Synthesis of N-substituted 2-aminomethyl-5-methyl-7-phenyloxazolo[5,4-b]pyridines

Article abstract of DOI:10.1007/s10593-019-02537-y

[Figure not available: see fulltext.] 2-(Chloromethyl)-5-methyl-7-phenyloxazolo[5,4-b]pyridine was obtained by intramolecular cyclization based on the previously synthesized 2-chloro-N-(6-methyl-2-oxo-4-phenyl-1,2-dihydropyridin-3-yl)acetamide. The possibility of its use in the synthesis of previously unknown 2-aminomethyloxazolo[5,4-b]pyridine derivatives by nucleophilic substitution with various amines and a cyclic amide has been shown.

Full text of DOI:10.1007/s10593-019-02537-y

DOI 10.1007/s10593-019-02537-y
Chemistry of Heterocyclic Compounds 2019, 55(8), 788–791
Synthesis of N-substituted
2-aminomethyl-5-methyl-7-phenyloxazolo[5,4-b]pyridines
Irina V. Palamarchuk1, Mariya V. Matsukevich2, Ivan V. Kulakov1*,
Tulegen М. Seilkhanov3, Aleksander S. Fisyuk2,4
1 Institute of Chemistry, University of Tyumen,
15a Perekopskaya St., Tyumen 625003, Russia; e-mail: i.v.kulakov@utmn.ru
2 F. M. Dostoevsky Omsk State University,
55a Mira Ave., Omsk 644077, Russia; е-mail: fisyuk@chemomsu.ru
3 Sh. Ualikhanov Kokshetau State University,
76 Abaya St., Kokshetau 020000, Kazakhstan; e-mail: tseilkhanov@mail.ru
4 Omsk State Technical University,
11 Mira Ave., Omsk 644050, Russia; e-mail: fisyuk@chemomsu.ru
Submitted January 8, 2019
Accepted May 15, 2019
Translated from Khimiya Geterotsiklicheskikh Soedinenii,
2019, 55(8), 788–791
Ph
Ph
Ph
Ph
N
H
N
NHR1R2
NR1R2
N
NH2
O
O
ClCH2C(O)Cl
POCl3, P2O5
Cl
N
O
K2CO3, KI
Me2CO, , 4 h
38–51%
CH2Cl2, Py
rt
, 4 h
50%
O
N
Me
Me
N
H
Me
N
H
O
Cl
Me
2-(Chloromethyl)-5-methyl-7-phenyloxazolo[5,4-b]pyridine was obtained by intramolecular cyclization based on the previously synthe-
sized 2-chloro-N-(6-methyl-2-oxo-4-phenyl-1,2-dihydropyridin-3-yl)acetamide. The possibility of its use in the synthesis of previously
unknown 2-aminomethyloxazolo[5,4-b]pyridine derivatives by nucleophilic substitution with various amines and a cyclic amide has been
shown.
Keywords: 2-aminomethyloxazolo[5,4-b]pyridine derivatives, 3-amino-4-phenylpyridin-2(1Н)-one, chloroacetamide, oxazolo[5,4-b]-
pyridine, intramolecular cyclization, nucleophilic substitution.
Derivatives of oxazolo[5,4-b]pyridine and oxazolo[4,5-b]-
pyridine derivatives are known to exhibit antimicrobial,1
antitumor,2 pronounced anti-inflammatory,3 and analgesic
activity.4 Anti-inflammatory activity of some of them, for
example, is comparable to that of phenylbutazone or
indomethacin, while at the same time they do not cause
irritation of the mucous membrane of the gastrointestinal
tract, which can result from taking acidic anti-inflammatory
drugs.3
Scheme 1
There are several synthetic routes to access 2-substituted
oxazolo[5,4-b]- and oxazolo[4,5-b]pyridines.5–10 To date,
the most common method is to use 3-amino-2-hydroxy- or
3-amino-2-halopyridines 1 or 2-amino-3-hydroxy- or
2-amino-3-halopyridines 2 as precursors, which, after
forming the corresponding benzamides 3, 4, cyclize into
the corresponding oxazolopyridines 5, 6 in acidic media,
for example, in the presence of polyphosphoric acid or
phosphorus oxychloride (Scheme 1).
amides of aromatic, and not aliphatic acids are widely
represented in the literature. 5,7-Disubstituted and 2-alkyl-
substituted oxazolo[5,4-b]pyridines are presented in the
literature only by a few examples.10,11 The corresponding
4,6-disubstituted 3-aminopyridin-2(1H)-ones have not been
used for the synthesis of oxazolo[5,4-b]pyridines 5.
