Synthesis of novel [1,3]thiazino[3,2:2,3][1,2,4]triazino[5,6-b]indole derivatives

Article abstract of DOI:10.1007/s11172-015-0952-0

4-Substituted 2,3-dihydro-11H-[1,3]thiazino[3,2:2,3][1,2,4]triazino[5,6-b]indolium halides were first synthesized by the reactions of 3-(3-butenylthio)and 3-prenylthio-5H[1,2,4]thiazino[5,6-b]indoles with bromine and iodine. The structures of the synthesized compounds were evaluated by ¹H and ¹³C NMR spectroscopy involving 2D NMR techniques (¹H - ¹H COSY, ¹H - ¹³C HSQC, and ¹H - ¹³C HMBC).

Full text of DOI:10.1007/s11172-015-0952-0

Russian Chemical Bulletin, International Edition, Vol. 64, No. 4, pp. 901—904, April, 2015
901
Synthesis of novel
[1,3]thiazino[3´,2´:2,3][1,2,4]triazino[5,6ꢀb]indole derivatives
A. V. Rybakova,a D. G. Kim,a M. A. Ezhikova,b M. I. Kodess,b and I. A. T. Taherc
aSouth Ural State University,
76 prosp. V. I. Lenina, 454080 Chelyabinsk, Russian Federation.
Fax: +7 (351) 267 9900. Eꢀmail: kim_dg48@mail.ru, dgkim@susu.ac.ru
bI. Ya. Postovsky Institute of Organic Chemistry, Russian Academy of Sciences,
22/20 ul. S. Kovalevskoy, 620990 Yekaterinburg, Russian Federation.
Fax: +7 (343) 369 3058. Eꢀmail: nmr@ios.uran.ru
cAlꢀMuthanna University,
Samawah, AlꢀMuthanna Province, Irag.
Eꢀmail: ehababbas81_fz@yahoo.com
4ꢀSubstituted 2,3ꢀdihydroꢀ11Hꢀ[1,3]thiazino[3´,2´:2,3][1,2,4]triazino[5,6ꢀb]indolium
halides were first synthesized by the reactions of 3ꢀ(3ꢀbutenylthio)ꢀ and 3ꢀprenylthioꢀ5Hꢀ
[1,2,4]thiazino[5,6ꢀb]indoles with bromine and iodine. The structures of the synthesized comꢀ
pounds were evaluated by 1H and 13C NMR spectroscopy involving 2D NMR techniques
(1H—1H COSY, 1H—13C HSQC, and 1H—13C HMBC).
Key words: 3ꢀ(3ꢀbutenylthio)ꢀ and 3ꢀprenylthioꢀ5Hꢀ[1,2,4]triazino[5,6ꢀb]indoles, 2,3,4,11ꢀ
tetrahydro[1,3]thiazino[3´,2´:2,3][1,2,4]triazino[5,6ꢀb]indolium halides, halocyclization.
Earlier, derivatives of [1,3]thiazino[3´,2´:2,3][1,2,4]ꢀ
triazino[5,6ꢀb]indoles possessing high level of antibacterial
activity have been synthesized by the reaction of 2,3ꢀsubꢀ
stituted 2,3ꢀdihydroꢀ5Hꢀ[1,2,4]triazino[5,6ꢀb]indoleꢀ3ꢀ
thione with 1,3ꢀdibromopropane in DMF—anhydrous
EtOH.1—7
With the aim to synthesize novel derivatives of [1,3]ꢀ
thiazino[3´,2´:2,3][1,2,4]triazino[5,6ꢀb]indoles, we first
studied in detail the reactions of 3ꢀ(3ꢀbutenylthio)ꢀ5Hꢀ
[1,2,4]triazino[5,6ꢀb]indole (1a) and 3ꢀprenylthioꢀ5Hꢀ
[1,2,4]triazino[5,6ꢀb]indole (1b) with bromine and iodine
(Scheme 1). Synthesis of compounds 1a,b can be accomꢀ
plished by either alkylation of 5Hꢀ[1,2,4]triazino[5,6ꢀb]ꢀ
indoleꢀ3ꢀthione (2) with 4ꢀbromobutene and 4ꢀbromoꢀ2ꢀ
methylꢀ2ꢀbutene (prenyl bromide) in KOH—H2O—DMSO,
or oneꢀpot procedure from isatin ꢀthiosemicarbazone (3)
without isolation of intermediate 2 following the known
method.8
We found that the reactions of compound 1a with broꢀ
mine and iodine give 2,3ꢀdihydroꢀ4H,11Hꢀ4ꢀhalomethylꢀ
[1,3]thiazino[3´,2´:2,3][1,2,4]triazino[5,6ꢀb]indolium haꢀ
lides (4, 5). We suggest that cyclization of compound 1a
involves the N(2) atom similarly to previously described9,10
iodocyclization of 3ꢀallylthioꢀ5Hꢀ[1,2,4]triazino[5,6ꢀb]ꢀ
indole of a linear structure (Xꢀray diffraction data). It
should be noted that according to Xꢀray diffraction analysis
protonation of 3ꢀallylthioꢀ5Hꢀ[1,2,4]triazino[5,6ꢀb]indole
occurs also at the N(2) atom.11
Structures of the synthesized compounds 4, 5 were
evaluated by 1H and 13C NMR spectroscopy involving 2D
NMR homoꢀ and heteronuclear correlation techniques
1
(1H—1H COSY, H—13C HSQC, and 1H—13C HMBC).
