Synthesis of furan-oxazole conjugated fluorescent materials from biomass-derived furfural through cross-coupling reactions

Article abstract of DOI:10.3987/COM-15-S(T)9

Synthesis of furyloxazole was performed from biomass-derived furfural and serine methyl ester through dehydrative condensation and oxidation in one pot. Bromination and subsequent palladium-catalyzed arylation with arylboronates proceeded smoothly at the

Full text of DOI:10.3987/COM-15-S(T)9

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HETEROCYCLES, Vol. 93, No. 1, 2016
HETEROCYCLES, Vol. 93, No. 1, 2016, pp. 140 - 149. © 2016 The Japan Institute of Heterocyclic Chemistry
Received, 28th July, 2015, Accepted, 30th September, 2015, Published online, 22nd October, 2015
DOI: 10.3987/COM-15-S(T)9
SYNTHESIS OF FURAN-OXAZOLE CONJUGATED FLUORESCENT
MATERIALS FROM BIOMASS-DERIVED FURFURAL THROUGH
CROSS-COUPLING REACTIONS
Yuki Murase, Kana Ashida, Shota Tanaka, Kentaro Okano, and Atsunori
Mori*
Department of Chemical Science and Engineering, Kobe University, 1-1
Nada, Kobe 657-8501, Japan
E-mail: amori@kobe-u.ac.jp
‡This paper is dedicated to Professor Dr. Lutz F. Tietze on celebration of his 75th
birthday.
Abstract – Synthesis of furyloxazole was performed from biomass-derived
furfural and serine methyl ester through dehydrative condensation and oxidation
in one pot. Bromination and subsequent palladium-catalyzed arylation with
arylboronates proceeded smoothly at the furan ring to provide arylated
furylthiazoles. Arylation of C–H bond at the 5 position of the oxazole ring under
Fagnou’s conditions led to formation of diarylated furyloxazoles, which exhibit
higher quantum yields over those of the related furylthiazole derivatives.
INTRODUCTION
The transition metal-catalyzed aromatic coupling reactions have been utilized as a reliable method for the
1
construction of π-conjugated system in material sciences. Most of the aromatic compounds for the
cross-coupling reactions have been obtained by fossil oil. Recent serious decrease of fossil oil prompted
2
us to explore its alternative such as biomass, biological material mainly derived from plants. Among
these plant-derived resources, furfural (1), which is readily prepared from xylose, has an aromatic furan
3
ring, thus attracting a great deal of attention as a “non-edible” biomass. Several research groups have
4
5
6
employed furfural as a starting material to synthesize resins, pesticides, and fuels. In addition to the
furan ring, we converted the formyl group of furfural to a thiazole ring through condensation with
cysteine and accomplished the construction of novel furan-thiazole conjugated framework (Scheme 1),7

HETEROCYCLES, Vol. 93, No. 1, 2016
141
8
which was expected to show photoluminescent property. Herein, we report the synthesis of
furan-oxazole conjugated compounds from serine methyl ester and higher quantum yields over those of
the furan-thiazole conjugated compounds.
Scheme 1. Extended π-conjugated heteroaromatic compounds from furfural and cysteine
RESULTS AND DISCUSSION
First, we prepared 2-furyloxazole-4-carboxylic acid methyl ester (2) through dehydrative condensation of
furfural and L-serine methyl ester hydrochloride (3) followed by oxidation of the resultant oxazoline
9
according to Graham’s procedure (Scheme 2). With the obtained furyloxazole 2 in hand, we then
introduced an aryl group into the 5 position of the furan ring in a two-step sequence, namely, bromination
and palladium-catalyzed cross-coupling reaction. Treatment of 2-furyloxazole
2
with
N-bromosuccinimide (NBS) in DMA at 0 °C exclusively gave the desired brominated product. Since
column chromatographic separation led to the formation of a deteriorated mixture, the crude bromide
2-Br was readily subjected to the palladium-catalyzed Suzuki-Miyaura cross-coupling conditions to
1
0
afford the arylated product. We chose 2-pyridyl and Ph N- groups as electron-withdrawing/donating
2
substituents to investigate the electronic effects on UV-vis absorption and photoluminescent properties.
1
Thus, the reaction with 4a (R = 2-pyridyl) was found to proceed successfully to give the corresponding
1
product 5a in 84% yield. The one-pot reaction of 2 with boronate ester 4b (R = Ph
provide arylated product 5b in 45% yield.
2
N-) also took place to

