Oxidative conversion of 3-alkoxyfurans to 2-hydroxy-3(2H)-furanones and 2-hydroxy-2-butene-1,4-diones with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or phenyltrimethylammonium tribromide (PTAB) in t-BuOH

Article abstract of DOI:10.1080/00397910701543036

2-Alkoxy-1,3,4-triphenylfurans were oxidized to 3-alkoxy-2,4,5-triphenyl- 2-butene-1,4-diones with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in t-BuOH. In contrast, various 3-alkoxy-2,4,5-triphenylfurans were directly converted to 2-hydroxy-3(2H)-fu

Full text of DOI:10.1080/00397910701543036

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Oxidative Conversion of 3‐Alkoxyfurans
to 2‐Hydroxy‐3(2H)‐furanones and
2‐Hydroxy‐2‐butene‐1,4‐diones with
2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone
(DDQ) or Phenyltrimethylammonium
Tribromide (PTAB) in t‐BuOH
Shinsei Sayama a
a Department of Chemistry , Fukushima Medical University , Hikariga‐oka,
Fukushima, Japan
Published online: 10 Sep 2007.
To cite this article: Shinsei Sayama (2007) Oxidative Conversion of 3‐Alkoxyfurans
to 2‐Hydroxy‐3(2H)‐furanones and 2‐Hydroxy‐2‐butene‐1,4‐diones with
2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) or Phenyltrimethylammonium Tribromide (PTAB) in t‐BuOH,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
37:18, 3067-3075, DOI: 10.1080/00397910701543036
To link to this article: http://dx.doi.org/10.1080/00397910701543036
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Synthetic Communicationsw, 37: 3067–3075, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701543036
Oxidative Conversion of 3-Alkoxyfurans
to 2-Hydroxy-3(2H)-furanones
and 2-Hydroxy-2-butene-1,4-diones with
2,3-Dichloro-5,6-dicyano-1,4-benzoquinone
(DDQ) or Phenyltrimethylammonium
Tribromide (PTAB) in t-BuOH
Shinsei Sayama
Department of Chemistry, Fukushima Medical University, Hikariga-oka,
Fukushima, Japan
Abstract: 2-Alkoxy-1,3,4-triphenylfurans were oxidized to 3-alkoxy-2,4,5-triphenyl-
2-butene-1,4-diones with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in
t-BuOH. In contrast, various 3-alkoxy-2,4,5-triphenylfurans were directly converted
to 2-hydroxy-3(2H)-furanone with phenyltrimethylammonium tribromide (PTAB) in
t-BuOH. The oxidative ring opening of 3-alkoxy-2,5-diphenylfurans to cis-2-
hydroxy-2-butene-1,4-dione was also accomplished with PTAB in t-BuOH under the
same reaction conditions.
Keywords: 3-alkoxyfuran, DDQ, 2-hydroxy-2-butene-1,4-dione, 2-hydroxy-3(2H)-
furanone, phenyltrimethylammonium tribromide, t-BuOH
Furans have been expected to be key intermediates for the synthesis of various
natural products containing cyclopentenone, furanone, and enedione moieties,
because of having latent functionalities of enedione and lactone.[1–5]
Therefore, synthetic methods for the 3-furanone and 2-alkoxy-2-butene-1,
Received in Japan January 29, 2007
Address correspondence to Shinsei Sayama, Department of Chemistry, Fukushima
Medical University, Hikariga-oka, Fukushima 960-1295, Japan. E-mail: ssayama@
fmu.ac.jp
3067

