Formation of the fused system 5H,7H-pyrido[2,3-b:6,5-b′]diindole from 3-arylidene-2-ethoxyindolenines and hydrazine hydrate

Article abstract of DOI:10.1007/s11172-012-0045-2

Three 12-aryl-5H,7H-pyrido[2,3-b:6,5-b′]diindoles (Ar = Ph, 4-BrC₆H₄, and 4-MeOC₆H₄) were obtained from appropriate 3-arylidene-2-ethoxyindolenines and hydrazine hydrate.

Full text of DOI:10.1007/s11172-012-0045-2

Russian Chemical Bulletin, International Edition, Vol. 61, No. 2, pp. 326—331, February, 2012
326
Formation of the fused system 5H,7Hꢀpyrido[2,3ꢀb:6,5ꢀb´]diindole
from 3ꢀarylideneꢀ2ꢀethoxyindolenines and hydrazine hydrate
V. P. Borovik, Yu. V. Gatilov, M. M. Shakirov, and O. P. Shkurko
N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences,
9 prosp. Akad. Lavrent´eva, 630090 Novosibirsk, Russian Federation.
Fax: +7 (383 2) 34 4752. Eꢀmail: oshk@nioch.nsc.ru
Three 12ꢀarylꢀ5H,7Hꢀpyrido[2,3ꢀb:6,5ꢀb´]diindoles (Ar = Ph, 4ꢀBrC6H4, and 4ꢀMeOC6H4)
were obtained from appropriate 3ꢀarylideneꢀ2ꢀethoxyindolenines and hydrazine hydrate.
Key words: 3ꢀarylideneꢀ2ꢀethoxyindoleninium tetrafluoroborates, 12ꢀarylꢀ5H,7Hꢀpyridoꢀ
[2,3ꢀb:6,5ꢀb´]diindoles, cyclocondensation.
Earlier, we have proposed a route to a number of
that the starting lactams containing a cyano or ester group
in the ꢀposition relative to the carbonyl group are first
transformed into reactive lactim ethers. These data sugꢀ
gested that an analogous reaction of compound 5 with
hydrazine hydrate could result in the formation of the
pyrazole ring annulated to the indole one, thus yielding
3ꢀphenylpyrazolo[3,4ꢀb]indole (8).
2ꢀsubstituted 4ꢀarylꢀ9Hꢀpyrimido[4,5ꢀb]indoles 1 via reꢀ
actions of 3ꢀarylideneindolinꢀ2ꢀones 2—4 (preconverted
into reactive lactim ether forms) with such binucleophiles
as amidines, guanidine, nitroguanidine, and alkylisothioꢀ
ureas1—4 (Scheme 1). The next step in this direction was
the synthesis of other fused heterocyclic systems from preꢀ
paratively accessible indolinꢀ2ꢀones. For this purpose, we
studied reactions of hydrazine hydrate with a lactim ether
generated from 3ꢀbenzylideneꢀ2ꢀethoxyindoleninium tetꢀ
rafluoroborate (5). It has been reported5,6 that hydrazine
hydrate reacts with carbocyclic and heterocyclic lactams
to give heterocyclic systems of five fused rings, provided
However, this reaction did not lead to the expected
product 8. Instead, we obtained a compound in 23% yield,
its molecular weight corresponding to the empirical forꢀ
mula C23H15N3 (HRMS data).
1
We examined the H and 13C NMR spectra of this
compound using 2D experiments (COSY, HSQC, and
Scheme 1
R = Me, Ph, NH2, NHNO2, NHSO2Ar, SMe, SEt (1); R´ = H (2, 5), 4ꢀBr (3, 6, 10), 4ꢀMeO (4, 7, 11)
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 324—329, February, 2012.
1066ꢀ5285/12/6102ꢀ326 © 2012 Springer Science+Business Media, Inc.