It should also be noted that oxazolo[5,4-b]pyridine
derivatives 5, derived from N-(2-hydroxypyridin-3-yl)-
benzamides 3 with unsubstituted pyridine ring, that is,
As part of an ongoing study on the synthesis of
3-aminopyridin-2(1H)-one derivatives,12–17 it was of
interest to synthesize oxazolo[5,4-b]pyridine 9 from
0009-3122/19/55(8)-0788©2019 Springer Science+Business Media, LLC
788

Chemistry of Heterocyclic Compounds 2019, 55(8), 788–791
Scheme 2
Scheme 3
chloroacetamide 8, which we previously obtained by
acylation of 3-amino-6-methyl-4-phenylpyridin-2(1H)-one
(7),17 and to study the possibility of using compound 9 in the
synthesis of 2-aminomethyl derivatives of oxazolo[5,4-b]-
pyridines which are not described in literature (Scheme 2).
Cyclization of chloroacetamide 8 by heating with POCl3
using the well-known classical procedure for the synthesis
of oxazolo[5,4-b]pyridines
3 allowed us to obtain
oxazolopyridine 9 with a rather low yield of about 20%.
The reaction was complicated by the formation of by-
products. When analyzing the chromato-mass spectra of the
crude reaction product, we fixed 1H-pyrido[2,3-b][1,4]-
oxazin-2(3H)-one 10, resulting from the cyclization of
compound 8. Earlier, we already described the preparation
of this compound in basic media.17
In order to increase the yield of oxazolo[5,4-b]pyridine
9, we optimized the reaction conditions, which consisted in
varying the excess of POCl3 and the reaction time. The best
yield of 2-(chloromethyl)-5-methyl-7-phenyloxazolo[5,4-b]-
pyridine (9) (50%) was obtained by heating under reflux
with a tenfold excess of POCl3 with the addition of a
threefold excess of P2O5 for 4 h. Longer heating resulted in
increasing formation of a difficult to separate mixture of
products, the 1H NMR spectra of which revealed, in
addition to signals from protons of compounds 9, 10, a
distinct singlet at 8.11 ppm, most likely belonging to the
proton H-5 of the formed 2-chloropyridine derivative 11
(Scheme 2).18 The resulting 2-(chloromethyl)-5-methyl-
7-phenyloxazolo[5,4-b]pyridine (9) was isolated in the
form of light-beige crystals, easily soluble in almost all
organic solvents, except hydrocarbons.
Next, we studied substitution of the chlorine atom in
oxazolo[5,4-b]pyridine 9 by the amino group in reactions
with morpholine, piperidine, 1-(adamantan-1-yl)ethan-
1-amine (active ingredient of the antiviral drug rimantadine),
4-iodopyrazole, 4-iodo-3,5-dimethylpyrazole, and 1H-pyrido-
[2,3-b][1,4]oxazin-2(3H)-one. Nucleophilic substitution was
performed by heating in Me2CO in the presence of K2CO3
and catalytic amounts of KI. The yields of products 12a–f
were in the range of 38–51% (Scheme 3). Although
carrying the reaction in DMF significantly shortened the
reaction time (from 10–12 to 3 h), it was accompanied by
the formation of byproducts (according to TLC).
Compounds 12a,c–f represent beige or light-beige
crystalline substances (compound 12b is an oil), easily
soluble in most organic solvents and partially in hexane
when heated. The structures of the obtained compounds
1
12a–f were confirmed by H and 13C NMR spectroscopy
and mass spectrometry.