3068
S. Sayama
4-(L40), dione (L46) skeletones have been developed.[6–9] The conversion of
furans to enediones was achieved by using oxidative reagents such as pyridi-
nium chlorochromate (PCC), m-chloroperbenzoic acid (mCPBA), magnesium
monoperoxyphtalate, dioxirane, methyltrioxorhenium/urea hydrogen
peroxide, and Mo(CO)6/cumyl hydroperoxide.[10–18] Commercially
available phenyltrimethylammonium tribromide (PTAB) and 2,3-dichloro-
5,6-dicyano-1,4-benzoquinone (DDQ) are easy to handle and are useful for
the oxidation of organic compounds to maintain the desired stoichiometry
as well as other oxidizing reagents.[19,20] In a previous article, the conversion
of 3-alkoxyfurans to 2-alkoxy-2-butene-1,4-diones was reported with PTAB
in dimethyl sulfoxide (DMSO) or DDQ in CH2Cl2, respectively.[20] Because
3-alkoxyfurans were smoothly transformed to various 2-alkoxy-3(2H)-
furanones with PTAB in alcohols, there has been much interest in the
oxidation of 3-alkoxyfurans with DDQ in alcohols in comparison with that
of PTAB. The oxidation of 3-alkoxyfurans with DDQ or PTAB in t-BuOH
was subsequently found to afford 2-hydroxy-3(2H)-furanone and 2-hydroxye-
nediones. We report the results of our studies concerning the oxidation of
3-alkoxyfurans to hydroxyfuranone and hydroxyenedione with DDQ or
PTAB in t-BuOH.
At first, the oxidation of 3-alkoxy-2,5-diphenylfurans (1, 4) was carried
out with DDQ in various alcohols at room temperature in comparison
with that of PTAB. The results are summarized in Table 1. The oxidation
of alkoxyfurans (1, 4) with DDQ in ethyl alcohol or propyl alcohol afforded
2-ethoxy- or 2-propoxy-3(2H)-furanones (2, 3) in good yields (runs 1–3).[20]
Table 1. Reaction of 3-alkoxyfurans with DDQ in alcohola
Products, yield
Run
I
R1
R2OH/R2
Time/(h)
II
(%)
III
(%)
1
2
3
4
5
6
7
8
9
1
C2H5
C2H5
C3H7
C2H5
CH3
C2H5
C3H7
C3H7
39
37
24
14
22
14
21
20
15
2
3
3
86
90
88
1
4
1
t-C4H9
t-C4H9
t-C4H9
t-C4H9
t-C4H9
t-C4H9
5
7
93
95
92
94
95
90
6
4
C3H7
C3H7
C4H9
i-C4H9
8
9
10
12
14
11
13
aI: 0.1 mmol; DDQ: 0.1 mmol; temp.: room temperature; alcohol (R2OH): 6 mL.

Conversion of Alkoxyfuran to Hydroxyfuranone
3069
In contrast, cis-1,4-diphenyl-2-ethoxy-2-butene-1,4-dione (5) was obtained
with DDQ in t-BuOH (run 4). To clarify the particular solvent effect of t-
BuOH in alcohols, various 3-alkoxyfurans were oxidized under the same
reaction conditions. 3-Methoxy-, 3-propoxy-, 3-isopropoxy-, 3-butoxy-, and
3-isobutoxyfurans were also converted to corresponding 2-alkoxyenediones
(7, 8, 10, 12, and 14) in 92–95% yields in t-BuOH (runs 5–9). Consequently,
the oxidation of 3-alkoxy-2,5-diphenylfurans with DDQ in t-BuOH was
confirmed to give 2-alkoxy-2-butene-1,4-diones chemoselectively.[20]
The oxidation of various 3-alkoxy-2,4,5-triphenylfurans was also carried
out to clarify oxidizing power of DDQ in t-BuOH under the same reaction
conditions. The results are shown in Table 2. The oxidation of 3-ethoxy-
2,4,5-triphenylfuran (16) was examined with DDQ. 2-Ethoxy-1,3,4-
triphenyl-2-butene-1,4-dione (17) was mainly obtained as crude product
(run 1). 2-Ethoxy-1,3,4-triphenyl-2-butene-1,4-dione (17) spontaneously
transformed to 2-hydroxy-2,4,5-triphenyl-3(2H)-furanone (15) during the
purification of crude product by silica-gel column chromatography (run 1).
To examine the generation of 2-hydroxy-2,4,5-triphenyl-3(2H)-furanone
(15) on this reaction system, the ring opening of various 3-alkoxy-2,4,5-tri-
phenylfurans (18, 20, 22, and 24) to 2-alkoxy-2-butene-1,4-diones was
carried out with DDQ under the same reaction conditions. The oxidation of
3-alkoxy-2,4,5-triphenylfurans (18, 22) afforded the respective cis-2-alkoxy-
1,3,4-triphenyl-2-butene-1,4-diones (19, 23) as crude product (runs 2, 4).
The oxidation of branched alkoxyfurans (20, 24) also took place to give the
corresponding cis-2-alkoxyenediones (21, 25) (runs 3, 5). Similarly, cis-2-
Table 2. Reaction of 3-alkoxyfurans with DDQ in t-BuOHa
Products, yield
Run
IV
R1
Time/(h)
Vb
(%)
15 (%)b
1
2
3
4
5
16
18
20
22
24
C2H5
C3H7
14
19
20
20
15
17
19
21
23
25
92
84
90
85
90
91
81
87
84
89
i-C3H7
C4H9
i-C4H9
aIV: 0.1 mmol; DDQ: 01 mmol; temp.: room temperature; t-BuOH: 6 mL.
bYield of V was determined with 1H NMR, 13C NMR of crude product. Alkoxyene-
diones V were not isolated after purification. Alkoxyenediones V were easily trans-
formed to hydroxyfuranone 15 during purification by column chromatography over SiO2.