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HETEROCYCLES, Vol. 93, No. 1, 2016
Scheme 2. Extension of π-conjugation of furfural through oxazole formation and subsequent
Suzuki-Miyaura cross-coupling reaction
Having extended π-conjugation at the 5 position of the furan ring, we then attempted the
palladium-catalyzed direct C–H arylation of 5b at the 5 position of oxazole with ethyl 4-iodobenzoate
7
according to our reported conditions for thiazole derivatives. But, disappointingly, the desired product 7
was not obtained at all with concomitant generation of unidentified compounds. Finally, Fagnou’s
11
conditions with aryl bromides were found to be effective for the smooth C–H arylation to provide the
corresponding products in moderate to good yields (Table 1).
Table 1. Palladium-catalyzed direct C–H arylation of 5 at the 5 position of oxazole
R1
R2
yield (%)
compd
7aa
7ab
7ac
7ad
2
2
2
2
2
-pyridyl
-pyridyl
-pyridyl
-pyridyl
-pyridyl
SF
5
78
41
89
59
75
NMe
2-pyridyl
OMe
2
CO
2
Et
7ae

HETEROCYCLES, Vol. 93, No. 1, 2016
143
NPh
NPh
NPh
NPh
NPh
2
2
2
2
2
SF
NMe
2-pyridyl
OMe
5
68
88
66
54
69
7ba
7bb
7bc
7bd
7be
2
CO Et
2
Table 2 describes UV-vis absorption and photoluminescent properties of the obtained furyloxazole
derivatives. Absorption and emission maxima of furyloxazole 5a exhibited 375 nm and 399 nm,
respectively, with quantum yield (Φ = 0.33). It was found that monoarylated products 7aa–7ae showed
emission at higher wavelengths than those of 5a. The quantum yields have remarkably increased up to
0
.95 (7ac). While furyloxazole 5b shows excellent quantum yield (Φ = 0.98), monoarylated derivatives
ba–7be have lower quantum yields. Accordingly, introduction of electron-withdrawing pyridyl group
7
into the 5-position of the furan ring effectively improve photoluminescent performance whereas little
shifts of absorption and emission maxima to higher wavelengths. By contrast, substantial shifts of both
absorption and emission maxima to longer wavelengths were observed in the compounds bearing
electron-donating 4-(N,N-diphenylamino)phenyl group, 7ba and 7be, which showed yellow fluorescence.
Table 2. UV-vis absorption and photoluminescent properties of furyloxazole derivatives
compd
λ
max (nm)
375
362
384
367
361
368
345
396
397
392
379
397
Em (nm)
399
435
461
440
430
446
435
521
449
507
451
529
Φ
5
a
0.33
0.88
0.70
0.95
0.86
0.78
0.98
0.26
0.60
0.29
0.67
0.18
7aa
7ab
7ac
7ad
7ae
5
b
7
ba
7bb
7bc
7bd
7be
7
Compared with the furylthiazole derivatives, furyloxazoles thus synthesized exhibited slightly shorter
shifts except 5a and 7ba (Table 3), which would be the difference of bond lengths of C-S and C-O bonds
in the heteroaromatic ring. The longer bond length of C-S bond expands angles of substituents at the 2-
and 5-positions of the furan ring to result in a more extended -conjugation. Worthy of note is that
quantum yields of furyloxazoles were generally higher than those of furylthiazoles.