To conclude, we obtained for the first time the corres-
ponding 2-(chloromethyl)-5-methyl-7-phenyloxazolo[5,4-b]-
pyridine on the basis of 2-chloro-N-(6-methyl-2-oxo-
4-phenyl-1,2-dihydropyridin-3-yl)acetamide. It can be used
further in the nucleophilic substitution reaction for the
synthesis of N-substituted 2-aminomethyloxazolo[5,4-b]-
pyridine derivatives.
Experimental
IR spectra were registered on an FT-801 spectrometer in
1
KBr pellets. H and 13C NMR spectra were acquired on a
Jeol JNM-ECA 400 spectrometer (400 and 100 MHz,
respectively) in CDCl3, with TMS as internal standard or
using residual solvent signals (7.26 ppm) to assign
chemical shifts. Signals of 13C atoms were assigned using
the APT method, taking into consideration the known
range of chemical shifts of carbon atoms in functional
groups and those in the starting materials previously
established by two-dimensional correlation spectra.17 Mass
spectra were recorded on an Agilent Technologies 5977E
789

Chemistry of Heterocyclic Compounds 2019, 55(8), 788–791
(MSD) GC-MS, 7820A (GC System), helium carrier gas,
Н-2,6 Ph). 13C NMR spectrum, δ, ppm.: 24.4 (СН3); 53.2
(N(CH2)2); 55.6 (NСН2); 66.8 (O(CH2)2); 118.5 (С-6);
127.7; 128.8 (С-2,6 Ph); 128.9 (С-3,5 Ph); 129.5 (С-4 Ph);
134.7; 141.0; 154.8 (С-3а); 160.4 (C-2); 162.0 (C-5). Mass
spectrum, m/z (Irel, %): 309 [М]+ (0.5), 226 (16), 224 (100),
195 (4), 127 (5), 86 (7). Found, %: C 69.41; H 6.61;
N 13.19. C18H19N3O2. Calculated, %: C 69.88; H 6.19;
N 13.58.
5-Methyl-2-(piperidin-1-ylmethyl)-7-phenyloxazolo-
[5,4-b]pyridine (12b). Yield 138 mg (45%), viscous oil.
IR spectrum, ν, cm–1: 1600 (C=N), 2853, 2960 (C-H).
1H NMR spectrum, δ, ppm: 1.40–1.42 (2Н, m, 4'-СН2);
1.60–1.63 (4Н, m, 3',5'-CH2); 2.61 (4Н, br. s, N(CH2)2);
2.68 (3Н, s, СН3); 3.90 (2Н, s, CH2); 7.36 (1Н, s, Н-6);
7.44 (1Н, t, J = 7.6, Н-4 Ph); 7.52 (2Н, t, J = 6.9 Н-3,5 Ph);
8.04 (2Н, d, J = 7.6, Н-2,6 Ph). 13C NMR spectrum,
δ, ppm: 23.8 (С-4'); 24.3 (СН3); 25.9 (С-3',5'); 54.2 (С-2',6');
56.0 (NСН2); 118.3 (С-6); 127.8; 128.8 (С-2,6 Ph); 128.9
(С-3,5 Ph); 129.4 (С-4 Ph); 129.9; 134.8; 140.8; 154.5
(С-3а); 160.5 (C-2); 162.9 (C-5). Found, %: C 73.81;
H 6.45; N 13.29. C19H21N3O. Calculated, %: C 74.24;
H 6.89; N 13.67.
carrier gas flow 0.9 ml/min, Agilent 1901S 433UI column:
evaporator temperature 250°С, thermostat temperature 70–
290°С, temperature gradient 10°С/min, EI ionization, 70 eV.
Recording of the mass spectrum of compound 12f as well
as the determination of its molecular mass was performed
on a Thermo Electron Double Focusing System high-
resolution mass spectrometer (EI ionization, 70 eV) using
perfluorokerosene (PFK) as the standard. Elemental
analysis was performed on a Fisons EA 1106 Elemental
analyzer. Melting points were determined on a Kofler
bench. Monitoring of the reaction progress and assessment
of the purity of synthesized compounds was done by TLC
on Sorbfil АF-А-UV plates, visualization with UV light or
in the iodine chamber.