3070
S. Sayama
alkoxyenediones (19, 21, 23, and 25) were easily transformed to 2-hydroxy-
2,4,5-triphenyl-3(2H)-furanone (15) after purification by silica-gel column
chromatography. In the present experiments, the oxidative ring opening of
3-alkoxy-2,4,5-triphenylfurans with DDQ in t-BuOH was ascertained to
afford 2-hydroxy-2,4,5-triphenyl-3(2H)-furanone (15) by the path, giving
cis-2-alkoxyenediones as intermediate.
On the other hand, the oxidation of various 3-alkoxy-2,5-diphenyl- and
3-alkoxy-2,4,5-triphenylfurans with PTAB in alcohols such as methyl
alcohol, ethyl alcohol, isopropyl alcohol, and isobutyl alcohol was also
reported to easily convert them to respective 2-alkoxy-3(2H)-furanones.[20b]
Therefore, the oxidation of alkoxyfurans with PTAB in t-BuOH was carried
out to compare with those of DDQ and PTAB in other alcohols. The results
are summarized in Table 3. Treating 2,5-diphenyl-3-methoxyfurans (6) with
an equivalent molar of PTAB over methoxyfuran (6) in t-BuOH, 1,4-
diphenyl-2-hydroxy-2-butene-1,4-dione (26) was obtained (run 1). 2-Methox-
yenedione (7), 2-t-butoxyenedione, and 2-t-butoxy-3(2H)-furanone were not
afforded. To test the solvent effect of t-BuOH for the transformation of
alkoxy-(L152), furan (L153) to hydroxyenedione with PTAB, the ring
opening reaction of various 3-alkoxyfurans (1, 4, 9, 11, 13) was carried out
in t-BuOH. Hydroxyenedione (26) was afforded in good yields (runs 2–6).
The system PTAB in t-BuOH was ascertained to give 2-hydroxy-2-butene-
1,4-diones easily. These results suggested that the system PTAB in t-BuOH
was an alternative and efficient method for the cleavage of ethers to
alcohols.[8b]
Table 3. Reaction of 3-alkoxyfurans with PTAB in t-BuOHa
Run
VI
R1
R2
Time/(h)
Products, yield (%)
1
2
3
4
5
6
7
8
9
6
1
CH3
H
13
18
19
24
13
15
21
20
20
26
26
26
26
26
26
15
15
15
80
83
92
80
90
83
84
83
85
C2H5
C3H7
i-C3H7
C4H9
i-C4H9
C2H5
C4H9
i-C4H9
H
4
H
9
H
11
13
16
22
24
H
H
Ph
Ph
Ph
aVI: 0.1 mmol; PTAB: 0.1 mmol; temp.: room temperature; t-BuOH: 6 mL.