12ꢀArylꢀ5H,7Hꢀpyrido[2,3ꢀb:6,5ꢀb´]diindoles
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 2, February, 2012
327
COLOC). The 1H NMR spectrum shows a lowꢀfield sinꢀ
glet for two NH groups, a complex multiplet for one
phenyl group, and four multiplets of double intensity at
 6.90—7.80 characteristic of indoles having no substituꢀ
ents in the benzene ring. This spectral pattern suggested
the presence of two symmetrical indole moieties and a
phenyl group in the structure of the compound obtained.
So we formulated it as 12ꢀphenylꢀ5H,7Hꢀpyridoꢀ
[2,3ꢀb:6,5ꢀb´]diindole (9). The chemical shifts of the sigꢀ
nals for the indole protons and carbon atoms mostly agree
with the NMR data for substituted 9Hꢀpyrimido[4,5ꢀb]ꢀ
indole7 and 6Hꢀindolo[2,3ꢀb]quinoline.8 However, the
doublet we assigned to the H(1) and H(11) protons is
substantially shifted upfield compared to the signal for the
analogous H(5) proton in both the parent 9Hꢀpyrimidoꢀ
[4,5ꢀb]indole and structurally related compound 1 (R = Me).
This discrepancy can stem from the conformational feaꢀ
tures of compound 9.
phenyl substituent with allowance for the aforementioned
geometrical parameters of structure 9 reveal that the anisoꢀ
tropic effect of the orthogonally oriented phenyl substituꢀ
ent on the nearest H(1) and H(11) protons should be
2—1 ppm when the resonating proton is distant from the
plane of the benzene ring by 3—4 Å, respectively.9
The positions of the signals for the indole protons in
1
the H NMR spectrum of compound 9 as well as the
positions of the signals for analogous protons in unsubꢀ
stituted 9Hꢀpyrimido[4,5ꢀb]indole and its 2ꢀmethylꢀ4ꢀ
phenyl derivative 1 (R = Me) are schematically shown in
Fig. 2. The diamagnetic shift of the signal for the H(1) and
H(11) protons in compound 9 compared to the signal for
the H(5) proton in pyrimidoindole (P) is 1.2 ppm, which
agrees with the theoretical prediction.
To refine its structure, we studied Xꢀray diffraction
from the crystalline solvate 2C23H15N3•CHCl3 grown
from a chloroform solution (Fig. 1).
According to the data obtained, the unit cell of the
crystal structure 9 consists of two crystallographically inꢀ
dependent molecules. The pentacyclic framework is nearꢀ
ly planar (to within 0.08 and 0.09 Å), making an angle
of 73.30(8) and 83.57(8) with the phenyl ring. When an
external magnetic filed is applied to a sample of comꢀ
pound 9 during an NMR experiment, this field induces a
ring current in the phenyl substituent that creates diamagꢀ
netic shielding around the aromatic H(1) and H(11) proꢀ
tons and causes their resonance signal to shift upfield.
According to our calculations, the H(1) and H(11) proꢀ
tons are distant from the center of the benzene ring of the
phenyl substituent at, on average, 3.02 Å for normalized
C—H bond lengths. The GIAO—HF/6ꢀ31G*ꢀcalculated
maps9 of the anisotropic effect of the ring current in the
In compound 1, the ring current of the phenyl group
produces a weaker shielding effect on the indole protons
(see Fig. 2) because the angle between the plane of
this substituent and the heterocyclic framework does
not exceed 42.7 (Xꢀray diffraction data3); in addition,
the distance between the H(5) atom and the center
of the benzene ring of the phenyl substituent increases
to 3.40 Å.
In compound 9, the aromatic protons H(2), H(10),
H(3), H(9), and H(4), H(8) are farther away from the
phenyl substituent and the diamagnetic shielding of these
protons gradually becomes weaker, which is manifested in
the positions of the signals for H(2) and H(10) in the
1H NMR spectrum.
C(17)
C(16)
C(18)
C(11)
C(15)
C(10)
C(13)
C(12)
C(2)
C(1)
C(9)
C(8)
C(11B)
C(14)
C(3)
C(11A)
C(12B)
C(12A)
C(5A)
C(7A)
N(7)
C(6A)
C(4A)
C(4)
N(5)
N(6)
Fig. 1. One of two crystallographically independent molecules in structure 9 with atomic displacement ellipsoids (p = 50%).

