8, 147.7 (4s,
‡
‡
C(2), C(3), C(5), C(6)); 185.9 (d, CHO). EI-MS: 312 (8, M ), 242 (14, [M À C5H10] ), 224 (12), 194 (5), 70
‡
‡
‡
‡
(84, C5H10 ), 43 (100, C3H7 ). HR-MS: 312.0956 (M , C13H16N2O7 ; calc. 312.0957).
From polar fractions, a sample was recrystallized from cyclohexane: 9d. Yellow platelets. M.p. 93.2 94.18.
Rf (toluene/AcOEt 19 :1) 0.36. GC: tR 24.8. IR (KBr): 3016, 2965, 2934, 2862, 2848, 1550, 1495, 1352, 1276, 1059,
814. 1H-NMR (270 MHz, (D6)DMSO): 0.86 (t, 3J ˆ 7.4, Me(5')); 1.20 1.40 (CH2(3'); CH2(4')); 1.67 (m,
CH2(2')); 3.93 (s, MeO); 4.16 (t, 3J ˆ 6.5, CH2(1')); 7.63, 7.69 (2d, 3J ˆ 9.6, HÀC(5), HÀC(6)). 13C-NMR
(67.9 MHz, (D6)DMSO): 14.2 (q, Me(5')); 22.2 (t, C(4')); 27.8 (t, C(3')); 28.5 (t, C(2')); 58.3 (q, MeO); 71.1 (t,
C(1')); 119.4, 120.4 (2d, C(5), C(6)); 133.3, 133.7 (2s, C(2), C(3)); 144.7, 145.4 (2s, C(1), C(4)). EI-MS: 284 (10,
‡
‡
‡
‡
M ), 214 (100, [M À C5H10] ), 184 (5), 151 (5), 136 (5). HR-MS: 284.1008 (M , C12H16N2O6 ; calc. 284.1008).
2-(Hexyloxy)-5-methoxy-3,6-dinitrobenzaldehyde (5e) and 1-(Hexyloxy)-4-methoxy-2,3-dinitrobenzene
(9e). According to GP B, with 6e (21.5 g, 91.1 mmol) and 65% HNO3 soln. (240 ml) (Tꢁ 398): 11.8 g of 5e
(impure, <39%). A sample was recrystallized from cyclohexane/AcOEt 19 :1. Pale yellow crystals. M.p. 79.0
80.18. Rf (toluene/AcOEt 19 :1) 0.60. GC: tR 28.4 min. IR (CCl4): 3022, 2959, 2933, 2874, 2762, 1713 (CO), 1561,
1546, 1479, 1467, 1438, 1419, 1380, 1360, 1310, 1241, 1101, 1023, 954. 1H-NMR (270 MHz, (D6)DMSO): 0.89 (m,
Me(6')); 1.20 1.42 (CH2(3'), CH2(4'), CH3(5')); 1.69 (quint., 3J ˆ 7.0, CH2(2')); 3.96 (s, MeO); 4.20 (t, 3J ˆ 6.5,
CH2(1')); 8.32 (s, HÀC(4)); 10.15 (s, CHO). 13C-NMR (67.9 MHz, (D6)DMSO): 14.4 (q, Me(6')); 22.5 (t, C(5'));
25.5 (t, C(4')); 29.7 (t, C(3')); 31.4 (t, C(2')); 58.6 (q, MeO); 80.1 (t, C(1')); 116.4 (d, C(4)); 122.9 (s, C(1)); 139.1,
‡
‡
146.1, 146.8, 147.4 (4s, C(2), C(3), C(5), C(6)); 186.0 (d, CHO). EI-MS: 326 (9, M ), 242 (18, [M À C6H12] ),
‡
‡
‡
‡
224 (60), 194 (14), 84 (100, C6H12 ), 43 (92, C3H7 ). HR-MS: 326.1114 (M , C14H18N2O7 ; calc. 326.1114).
From polar fractions, a sample was recrystallized from cyclohexane: 9e. Pale yellow solid. M.p. 76.2 77.98.
Rf (toluene/AcOEt 19 :1) 0.40. GC: tR 26.8. IR (KBr): 3016, 2958, 2935, 2862, 1542, 1494, 1361, 1282, 1060, 813.
1H-NMR (270 MHz, (D6)DMSO): 0.86 (m, Me(6')), 1.10 1.50 (CH2(3'), CH2(4'), CH2(5')); 1.66 (m, CH2(2'));
3.95 (s, MeO); 4.18 (t, 3J ˆ 6.5, CH2(1')), 7.63, 7.69 (2d,3J ˆ 9.6, HÀC(5), HÀC(6)). 13C-NMR (67.9 MHz,
(D6)DMSO): 14.2 (q, Me(6')); 22.5 (t, C(5')); 25.3 (t, C(4')); 28.8 (t, C(3')); 31.3 (t, C(2')); 58.3 (q, MeO); 71.1 (t,
C(1')); 119.4, 120.5 (2d, C(5), C(6)); 133.3, 133.7 (2s, C(2), C(3)); 144.7, 145.4 (2s, C(1), C(4)). EI-MS: 298 (8,
‡
‡
‡
‡
M ), 214 (100, [M À C6H12] ), 197 (12), 179 (6), 149 (7). HR-MS: 298.1165 (M , C13H18N2O6 ; calc. 298.1165).