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HETEROCYCLES, Vol. 93, No. 1, 2016
Table 3. Comparison of UV-Vis absorption and photoluminescent properties between furyloxazoles and
furylthiazoles
compd
a’
R
1
R
H
H
2
X
S
O
S
O
S
O
S
O
S
O
S
O
λ
max (nm)
356
375
373
368
373
362
391
345
408
397
391
396
Em (nm)
418
399
462
446
460
435
472
435
539
529
537
521
Φ
5
2-pyridyl
2-pyridyl
2-pyridyl
2-pyridyl
2-pyridyl
2-pyridyl
NPh
NPh
NPh
NPh
NPh
NPh
0.32
0.33
0.40
0.78
0.43
0.88
0.61
0.98
0.18
0.18
0.20
0.26
5
a
7
7
ae’
CO
CO
2
Et
Et
5
7
ae
2
aa’
SF
SF
H
7
5
aa
b’
5
2
2
2
2
2
2
5
b
H
7
be’
CO
CO
2
Et
Et
5
7
be
ba’
ba
2
7
7
SF
SF
5
CONCLUSION
In summary, we have synthesized furan-oxazole conjugated heteroaromatic compounds from furfural (1)
and serine methyl ester hydrochloride (3). The desired 2-furyloxazole-4-carboxylic acid methyl ester (2)
was readily prepared in one pot, which was further converted to arylated furyloxazole 5 through one-pot
bromination/Suzuki–Miyaura coupling sequence. Palladium-catalyzed direct C–H arylation of 5 furnished
to provide 5-aryl-2-furyloxazole 7, which exhibit higher quantum yields over those of the related
furylthiazoles. The facile method for the synthesis of π-conjugated furyloxazole would extend utilities of
biomass-based organic electronic materials.
EXPERIMENTAL
1
General. All the reactions were carried out under nitrogen atmosphere. H NMR (300 or 400 MHz) and
13C NMR (100 MHz) spectra were measured on Varian Gemini 300 and JEOL ECZ400 as a CDCl
3
1
solution unless noted. The chemical shifts were expressed in ppm with CHCl
3
(7.26 ppm for H) or
13
CDCl (77.0 ppm for C) as internal standards. IR spectra were recorded on Bruker Alpha with an ATR
3
attachment (Ge). High resolution mass spectra (HRMS) were measured by JEOL JMS-T100LP AccuTOF
LC-Plus (ESI) with a JEOL MS-5414DART attachment. For thin layer chromatography (TLC) analyses
throughout this work, Merck precoated TLC plates (silica gel 60 F254) were used. Purification by HPLC
with preparative SEC column (JAI-GEL-2H) was performed by JAI LC-9201. UV–vis spectra were

HETEROCYCLES, Vol. 93, No. 1, 2016
145
measured by ALS SEC-2000 UV/VIS spectrometer with SEC-2000 DH as a light source.
Photoluminescent spectra were measured with JASCO FP-6200. Other chemicals were purchased and
used without further purification.
9
Synthesis of 2-furyloxazole-4-carboxylic acid methyl ester 2: To a 200-mL Schlenk tube equipped
with a magnetic stirring bar were added magnesium sulfate (3.61 g, 30 mmol), L-serine methyl ester
hydrochloride (4.67 g, 30 mmol), potassium carbonate (8.29 g, 60 mmol) and N,N-dimethylacetamide (80