The precursors 3-amino-6-methyl-4-phenylpyridin-2(1H)-
one (7) and 2-chloro-N-(6-methyl-2-oxo-4-phenyl-1,2-dihydro-
pyridin-3-yl)acetamide (8) were prepared following methods
published by us previously.17
2-(Chloromethyl)-5-methyl-7-phenyloxazolo[5,4-b]-
pyridine (9). A mixture of 2-chloro-N-(6-methyl-2-oxo-
4-phenyl-1,2-dihydropyridin-3-yl)acetamide (8) (277 mg,
1.0 mmol), POCl3 (1.0 ml, 10 mmol), and P2O5 (426 mg,
3.0 mmol) was heated under reflux for 4 h. The excess
POCl3 was evaporated, and the thick residue was carefully
treated with ice water. The formed precipitate was thoroughly
triturated, filtered, washed with water, and air-dried. It was
recrystallized from hexane–i-PrOH, 5:1 mixture. Yield
127 mg (50%), light-beige crystals, mp 126–128°С.
2-[(4-Iodo-1H-pyrazol-1-yl)methyl]-5-methyl-7-phenyl-
oxazolo[5,4-b]pyridine (12c). Yield 172 mg (40%), beige
crystals, mp 145–148°С. IR spectrum, ν, cm–1: 688 (C–I),
1
1616 (C=N), 2926 (C–H), 3051, 3125 (H–C=). H NMR
spectrum, δ, ppm: 2.69 (3H, s, СH3); 5.62 (2Н, s, CH2);
7.41 (1Н, s, Н-6); 7.47–7.56 (3Н, m, Н-3,4,5 Ph); 7.57
(1Н, s, Н-3'); 7.71 (1Н, s, Н-5'); 8.04 (2Н, d, J = 6.1, Н-2,6
Ph). 13C NMR spectrum, δ, ppm.: 24.4 (СН3); 49.7 (СН2);
57.7 (С–I); 118.8 (С-6); 127.6; 128.8 (С-2,6 Ph); 128.9
(С-3,5 Ph); 129.7 (С-4 Ph); 134.3; 134.5 (C-5'); 141.7;
145.5 (C-3'); 155.7; 158.6 (C-2); 160.3 (C-5). Found, %:
C 49.44; H 3.41; N 13.22. C17H13IN4O. Calculated, %:
C 49.06; H 3.18; N 13.46.
1
IR spectrum, ν, cm–1: 1622 (C=N), 2875 (C–H). H NMR
spectrum, δ, ppm: 2.68 (3H, s, СH3); 4.74 (2H, s, CH2Cl);
7.38 (1H, s, H-6); 7.45–7.53 (3H, m, H-3,4,5 Ph); 8.0 (2H,
3
4
dd, J = 8.3, J = 1.5, H-2,6 Ph). 13C NMR spectrum,
δ, ppm: 24.4 (СН3); 36.5 (СН2Cl); 118.8 (С-6); 127.8;
128.8 (С-2,6 Ph); 128.9 (С-3,5 Ph); 129.7 (С-4 Ph); 134.4;
141.6; 155.9 (С-3а); 160.0 (C-2); 160.4 (C-5). Mass
spectrum, m/z (Irel, %): 260 [М]+ (33), 258 [М]+ (100), 218
(16), 154 (9), 127 (11). Found, %: C 64.66; H 4.41; N 10.99.
C14H11ClN2O. Calculated, %: C 65.00; H 4.29; N 10.83.
Synthesis of N-substituted 2-(aminomethyl)-5-methyl-
7-phenyloxazolo[5,4-b]pyridines 12a–f (General method).
A mixture of 2-(chloromethyl)-5-methyl-7-phenyloxazolo-
[5,4-b]pyridine (9) (260 mg, 1.0 mmol) and the
corresponding amine (1.1 mmol) was heated under reflux in
Me2CO (10 ml) in the presence of K2CO3 (276 mg, 2.0 mmol)
(twofold excess of the amine was used for the synthesis of
compounds 12а,b) and a catalytic amount of KI (3 mg).