2-(Heptyloxy)-5-methoxy-3,6-dinitrobenzaldehyde (5f) and 1-(Heptyloxy)-4-methoxy-2,3-dinitrobenzene
(9f). According to GP B, with 6f (29.1 g, 85.9 mmol) and 65% HNO3 soln. (230 ml) (Tꢁ 488): 12.3 g of 5f
(impure, <41%). A sample was recrystallized from cyclohexane/toluene 19 :1). Pale yellow solid. M.p. 74.0
75.98. Rf (toluene/AcOEt 19 :1) 0.64. GC: tR 30.4. IR (CCl4): 3025, 2950, 2931, 2874, 2760, 1712 (CO), 1545, 1539,
1479, 1467, 1438, 1419, 1380, 1363, 1310, 1277, 1241, 1101, 1023, 954. 1H-NMR (270 MHz, (D6)DMSO): 0.86 (m,
Me(7')); 1.20 1.42 (CH2(3'), CH2(4'), CH2(5'), CH2(6')); 1.73 (quint., 3J ˆ 6.8, CH2(2')); 3.96 (s, MeO); 4.13 (t,
3J ˆ 6.5, CH2(1')); 8.30 (s, HÀC(4)); 10.14 (s, CHO). 13C-NMR (67.9 MHz, (D6)DMSO): 14.4 (q, Me(7')); 22.6
(t, C(6')); 25.5 (t, C(5')); 28.9 (t, C(4')); 29.7 (t, C(3')); 31.7 (t, C(2')); 58.6 (q, MeO); 80.1 (t, C(1')); 116.4 (d,
C(4)); 123.0 (s, C(1)); 139.4, 146.1, 146.8, 147.4 (4s, C(2), C(3), C(5), C(6)); 186.0 (d, CHO). EI-MS: 340 (2,
‡
‡
‡
‡
‡
M ), 242 (5, [M À C7H14] ), 224 (10), 194 (5), 98 (62, C7H14 ), 57 (100, C4H9 ). HR-MS: 340.1270 (M ,
‡
C15H20N2O7 ; calc. 340.1269).

Helvetica Chimica Acta Vol. 86 (2003)
1999
From the polar fractions, 9f was isolated. Yellow solid. Rf (toluene/AcOEt 19 :1) 0.50.
Crystal-Structure Determination of 5f 8). A crystal of 5f was selected and mounted onto a needle, and a
rotational photo was taken to check the crystal quality prior to the data collection. From the photo, 13 reflections
were chosen to determine a reasonable cell to start with. Then the reduced cell was determined with the
automatic routine of the Bruker xscans software. The data collection was done on a Bruker-P4-four-circle
diffractometer with graphite monochromator in routine w-scan. The structure was solved by direct methods
(Bruker SHELXTL) and refined by the full-matrix least-squares methods of SHELXL-97 [38]. All non-H-
atoms were refined anisotropically while the H-atoms were put into theoretical positions and refined according
to the riding model. The nitro groups in the 3- and 6-positions are tilted against the aromatic ring at angles of
39.35 and 87.408, resp. Data in the Table.
Table. Crystallographic Data of 5f
Crystallized from
Empirical formula
Mr
EtOH
C15H20N2O7
340.33
Crystal color, habit
Crystal dimensions [mm]
Temp. [K]
Crystal system
Space group
Z
pale yellow, plate
0.66 Â 0.52 Â 0.12
293
monoclinic
P21/n
4
Unit cell dimensions:
a [ä]
8.886 (1)
b [ä]
7.467 (1)
c [ä]
26.202 (4)
b [8]
93.71 (1)
1734.9 (4)
1.303
0.104
V [ä3]
Dx [Mg mÀ3
]
m(MoKa) [mmÀ1
Scan type
]
w-scan
V range
2.38 22.49
Total reflections measured
Symmetry-independent reflections
Reflections used [I > 2s (I)]
Parameters refined
R1
3285
2269
1315
217
0.497 (obs.), 0.959 (all)
0.1175 (obs.), 0.1426 (all)
1.022
wR2
Goodness-of-fit
D/1 (max; min) [e äÀ3
]
0.139; 0.150
3-Methoxy-2-nitro-6-(nonyloxy)benzaldehyde (8g). According to GP B, with 6g (13.9 g, 50.0 mmol) and
65% HNO3 soln. (130 ml) (Tꢁ 458): 8.83 g of 8g (impure, <49%). For analysis, a sample was recrystallized
from cyclohexane. Pale yellow solid. M.p. 81.0 82.18. Rf (toluene/AcOEt 19 :1) 0.45. GC: tR 32.8. IR (CCl4):
3018, 2957, 2928, 2856, 2745, 1703 (CO), 1553, 1490, 1469, 1440, 1368, 1287, 1270, 1310, 1188 1092, 954. 1H-NMR
(270 MHz, (D6)DMSO): 0.83 (t, 3J ˆ 6.5, Me(9')); 1.15 1.50 (12 H, CH2(3') to CH2(8')); 1.74 (quint., 3J ˆ 6.5,
CH2(2')); 3.84 (s, MeO); 4.13 (t, 3J ˆ 6.5, CH2(1')); 7.44, 7.65 (2d, 3J ˆ 9.2, HÀC(4), HÀC(5)); 10.26 (s, CHO).
13C-NMR (67.9 MHz, (D6)DMSO): 14.5 (q, Me(9')); 22.6 (t, C(8')); 25.90 (t, C(7')); 28.93 (t, C(6')); 29.18 (t,
C(5')); 29.25 (t, C(4')); 29.45 (t, C(3')); 31.8 (t, C(2')); 57.8 (q, MeO); 70.4 (t, C(1')); 115.7 (s, C(1)); 117.6, 122.3
8
)
Crystallographic data for structure 5f have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication No. CCDC-189589. Copies of the data can be obtained, free of
charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: ‡44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk).

2000
Helvetica Chimica Acta Vol. 86 (2003)
‡
(2d, C(4), C(5)), 137.7, 144.2, 155.2 (3s, C(2), C(3), C(6)); 187.2 (d, CHO). EI-MS: 323 (62, M ), 197 (100,
‡
‡
‡
[M À C9H18] ), 179 (78), 149 (60), 121 (76). HR-MS: 323.1733 (M , C17H25NO5 ; calc. 323.1733).
4,4'-Diethoxy-7,7'-dimethoxy-5,5'-dinitroindigotin (ˆ4-Ethoxy-2-(4-ethoxy-1,3-dihydro-7-methoxy-5-nitro-
3-oxo-2H-indol-2-ylidene)-1,2-dihydro-7-methoxy-5-nitro-3H-indol-3-one; 2a). According to GP C, with im-
pure 5a (8.25 g, < 30.5 mmol; from 104 mmol of 6a), acetone (165 ml) and KOH (16 ml of 0.2m; 120 ml of
0.4m): 1.85 g (7% rel. to 6a) of 2a. Dark blue solid. Dec.p. (2418) 3358(DSC). Rf (cylohexane/AcOEt 4 :1) 0.18.