mL). To the solution was added furfural (2.45 mL, 30 mmol) and stirring was continued under rt for 12 h.
The resulting mixture was cooled to 0 °C and treated with bromotrichloromethane (8.9 mL, 90 mmol) and
1
,8-diazabicyclo[5.4.0]undec-7-ene (13.3 mL, 90 mmol). After stirring at 0 °C for 2 h and then at rt for 10
h, the mixture was treated by water and the solution was poured into the mixture of diethyl ether/water to
result in separation into two phases. Aqueous layer was extracted with diethyl ether repeatedly and the
combined organic extracts were dried over anhydrous sodium sulfate and concentrated under reduced
pressure to leave a crude solid, which was purified by column chromatography on silica gel
1
(
hexane/diethyl ether = 3/2) to afford 3.02 g of 2 (52%), whose H NMR spectra were corresponding to
those reported in the literature.9
General procedure for the one-pot bromination and Suzuki-Miyaura coupling: To a 20-mL Schlenk
tube equipped with a magnetic stirring bar were added 2 (386.3 mg, 2.0 mmol) and 1,2-dimethoxyethane
(7 mL) under nitrogen atmosphere. After cooling to 0 °C, N-bromosuccinimide (NBS, 195.8 mg, 1.1
mmol) was added and the resulting mixture was stirred at 0 °C for 1 h. NBS (117.5 mg, 0.66 mmol) was
further added to the reaction mixture and the solution was stirred at 0 °C for 1 h. Another NBS (117.5 mg,
0
.66 mmol) was added again and further stirring was continued for 2 h. The reaction mixture warmed to
room temperature. To the solution were added 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenylpyri-
dine (674.8 mg, 2.4 mmol), aqueous potassium carbonate (2 M, 6 mmol), and PdCl (PPh (70.2 mg,
.10 mmol), successively. The mixture was allowed to stir under reflux for 24 h. After cooling to room
temperature, the mixture was poured into the mixture of CH Cl /water and the two phases were separated.
Aqueous layer was extracted with CH Cl three times and the combined organic layer was dried over
anhydrous sodium sulfate and concentrated under reduced pressure to leave a crude solid, which was
purified by recrystallization (CHCl /MeOH) to afford 582 mg of methyl
-(5-(4-(pyridin-2-yl)phenyl)furan-2-yl)oxazole-4-carboxylate (5a, orange solid, 84%): H NMR δ 3.97 (s,
H), 6.88 (d, J = 3.6 Hz, 1H), 7.28 (d, J = 3.9 Hz, 2H), 7.80 (d, J = 3.6 Hz, 2H), 7.92 (d, J = 8.3 Hz, 2H),
2
)
3 2
0
2
2
2
2
3
1
2
3
8
1
1
3
.09 (d, J = 8.3 Hz, 2H), 8.28 (s, 1H), 8.73 (d, J = 3.9 Hz, 1H); C NMR δ 52.3, 107.8, 115.5, 120.5,
22.4, 124.9, 127.3, 129.9, 134.4, 137.0, 139.0, 141.2, 143.2, 149.5, 154.9, 156.2, 156.3, 161.5; IR (ATR)

