Ecofriendly iodination of activated aromatics and coumarins using potassium iodide and ammonium peroxodisulfate

Article abstract of DOI:10.1055/s-0029-1218698

An environmentally benign protocol for the iodination of activated aromatics, such as phenols, anilines, and hydroxycou-marins, using inexpensive commercially available potassium iodide and ammonium peroxodisulfate (1:2.5 molar equivalents per mole of substrate) in aqueous methanol (MeOH-H ₂O, 6:1) at room temperature has been developed. The protocol provides for ortho-selective monoiodination as the predominant product without added acid and it is compatible with a number of common oxidizible functional groups, such as formyl, benzylic C-H, aromatic amines and hydroxymethyl. Good to acceptable yields of monoiodinated products in acceptable reaction times and exclusive ortho-iodination for 7-hydroxycoumarins, despite the presence of vinylogous electronrich C3, are some of the key advantageous features of the method. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0029-1218698

PAPER
1467
Ecofriendly Iodination of Activated Aromatics and Coumarins Using
Potassium Iodide and Ammonium Peroxodisulfate
I
N
odination of
A
ctiv
e
ated Arom
m
atics and Coumarin sa i C. Ganguly,* Sujoy Kumar Barik, Sanjoy Dutta
Department of Chemistry, University of Kalyani, Kalyani 741235, WB, India
Fax +91(33)25828282; E-mail: nemai_g@yahoo.co.in
Received 19 January 2010; revised 1 February 2010
have been used as a hydrogen iodide trap. However, these
oxidizers are often harsh and involve toxic heavy metals,
hence they are environmentally unacceptable. It was our
Abstract: An environmentally benign protocol for the iodination of
activated aromatics, such as phenols, anilines, and hydroxycou-
marins, using inexpensive commercially available potassium iodide
and ammonium peroxodisulfate (1:2.5 molar equivalents per mole aim to develop a mild, selective method for the iodofunc-
of substrate) in aqueous methanol (MeOH–H O, 6:1) at room tem- tionalization of activated aromatics, particularly for phe-
2
perature has been developed. The protocol provides for ortho-selec-
nols and hydroxycoumarins using commercially available
tive monoiodination as the predominant product without added acid
inexpensive reagents under environmentally benign con-
and it is compatible with a number of common oxidizible functional
ditions. The oxyiodination strategy that utilizes an iodide
groups, such as formyl, benzylic C–H, aromatic amines and hy-
salt in combination with a metal-free ecofriendly oxidiz-
ing agent appealed to us. In fact, halogenation in Nature
droxymethyl. Good to acceptable yields of monoiodinated products
in acceptable reaction times and exclusive ortho-iodination for 7-
hydroxycoumarins, despite the presence of vinylogous electron- occurs by way of oxidative halogenation involving halo-
rich C3, are some of the key advantageous features of the method.
peroxidase enzymes that oxidize halide salts into reactive
hypohalous derivatives. To this end, potassium iodide in
combination with ammonium peroxodisulfate was an at-
tractive candidate. Potassium iodide is available in high
purity and it is less expensive than sodium and ammonium
iodide. It can be oxidized with ammonium peroxodisul-
fate, which is also an inexpensive, easily available re-
agent. It is a ‘green’ oxidizer that is widely used in
industry for bleaching waste water treatment and it has
Key words: iodination, potassium iodide, ammonium peroxodisul-
fate, activated aromatics, coumarins
Iodinated aromatic and heteroaromatic compounds have
attracted active contemporary interest because of their
versatile synthetic utility ranging from precursors of orga-
nometallic compounds and benzynes to substrates for pal-
ladium-, nickel-, and copper-catalyzed cross-coupling
6
been utilized to accomplish the oxidation of alkenes, ben-
7
8
1
zyl alcohols, and substituted aromatics, the cleavage of