UV/VIS (CHCl3): 622 (19212), 368 (8484), 300 (16277). IR (KBr): 3417 (NH), 2984, 1624 (CO), 1588, 1535,
1490, 1474, 1449, 1414, 1340, 1274, 1201, 1154, 1112, 1079, 1156, 1004. 1H-NMR (270 MHz, CDCl3): 1.05 (t, 3J ˆ
7.0, 2 MeCH2O); 3.97 (s, 2 MeO); 4.38 (t, 3J ˆ 7.0, 2 MeCH2O); 7.59 (s, 2 arom. H); 9.30 (2 NH). EI-MS: 501 (18,
‡
‡
‡
‡
M ), 500 (100, M ), 456 (30), 439 (32), 411 (38), 395 (90). HR-MS: 500.1179 (M , C22H20N4O10 ; calc.
500.1179).
7,7'-Dimethoxy-5,5'-dinitro-4,4'-dipropoxyindigotin (ˆ2-(1,3-Dihydro-7-methoxy-5-nitro-4-propoxy-3-oxo-
2H-indol-2-ylidene)-1,2-dihydro-7-methoxy-5-nitro-4-propoxy-3H-indol-3-one; 2b). According to GP C, with
impure 5b (11.2 g, <39.4 mmol; from 103 mmol of 6b), acetone (170 ml) and KOH (20 ml of 0.2m; 170 ml of
0.4m): 2.97 g (11% rel. to 6b) of 2b. Dec.p. (1998) 2968 (DSC). Rf (cylohexane/AcOEt 4 :1) 0.26. UV/VIS
(CHCl3): 622 (21090), 372 (12479), 298 (18073). IR (KBr): 3433 (NH), 2963, 2938, 2878, 2839, 1615 (CO), 1588,
1532, 1501, 1406, 1260, 1250, 1206, 1077, 1057, 976, 915. 1H-NMR (270 MHz, CDCl3): 1.06 (t, 3J ˆ 7.3, 2
MeCH2CH2O); 1.60 (m, 2 MeCH2CH2); 4.00 (s, 2 MeO); 4.30 (t, 3J ˆ 6.6, 2 MeCH2CH2O); 7.60 (s, 2 arom. H);
‡
‡
9.31 (2 NH). EI-MS: 529 (20, M ), 528 (100, M ), 483 (12), 470 (42), 444 (32), 428 (35), 411 (55), 395 (30).
‡
‡
‡
HR-MS: 528.1492 (M , C24H24N4O10 ; calc. 528.1492); 483.1642 (C24H25N3O8 ; calc. 483.1642); 470.1074
(C21H18N4O9 ; calc. 470.1074); 444.0553 (C18H12N4O10 ; calc. 444.0553); 428.0604 (C18H12N4O9 ; calc. 428.0604);
‡
‡
‡
‡
‡
411.0577 (C18H11N4O8 ; calc. 411.0577); 395.0627 (C18H11N4O7 ; calc. 395.0627).
Monoanion of 2b (monomer). 1H-NMR (270 MHz, sat. soln. in (D6)DMSO): 0.95 1.00 (2 MeCH2CH2O);
1.65 1.85 (2 MeCH2CH2O); 3.82, 3.98 (2s, 2 MeO); 4.14, 4.32 (2t, 3J ˆ 6.5, 2 MeCH2CH2O); 7.24, 7.52 (2s, 2
arom. H); 10.15 (1 NH).
Monoanion of 2b (dimer). UV/VIS (DMF)9): 784 (21335), 506 (16049), 350 (14210). UV/VIS (DMSO)9):
786 (21877), 512 (16809), 350 (16327).
Dianion of 2b. UV/VIS (DMF/2m KOH): 808 (38554), 742 (sh, 19157), 560 (14824), 414 (15877), 390
(15234).
4,4'-Dibutoxy-7,7'-dimethoxy-5,5'-dinitroindigotin (ˆ4-Butoxy-2-(4-butoxy-1,3-dihydro-7-methoxy-5-nitro-
3-oxo-2H-indol-2-ylidene)-1,2-dihydro-7-methoxy-5-nitro-3H-indol-3-one; 2c). According to GP C, with impure
5c (10.4 g, <34.9 mmol; from 91.8 mmol of 6c), acetone (150 ml) and KOH (20 ml of 0.2m; 160 ml of 0.4m):
3.73 g (15% rel. to 6c) of 2c. Dark blue solid. Dec.p. (2438) 3008(DSC). Rf (cylohexane/AcOEt 4 :1) 0.32. UV/
VIS (CHCl3): 622 (22631), 370 (9568), 298 (18474). IR (KBr): 3409 (NH), 2959, 2918, 2870, 1627 (CO), 1585,
1527, 1506, 1465, 1443, 1386,1318, 1258, 1239, 1204, 1171, 1143, 1070, 1050, 1003, 904. 1H-NMR (270 MHz,
CDCl3): 1.01 (t, 3J ˆ 7.3, 2 Me(4'); 1.50 (m, 2 CH2(3')); 1.86 (quint., 3J ˆ 7.3, 2 CH2(2')); 3.97 (s, 2 MeO), 4.33 (t,
‡
‡
3J ˆ 6.5, 2 CH2(1')); 7.59 (s, 2 arom. H); 9.30 (2 NH). EI-MS: 557 (26, M ), 556 (100, M ), 511 (16), 484 (26),
‡
‡
467 (55), 444 (52), 428 (34), 411 (48), 395 (29). HR-MS: 556.1805 (M , C26H28N4O10 ; calc. 556.1805).
Monoanion of 2c (monomer). UV/VIS (ꢁ10À6 m in DMSO): 710. 1H-NMR (270 MHz, ꢁ10À6 m in
(D6)DMSO): 0.92 0.96 (2 Me(4')); 1.40 1.45 (2 CH2(3')); 1.71 1.76 (2 CH2(2')); 3.81, 3.98 (2s, 2 MeO); 4.17,
4.29 (2m, 2 CH2(1')); 7.24, 7.52 (2s, 2 arom. H); 10.23 (1 NH).
Monoanion of 2c (dimer). UV/VIS (DMF)9): 784 (20663), 506 (15936), 350 (15155). 1H-NMR (270 MHz,
(D6)DMSO): 2  [0.91 (t, 3J ˆ 7.5, 2 Me(4')); 1.43 (sext., 3J ˆ 7.5, 2 CH2(3')); 1.72 (quint., 3J ˆ 7.5, 2 CH2(2'));
3.89 (s, 2 MeO); 4.22 (t, 3J ˆ 6.5, 2 CH2(1')); 7.37 (s, 2 arom. H); 10.0 (1 NH)].