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HETEROCYCLES, Vol. 93, No. 1, 2016
-1
1
725, 1583, 1465, 1437, 1316, 1265, 1149, 1110, 782, 725 cm ; HRMS (ESI+) Calcd for C20
H
14
N O
2 4
Na
+
[
M+Na] : 369.0851; found: m/z 369.0842.
1
Methyl 2-(5-(4-(diphenylamino)phenyl)furan-2-yl)oxazole-4-carboxylate (5b, orange solid, 45%): H
NMR δ 3.95 (s, 3H), 6.65 (d, J = 3.6 Hz, 1H), 7.04-7.11 (m, 4H), 7.13 (d, J = 8.5 Hz, 4H), 7.23 (d, J = 3.6
1
3
Hz, 1H), 7.25-7.31 (m, 4H), 7.64 (d, J = 8.8 Hz, 2H), 8.24 (s, 1H); C NMR δ 52.1, 105.8, 115.5, 122.6,
1
1
23.0, 123.4, 124.7, 125.4, 129.3, 134.2, 140.3, 142.9, 147.1, 148.1, 155.0, 156.7, 161.4; IR (ATR) 1744,
-1
592, 1487, 1319, 1280, 1148, 1113, 791, 753, 725, 697 cm ; HRMS (ESI+) Calcd for C27
H
20
N
2
O Na
4
+
[
M+Na] : 459.1321; found: m/z 459.1323.
General procedure for the palladium-catalyzed C-H coupling of 5 with aryl bromide: To a 20-mL
Schlenk tube equipped with a magnetic stirring bar were added 5a (97.4 mg, 0.28 mmol) at room
temperature. 4-Bromophenylsulfur-pentafluoride (79.3 mg, 0.28 mmol), palladium acetate (3.1 mg, 0.014
mmol), JohnPhos (8.4 mg, 0.028 mmol), potassium carbonate (77.4 mg, 0.56 mmol), pivalic acid (8.6 mg,
0
.084 mmol), 1,4-dioxane (1.5 mL) were added successively. The mixture was allowed to stir at 110 °C
for 21 h. After cooling to room temperature, the mixture was poured into the mixture of Et O ether/water
and two phases were separated. Aqueous layer was extracted with Et O three times and the combined
2
2
organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure to leave
a crude solid, which was purified by column chromatography on silica gel (hexane/i-PrOAc = 3/1) to
6
afford 120.5 mg of methyl 5-(4-(pentafluoro- -sulfanyl)phenyl)-2-(5-(4-(pyridin-2-yl)phenyl)furan-2-yl)
1
oxazole-4-carboxylate (7aa, orange solid, 78%): H NMR δ 4.02 (s, 3H), 6.92 (d, J = 3.6 Hz, 1H),
7
.23-7.32 (m, 1H), 7.36 (d, J = 3.6 Hz, 1H), 7.80 (d, J = 3.6 Hz, 2H), 7.85-7.97 (m, 4H), 8.11 (d, J = 8.7
13
Hz, 2H), 8.32 (d, J = 8.7 Hz, 2H), 8.73 (d, J = 4.8 Hz, 1H); C NMR δ 52.7, 108.0, 116.1, 120.5, 122.4,
1
1
24.9, 126.2 (m), 127.3, 128.6, 129.6 (×2), 129.7, 137.0, 139.3, 140.8, 149.6, 152.2, 153.1, 154.5 (m),
56.3, 156.6, 162.2; IR (ATR) 1723, 1587, 1465, 1436, 1219, 1092, 835, 811, 781, 756, 664, 598, 580
-1
+
cm ; HRMS (ESI+) Calcd for C26
H
17
F
5
N
2
O SNa [M+Na] : 571.0727; found: m/z 571.0711.
4
Methyl 5-(4-(dimethylamino)phenyl)-2-(5-(4-(pyridin-2-yl)phenyl)furan-2-yl)oxazole-4-carboxylate
1
(
7ab, orange solid, 41%): H NMR δ 3.06 (s, 6H), 3.98 (s, 3H), 6.78 (d, J = 8.4 Hz, 2H), 6.87 (d, J = 4.0
Hz, 1H), 7.23-7.29 (m, 2H), 7.79 (d, J = 4.0 Hz, 2H), 7.92 (d, J = 7.8 Hz, 2H), 8.09 (d, J = 7.8 Hz, 2H),
1
3
8
1
1
.14 (d, J = 8.0 Hz, 2H), 8.72 (d, J = 4.8 Hz, 1H); C NMR δ 40.1, 52.2, 107.9, 111.3, 113.9, 114.6,
20.6, 122.3, 124.8, 125.0, 127.3, 129.8, 130.2, 137.2, 138.6, 141.7, 149.4, 151.0, 151.6, 155.7, 156.3,
-1
56.4, 162.9; IR (ATR) 1714, 1608, 1512, 1464, 1435, 1360, 1196, 1086, 781, 754 cm ; HRMS (ESI+)
+
Calcd for C28
H
23
N
3
O
4
Na [M+Na] : 488.1586; found: m/z 488.1583.