Conversion of Alkoxyfuran to Hydroxyfuranone
3071
Further, the reaction of 3-alkoxy-2,4,5-triphenylfurans (16, 22, and 24)
with PTAB in t-BuOH under the same reaction conditions was carried out
to clarify the limitations and chemoselectivity for the transformation of
alkoxyfurans to hydroxyenediones. Alkoxyfurans (16, 22, and 24)
were smoothly converted to 2-hydroxy-2,4,5-triphenyl furanone (15) (runs
7–9). Both 2-t-butoxy-3(2H)-furanone and alkoxyenediones (17, 23, 25)
generated in Table 2 were not observed with PTAB in t-BuOH. The
oxidation of 3-alkoxy-2,4,5-triphenylfurans with PTAB was favorable and
more easily gave 2-hydroxy-3(2H)-furanone (15) in comparison with that
of DDQ.
In addition, 3-chloro- and 3-bromo-2,5-diphenylfurans were recovered
unchanged with DDQ or PTAB in t-BuOH. 3-Chloro- and 3-bromo-2,4,5-tri-
phenylfurans were also recoverd unchanged. 2,5-Diphenyl-3-propionylfuran
was recovered unchanged under the same reaction conditions. 2-Methoxy-
furan gave no corresponding enediones with DDQ. 4-(2-Furoyl)-2-
butanone and 3-(2-furoyl)propanenitrile were also recovered unchanged
with DDQ. Similarly, furil, 4-(2-furoyl)-2-butanone, and 3-(2-Furoyl)propa-
nenitrile were not converted to corresponding furanones with PTAB.
Furfuryl benzoate did not give corresponding enediones with PTAB.
In the present experiments, 3-alkoxy substituents were required for the trans-
formation of furans with DDQ or PTAB in t-BuOH to 2-hydroxy-2-butene-
1,4-diones. As mentioned previously, 3-alkoxy substituents were also
considered to play an important role in the direct transformation of
3-alkoxy-2,4,5-triphenylfurans to 2-hydroxy-3(2H)-furanone with PTAB in
t-BuOH.[20]
In conclusion, the oxidation system DDQ in t-BuOH was confirmed
to be an alternative convenient method for the transformation of
3-alkoxy-2,4,5-triphenylfurans to 2-alkoxy-2-butene-1,4-diones chemose-
lectively. 2-Alkoxy-1,3,4,-triphenyl-2-butene-1,4-diones were found to be
spontaneously transformed to 2-hydroxy-2,4,5-triphenyl-3(2H)-furanone
by silica gel. On the contrary, the system PTAB in t-BuOH was establi-
shed to be useful for the transformation of 3-alkoxy-2,5-diphenylfurans to
2-hydroxy-2-butene-1,4-diones. The system PTAB in t-BuOH was
also found to be more effective for the direct conversion of 3-alkoxy-
2,4,5-triphenylfurans to 2-hydroxy-2,4,5-triphenyl-3(2H)-furanone than
DDQ.
EXPERIMENTAL
IR spectra were recorded on a Perkin-Elmer Spectrum One FT-IR spectro-
1
photometer. H and 13C NMR spectra were recorded on a Jeol JNM-EX270
spectometer, and the chemical shifts are given relative to the internal SiMe4
standard. MS spectra were run on a Bruker Daltonics-Apex III. Analyses
were run on a Yanagimoto MT-6.