Dianion of 2c. UV/VIS (DMF/2m KOH): 808 (43016), 742 (sh, 21592), 562 (16360), 416 (17127), 392
(17001). 1H-NMR (270 MHz, (D6)DMSO/KOD/D2O): 0.91 (t, 3J ˆ 7.5, 2 Me(4')); 1.43 (sext., 3J ˆ 7.3, 2
CH2(3')); 1.71 (quint., 3J ˆ 7.3, 2 CH2(2')); 3.80 (s, 2 MeO); 4.16 (t, 3J ˆ 6.5, 2 CH2(1')); 7.07 (s, 2 arom. H).
7,7'-Dimethoxy-5,5'-dinitro-4,4'-bis(pentyloxy)indigotin (ˆ2-[1,3-Dihydro-7-methoxy-5-nitro-3-oxo-4-
(pentyloxy)-2H-indol-2-ylidene]-1,2-dihydro-methoxy-5-nitro-4-(pentyloxy)-3H-indol-3-one; 2d). According
to GP C, with impure 5d (11.0 g, <35.2 mmol; from 73.4 mmol of 6d), acetone (150 ml) and KOH (22 ml of
0.2m; 15 ml of 0.4m): 2.72 g (13% rel. to 6d) of 2d. Dark blue solid. Dec.p. (1758) 2978 (DSC). Rf (cylohexane/
AcOEt 4 :1) 0.36. UV/VIS (CHCl3): 622 (21208), 370 (11483), 298 (19578). IR (KBr): 3408 (NH), 2954, 2950,
2870, 1627 (CO), 1584, 1532, 1505, 1406, 1320, 1261, 1240, 1169, 1143, 1070, 1052, 1004, 905. 1H-NMR (270 MHz,
9
)
Concentration calculated to 2.

Helvetica Chimica Acta Vol. 86 (2003)
2001
CDCl3): 0.93 (t, 3J ˆ 7.3, 2 Me(5')); 1.25 1.55 (2 CH2(3'), 2 CH2(4')); 1.89 (quint., 3J ˆ 7.3, 2 CH2(2')); 3.97 (s, 2
‡
‡
MeO), 4.33 (t, 3J ˆ 6.5, 2 CH2(1')), 7.56 (s, 2 arom. H); 9.27 (2 NH). EI-MS: 585 (23, M ), 584 (100, M ), 498
‡
‡
(92), 444 (72), 428 (74), 411 (63), 395 (22). HR-MS: 584.2118 (M , C28H32N4O10 ; calc. 584.2118).
Monoanion of 2d (dimer). UV/VIS (DMF)9): 784 (20921), 506 (16195), 350 (15576). 1H-NMR (270 MHz,
(D6)DMSO): 2  [0.90 (t, 3J ˆ 7.5, 2 Me(5')); 1.20 1.50 (2 CH2(3'), 2 CH2(4')); 1.72 (quint., 3J ˆ 7.3, 2 CH2(2'));
3.90 (s, 2 MeO); 4.22 (t, 3J ˆ 6.5, 2 CH2(1')); 7.38 (s, 2 arom. H); 10.18 (1 NH)].
Dianion of 2d. UV/VIS (DMF/2m KOH): 808 (41015), 742 (sh, 20531), 562 (15840), 410 (17850), 390
(18253). 1H-NMR (270 MHz, (D6)DMSO/KOD/D2O): 0.87 (t, 3J ˆ 7.5, 2 Me(5')); 1.25 1.45 (2 CH2(3'), 2
CH2(4')); 1.71 (quint., 3J ˆ 7.2, 2 CH2(2')); 3.78 (s, 2 MeO); 4.14 (t, 3J ˆ 6.5, 2 CH2(1')); 7.06 (s, 2 arom. H).
4,4'-Bis(hexyloxy)-7,7'-dimethoxy-5,5'-dinitroindigotin (ˆ4-(Hexyloxy)-2-[4-(hexyloxy)-1,4-dihydro-7-me-
thoxy-5-nitro-3-oxo-2H-indol-2-ylidene]-1,2-dihydro-7-methoxy-5-nitro-3H-indol-3-one; 2e). According to
GP C, with impure 5e (116.6 g, <35.6 mmol; from 91.1 mmol of 6e); acetone (165 ml) and KOH (32 ml of
0.2m; 160 ml of 0.4m): 4.22 g (15% rel. to 6e) of 2e. Dark blue solid. Dec.p. (1958) 3018(DSC). Rf (cylohexane/
AcOEt 4 :1) 0.39. UV/VIS (CHCl3): 622 (22948), 368 (10878), 298 (19919). IR (KBr): 3408 (NH), 2928, 2932,
2857, 1628 (CO), 1585, 1528, 1505, 1466, 1443, 1385, 1317, 1260, 1240, 1207, 1170, 1142, 1070, 1051, 1003, 976, 904.
1H-NMR (270 MHz, CDCl3): 0.89 (t, 3J ˆ 7.3, 2 MeO(6')); 1.25 1.55 (2 CH2(3'), 2 CH2(4'), 2 CH2(5')); 1.90
(quint., 3J ˆ 7.3, 2 CH2(2')); 3.96 (s, 2 MeO); 4.33 (t, 3J ˆ 6.5, 2 CH2(1')); 7.59 (s, 2 arom. H); 9.28 (2 NH). EI-MS:
‡
‡
613 (20, M ), 612 (100, M ), 567 (96), 512 (82), 467 (55), 444 (85), 428 (55), 411 (50), 395 (22). HR-MS:
‡
‡
612.2433 (M , C30H36N4O10 ; calc. 612.2432).
Monoanion of 2e (dimer). UV/VIS (DMF)9): 784 (21219), 506 (16099), 350 (14986). 1H-NMR (270 MHz,
(D6)DMSO): 2  [0.88 (t, 3J ˆ 7.3, 2 Me(6')); 1.25 1.55 (2 CH2(3'), 2 CH2(4'), 2 CH2(5')); 1.73 (quint., 3J ˆ 7.3, 2
3
CH2(2')); 3.98 (s, 2 MeO), 4.22 (t, J ˆ 6.5, 2 CH2(1')); 7.38 (s, 2 arom. H); 10.20 (1 NH)].