328
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 2, February, 2012
Borovik et al.
a
b
7
6
8
5
c
1, 11
2, 10
4, 8
3, 9
8.0
7.5
7.0

Fig. 2. Positions of the signals for the aromatic protons of the indole fragments in the 1H NMR spectra (DMSOꢀd6) of 9Hꢀpyrimidoꢀ
[4,5ꢀb]indole (P) (a), 2ꢀmethylꢀ4ꢀphenylꢀ9Hꢀpyrimido[4,5ꢀb]indole 1 (b), and 12ꢀphenylꢀ5H,7Hꢀpyrido[2,3ꢀb:6,5ꢀb´]diindole (9) (c).
Earlier,10—12 structurally related N(5),N(7)ꢀdimethylꢀ
and N(5),N(7)ꢀdibenzylpyridodiindoles have been obꢀ
tained by reactions of 2ꢀaminoꢀ1ꢀmethylꢀ and 2ꢀaminoꢀ
1ꢀbenzylindoles with carbonyl compounds. The proꢀ
posed10—12 sequence of transformations leading to the anꢀ
nulated pyridine ring implies the formation of a bis(aminoꢀ
indolyl)methylene intermediate containing two identical
enamine moieties. At a final step, the amino group of one
moiety attacks the ꢀC atom of the other enamine moiety
to give, through elimination of an ammonia molecule and
dehydrogenation, the pyridodiindole system. The ratio of
the nucleophilicity of the amino group and the electroꢀ
philicity of the ꢀC atom of the enamine moieties is essential
for the cyclization reaction. Attempts to increase the yield
of the target product by using an oxindole derivative as
a second condensation component (instead of aminoindole)
in the final step of the reaction were unsuccessful. This
provides clear evidence that the amide CO group of oxinꢀ
dole is inert to Nꢀnucleophiles in these transformations.11
We propose a hypothetical scheme for the formation
of pyridodiindole 9 (Scheme 2). The starting lactim ether
12 generated by decomposition of tetrafluoroborate 5 is
a mixture of Eꢀ/Zꢀstereoisomers in a very unequal ratio
(1H NMR). The identification of the major isomer from
spectroscopic data for the Eꢀ and Zꢀisomers of 3ꢀbenzylꢀ
ideneoxindole proved to be inconclusive because their
spectroscopic characteristics differ only slightly,13—15 exꢀ
cept for the chemical shifts of the signals for the orthoꢀ
protons of the benzylidene group ( 8.28 for Zꢀisomer and
 7.62 for Eꢀisomer16). This agrees well with  7.64 found
by us for the major isomer of compound 12. The actual
configuration of this isomer was unambiguously deterꢀ
mined by a NOESY experiment that revealed the Overꢀ
hauser effect between the orthoꢀprotons of the phenyl subꢀ
stituent and the indole H(4) proton, which are spatially
close to each other: by analogy with the Eꢀisomer of
3ꢀbenzylideneoxindole in the twist(49)ꢀconformation of
the phenyl group, they are spaced at 2.48 Å (see Ref. 16).
The presence of a small impurity of the Zꢀisomer in comꢀ
pound 12 is evident from a triplet and a quartet for the
1
group —OCH2Me in the H NMR spectrum, which are
shifted upfield by 0.10 and 0.05 ppm, respectively, comꢀ
pared to analogous signals for the Eꢀisomer. The E/Z ratio
of compound 12 is ~13 : 1.
Tetrafluoroborate 5 was treated with an equimolar
amount of EtONa and the resulting lactim ether 12 was
used in situ in a reaction with hydrazine hydrate. During
the condensation, the reactants underwent a number
of hypothetical transformations (Scheme 2) leading to
pyridodiindole 9. It is not improbable, however, that
the sequence of some steps can be different or they can
occur simultaneously, involving prototropic tautomers
17,18

13A
13B.

Apparently, the first step of this reaction is partial retꢀ
roꢀcrotonic decomposition of the starting compound into
benzaldehyde (identified as 2,4ꢀdinitrophenylhydrazone
in a model experiment) and unsubstituted lactim ether 13.