The progress of the reaction was monitored by TLC, eluent
hexane–CHCl3–Me2CO, 1:2:1. The reaction mixture was
filtered from the precipitate of salts, washed with Me2CO,
and the solvent was evaporated. The residue was
recrystallized from hexane–iPrOH, 2:1 mixture.
2-[(4-Iodo-3,5-dimethyl-1H-pyrazol-1-yl)methyl]-
5-methyl-7-phenyloxazolo[5,4-b]pyridine (12d). Yield
206 mg (43%), beige crystals, mp 160–163°С. IR spect-
rum, ν, cm–1: 624 (C–I), 1620 (C=N), 1638 (C=N), 2924
1
(C–H). H NMR spectrum, δ, ppm: 2.19 (3H, s, 3'-СH3);
2.41 (3H, s, 5'-СH3); 2.66 (3H, s, СH3); 5.52 (2Н, s, CH2);
7.38 (1Н, s, Н-6); 7.43–7.53 (3Н, m, Н-3,4,5 Ph); 8.03
(2Н, d, J = 7.6, Н-2,6 Ph). 13C NMR spectrum, δ, ppm:
12.2 (3'-СH3); 14.1 (5'-СH3); 24.3 (СН3); 47.7 (СН2); 64.2
(С–I); 118.6 (С-6); 127.7; 128.8 (С-2,6 Ph); 128.9
(С-3,5 Ph); 129.6 (С-4 Ph); 134.4; 141.5; 141.6; 150.7;
155.4; 159.3 (C-2); 160.3 (C-5). Found, %: C 50.96;
H 4.18; N 12.99. C19H17IN4O. Calculated, %: C 51.37;
H 3.86; N 12.61.
(S)-1-(Adamantan-1-yl)-N-[(5-methyl-7-phenyloxazolo-
[5,4-b]pyridin-2-yl)methyl]ethan-1-amine (12e). Yield
191 mg (51%), light-beige crystals, mp 157–160°С.
IR spectrum, ν, cm–1: 1619 (C=N), 2846, 2910 (C–H).
1H NMR spectrum, δ, ppm: 1.00 (3H, d, J = 6.1,
NHCHCH3); 1.60–1.67 (12H, m, 6CH2 Ad); 1.97 (3Н, br. s,
3,5,7-CH Ad); 2.20 (1Н, q, J = 6.1, 1-СН Ad); 2.68 (3Н, s,
СН3); 4.05 (1Н, d, J = 15.3) и 4.16 (1Н, d, J = 15.2,
NHСН2); 5.29 (1Н, br. s, NH); 7.36 (1Н, s, Н-6); 7.49–7.53
(3Н, m, Н-3,4,5 Ph); 8.06 (2Н, d, J = 7.6, Н-2,6 Ph). 13C NMR
5-Methyl-2-(morpholin-4-ylmethyl)-7-phenyloxazolo-
[5,4-b]pyridine (12a). Yield 118 mg (38%), light-beige
crystals, mp 74–76°С. IR spectrum, ν, cm–1: 1620 (C=N),
1
2960 (C–H). H NMR spectrum, δ, ppm: 2.70–2.72 (7Н, m,
СН3, N(CH2)2); 3.76 (4Н, br. t, J = 4.6, O(CH2)2); 3.93
(2Н, s, CH2); 7.39 (1Н, s, Н-6); 7.47 (1Н, t, J = 7.6, Н-4
Ph); 7.52–7.55 (2Н, m, Н-3,5 Ph); 8.05 (2Н, d, J = 7.6,
790

Chemistry of Heterocyclic Compounds 2019, 55(8), 788–791
4. Boger, D. L.; Miyauchi, H.; Du, W.; Hardouin, C.; Fecik, R. A.;
spectrum, δ, ppm.: 13.3 (2-CH3); 24.3 (СН3); 28.5 (3,5,7-CH
Ad); 36.1 (1-C Ad); 37.2 (4,6,10-СН2 Ad); 38.5 (2,8,9-СН2
Ad); 45.7 (NHСН2); 61.6 (СНN); 118.2 (С-6); 127.8; 128.8
(С-2,6 Ph); 128.9 (С-3,5 Ph); 129.4 (С-4 Ph); 134.8; 140.7;
154.2; 160.4 (C-2); 165.1 (C-5). Found, %: C 77.29; H 8.18;
N 10.87. C26H31N3O. Calculated, %: C 77.77; H 7.78;
N 10.46.
