Molecules 2018, 23, 2335
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times using each half of the volume of the water phase. The unified organic layer was dried over
sodium sulphate and filtered. The oily residue was purified by column chromatography over silica gel
using an eluent mixture of cyclohexane and ethyl acetate in a ratio of 4:1 (v:v). After evaporation of the
collected compound fractions, the target compounds crystallized from diethyl ether.
3-Ethoxy-4-phenylbenzo[4,5]furo[2,3-b]pyridine-6-ol (3a). Yield 10%; mp 231–235 ◦C; IR (KBr)
(OH), 1277 (C-O-C) cm−1; 1H-NMR (DMDO-d6)
= 9.33 (s, 1H, OH), 8.25 (s, 1H, 2-H), 7.59–7.51 (m,
5H, C6H5), 7.49 (d, J = 8.9 Hz, 1H, 8-H), 6.91 (dd, J = 8.9, 2.5 Hz, 1H, 7-H), 6.51 (d, J = 2.5 Hz, 1H, 5-H),
4.09 (q, J = 7.0 Hz, 2H, OC 2CH3), 1.18 (t, J = 7.0 Hz, 3H, OC
2CH3); m/z (ESI) 306.35 (M + H+). Anal.
(C19H15NO3) Calc. C 74.74, H 4.95, N 4.59; Found C 74.99, H 4.81, N 4.70.
ν = 3435
δ
H
H
◦
3-Benzyloxy-4-phenylbenzo[4,5]furo[2,3-b]pyridine-6-ol (3b). Yield 13%; mp 220–224 C; IR (KBr)
(OH), 1276 (C-O-C) cm−1; 1H-NMR (DMDO-d6)
= 9.34 (s, 1H, OH), 8.32 (s, 1H, 2-H), 7.60–7.54 (m,
5H, C4-C6H5), 7.49 (d, J = 8.9 Hz, 1H, 8-H), 7.31–7.26 (m, 5H, OCH2C6 5), 6.92 (dd, J = 8.9, 2.7 Hz,
1H, 7-H), 6.51 (d, J = 2.7 Hz, 1H, 5-H), 5.17 (s, 2H, OC
2C6H5); m/z (ESI) 368.42 (M + H+). Anal.
ν = 3401
δ
H
H
(C24H17NO3) Calc. C 78.46, H 4.66, N 3.81; Found C 78.95, H 4.59, N 3.76.
3-Methoxy-4-phenylbenzo[4,5]furo[2,3-b]pyridine-6-ol (3c). Yield 8%; mp 240–245 ◦C; IR (KBr)
ν = 3434
(OH), 1275 (C-O-C) cm−1; 1H-NMR (DMDO-d6)
δ = 9.34 (s, 1H, OH), 8.25 (s, 1H, 2-H), 7.61–7.53 (m,
3H, 30-, 40-, 50-H), 7.51-7.49 (m, 2H, 20-, 60-H), 7.49 (d, J = 8.8 Hz, 1H, 8-H), 6.91 (dd, J = 8.8, 2.5 Hz, 1H,
7-H), 6.47 (d, J = 2.5 Hz, 1H, 5-H), 3.84 (s, 3H, OCH3); m/z (ESI) 292.32 (M + H+). Anal. (C18H15NO3)
Calc. C 74.22, H 4.50, N 4.81; Found C 73.89, H 4.45, N 4.95.
◦
3-Fluoro-4-phenylbenzo[4,5]furo[2,3-b]pyridine-6-ol (3d). Yield 6%; mp 266–274 C; IR (KBr)
ν = 3162
1
(OH), 1185 (C-O-C) cm−1; H-NMR (DMDO-d6)
δ = 9.48 (s, 1H, OH), 8.51 (d, J = 2.3 Hz, 1H, 2-H),
7.68–7.66 (m, 5H, C4-C6H5), 7.59 (d, J = 8.9 Hz, 1H, 8-H), 7.00 (dd, J = 8.9, 2.6 Hz, 1H, 7-H), 6.70 (d,
J = 2.6 Hz, 1H, 5-H); m/z (ESI) 280.27 (M + H+). Anal. (C17H10FNO2) Calc. C 73.11, H 3.61, N 5.02;
Found C 72.97, H 3.69, N 4.97.
3-Benzyloxy-4-phenylnaphtho[10,20:4,5]furo[2,3-b]pyridine-6-ol (4a). Yield 6%; mp 219–222 ◦C; IR (KBr)
= 3176 (OH), 1261 (C-O-C) cm−1; 1H-NMR (DMDO-d6)
= 10.10 (s, 1H, OH), 8.37 (s, 1H, 2-H), 8.32
(d, J = 8.2 Hz, 1H, 10-H), 8.23 (d, J = 8.4 Hz, 1H, 7-H), 7.72 (t, J = 7.5 Hz, 1H, 9-H), 7.66–7.57 (m, 6H,
C4-C6H5, 8-H), 7.38–7.25 (m, 5H, OCH2C6 5), 6.64 (s, 1H, 5-H), 5.20 (s, 2H, OC 2C6H5); m/z (ESI)
418.47 (M + H+). Anal. (C28H19NO3) Calc. C 80.56, H 4.59, N 3.36; Found C 80.23, H 4.35, N 3.25.
ν
δ
H
H
◦
3-Fluoro-4-phenylnaphtho[10,20:4,5]furo[2,3-b]pyridine-6-ol (4b). Yield 2%; mp 246–248 C; IR (KBr)
1
ν
= 3140 (OH), 1178 (C-O-C) cm−1; H-NMR (DMDO-d6)
δ
= 9.63 (s, 1H, OH), 8.87–8.82 (m, 2H,
2-, 10-H), 8.80 (d, J = 8.4 Hz, 1H, 7-H), 8.23-8.08 (m, 7H, C4-C6H5, 8-, 9-H), 7.27 (s, 1H, 5-H); m/z (ESI)
330.32 (M + H+). Anal. (C21H12FNO2) Calc. C 76.59, H 3.67, N 4.25; Found C 76.25, H 3.42, N 4.15.
3.5. General Procedure for the Synthesis of 3-Hydroxy Compounds 3e and 4c
One equivalent of the respective 3-benzyloxy compound 3b or 4a was dissolved in 20 mL of
distilled dried methanol at room temperature and 0.3 equivalent of palladium on charcoal (10%)
were added. The solution was shaken under hydrogen atmosphere with a pressure of 2 bar. After
2–3 h, the reaction was stopped and the solution filtered. After removal of the solvent in vacuum,
the 3-hydroxy compounds crystallized from diethyl ether.
4-Phenylbenzo[4,5]furo[2,3-b]pyridine-3,6-diol (3e). Yield 91%; mp 214–217 ◦C; IR (KBr)
1183 (C-O-C) cm−1; 1H-NMR (DMDO-d6)
= 9.72 (s br, 1H, OH), 9.29 (s br, 1H, OH), 8.07 (s, 1H, 2-H),
ν = 3350 (OH),
δ
7.61–7.51 (m, 5H, C4-C6H5), 7.46 (d, J = 8.9 Hz, 1H, 8-H), 6.89 (dd, J = 8.9, 2.6 Hz, 1H, 7-H), 6.54 (d,
J = 2.6 Hz, 1H, 5-H); m/z (ESI) 278.25 (M + H+). Anal. (C17H11NO3) Calc. C 73.64, H 4.00, N 5.05;
Found C 73.38, H 3.85, N 4.99.