The latter is unstable and known to react as either or both
of its tautomers (13A and 13B) at the CH2/CH and lactim
ether fragments with nucleophiles, electrophiles, and unꢀ
saturated compounds. In addition, it can undergo selfꢀ
condensation, e.g., into indirubin.19—21 Indirubin was deꢀ
tected by TLC among the reaction products obtained from
hydrazine hydrate or phenylhydrazine and lactim ether
12, which provides indirect evidence for its retroꢀcrotonic
decomposition. Possible cleavage of the exocyclic double
bond of the arylidene group in a series of 3ꢀsubstituted
indoles has been noted earlier.11
Having an active CH2 group, lactim ether 13 easily
adds to the double bond of the starting ylidene derivative
12 to give compound 14 containing two indole moieties,
in accord with similar transformations of such indole deꢀ
rivatives in the Michael reaction.12,22,23 Since comꢀ
pound 14 contains two lactim ether fragments, its reacꢀ

12ꢀArylꢀ5H,7Hꢀpyrido[2,3ꢀb:6,5ꢀb´]diindoles
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 2, February, 2012
329
Scheme 2
tion with hydrazine hydrate can follow two pathways:
(1) hydrolysis of one lactim ether to lactam 15 and (2) reꢀ
placement of the ethoxy group by the hydrazine residue,
giving rise to compound 16. However, the latter pathway
seems to be preferred because hydrazine is a stronger nuꢀ
cleophile than water. The presence of a reactive amidraꢀ
zone fragment in the indole ring of compound 16, which
becomes even more nucleophilic in the anionic form, enꢀ
ables the imine N atom to attack the neighboring lactim C
atom with elimination of the ethoxy group. This results in
closure of the pyridine ring, with an ammonia molecule
being released.
Structure 18, even though formed from precursors 15
and/or 16, can hardly undergo cyclization according to
available data on the lowered reactivity of the carbonyl
group in the oxindole structure.11
To find out whether the aforementioned transformaꢀ
tions are of general character, we also used 3ꢀ(4ꢀbromoꢀ
benzylidene)ꢀ2ꢀethoxyindoleninium tetrafluoroborate (6)
and 2ꢀethoxyꢀ3ꢀ(4ꢀmethoxybenzylidene)indoleninium
tetrafluoroborate (7) in reactions with hydrazine hydrate.
Compounds 6 and 7 were prepared from 3ꢀarylideneꢀ
oxindoles 3 and 4, respectively, as described1 for benzylꢀ
idene analog 5. The yields of the corresponding bromoꢀ
phenylꢀ and methoxyphenylpyridodiindoles 10 and 11
were as low as that of phenylpyridodiindole 9. The low
yields of the target pyridodiindoles 9—11 and the formaꢀ
tion of many minor byꢀproducts (TLC) are due to the
formation of several intermediates during the condensaꢀ
tion that are comparable in reactivity and complicate the
desired process.
To sum up, our method for the synthesis of 5H,7Hꢀ
pyrido[2,3ꢀb:6,5ꢀb´]diindoles involves 3ꢀarylideneꢀ2ꢀethꢀ
oxyindolenines as the starting materials, which is fundaꢀ
mentally different from a previous approach.10—12 In our case,
the closure of the pyridine ring proceeds by a nucleophilic
attack of the hydrazino group that has been introduced
into the indolenine structure under the action of hydrazine
hydrate. Our method affords earlier unknown N(5),N(7)ꢀ
unsubstituted analogs 9—11 of this heterocyclic system.
Experimental
Mass spectra were measured on a Thermo DFS instrument
(EI, 70 eV, direct inlet probe). 1H and 13C NMR spectra were
recorded on Bruker AVꢀ400 and Bruker AVꢀ600 spectrometers;

330
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 2, February, 2012
Borovik et al.
the following solvents (and their signals as the internal stanꢀ
dards) were used: DMSOꢀd6 (H 2.50, C 39.50) for compounds
9—11 and CDCl3 ( 7.24,  76.91) for compound 12. The
course of the reactions was monitored and the purity of the
products was checked by TLC on Silufol UVꢀ254 plates with
EtOAc—CHCl3 (1 : 1 and 1 : 3) as an eluent; spots were visualꢀ
ized under UV light.