HETEROCYCLES, Vol. 93, No. 1, 2016
147
Methyl 5-(4-(pyridin-2-yl)phenyl)-2-(5-(4-(pyridin-2-yl)phenyl)furan-2-yl)oxazole-4-carboxylate
1
(7ac, orange solid, 89%: further purified by recrystallization from CHCl
3
/MeOH): H NMR δ 4.02 (s, 3H),
6
.91 (d, J = 3.6 Hz, 1H), 7.21-7.32 (m, 2H), 7.34 (d, J = 3.6 Hz, 1H), 7.75-7.84 (m, 4H), 7.94 (d, J = 8.6
Hz, 2H), 8.10 (d, J = 8.6 Hz, 2H), 8.17 (d, J = 8.4 Hz, 2H), 8.31 (d, J = 8.4 Hz, 2H), 8.71-8.78 (m, 2H);
13C NMR δ 52.5, 107.9, 115.6, 120.5, 120.8, 122.4, 122.7, 124.9, 126.9, 127.0, 127.3, 128.2, 128.8, 129.9,
1
1
36.8, 136.9, 139.3, 141.1, 141.2, 149.8, 149.9, 152.6, 154.4, 156.3, 156.4, 156.5, 162.5; IR (ATR) 1721,
-1
633, 1586, 1568, 1504, 1465, 1435, 1354, 1318, 1215, 1128, 1091, 1025, 1011, 852, 780, 729 cm ;
+
HRMS (ESI+) Calcd for C31
H
21
N
3
NaO
4
[M+Na] :522.1430; found: m/z 522.1428.
Methyl 5-(4-methoxyphenyl)-2-(5-(4-(pyridin-2-yl)phenyl)furan-2-yl)oxazole-4-carboxylate (7ad,
1
orange solid, 59%): H NMR δ 3.89 (s, 3H), 4.00 (s, 3H), 6.88 (d, J = 3.6 Hz, 1H), 7.04 (d, J = 9.2 Hz,
2
9
1
H), 7.22-7.29 (m, 2H), 7.75-7.79 (m, 2H), 7.92 (d, J = 8.4 Hz, 2H), 8.09 (d, J = 8.4 Hz, 2H), 8.18 (d, J =
1
3
.2 Hz, 2H), 8.72 (d, J = 4.8 Hz, 1H); C NMR δ 52.3, 55.3, 107.8, 113.9, 115.0, 119.1, 120.4, 122.3,
24.8, 126.4, 127.2, 129.9, 130.2, 136.7, 139.1, 141.3, 149.7, 151.7, 155.0, 156.0, 156.4, 161.3, 162.6; IR
-1
(
ATR) 1717, 1609, 1585, 1505, 1464, 1436, 1259, 1216, 1180, 1091, 835, 780, 720 cm ; HRMS (ESI+)
+
Calcd for C27
H
20
N
2
O
5
Na [M+Na] : 475.1270; found: m/z 475.1263.
Methyl 5-(4-(ethoxycarbonyl)phenyl)-2-(5-(4-(pyridin-2-yl)phenyl)furan-2-yl)oxazole-4-carboxylate
1
(
7ae, orange solid, 75%): H NMR δ 1.37 (t, J = 7.2 Hz, 3H), 3.94 (s, 3H), 4.35 (q, J = 7.2 Hz, 2H), 6.77
d, J = 3.6 Hz, 1H), 7.14-7.19 (m, 1H), 7.21 (d, J = 3.6 Hz, 1H), 7.64-7.72 (m, 2H), 7.80 (d, J = 8.0 Hz,
(
2
H), 7.99 (d, J = 8.0 Hz, 2H), 8.10 (d, J = 8.4 Hz, 2H), 8.19 (d, J = 8.4 Hz, 2H), 8.64 (d, J = 4.4 Hz, 1H);
13C NMR δ 14.1, 52.4, 61.1, 107.8, 115.7, 120.3, 122.2, 124.7, 127.1, 128.0, 129.0, 129.4, 129.6, 130.3,
1
1
31.5, 136.8, 138.9, 140.7, 149.4, 152.6, 153.0, 156.1, 156.2, 162.1, 165.7; IR (ATR) 1715, 1585, 1465,
-1
435, 1352, 1282, 1231, 1215, 1101, 1014, 771, 722 cm ; HRMS (ESI+) Calcd for C29
H
22
N
2
6
O Na
+
[
M+Na] : 517.1376; found: m/z 517.1361.
6
Methyl 2-(5-(4-(diphenylamino)phenyl)furan-2-yl)-5-(4-(pentafluoro- -sulfanyl)phenyl)oxazole-4-
1
carboxylate (7ba, orange solid, 68%): H NMR δ 4.00 (s, 3H), 6.70 (d, J = 3.6 Hz, 1H), 7.03-7.17 (m,
13
9
H), 7.27-7.34 (m, 4H), 7.66 (d, J = 8.7 Hz, 2H), 7.88 (d, J = 9.0 Hz, 2H), 8.30 (d, J = 8.1 Hz, 2H); C
NMR δ 52.7, 106.1, 116.3, 122.6, 122.9, 123.6 , 125.0, 125.7, 126.2 (m), 128.5, 129.4, 129.5, 129.5,
1
1
29.8, 139.9, 147.1, 148.5, 151.9, 153.4, 154.5 (m), 157.3, 162.2; IR (ATR) 1722, 1592, 1486,
-1
322 ,1282, 1222, 1091, 1026, 835, 754, 697, 664, 598 cm ; HRMS (ESI+) Calcd for C33
H
23
F
5
N
2
4
O SNa
+
[
M+Na] : 661.1196; found: m/z 661.1204.