Dianion of 2e. UV/VIS (DMF/2m KOH): 808 (40549), 742 (sh, 20245), 560 (15413), 412 (17025), 392
(17294). 1H-NMR (270 MHz, (D6)DMSO/KOD/D2O): 0.86 (t, 3J ˆ 7.5, 2 Me(6')); 1.20 1.50 (2 CH2(3'), 2
CH2(4'), 2 CH2(5')); 1.71 (quint., 3J ˆ 7.3, 2 CH2(2')); 3.79 (s, 2 MeO); 4.15 (t, 3J ˆ 6.5, 2 CH2(1')); 7.07 (s, 2 arom.
H).
4,4'-Bis(heptyloxy)-7,7'-dimethoxy-5,5'-dinitroindigotin (ˆ4-(Heptyloxy)-2-[4-heptyloxy-1,3-dihydro-7-me-
thoxy-5-nitro-3-oxo-2H-indol-2-ylidene]-1,2-dihydro-7-methoxy-5-nitroindol-3-one; 2f). According to GP C,
reaction of impure 5f (12.1 g, < 35.5 mmol; from 85.9 mmol of 6f), acetone (150 ml) and KOH (26 ml of 0.2m;
150 ml of 0.4m): 3.71 g (14% rel. to 6f) of 2f. Dark blue solid. Dec.p. (1918) 3058(DSC). Rf (cylohexane/AcOEt
4 :1) 0.44. UV/VIS (CHCl3): 622 (22579), 372 (11478), 298 (19714). IR (KBr): 3382 (NH), 2950, 2927, 2855,
1616 (CO), 1583, 1534, 1506, 1458, 1443, 1394, 1317, 1268, 1241, 1207, 1175, 1143, 1066, 1050, 901. 1H-NMR
(270 MHz, CDCl3): 0.89 (t, 3J ˆ 7.3, 2 Me(7')); 1.25 1.55 (16 H, 2 CH2(3') to 2 CH2(6')); 1.89 (quint., 3J ˆ 7.5, 2
‡
CH2(2')); 3.94 (s, 2 MeO); 4.33 (t, 3J ˆ 6.5, 2 CH2(1')); 7.59 (s, 2 arom. H); 9.29 (2 NH). EI-MS: 641 (18, M ), 640
‡
‡
(48, M ), 595 (38), 526 (45), 435 (63), 444 (40), 428 (38), 411 (30), 395 (20). HR-MS: 640.2744 (M ,
‡
C32H40N4O10 ; calc. 640.2744).
Monoanion of 2f (dimer). UV/VIS (DMF)9): 782 (21179), 502 (15110), 350 (14830). 1H-NMR (270 MHz,
(D6)DMSO): 2  [0.87 (t, 3J ˆ 7.3, 2 Me(7')); 1.20 1.50 (16 H, 2 CH2(3') to 2 CH2(6')); 1.73 (quint., 3J ˆ 7.5, 2
3
CH2(2')); 3.91 (s, 2 MeO); 4.21 (t, J ˆ 6.5, 2 CH2(1')); 7.40 (s, 2 arom. H); 10.17 (1 NH)].
Dianion of 2f. UV/VIS (DMF/2m KOH): 808 (35226), 742 (sh, 17654), 558 (14163), 414 (17464), 392
(17355). 1H-NMR (270 MHz, (D6)DMSO/KOD/D2O): 0.84 (t, 3J ˆ 7.5, 2 Me(7')); 1.15 1.45 (16 H, 2 CH2(3') to
3
3
2 CH2(6')); 1.73 (quint., J ˆ 7.2, 2 CH2(2')); 3.78 (s, 2 MeO); 4.15 (t, J ˆ 6.1, 2 CH2(1')); 7.05 (s, 2 arom. H).
7,7'-Dimethoxy-4,4-bis(nonyloxy)indigotin (ˆ2-1,3-Dihydro[7-methoxy-4-nonyloxy-3-oxo-2H-indol-2-yli-
dene]-1,2-dihydro-7-methoxy-4-(nonyloxy)-3H-indol-3-one; 3g). According to GP C, with impure 8g (8.81 g,
<24.8 mmol; from 50.0 mmol of 6g), acetone (115 ml) and KOH (11 ml of 0.2m; 120 ml of 0.4m): 3.56 g (24%
rel. to 6g) of 3g. A sample was recrystallized from CHCl3. Dark blue solid with an intensive coppery luster. Rf
(cylohexane/AcOEt 4 :1) 0.32. M.p. (1278) 2468 (DSC). Solubility: 42 mg/ml of CHCl3. UV/VIS (CHCl3): 645
(23560), 396 (2900), 318 (9903), 292 (16220). IR (KBr): 3420 (NH), 3008, 2922, 2851, 1642 (CO), 1627, 1597,
1
1514, 1471, 1455, 1403, 1343, 1293, 1270, 1242, 1204, 1148, 1102, 1074, 1042, 934. H-NMR (270 MHz, CDCl3):
0.86 (t, 3J ˆ 6.8, 2 Me(9')); 1.20 1.35 (10 H, 2 CH2(4') to 2 CH2(8')); 1.52 (m, 2 CH2(3')); 1.87 (quint., 3J ˆ 6.8, 2
CH2(2')); 3.85 (s, 2 MeO); 4.05 (t, 3J ˆ 6.7, 2 CH2(1')); 6.24, 6.86 (2d, 3J ˆ 8.1, 4 arom. H); 8.98 (2 NH). 1H-NMR
(500 MHz, CDCl3): 8.98 (d, 1J (N,H) ˆ 102.0 Æ 0.5, NH). 13C-NMR (67.9 MHz, CDCl3): 14.1 (q, Me(9')); 22.7 (t,
C(8')), 25.9, 25.1, 29.3, 29.4, 29.5 (5t, C(3'), C(4'), C(5'), C(6'), C(7')); 31.9 (t, C(2')); 56.3 (q, 2 MeO); 68.9 (t,
C(1')); 102.5 (s, arom. C(5,5')); 110.1 (s, arom. C(3a,3'a)); 118.3 (d, arom. C(6,6')), 121.6 (s, arom. C(2,2')); 139.6,
142.9 (2s, arom. C(7,7'), arom. C(7a,7a')); 152.2 (s, arom. C(4,4')); 186.2 (s, arom. C(3,3')). 15N-NMR (50.7 MHz,

2002
Helvetica Chimica Acta Vol. 86 (2003)
‡
‡
‡
‡
CDCl3): 210. EI-MS: 607 (12, M ), 606 (100, M ), 480 (12), 479 (20). HR-MS: 606.3667 (M , C36H50N2O6
;
calc. 606.3668).