Steric shielding of the carbon atom of the iodomethyl
group of compound 5 leads to its noticeable strong field
shift ( 3.9). According to 1H—13C HSQC data, this carbon
atom is bonded to two magnetically nonequivalent proꢀ
tons ( 3.72 and 3.85), which together with the C(4)H
proton ( 5.15) form the ABX system. This fact was conꢀ
firmed by the relevant correlations in the COSY and
HMBC experiments.
In the case of compound 4, the chemical shift of the
C(1´) atom is not indicative and its value is close to those
of the C(2) and C(3) atoms. It is known that the introducꢀ
tion of the halogen atom results in significant increase in
the direct 13C—1H spinꢀspin coupling constant.12 For sp3
hybridized C atoms of compound 4, the coupling conꢀ
1
stants are as follows: JC—H = 155 Hz (C 38.4), 1JC—H
=
1
= 140 Hz (C 28.0), JC–H = 130 Hz (C 35.8). Conseꢀ
quently, the chemical shift of the C atom of the bromomꢀ
ethyl group is  38.4. Other proton and carbon atom sigꢀ
nals were attributed using homoꢀ and heteronuclear 2D
NMR experiments. Moreover, in the case of compounds 4
and 5, the SCH2 protons were identified by the crossꢀpeak
with the bridgehead C(12a) atom in the HMBC spectrum.
In contrast to 3ꢀallylthioꢀ5Hꢀ[1,2,4]triazino[5,6ꢀb]ꢀ
indole,9,10 reactions of compound 1b with bromine and
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 0901—0904, April, 2015.
1066ꢀ5285/15/6404ꢀ0901 © 2015 Springer Science+Business Media, Inc.

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Rybakova et al.
Scheme 1
R = CH2CH2CH=CH2 (1a), CH2CH=CMe2 (1b); Hal = Br (4), I (5); Hal = Br, n = 3 (6); I, n = 1 (7)
Reagents and conditions: i. RBr, KOH, DMSO, H2O, ~20 C, 3 h; ii. RBr, NaOH, H2O; iii. for compound 6: Br2, AcOH; for
compound 7: 1) I2, CHCl3; 2) NaI, Me2CO; iv. for compound 4: Br2, AcOH; for compound 5: 1) I2, CHCl3; 2) NaI, Me2CO.
iodine proceed with annulation of sixꢀmembered cycle to
give 3ꢀbromoꢀ4,4ꢀdimethylꢀ2,3ꢀdihydroꢀ11Hꢀ[1,3]thiꢀ
azino[3´,2´:2,3][1,2,4]triazino[5,6ꢀb]indolium tribromide
(6) and 3ꢀiodoꢀ4,4ꢀdimethylꢀ2,3ꢀdihydroꢀ11Hꢀ[1,3]ꢀ
thiazino[3´,2´:2,3][1,2,4]triazino[5,6ꢀb]indolium iodide (7),
respectively. This reaction direction is apparently due to
electrophilic attack of halogen atom to ꢀcarbon atom to
give more stable ternary carbocation 8. Structure of comꢀ
pound 6 was confirmed and signals in its 1H and 13C NMR
spectra were assigned using 1H—13C HSQC and 1H—13C
HMBC 2D NMR experiments. According to HSQC specꢀ
trum, the C(3)H and C(2)H2 protons, which form the
ABX spin system, are bonded to the carbon atoms resoꢀ
nating at C 51.64 and 32.97, respectively. Signal of the
C(4) atom located at ꢀposition to the N+ cation exhibits
a low field shift (C 71.61).