3072
S. Sayama
Typical Procedure for the Transformation of 3-Ethoxy-2,4,5-
triphenylfuran (16) to 2-Ethoxy-1,3,4-triphenyl-2-butene-1,4-dione
(17) with DDQ
To a solution of 3-ethoxy-2,4,5-triphenylfuran (16, 34 mg, 0.1 mmol) in t-butyl
alcohol (6 mL) at rt, DDQ (23 mg, 0.1 mmol) was added. The reaction mixture
was treated with 0.5 M aq Na2S2O3 and saturated aq NaCl after stirring for 14 h
at rt and extracted with ethyl acetate. The organic layer was washed with 0.5 M
aq Na2S2O3 and saturated aq NaCl and dried by MgSO4. After removal of
1
solvent in vacuo, the H and 13C NMR spectra of slightly soluble crude
products were recorded in CDCl3. 2-Ethoxy-1,3,4-triphenyl-2-butene-1,4-
dione (17) was obtained (ca. 92% by NMR). The crude products were
purified by column chromatography on silica gel (Wako C-200) with CCl4
and CCl4-CHCl3 (3:2, v/v). 2-Hydroxy-2,4,5-triphenyl-3(2H)-furanone
(15, 32 mg, 0.091 mmol) was obtained in 91% yield.
Data
1
Compound 17: H NMR (CDCl3) d 1.22 (3H, t, J ¼ 7.2Hz), 3.88 (2H, q,
J ¼ 7.2 Hz), 7.20–8.03 (15H, m). 13C NMR (CDCl3) d 15.09, 67.24,
125.75, 127.83, 127.96, 128.03, 128.35, 128.55, 128.66, 129.16, 129.63,
132.34, 132.63, 133.96, 136.02, 137.53, 156.44, 192.68, 194.98.
Compound 15: mp 1928C. IR (KBr, cm21) 3244, 3060, 1689, 1613, 1590,
1568, 1501, 1483, 1447, 1394, 1314, 1241, 1220, 1157, 1110, 1072, 1028,
1
1001, 969, 957, 908, 795, 779, 756, 731. H NMR (CDCl3) d 7.25–7.77
(15H, m). 13C NMR (CDCl3) d 102.04, 112.13, 125.06, 126.90, 127.60,
127.79, 128.33, 128.82, 129.21, 131.55, 136.02, 177.82, 198.36. HR-ESI-
MS[M þ Na]þ m/z 351.0992 (calcd. 351.0997 for C22H16O3Na).
Preparative Scale of Oxidation of 3-Butoxy-2,5-diphenylfuran (11)
with DDQ in t-BuOH
To a solution of 3-butoxy-2,5-diphenylfuran (11, 292 mg, 1.0 mmol) in
t-butyl alcohol (10 mL) at rt, DDQ (227 mg, 1.0 mmol) was added. The
reaction mixture was treated with 0.5 M aq Na2S2O3 and saturated aq NaCl
after stirring for 17 h at rt and extracted with ethyl acetate. The organic
layer was washed by 0.5 M aq Na2S2O3 and saturated aq NaCl and dried by
1
MgSO4. After removal of solvent in vacuo, the H and 13C NMR spectra of
crude products were recorded. 2-Butoxy-1,4-diphenyl-2-butene-1,4-dione
(12) was obtained. The crude products were purified by column chromato-
graphy on silica gel (Wako C-200) with CCl4 and CHCl3 (3:2, v/v).
2-Butoxy-1,4-diphenyl-2-butene-1,4-dione (12, 280 mg, 0.91 mmol) was
obtained in 91% yield.

Conversion of Alkoxyfuran to Hydroxyfuranone
3073
Compound 19: IR (neat, cm21) 1660. 1H NMR (CDCl3) d 0.82
(3H, t, J ¼ 6.7 Hz), 1.60 (2H, sext, J ¼ 6.7 Hz), 3.76 (2H, t, J ¼ 6.7 Hz),
7.19–8.03 (15H, m). 13C NMR (CDCl3) d 10.17, 22.87, 72.92, 125.75,
127.78, 127.88, 128.01, 128.30, 128.57, 128.67, 128.73, 129.14, 129.23,
129.61, 129.72, 132.29, 132.56, 133.65, 136.02, 137.57, 156.89, 192.72,
194.94.
1
Compound 21: IR (neat, cm21) 1660. H NMR (CDCl3) d 1.22 (6H, d,
J ¼ 6.0 Hz), 4.15 (1H, sept, J ¼ 6.0 Hz), 7.21–8.04 (15H, m). 13C NMR
(CDCl3) d 22.53, 74.41, 126.11, 127.81, 128.05, 128.28, 128.64, 128.71,
129.20, 129.65, 132.36, 133.63, 133.98, 136.08, 137.61, 155.66, 192.97,
195.21.
Compound 23: IR (neat, cm21) 1672. 1H NMR (CDCl3) d 0.79 (3H, t,
J ¼ 7.2 Hz), 1.23 (2H, m), 1.56 (2H, m), 3.80 (2H, t, J ¼ 6.7 Hz), 7.19–
8.03 (15H, m). 13C NMR (CDCl3) d 13.49, 18.72, 31.50, 71.10, 125.75,
128.01, 128.30, 128.55, 128.66, 128.73, 129.12, 129.61, 129.68, 132.29,
133.63, 133.99, 136.04, 137.59, 156.85, 192.73, 194.94.
1
Compound 25: H NMR (CDCl3) d 0.80 (6H, d, J ¼ 6.4 Hz), 1.86 (1H, m),
3.57 (2H, d, J ¼ 6.2 Hz), 7.18–8.02 (15H, m). 13C NMR (CDCl3) d 18.87,
26.64, 77.44, 125.75, 127.85, 127.92, 127.99, 128.23, 128.57, 128.67,
129.11, 129.59, 129.79, 132.25, 133.65, 133.98, 136.04, 137.62, 157.14,
192.72, 194.89.
Typical Procedure for the Transformation of 2,5-Diphenyl-3-
isobutoxyfuran (13) to 1,4-Diphenyl-2-hydroxy-2-butene-1,4-dione
(26) with PTAB
To a solution of 2,5-diphenyl-3-isobutoxyfuran (13, 29 mg, 0.1 mmol) in t-
butyl alcohol (10 mL) at rt, PTAB (38 mg, 0.1 mmol) was added. The
reaction mixture was treated with 0.5 M aq Na2S2O3 and saturated aq
NaCl after stirring for 15 h at rt and extracted with ethyl acetate. The
organic layer was washed by 0.5 M aq Na2S2O3 and saturated aq NaCl
1
and dried by MgSO4. After removal of solvent in vacuo, the H and 13C
NMR spectra of crude products were recorded. 1,4-Diphenyl-2-hydroxy-2-
butene-1,4-dione (26) were obtained. The crude products were purified by
column chromatography on silica gel (Wako C-200) with CCl4 and
CHCl3 (3:2, v/v). 1,4-Diphenyl-2-hydroxy-2-butene-1,4-dione (26, 21 mg,
0.83 mmol) was obtained in 83% yield.
Data
Compound 26: IR (neat, cm21) 3381, 3065, 2926, 1681, 1600, 1566, 1490,
1449, 1358, 1320, 1267, 1181, 1144, 1100, 1076, 1053, 1026, 1001, 970,