7,7'-Dimethoxy-5,5'-dinitro-1-pentyl-4,4'-bis(pentyloxy)indigotin ( ˆ 2-[1,3-Didydro-7-methoxy-5-nitro-3-
oxo-4-(pentyloxy)-2H-indol-2-ylidene]-1,2-dihydro-7-methoxy-5-nitro-1-pentyl-4-(pentyloxy)-3H-indol-3-one;
4d). According to GP E with 2d: 4d containing 2d. Dark-colored solid. Rf (cylohexane/AcOEt 4 :1) 0.50. EI-
‡
‡
‡
‡
MS: 655 (40, M ), 654 (100, M ). HR-MS: 654.2901 (M , C33H42N4O10 ; calc. 654.2901).
4,4'-Bis(hexyloxy)-7,7'-dimethoxy-5,5'-dinitro-1-pentylindigotin ( ˆ 4-(Hexyloxy)-2-[4-(hexyloxy)-1,3-dihy-
dro-7-methoxy-5-nitro-3-oxo-2H-indol-2-ylidene]-1,2-dihydro-7-methoxy-5-nitro-1-pentyl-3H-indol-3-one; 4e).
According to GP E with 2e: 4e containing 2e. Dark-colored solid. Rf (cylohexane/AcOEt 4 :1) 0.53. EI-MS: 683
‡
‡
‡
‡
(40, M ), 682 (100, M ). HR-MS: 682.3214 (M , C35H46N4O10 ; calc. 682.3214).
4,4'-Bis(heptyloxy)-7,7'-dimethoxy-5,5'-dinitro-1-pentylindigotin (ˆ4-(Heptyloxy)-2-[4-(heptyloxy)-1,3-di-
hydro-7-methoxy-5-nitro-3-oxo-2H-indol-2-ylidene]-1,2-dihydro-7-methoxy-5-nitro-1-pentyl-3H-indol-3-one;
4f). According to GP E with 2f: 4f containing 2f. Dark-colored solid. Rf (cylohexane/AcOEt 4 :1) 0.57. UV/VIS
(CHCl3): 635, 370, 295. IR (CHCl3): 3402 (NH), 2931, 2858, 1651 (CO), 1586, 1531 , 1412, 1330, 1272, 1076, 1053.
1H-NMR (270 MHz, CDCl3): 0.78 0.92 (2 Me(7'), Me(CH2)4N); 1.20 1.60 (2 CH2(3'), 2 CH2(4'), 2 CH2(5'), 2
CH2(6'), MeCH2CH2(CH2)2N); 1.85 1.95 (2 CH2(2'), Me(CH2)2CH2CH2N); 3.97, 3.98 (2s, 2 MeO); 4.23, 4.26
(2t, 3J ˆ 7.0, 2 CH2(1')), 4.73 (t, 3J ˆ 7.5, Me(CH2)3CH2N); 7.58, 7.60 (2s, 2 arom. H); 11.08 (1 NH). EI-MS:
‡
‡
‡
‡
among others 711 (34, M ), 710 (100, M ). HR-MS: 710.3527 (M , C37H50N4O10 ; calc. 710.3527).
5,5'-Diamino-4,4'-diethoxy-7,7'-dimethoxyindigotin (ˆ 5-Amino-2-(5-amino-4-ethoxy-1,3-dihydro-7-me-
thoxy-3-oxo-2H-indol-2-ylidene)-4-ethoxy-1,2-dihydro-7-methoxy-3H-indol-3-one; 1a). According to GP D,
with 2a (1.21 g, 2.42 mmol), Na2S2O4 (5.5 g, 27 mmol), and 1m NaOH (100 ml)): 0.12 g (11%) of 1a. A sample
was recrystallized from CHCl3. Dark blue solid. M.p. 2578 (dec., DSC). Rf (cyclohexane/AcOEt 1:1) 0.14.
Solubility: 28 mg/ml of CHCl3. UV/VIS (CHCl3): 732 (13580), 375 (sh, 8090), 330 (21670). IR (CHCl3): 3416
(NH, NH2), 2986, 2938, 2846, 1619 (CO), 1467, 1398, 1344, 1270, 1120, 1055, 933. 1H-NMR (360 MHz, CDCl3):
1.42 (t, 3J ˆ 8.1, 2 MeCH2O); 3.6 (2 NH2); 3.83 (s, 2 MeO); 4.29 (q, 3J ˆ 7.0, 2 MeCH2O); 6.51 (s, 2 arom. H); 8.7
(2 NH). 13C-NMR (90.5 MHz, CDCl3): 15.8 (q, MeCH2O); 56.0 (q, MeO), 76.7 (t, MeCH2O); 107.2 (d, arom.
C(6,6')); 113.5 (s, arom. C(3a,3'a)); 122.1 (s, arom. C(2,2')); 132.8 (s, arom. C(5,5')); 135.1 (s, arom. C(7a,7'a));
‡
‡
136.7 (s, arom. C(4,4')); 141.4 (s, arom. C(7,7')); 186.2 (s, arom. C(3,3')). EI-MS: 441 (21, M ), 440 (100, M ) 425
‡
(10), 412 (15), 411 (92), 383 (12), 382 (10), 368 (10), 367 (15), 192 (10), 191 (8). HR-MS: 440.1696 (M ,
‡
C22H24N4O6 ; calc. 440.1696).