The HMBC spectrum reveals the cross peaks of C(4)
atom with methyl group protons, SCH2 protons, C(3)H
protons, and C atoms of the methyl groups at C(4). Quaꢀ
ternary C(6a), C(6b), and C(10a) carbon atoms of the
triazinoindole moiety were identified by cross peaks with
the aromatic protons; the only signal ( 145.9) lacking the
cross peaks in HSQC and HMBC spectra belongs to the
C(11a) atom.
Analysis of NMR spectra completely excluded formaꢀ
tion of 3ꢀ(1ꢀhaloꢀ1ꢀmethylethyl)ꢀ2,3ꢀdihydroꢀ10Hꢀ[1,3]ꢀ
thiazolo[3´,2´:2,3][1,2,4]triazino[5,6ꢀb]indolium halides
(9). In the case of 9, the C(3)H carbon has to be the most
deshielded sp3 carbon atom, which contradicts to our data.
In summary, compound 1a reacts with bromine and
iodine to give 4ꢀhalomethylꢀ2,3ꢀdihydroꢀ4H,11Hꢀ[1,3]ꢀ
thiazino[3´,2´:2,3][1,2,4]triazino[5,6ꢀb]indolium halides

Synthesis of thiazino[1,2,4]triazinoindole
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 4, April, 2015
903
(5 mL), a solution of bromine (0.06 mL, 1.2 mmol) in AcOH
(5 mL) was added dropwise. The reaction mixture was kept at
~20 °C for 24 h, the volatiles were removed in vacuo, and the
residue was treated with acetone. Orange precipitate formed was
collected by filtration, washed with acetone, and dried. Yield
180 mg (68%). M.p. 177—178 C (decomp.). 1H NMR
(500 MHz), : 2.30 (dtd, 1 H, C(3)HA, J = 14.5 Hz, J = 9.1 Hz,
J = 5.0 Hz); 2.52—2.54 (m, 1 H, C(3)HB)*; 3.31 (ddd, 1 H,
C(2)HA, J = 13.6 Hz, J = 8.5 Hz, J = 6.9 Hz); 3.57 (ddd, 1 H,
C(2)HB, J = 13.6 Hz, J = 8.7 Hz, J = 5.0 Hz); 3.99 (dd, 1 H,
C(1´)HA, J = 10.8 Hz, J = 6.9 Hz); 4.06 (dd, C(1´)HB, J = 10.8 Hz,
J = 5.1 Hz); 4.60 (dddd, 1 H, C(4)H, J = 9.1 Hz, J = 6.9 Hz,
J = 5.1 Hz, J = 3.6 Hz); 7.45 (dd, 1 H, H(8), J = 7.7 Hz, J = 7.3 Hz);
7.59 (d, 1 H, H(10), J = 8.2 Hz); 7.71 (dd, 1 H, H(9), J = 8.2 Hz,
J = 7.3 Hz); 8.31 (d, 1 H, H(7), J = 7.7 Hz); 12.69 (s, 1 H, NH).
13C NMR (126 MHz), : 28.0 (C(2)), 35.8 (C(3)), 38.4
(C(1´)), 53.4 (C(4)), 112.7 (C(10)), 117.6 (C(6b)), 121.5 (C(7)),
122.6 (C(8)), 131.0 (C(9)), 140.4 (C(10a)), 141.1 (C(6a)),
146.7 (C(11a)), 166.4 (C(12a)). Found (%): C, 37.14; H, 2.73;
N, 13.26. C13H12Br2N4S. Calculated (%): C, 37.52; H, 2.91;
N, 13.46.
4ꢀIodomethylꢀ2,3ꢀdihydroꢀ4H,11Hꢀ[1,3]thiazino[3´,2´:2,3]ꢀ
[1,2,4]triazino[5,6ꢀb]indolium iodide (5). To a solution of iodine
(203 mg, 0.8 mmol) in CHCl3 (20 mL), compound 1a (102 mg,
0.4 mmol) was added. The reaction mixture was kept at ~20 C
for 24 h, the solvent was removed in vacuo, the residue was
dissolved in acetone (10 mL) and treated with NaI (89 mg,
0.6 mmol). Yellow precipitate formed was collected by filtration,
washed with acetone, and dried. Yield 164 mg (81%). M.p.