(E)ꢀ3ꢀBenzylideneꢀ2ꢀethoxyindolenine (12). A 50% aqueous
solution of K2CO3 was added dropwise at 0—5 C to a stirred
solution of tetrafluoroborate 5 (5.0 g, 14.8 mmol) in CH2Cl2
(50 mL) to pH 8. The mixture was stirred for 0.5 h and then
water (100 mL) was added. The organic phase was separated and
the organic material from the aqueous phase was extracted with
CH2Cl2 (4×30 mL). The combined organic extract was washed
with water to pH 6, dried over MgSO4, concentrated to dryness
on a vacuum evaporator, and desiccated in vacuo over P2O5 and
KOH. Yield 2.53 g (68%), m.p. 75—79 C. Found (%): C, 81.29,
81.16; H, 5.81, 5.98; N, 5.68, 5.71. C17H15N3O. Calculated (%):
C, 81.90; H, 6.06; N, 5.62. MS, m/z (Irel (%)): 249 [M]+ (88),
221 (83), 220 [M – C2H5]+ (100), 193 (46), 165 (46), 144 (41),
105 (12). HRMS: found: m/z 249.1147 [M]+; C17H15N3O; calꢀ
culated: M = 249.1148. 1H NMR (600 MHz), : 1.48 (t, 3 H,
120.223 (C(1), C(2)); 121.258 (C(11a), C(12b)); 124.607 (C(3),
C(9)); 128.173 (oꢀC); 128.735 (pꢀC); 129.324 (mꢀC); 137.239
(ipsoꢀC); 138.461 (C(4a), C(7a)); 139.258 (C(12); 151.374
(C(5a), C(6a)).
3ꢀ(4ꢀBromobenzylidene)ꢀ2ꢀethoxyindoleninium tetrafluoroꢀ
borate (6) and 2ꢀethoxyꢀ3ꢀ(4ꢀmethoxybenzylidene)indoleninium
tetrafluoroborate (7) were obtained by alkylation of appropriate
3ꢀarylideneindolinones 3 and 4 with Et3O—BF4 as described1
for compound 5.
Compound 6, m.p. 157—160 C. Found (%): C, 48.97, 48.34;
H, 3.49, 3.32; Br, 19.40, 19.80; F, 18.29, 18.44; N, 3.46, 3.68.
C17H15BrNO•BF4. Calculated (%): C, 49.07; H, 3.63; Br, 19.21;
F, 18.27; N, 3.37.
Compound 7, m.p. 187—190 C. Found (%): C, 58.79, 58.48;
H, 4.90, 4.88; F, 20.65, 20.35; N, 4.02, 4.12. C18H18NO2•BF4.
Calculated (%): C, 58.88; H, 4.94; F, 20.70; N, 3.82.
12ꢀ(4ꢀBromophenyl)ꢀ5H,7Hꢀpyrido[2,3ꢀb:6,5ꢀb´]diindole
(10) was obtained from tetrafluoroborate 6 as described for comꢀ
pound 9. Yield 23%, m.p. 297—299 C (from EtOH). Found (%):
C, 67.00, 67.00; H, 3.62, 3.73; Br, 19.14, 19.06; N, 9.87, 9.82.
C23H14BrN3. Calculated (%): C, 67.00; H, 3.42; Br, 19.38;
N, 10.19. MS, m/z (Irel (%)): 413 [M]+ (99), 411 [M]+ (100), 332
[M – Br]+ (13), 331 (33), 330 (13), 166 (22), 165 (20), 149 (24).