Cheng, H.; Hwang, I.; Hedrick, M. P.; Leung, D.; Acevedo, O.;
Guimarães, C. R. W.; Jorgensen, W. L.; Cravatt, B. F. J. Med.
Chem. 2005, 48, 1849.
5. Doise, M.; Dennin, F.; Blondeau, D.; Sliwa, H. Tetrahedron
Lett. 1990, 31, 1155.
6. Doise, M.; Blondeau, D.; Sliwa, H. Synth. Commun. 1992, 22,
2891.
6-Methyl-1-[(5-methyl-7-phenyloxazolo[5,4-b]pyri-
din-2-yl)methyl]-8-phenyl-1H-pyrido[2,3-b][1,4]oxazin-
2(3H)-one (12f). Yield 185 mg (40%), beige crystals,
mp 207–209°С. IR spectrum, ν, cm-1: 1620 (C=N), 1699
7. Myllymäki, M. J.; Koskinen, A. MP Tetrahedron Lett. 2007,
48, 2295.
8. Heuser, S.; Keenan, M.; Weichert, A. G., Tetrahedron Lett.
2005, 46, 9001.
1
9. Phoon, C. W.; Ng, P. Y.; Ting, A. E.; Yeo, S. L.; Sima, M. M.
Bioorg. Med. Chem. Lett. 2001, 11, 1647.
(C=O), 2953, 2988 (C–H). H NMR spectrum, δ, ppm:
2.46 (3H, s, СH3); 2.63 (3H, s, СH3); 4.74 (2H, s, NСH2);
4.86 (2H, s, OCH2); 6.77 (1H, s, H-7'); 7.28–7.31 (5H, m,
H 8'-Ph); 7.33 (1H, s, H-6); 7.43 (1H, t, J = 7.6, H-4 7-Ph);
7.48 (2H, t, J = 7.6, H-3,5 7-Ph); 7.90 (2H, d, J =7.6, H-2,6
7-Ph). 13C NMR spectrum, δ, ppm: 23.4 (CH3); 24.3 (CH3);
42.2 (NCH2); 68.1 (OCH2); 118.0 (H-6); 118.9 (C-8a');
121.1 (C-7'); 127.5; 128.2; 128.6; 128.8; 129.0; 129.3 (C-4
7-Ph); 129.5 (C-4 8'-Ph); 134.2; 136.6; 140.4; 141.1; 152.4;
154.5; 155.2; 159.4; 160.0; 165.9 (C=O). Mass spectrum,
m/z (Irel, %): 462 [М]+ (8), 200 (100), 199 (64), 171 (25),
100 (15). Found, m/z: 462.1686 [М]+. C28H22N4O3.
Calculated, m/z: 462.1688. Found, %: C 72.28; H 5.17;
N 12.53. C28H22N4O3. Calculated, %: C 72.71; H 4.79;
N 12.11.
10. Xu, D.; Xu, X.; Liu, Z.; Sun, L.-P.; You, Q. Synlett 2009,
1172.
11. Shatsauskas, A. L.; Abramov, A. A.; Saibulina, E. R.;
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12. Kulakov, I. V.; Nikitina, O. S.; Fisyuk, A. S.; Goncharov, D. S.;
Shul'gau, Z. T.; Gulyaev, A. E. Chem. Heterocycl. Compd.
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The study was carried out with the financial support of
the Russian Foundation for Basic Research within the
framework of research project No. 18-33-01143.
15. Kulakov, I. V.; Palamarchuk, I. V.; Shulgau, Z. T.;
Seilkhanov, T. M.; Gatilov, Y. V.; Fisyuk, A. S. J. Mol.
Struct. 2018, 1166, 262.
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Palamarchuk, I. V.; Seilkhanov, T. M.; Fisyuk, A. S. Synlett
2018, 1741.
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