199—200 C (decomp.). 1H NMR (500 MHz), : 2.56 (ddt, 1 H,
C(3)HA, J = 15.1 Hz, J = 11.6 Hz, J = 3.7 Hz); 2.89 (dq, 1 H,
C(3)HB, J = 15.1 Hz, J = 4.3 Hz); 3.47 (dt, 1 H, C(2)HA,
J = 12.5 Hz, J = 4.4 Hz); 3.57 (td, 1 H, C(2)HB, J = 12.5 Hz,
J = 3.6 Hz); 3.72 (dd, 1 H, C(1´)HA, J = 10.8 Hz, J = 4.7 Hz);
3.85 (dd, 1 H, C(1´)HB, J = 10.8 Hz, J = 9.0 Hz); 5.15 (dq, 1 H,
C(4)H, J = 9.0 Hz, J = 4.4 Hz); 7.57 (dd, 1 H, H(8), J = 7.7 Hz,
J = 7.5 Hz); 7.72 (d, 1 H, H(10), J = 8.1 Hz); 7.89 (dd, 1 H,
H(9), J = 8.1 Hz, J = 7.5 Hz); 8.32 (d, 1 H, H(7), J = 7.7 Hz);
13.97 (br.s, 1 H, NH). 13C NMR (126 MHz), : 3.9 (C(1´)), 22.8
(C(2)), 25.2 (C(3)), 66.5 (C(4)), 115.0 (C(10)), 116.6 (C(6b)),
123.7 (C(7)), 124.6 (C(8)), 134.6 (C(9)), 141.2 (C(6a)), 145.9
(br.s, C(10a)), 146.8 (C(11a)), 162.2 (C(12a)). Found (%):
C, 30.29; H, 2.28; N, 10.71. C13H12I2N4S. Calculated (%):
C, 30.61; H, 2.37; N, 10.98.
(4, 5); while compound 1b yields 3ꢀhaloꢀ4,4ꢀdimethylꢀ
2,3ꢀdihydroꢀ11Hꢀ[1,3]thiazino[3´,2´:2,3][1,2,4]triazinoꢀ
[5,6ꢀb]indolium halides (6, 7), which was confirmed by
1H and 13C NMR spectroscopy involving homoꢀ and
heteronuclear 2D NMR techniques (1H—1H COSY,
1H—13C HSQC, 1H—13C HMBC).
Experimental
1
H and 13C NMR spectra were recorded with Bruker DRXꢀ400
(400 MHz) and Avanceꢀ500 (500 and 126 MHz) instruments in
DMSOꢀd6. The chemical shifts are given in the  scale relative
to Me4Si (1H) or residual solvent signal (13C,  39.5). Elemental
analyses were performed on a Carlo Erba CHNSꢀO EA 1108
elemental analyzer. Melting points of compounds 1a,b and 4—7
were determined with a Stuart SMP 30 apparatus.
3ꢀ(3ꢀButenylthio)ꢀ5Hꢀ[1,2,4]triazino[5,6ꢀb]indole (1a). A.
To a mixture of compound 2 (202 mg, 1 mmol) and KOH (56 mg,
1 mmol) in H2O (1 mL) and DMSO (10 mL), 4ꢀbromobutene
(135 mg, 1 mmol) and benzyltriethylammonium chloride (40 mg,
0.18 mmol, phase transfer catalyst) were added. The reaction
mixture was stirred at ~20 C for 1.5 h. After 24 h, yellow precipꢀ
itate formed was collected by filtration, washed with water, and
dried. Yield 224 mg (88%). M.p. 262—263 C (from DMF—H2O,
1
5 : 1). H NMR (400 MHz), : 2.54 (m, 2 H, CH2CH=)*; 3.35
(t, 2 H, SCH2, J = 7.2 Hz); 5.08 (ddt, 1 H, J = 10.3 Hz, J = 1.9 Hz,
J = 1.1 Hz); 5.16 (ddt, 1 H, =CH2, J = 17.1 Hz, J = 1.9 Hz,
J = 1.6 Hz); 5.92 (ddt, 1 H, CH=, J = 17.1 Hz, J = 10.3 Hz,
J = 6.6 Hz); 7.43 (t, 1 H, H(8), J = 7.5 Hz); 7.57 (d, 1 H, H(6),
J = 8.1 Hz); 7.69 (dd, 1 H, H(7), J = 8.1 Hz, J = 7.4 Hz); 8.30
(d, 1 H, H(9), J = 7.6 Hz); 12.62 (br.s, 1 H, NH). Found (%):
C, 60.98; H, 4.77; N, 21.43. C13H12N4S. Calculated (%):
C, 60.91; H, 4.72; N, 21.86.