HRMS: found: m/z 411.0362 [M]+; C23H14Br79N3; calculated:
M = 411.0366. 1H NMR (400 MHz), : 6.94 (dd, 2 H, 3J = 7.0 Hz,
3J = 7.8 Hz); 7.08 (d, 2 H, 3J = 7.2 Hz); 7.29 (dd, 2 H, 3J = 7.0 Hz,
3J = 7.8 Hz); 7.46 (d, 2 H, 3J = 8.0 Hz); 7.63 (d, 2 H, 3J = 8.0 Hz);
7.93 (d, 2 H, 3J = 7.5 Hz); 11.83 (s, 2 H, NH). 13C NMR
(100 MHz), : 108.12; 111.23; 119.36; 120.49; 121.38; 122.44;
125.11; 130.96; 132.74; 136.80; 138.13; 138.85; 151.68.
12ꢀ(4ꢀMethoxyphenyl)ꢀ5H,7Hꢀpyrido[2,3ꢀb:6,5ꢀb´]diindole
(11) was obtained from tetrafluoroborate 7 as described for comꢀ
pound 9. Yield 23%, m.p. 273—279 C (from EtOH). Found
(%): C, 79.25, 78.87; H, 5.09, 5.15; N, 11.06, 10.70. C24H17N3O.
Calculated (%): C, 79.32; H, 4.72; N, 11.56. MS, m/z (Irel (%)):
363 [M]+ (100), 333 [M – OCH2]+ (13), 3.19 (12), 318 (14).
HRMS: found: m/z 363.1365 [M]+; C24H17N3O; calculated:
M = 363.1366. 1H NMR (400 MHz), : 3.95 (s, 3 H, Me); 6.93
(dd, 2 H, 3J = 7.3 Hz, 3J = 7.5 Hz); 7.08 (d, 2 H, 3J = 7.8 Hz);
7.28 (t, 2 H, 3J = 7.3 Hz); 7.29 (d, 2 H, 3J = 7.9 Hz); 7.45 (d, 2 H,
3J = 7.9 Hz); 7.58 (d, 2 H, 3J = 8.4 Hz); 11.76 (s, 2 H, NH).
13C NMR (100 MHz), : 55.26; 108.31; 110.76; 114.64;
118.87; 120.34; 121.41; 124.57; 129.11; 129.64; 138.45; 139.34;
151.42; 159.47.
H
C
3
3
Me, J = 7.1 Hz); 4.55 (q, 2 H, CH2, J = 7.1 Hz); 6.88 (ddd,
1 H, H(5), 3J = 7.7 Hz, 3J = 7.4 Hz, 4J = 0.9 Hz); 7.21 (ddd, 1 H,
H(6), 3J = 7.7 Hz, 3J = 7.6 Hz, 4J = 0.8 Hz); 7.27 (d, 1 H, H(7),
3J = 7.6 Hz); 7.41 (t, 1 H, pꢀH, Ph, J = 7.3 Hz); 7.45 (t, 2 H,
3
mꢀH, Ph, 3J = 7.3 Hz); 7.57 (d, 1 H, H(4), 3J = 7.6 Hz); 7.61
(s, 1 H, =CH); 7.64 (d, 2 H, oꢀH, Ph, J = 7.3 Hz). 13C NMR
3
(125 MHz), : 14.39 (Me); 64.89 (CH2); 118.28 (C(7)); 122.11
(C(4)); 122.79 (C(5)); 126.42 (C(3)); 128.49 (mꢀC); 129.37
(oꢀC); 129.48 (pꢀC); 129.66 (C(6)); 130.11 (iꢀC); 134.65 (C(3a)),
135.53 (=CH); 154.26 (C(7a)), 171.60 (C(2)).
12ꢀPhenylꢀ5H,7Hꢀpyrido[2,3ꢀb:6,5ꢀb´]diindole (9). Tetraꢀ
fluoroborate 5 (3.0 g, 8.9 mmol) was added in portions at 0—5 C
to a stirred solution of EtONa prepared from metallic sodium
(0.21 g, 8.9 mgꢀatom) and anhydrous ethanol (40 mL). Then
hydrazine hydrate (0.52 g, 10 mmol) was added. The mixture
was warmed to 20 C and then refluxed for 6 h. On cooling, the
precipitate of NaBF4 was filtered off, the filtrate was concentratꢀ
ed to dryness in vacuo on a rotary evaporator at 50 C. The yield
of crude product 9 containing several minor compounds (TLC)
was 2.5 g.