5,5'-Diamino-7,7'-dimethoxy-4,4'-dipropoxyindigotin (ˆ 5-Amino-2-(5-amino-1,3-dihydro-7-methoxy-4-
propoxy-3-oxo-2H-indol-2-ylidene)-1,2-dihydro-7-methoxy-4-propoxyindol-3H-one; 1b). According to GP D,
with 2b (2.10 g, 4.0 mmol), Na2S2O4 (8.6 g, 42 mmol), and 1m NaOH (160 ml): 1.66 g (88%) of 1b. A sample was
recrystallized from CHCl3. Dark blue fine crystals. M.p. (638) 2688 (dec., DSC). Rf (cyclohexane/AcOEt 1 :1)
0.26. Solubility: 32 mg/ml of CHCl3. UV/VIS (CHCl3): 735 (11570), 375 (sh, 8640), 330 (20220). IR (CCl4): 3458,
3421, 3375 (NH, NH2), 2967, 2926, 2880, 2854, 1622 (CO), 1508, 1447, 1399, 1340, 1264, 1200, 1120, 930. 1H-NMR
3
(360 MHz, CDCl3): 1.06 (t, J ˆ 7.5, 2 MeCH2CH2O); 1.83 (m, 2 MeCH2CH2O); 3.2 (4 H, (2 NH2); 3.83 (s, 2
MeO); 4.18 (t, 3J ˆ 7.0, 2 CH(1')); 6.49 (s, 2 arom. H); 8.76 (2 NH). 13C-NMR (90.5 MHz, CDCl3): 10.5 (q,
MeCH2CH2); 23.5 (t, MeCH2CH2O); 55.9 (q, MeO); 75.9 (t, MeCH2CH2); 107.1 (d, arom. C(6,6')); 113.0 (s,
arom. C(3a,3'a)); 122.1 (s, arom. C(2,2')); 132.6 (s, arom C(5,5')); 135.0 (s, arom. C(7a,7'a)); 136.9 (s, arom.
‡
‡
C(4,4')); 141.3 (s, arom. C(7,7')); 186.1 (s, arom. C(3,3')). EI-MS: 469 (20, M ), 468 (100, M ), 425 (85, [M À
‡
‡
‡
C3H7] ), 383 (48), 368 (18), 353 (16), 192 (22). HR-MS: 468.2009 (M , C24H28N4O6 ; calc. 468.2009); 425.1461
(C24H21N4O6 ; calc. 425.1461); 383.0992 (C18H15N4O6 ; calc. 383.0992); 368.0757 (C17H12N4O6 ; calc. 368.0757);
353.0522 (C16H9N4O6 ; calc. 353.0522); 192.0535 (C9H8N2O3 ; calc. 192.0535).
‡
‡
‡
‡
‡
5,5'-Diamino-4,4'-dibutoxy-7,7'-dimethoxyindigotin (ˆ 5-Amino-2-(5-amino-4-butoxy-1,3-dihydro-7-
methoxy-3-oxo-2H-indol-2-ylidene)-4-butoxy-1,2-dihydro-7-methoxy-3H-indol-3-one; 1c). According to GP D,
with 2c (4.80 g, 8.63 mmol), Na2S2O4 (19.2 g, 94 mmol), and 1m NaOH (250 ml): 3.62 g (85%) of 1c. A sample
was recrystallized from CHCl3. Dark blue needles. M.p. (1678) 2628 (dec., DSC). Rf (cyclohexane/AcOEt 1 :1)
0.33. Solubility: 33 mg/ml of CHCl3. UV/VIS (CHCl3): 735 (13480), 375 (sh, 8090), 328 (21567). IR (CCl4): 3459,
3424, 3375 (NH, NH2), 2960, 2932, 2874, 1622 (CO), 1510, 1447, 1398, 1341, 1272, 1200, 1120, 1057, 931. 1H-NMR
(360 MHz, CDCl3): 0.98 (t, 3J ˆ 7.3, 2 Me(4')); 1.52 (m, 2 CH2(3')); 1.79 (m, 2 CH2(2')); 3.5 (4 H, (2 NH2); 3.83 (s,
2 MeO); 4.20 (t, 3J ˆ 6.6, 2 CH2(1')); 6.50 (s, 2 arom. H); 8.76 (2 NH). 13C-NMR (90.5 MHz, CDCl3): 14.0 (q,
Me(4')); 19.3 (t, C(3')); 32.5 (t, C(2')); 56.0 (q, MeO); 74.3 (t, C(1')); 107.2 (d, arom. C(6,6')); 113.6 (s, arom.
C(3a,3'a)); 122.1 (s, arom. C(2,2')); 132.6 (s, arom. C(5,5')); 135.0 (s, arom. C(7a,7'a)); 137.0 (s, arom. C(4,4'));
‡
‡
‡
141.3 (s, arom. C(7,7')); 186.1 (s, arom. C(3,3')). EI-MS: 497 (20, M ), 496 (100, M ), 439 (80, [M À C4H9] ), 383
‡
‡
(55), 368 (18), 353 (14), 192 (15). HR-MS: 496.2320 (M , C26H32N4O6 ; calc. 496.2321).

Helvetica Chimica Acta Vol. 86 (2003)
2003
5,5'-Diamino-7,7'-dimethoxy-4,4'-bis(pentyloxy)indigotin (ˆ 5-Amino-2-[5-amino-1.3-dihydro-4-methoxy-
3-oxo-4-(pentyloxy)-2H-indol-2-ylidene]-1,2-dihydro-7-methoxy-4-(pentyloxy)-3H-indol-3-one; 1d). According
to GP D with 2d (2.41 g, 4.1 mmol), Na2S2O4 (8.80 g, 43 mmol), and 1m NaOH (180 ml): 1.69 g (79%) of 1d. A
sample was recrystallized from CHCl3. Dark blue fine crystals. M.p. (848) 2368 (dec., DSC). Rf (cyclohexane/
AcOEt 1:1) 0.40. Solubility: 97 mg/ml of CHCl3. UV/VIS (CHCl3): 736 (13430), 374 (sh, 8510), 330 (2075). IR
(CCl4): 3449, 3421, 3371 (NH, NH2), 2960, 2955, 2874, 1622 (CO), 1500, 1446, 1398, 1340, 1265, 1200, 1120, 1056,
932. 1H-NMR (360 MHz, CDCl3): 0.94 (t, 3J ˆ 7.1, 2 Me(5')); 1.3 1.5 (2 CH2(3'), 2 CH2(4')); 1.81 (m, 2 CH2(2'));
3.3 (2 NH2); 3.82 (s, 2 MeO); 4.20 (t, 3J ˆ 6.6, 2 CH2(1')); 6.47 (s, 2 arom H); 8.75 (2 NH). 13C-NMR (90.5 MHz,
CDCl3): 14.0 (q, Me(5')); 22.6 (t, C(4')); 28.2, 29.9 (2t, C(2'), C(3')); 55.9 (t, MeO); 74.5 (t, C(1')); 107.2 (d, arom.