B. A solution of compound 3 (352 mg, 1.6 mmol) in
1 M KOH (30 mL) was refluxed for 3 h, then 4ꢀbromobutene
(216 mg, 1.6 mmol) and benzyltriethylammonium chloride
(40 mg, 0.18 mmol) were added. The mixture was stirred at
~20 C for 1.5 h. Yellow precipitate was collected by filtration,
washed with water, and dried. Yield 158 mg (39%).
3ꢀPrenylthioꢀ5Hꢀ[1,2,4]triazino[5,6ꢀb]indole (1b) was synꢀ
thesized similarly to sulfide 1a by the reaction of compound 2
with prenyl bromide (method A) and oneꢀpot synthesis from
compound 3 (method B) with the exception that no benzyltriꢀ
ethylammonium chloride was added. Yields 83% (method A)
and 21% (method B). Yellow powder. M.p. 165—166 C (from
DMF—H2O, 5 : 1). 1H NMR (400 MHz), : 1.71 (d, 3 H, CH3,
J = 1.4 Hz); 1.77 (d, 3 H, CH3, J = 1.4 Hz); 3.93 (d, 2 H, SCH2,
J = 7.7 Hz); 5.42 (tsept, 1 H, CH=, J = 7.7 Hz, J = 1.4 Hz); 7.43
(ddd, 1 H, H(8), J = 7.8 Hz, J = 7.2 Hz, J = 0.9 Hz); 7.58 (dt, 1 H,
H(6), J = 8.2 Hz, J = 0.9 Hz); 7.69 (ddd, 1 H, H(7), J = 8.2 Hz,
J = 7.2 Hz, J = 1.2 Hz); 8.30 (d, 1 H, H(9), J = 7.8 Hz); 12.59
(s, 1 H, NH). Found (%): C, 62.64; H, 5.41; N, 20.27. C14H14N4S.
Calculated (%): C, 62.20; H, 5.22; N, 20.72.
3ꢀBromoꢀ4,4ꢀdimethylꢀ2,3ꢀdihydroꢀ11Hꢀ[1,3]thiazinoꢀ
[3´,2´:2,3][1,2,4]triazino[5,6ꢀb]indolium tribromide (6). To an
iceꢀcold solution of compound 1b (540 mg, 2 mmol) in AcOH
(30 mL), a solution of bromine (0.21 ml, 4 mmol) in AcOH
(30 mL) was added dropwise. The reaction mixture was kept at
~20 C for 24 h. The precipitate formed was collected by filtraꢀ
tion, washed with AcOH, and dried. Yield 665 mg (56%). M.p.
1
120—121 C (decomp.). H NMR (500 MHz), : 1.77 (s, 3 H,
CH3); 2.00 (s, 3 H, CH3); 3.80 (dd, 1 H, C(2)HA, J = 14.5 Hz,
J = 4.1 Hz); 4.33 (dd, 1 H, C(2)HB, J = 14.5 Hz, J = 3.3 Hz);
5.53 (t, 1 H, H(3), J = 3.7 Hz); 7.60 (dd, 1 H, H(8), J = 7.7 Hz,
J = 7.5 Hz); 7.73 (d, 1 H, H(10), J = 8.1 Hz); 7.91 (dd, 1 H,
H(9), J = 8.1 Hz, J = 7.5 Hz); 8.34 (d, 1 H, H(7), J = 7.7 Hz);
13.97 (br.s, 1 H, NH). 13C NMR (125 MHz): 26.2 (CH3), 26.7
(CH3), 33.0 (C(2)), 51.6 (C(3)), 71.6 (C(4)), 114.3 (C(10)), 116.7
(C(6b)), 123.7 (C(7)), 124.8 (C(8)), 134.6 (C(9)), 141.2 (C(6a)),
144.2 (C(10a)), 145.9 (C(11a)), 162.0 (C(12a)). Found (%):
4ꢀBromomethylꢀ2,3ꢀdihydroꢀ4H,11Hꢀ[1,3]thiazinoꢀ
[3´,2´:2,3][1,2,4]triazino[5,6ꢀb]indolium bromide (4). To an iceꢀ
cold solution of compound 1a (163 mg, 0.6 mmol) in AcOH
* Here and hereafter asterisk designates the signals partially overꢀ
lapped with the solvent signals.