Part of this product (157 mg) was separated by preparative
TLC on Silufol UVꢀ254 plates in EtOAc—CHCl3 (1 : 1). The
UVꢀluminescent zone with Rf  0.6 was collected. The individuꢀ
al product was extracted with hot ethanol. The extract was conꢀ
centrated in vacuo at 50 C. The yield of compound 9 was 22 mg
(23% with respect to the starting tetrafluoroborate 5), m.p.
309—311 C (from CHCl3). Found (%): C, 71.18, 70.36; H, 4.07,
4.01; N, 10.73, 10.71. 2C23H15N3•CHCl3. Calculated (%):
C, 71.71; H, 3.84; N, 10.68. MS, m/z (Irel (%)): 333 [M]+ (100),
332 [M – H]+ (22), 331 [M – 2H]+ (22), 166 (8). HRMS: found:
m/z 333.1258 [M]+; C23H15N3; calculated: M = 333.1261.
1H NMR (600 MHz), : 6.909 (ddd, 2 H, H(2), H(10), 3J = 7.9 Hz,
3J = 7.95 Hz, 4J = 0.6 Hz); 6.958 (dd, 2 H, H(1), H(11), 3J = 7.9 Hz,
4J = 1.0 Hz); 7.281 (ddd, 2 H, H(3), H(9), 3J = 8.0 Hz,
3J = 7.95 Hz, 4J = 0.7 Hz); 7.456 (dt, 2 H, H(4), H(8),
3J = 8.0 Hz, 4J = 0.6 Hz, 4J = 0.6 Hz); 7.64—7.67 (m, 2 H, oꢀH,
Ph); 7.69—7.73 (m, 1 H, pꢀH, Ph); 7.73—7.77 (m, 2 H, mꢀH,
Ph); 11.783 (s, 2 H, NH). 13C NMR (125 MHz), : 107.966
(C(11b), C(12a)); 110.770 (C(4), C(8)); 118.847 (C(2), C(10));
Singleꢀcrystal Xꢀray diffraction study of 12ꢀphenylꢀ5H,7Hꢀ
pyrido[2,3ꢀb:6,5ꢀb´]diindole (9) was carried out on a Bruker Kapꢀ
pa APEX II CCD diffractometer (graphite monochromator,
(MoꢀK) = 0.71073 Å, 173 K, , scan mode, 2 < 52.74).
Triclinic pink crystals, 2(C23H15N3) + CHCl3, M = 786.13, space
group P–1, a = 12.0759(4) Å, b = 12.9906(5) Å, c = 13.5779(5) Å,
3
 = 104.931(2),  = 111.853(2),  = 92.890(2), V = 1884.60(12) Å ,
Z = 2, Dcalc = 1.385 g cm–3,  = 0.288 mm–1. The intensities of
29 187 reflections from a single crystal (0.14×0.15×0.60 mm)
were measured. The number of independent reflections was 7695
(Rint = 0.0432); the number of reflections with I > 2(I) was
5742. The number of parameters refined was 549, R = 0.0677
(I > 2(I)), wR2 = 0.2000, GOOF = 1.067 (for all reflections).
An absorption correction was applied with the SADABS proꢀ
gram (Tmin/Tmax = 0.786/0.862). The structure was solved by
direct methods. The coordinates and thermal parameters of the
nonꢀhydrogen atoms were refined anisotropically by the fullꢀ

12ꢀArylꢀ5H,7Hꢀpyrido[2,3ꢀb:6,5ꢀb´]diindoles
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 2, February, 2012
331
matrix leastꢀsquares method. The amino H atoms were located
in difference electronꢀdensity maps and refined isotropically.
The other H atoms were refined using a riding model. The solꢀ
vate CHCl3 molecule is disordered over two positions in a ratio
of 0.604(4) : 0.396(4). All calculations were performed with the
SHELXTL program package. Atomic coordinates and thermal
parameters have been deposited with the Cambridge Crystalloꢀ
graphic Data Center (CCDC No. 824888).
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Received May 19, 2011;
in revised form October 11, 2011