3074
S. Sayama
1
899, 872, 832, 809, 774, 735. H NMR (CDCl3) d 6.85 (1H, s), 7.25–8.14
(10H, m). 13C NMR (CDCl3) d 96.20, 127.56, 128.62, 128.78, 128.84,
130.45, 133.44, 133.67, 134.21, 182.29, 187.04, 190.45. Anal. calcd. for
C16H12O3: C, 76.18; H, 4.80. Found: C, 76.31; H, 4.92. HR-ESI-
MS[M þ Na]þ m/z 275.0678 (calcd. 275.0679 for C16H12O3Na).
Preparative Scale of Oxidation of 3-Butoxy-2,4-diphenylfuran (11)
with PTAB in t-BuOH
To a solution of 3-butoxy-2,5-diphenylfuran (11, 292 mg, 1.0 mmol) in t-
butyl alcohol (10 mL) at rt, PTAB (376 mg, 1.0 mmol) was added.
The reaction mixture was treated with 0.5 M aq Na2S2O3 and
saturated aq NaCl after stirring for 17 h at rt and extracted with ethyl
acetate. The organic layer was washed by 0.5 M aq Na2S2O3 and
saturated aq NaCl and dried by MgSO4. After removal of solvent in
1
vacuo, the H and 13C NMR spectra of crude products were recorded.
1,4-Diphenyl-2-hydroxy-2-butene-1,4-dione (26) was obtained. The
crude products were purified by column chromatography on silica gel
(Wako C-200) with CCl4 and CHCl3 (3:2, v/v). 1,4-Diphenyl-2-
hydroxy-2-butene-1,4-dione (26, 222 mg, 0.88 mmol) was obtained in
88% yield.
Typical Procedure for the Transformation of 3-Isobutoxy-2,4,5-
triphenylfuran (24) to 2-Hydroxy-2,4,5-triphenyl-3
(2H)-(L340), furanone (L341) with PTAB
To a solution of 3-isobutoxy-2,4,5-triphenylfuran (24, 36 mg, 0.1 mmol) in
t-butyl alcohol (6 mL) at rt, PTAB (38 mg, 0.1 mmol) was added. The
reaction mixture was treated with 0.5 M aq Na2S2O3 and saturated aq
NaCl after stirring for 20 h at rt and extracted with ethyl acetate. The
organic layer was washed by 0.5 M aq Na2S2O3 and saturated aq NaCl
1
and dried by MgSO4. After removal of solvent in vacuo, the H and 13C
NMR spectra of slightly soluble crude products were recorded in CDCl3.
2-Hydroxy-2,4,5-triphenyl-3 (2H)-furanone (15) was obtained. The crude
products were purified by column chromatography on silica gel (Wako
C-200) with CCl4-CHCl3 (3:2, v/v). 2-Hydroxy-2,4,5-triphenyl-3(2H)-
furanone (15, 30 mg, 0.85 mmol) was obtained in 85% yield.
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