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Russ.Chem.Bull., Int.Ed., Vol. 64, No. 4, April, 2015
Rybakova et al.
C, 28.13; H, 2.16; N, 9.32. C14H14Br4N4S. Calculated (%):
C, 28.50; H, 2.39; N, 9.50.
3. J. Mohan, P. Verma, J. Indian Chem. Soc., 1990, 67, 438.
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5. J. Mohan, D. Khatter, Ind. J. Heterocycl. Chem., 2003,
12, 327.
6. J. Mohan, A. Kumar, Ind. J. Chem., Sect. B, 2002, 41, 2364.
7. J. Mohan, A. Rathee, Ind. J. Heterocycl. Chem., 2007, 17, 83.
8. D. G. Kim, A. V. Zhuravleva, Chem. Heterocycl. Compd.
(Engl. Transl.), 2009, 45, 1281 [Khim. Geterotsikl. Soedin.,
2009, 1590].
9. D. G. Kim, A. V. Zhuravleva, Chem. Heterocycl. Compd.
(Engl. Transl.), 2010, 46, 896 [Khim. Geterotsikl. Soedin.,
2010, 1107].
10. A. V. Rybakova, P. A. Slepukhin, D. G. Kim, Chem. Heteroꢀ
cycl. Compd. (Engl. Transl.), 2013, 49, 1231 [Khim. Geterotsikl.
Soedin., 2013, 1320].
3ꢀIodoꢀ4,4ꢀdimethylꢀ2,3ꢀdihydroꢀ4H,11Hꢀ[1,3]thiazinoꢀ
[3´,2´:2,3][1,2,4]triazino[5,6ꢀb]indolium iodide (7). To a soluꢀ
tion of iodine (305 mg, 1.2 mmol) in CHCl3 (15 mL), a solution
of compound 1b (160 mg, 0.59 mmol) in CHCl3 (10 mL) was
added. The reaction mixture was kept at ~20 C for 24 h, the
solvent was removed in vacuo, the residue was dissolved in aceꢀ
tone and treated with NaI (150 mg, 1 mmol). The precipitate
formed was collected by filtration and dried. Yield 149 mg (48%).
M.p. 83—85 C (decomp.). 1H NMR (500 MHz), : 1.81 (s, 3 H,
CH3); 1.98 (s, 3 H, CH3); 3.79 (dd, 1 H, C(2)HA, J = 14.4 Hz,
J = 4.8 Hz); 4.33 (dd, 1 H, C(2)HB, J = 14.4 Hz, J = 3.6 Hz);
5.47 (t, 1 H, H(3), J = 3.9 Hz); 7.60 (dd, 1 H, H(8), J = 7.7 Hz,
J = 7.3 Hz); 7.73 (d, 1 H, H(10), J = 8.1 Hz); 7.91 (dd, 1 H,
H(9), J = 8.1 Hz, J = 7.3 Hz); 8.34 (d, 1 H, H(7), J = 7.7 Hz);
13.97 (br.s, 1 H, NH). Found (%): C, 31.83; H, 2.46; N, 10.42.
C14H14I2N4S. Calculated (%): C, 32.08; H, 2.69; N, 10.69.
11. A. V. Rybakova, D. G. Kim, V. V. Sharutin, Russ. J. Gen.
Chem. (Engl. Transl.), 2014, 84, 272 [Zh. Obshch. Khim.,
2014, 84, 280].
12. H. Kalinowsky, S. Berger, S. Braun, Carbonꢀ13 NMR spectroꢀ
scopy, John Wiley, New York, 1988, 497.
References
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27, 346.
Received September 29, 2014;
2. J. Mohan, Ind. J. Chem., Sect. B, 1990, 29, 645.
in revised form December 1, 2014