C(6,6')); 113.6 (s, arom. C(3a,3'a)); 122.0 (s, arom. C(2,2')); 132.6 (s, arom. C(5,5')); 134.9 (s, arom. C(7a,7'a));
‡
‡
137.0 (s, arom. C(4,4')); 141.2 (s, arom. C(7,7')); 186.0 (s, arom. C(3,3')). EI-MS: 525 (19, M ), 524 (100, M ), 453
‡
‡
‡
(65, [M À C5H11] ), 383 (25), 368 (12), 353 (8), 192 (15). HR-MS: 524.2634 (M , C28H36N4O6 ; calc. 524.2633).
5,5'-Diamino-4,4'-bis(hexyloxy)-7,7'-dimethoxyindigotin (ˆ 5-Amino-2-[5-amino-4-(hexyloxy)-1,3-dihy-
dro-7-methoxy-3-oxo-2H-indol-2-ylidene]-4-(hexyloxy)-1,2-dihydro-7-methoxy-3H-indol-3-one; 1e). According
to GP D with 2e (4.01 g, 6.5 mmol), Na2S2O4 (14.1 g, 69 mmol), and 1m NaOH (250 ml): 3.10 g (86%) of 1e. A
sample was recrystallized from CHCl3. Dark blue solid. M.p. (1058) 2218 (dec., DSC). Rf (cyclohexane/AcOEt
1:1) 0.46. Solubility: 140 mg/ml of CHCl3. UV/VIS (CHCl3): 736 (13430), 374 (sh, 8510), 328 (20750). IR
(CCl4): 3442, 3424, 3374 (NH, NH2), 2958, 2935, 2861, 1622 (CO), 1508, 1446, 1398, 1339, 1270, 1199, 1120, 1058,
955, 933. 1H-NMR (360 MHz, CDCl3): 0.89 (t, 3J ˆ 7.0, 2 Me(6')); 1.2 1.5 (2 CH2(3'), 2 CH2(4'), 2 CH2(5')); 1.80
(m, 2 CH2(2')); 3.5 (2 NH2); 3.81 (s, 2 MeO); 4.20 (t, 3J ˆ 6.6, 2 CH2(1')); 6.47 (s, 2 arom. H); 8.74 (2 NH).
1H-NMR (500 MHz, CDCl3): 8.74 (d, 1J (N,H) ˆ 103.0 Æ 0.5, 2 NH). 13C-NMR (90.5 MHz, CDCl3): 14.0 (q,
Me(6')); 22.6 (t, C(5')); 25.7, 30.3, 31.7 (3t, C(2'), C(3'), C(4')); 55.9 (q, MeO)); 74.5 (t, C(1')); 107.1 (d, arom.
C(6')); 113.3 (s, arom. C(3a,3'a)); 122.0 (s, arom. C(2,2')); 132.6 (s, arom. C(5,5')); 134.9 (s, arom. C(7a,7'a));
‡
‡
136.9 (s, arom. C(4,4')); 141.2 (s, arom. C(7,7')); 186.0 (s, arom. C(3,3')). EI-MS: 553 (45, M ), 552 (100, M ),
‡
‡
‡
467 (52, [M À C6H13] ), 383 (37), 368 (28), 353 (16), 192 (22). HR-MS: 552.2947 (M , C30H40N4O6 ; calc.
552.2946).
Hydrochloride of 1e. Indigotin 1e was dissolved in a sat. HCl soln. in MeOH. After 1 d at r.t., the solvent
was evaporated: hydrochloride of 1e. Dark blue solid. UV/VIS (MeOH, sat. soln.): 648, 310, 296. IR (KBr):
‡
3415 (NH), 2930, 2858, 2585 (NH3 ), 1654, 1648, 1637 (CO), 1598, 1498, 1405, 1278, 1209, 1117, 1050, 923.
5,5'-Diamino-4,4'-bis(heptyloxy)-7,7'-dimethoxyindigotin (ˆ 5-Amino-2-[5-amino-4-(heptyloxy)-1,3-dihy-
dro-7-methoxy-3-oxo-2H-indol-2-ylidene]-4-heptyloxy-1,2-dihydro-7-methoxy-3H-indol-3-one; 1f). According
to GP D with 2f (3.27 g, 5.1 mmol), Na2S2O4 (11.2 g, 55 mmol) and 1m NaOH (250 ml): 2.38 g (80%) of 1f. A
sample was recrystallized from CHCl3. Dark blue solid. M.p. (1188) 1968 (dec., DSC). Rf (cyclohexane/AcOEt
1:1) 0.51. Solubility: 207 mg/ml of CHCl3. UV/VIS (CHCl3): 736 (11250), 376 (sh, 9150), 328 (1780). IR (CCl4):
3442, 3419, 3372 (NH, NH2), 2957, 2931, 2858, 1622 (CO), 1508, 1466, 1447, 1398, 1340, 1271, 1234, 1200, 1120,
1056, 931. 1H-NMR (360 MHz, CDCl3): 0.89 (t, 3J ˆ 7.0, 2 Me(7')); 1.2 1.5 (16 H, 2 CH2(3') to 2 CH2(6')); 1.80
3
(m, 2 CH2(2')); 3.1 (2 NH2); 3.82 (s, 2 MeO), 4.29 (t, J ˆ 6.6, 2 CH2(1')); 6.47 (s, 2 arom. H,); 8.76 (2 NH).
13C-NMR (90.5 MHz, CDCl3): 14.1 (q, Me(7')); 22.6 (t, C(6')); 26.0, 29.2, 30.4, 31.8 (4t, C(2'), C(3'), C(4'),
C(5')); 55.9 (q, 2 MeO), 74.5 (t, C(1')); 107.1 (d, arom. C(6,6')); 113.3 (s, arom. C(3a,3'a)); 122.0 (s, arom.
C(2,2')); 132.6 (s, arom. C(5,5')); 134.9 (s, arom. C(7a,7'a)); 136.9 (s, arom. C(4,4')); 141.2 (s, arom. C(7,7'));
‡
‡
‡
186.0 (s, arom. C(3,3')). EI-MS: 581 (38, M ), 580 (100, M ), 481 [(72, M À C7H15] ), 383 (85), 368 (60), 353
‡
‡
(58), 192 (45). HR-MS: 580.3259 (M , C32H44N4O6 ; calc. 580.3260).
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Received October 15, 2002