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HETEROCYCLES, Vol. 93, No. 1, 2016
Methyl 5-(4-(dimethylamino)phenyl)-2-(5-(4-(diphenylamino)phenyl)furan-2-yl)oxazole-4-carboxy-
1
late (7bb, orange solid, 88%): H NMR δ 3.04 (s, 6H), 3.97 (s, 3H), 6.66 (d, J = 3.6 Hz, 1H), 6.76 (d, J =
8
2
1
1
.8 Hz, 2H), 7.03-7.17 (m, 8H), 7.21 (d, J = 3.6 Hz, 1H), 7.29 (d, J = 8.4 Hz, 4H), 7.66 (d, J = 8.4 Hz,
13
H), 8.12 (d, J = 9.2 Hz, 2H); C NMR δ 39.9, 52.1, 105.8, 111.2, 113.9, 114.6, 122.7, 123.3, 123.4,
24.7, 124.8, 125.4, 129.3, 129.6, 140.7, 147.2, 147.9, 151.1, 151.4, 156.0, 156.2, 162.9; IR (ATR) 1715,
-1
608, 1512, 1487, 1280, 1196, 1085, 820, 786, 753, 697 cm ; HRMS (ESI+) Calcd for C35
H
29
N
3
O Na
4
+
[
M+Na] : 578.2056; found: m/z 578.2074.
Methyl 2-(5-(4-(diphenylamino)phenyl)furan-2-yl)-5-(4-(pyridin-2-yl)phenyl)oxazole-4-carboxylate
1
(
7bc, orange solid, 66%): H NMR δ 4.00 (s, 3H), 6.70 (d, J = 3.6 Hz, 1H), 7.04-7.17 (m, 9H), 7.26-7.31
m, 5H), 7.68 (d, J = 9.2 Hz, 2H), 7.79-7.83 (m, 2H), 8.15 (d, J = 8.6 Hz, 2H), 8.30 (d, J = 8.6 Hz, 2H),
(
1
3
8
1
.72-8.76 (m, 1H); C NMR δ 52.4, 106.0, 115.7, 120.7, 122.6, 122.7, 123.1, 123.4, 124.8, 125.6, 126.8,
27.0, 128.1, 128.7, 129.3, 136.9, 140.3, 140.8, 147.1, 148.2, 149.7, 152.6, 154.0, 156.2, 156.8, 162.5; IR
-1
(
ATR) 1722, 1588, 1487, 1280, 1216, 1089, 753, 697 cm ; HRMS (ESI+) Calcd for C38
H
27
N
3
4
O Na
+
[
M+Na] : 612.1899; found: m/z 612.1898.
Methyl 2-(5-(4-(diphenylamino)phenyl)furan-2-yl)-5-(4-methoxyphenyl)oxazole-4-carboxylate (7bd,
1
orange solid, 54%): H NMR δ 3.83 (s, 3H), 3.87 (s, 3H), 6.66 (d, J = 3.4 Hz, 1H), 6.99-7.16 (m, 10H),
7
.22 (d, J = 3.4 Hz, 1H), 7.24-7.32 (m, 4H), 7.44-7.51 (m, 1H), 7.56 (dd, J = 1.8 Hz, 1H), 7.65 (d, J = 9.2
13
Hz, 2H); C NMR δ 52.0, 55.6, 105.9, 111.2, 115.1, 116.2, 120.3, 122.8, 123.4, 124.8, 125.5, 129.3,
1
1
29.8, 131.2, 131.9, 140.7, 147.2, 148.0, 151.6, 153.3, 156.5, 157.5, 162.3; IR (ATR) 1730, 1591, 1487,
-1
+
282, 1078, 1025, 791, 752, 697, 524 cm ; HRMS (ESI+) Calcd for C34
H
26
N
2
O Na [M+Na] : 565.1739;
5
found: m/z 565.1721.
Methyl 2-(5-(4-(diphenylamino)phenyl)furan-2-yl)-5-(4-(ethoxycarbonyl)phenyl)oxazole-4-carboxy-
1
late (7be, orange solid, 69%): H NMR δ 1.42 (t, J = 7.2 Hz, 3H), 3.98 (s, 3H), 4.41 (q, J = 7.2 Hz, 2H),
6
.68 (d, J = 4.0 Hz, 1H), 7.02-7.20 (m, 9H), 7.26-7.34 (m, 4H), 7.66 (d, J = 8.4 Hz, 2H), 8.15 (d, J = 8.2
1
3
Hz, 2H), 8.25 (d, J = 8.2 Hz, 2H); C NMR δ 14.2, 52.5, 61.2, 106.0, 116.0, 122.6, 122.9, 123.5, 124.9,
1
1
25.6, 128.0, 129.0, 129.3, 129.5, 130.5, 131.5, 140.1, 147.1, 148.3, 153.0, 157.0, 162.3, 165.8; IR (ATR)
-1
719, 1591, 1487, 1316, 1275, 1229, 1124, 1108, 1026, 1013, 754, 725, 698, 518 cm ; HRMS (ESI+)
+
Calcd for C36
H
28
N
2
O
6
Na [M+Na] : 607.1845; found: m/z 607.1871.
ACKNOWLEDGEMENTS
This work was supported financially by Special Coordination Funds for Promoting Science and

HETEROCYCLES, Vol. 93, No. 1, 2016
149
Technology, Creation of Innovation Centers for Advanced Interdisciplinary Research Areas (Innovative
Bioproduction Kobe) and Kakenhi (Challenging Exploratory Research # 26620146, 2014-2016) by
MEXT, Japan. ST thanks JSPS for the Research Fellowship for Young Scientists.
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1
13
1
2. Suporting Information is available: Copies of H and C NMR spectra of the isolated products.