reactions to form C–C, C–N, C–O, and C–S bonds. Ad-
procarbonyl imine derivatives, such as oximes and phe-
ditionally, iodinated arenes possess a wide array of bio-
logical activity and find application in human and animal
9
10
nylhydrazones, the deprotection of allyl ethers, and the
solid-state microwave-assisted cleavage of 1,3-dithianes
and dithiolanes on wet montmorillonite K-10 clay.11
Herein, we describe the results of the iodination of a wide
variety of aromatics and hydroxycoumarins with potassi-
um iodide and ammonium peroxodisulfate in aqueous
methanol (Scheme 1).
2
medicine. Iodophenols, for example, are extensively
used in non-evasive medical diagnostic techniques and ra-
dioiodinated photoprobes, hence they are of immense val-
ue as therapeutic and diagnostic aids. Iodocoumarins are
utilized as fluorophores and intermediates for the synthe-
sis of coumarin C-ribosides that are effective photophysi-
cal probes for the study of oligonucleotide dynamics.3
Recently, iodinated umbelliferones have been elaborated
into dihydrofuroangelicins and dihydrofuropsoralins with
pronounced cytotoxicity against KB cells and they have
properties that combat skin diseases such as psoriasis and
KI, (NH4)2S2O8 (1:2.5 molar ratio)
ArH
ArI
MeOH–H2O, r.t. or reflux
Scheme 1
4
vitiligo. However, the iodofunctionalization of arenes
We selected phenol as representative of activated aromat-
ics and set out to optimize the iodination conditions. Se-
lective monoiodination of phenol is elusive unless some
directive influence of substituents is operative and, there-
fore, it was surmised that phenol represents a substrate
that would give a good feel for the mildness as well as the
selectivity of the iodinating reagent. Iodination of phenol
and heteroarenes is frequently not facile due to the weak
electrophilic nature of the iodonium ion coupled with the
relatively weak bond strength of C–I compared to C–Br
and C–Cl. The reversibility of the reaction with release of
hydrogen iodide necessitates the use of oxidizers to make
it practicable. Numerous oxidizing agents, including
5
a
5b
5c
5d
5e
5f
5j
HgO, Oxone, Ag SO , NaIO4, HIO , CrO3,
2
4
4
5
g
5h
5i
with KI–(NH) S O proved was unsuccessful in dry meth-
Pb(OAc) , I O , silica–Bi(NO) ·5 H O, and TlOAc,
4
2
8
4
2
5
3
2
anol and also in acetonitrile (Table 1, entries 1 and 2). On
the other hand, iodination with the same reagent system in
water, with and without anionic surfactant, sodium dode-
SYNTHESIS 2010, No. 9, pp 1467–1472
x
x
.
x
x
.2
0
1
0
Advanced online publication: 12.03.2010
DOI: 10.1055/s-0029-1218698; Art ID: Z01010SS
Georg Thieme Verlag Stuttgart · New York
cyl sulfate (SDS) [H O (5 mL), SDS (0.4 mmol)] well
2
©

1
468
N. C. Ganguly et al.
PAPER
above its critical miceller concentration (cmc), was also of methanol as solvent in iodination may be due to its sol-
disappointingly sluggish even at elevated temperatures ubilizing influence on iodine and the substrate as well.
(
50–60 °C) (entries 8–10). Attempted iodination in aque- However, the possibility of liberated iodine being oxi-
ous acetonitrile (MeCN–H O, 4:1) was also not encourag- dized to a stronger iodonium ion equivalent in the form of
2
ing either in terms of reaction time and yield of 2- methyl hypoiodite in the presence of an excess of a potent
iodophenol (1a) (entry 3). Aqueous methanol (6:1) was oxidizer such as peroxodisulfuric acid cannot be ruled out
found to be the medium of choice furnishing 1a and 2,6- and there is literature precedent for an analogous reaction
diiodophenol (1b) in 65% and 10% yields, respectively in in the case of benzyltrimethylammonium dichloroperio-
an acceptable reaction time (20 h) (entry 6). Observed re- date based aromatic iodinations.15
gioselectively was in sharp contrast to exclusive para-io-
Table 1 Optimization Experiments for the Oxyiodination of Phenol
dination of phenol with iodine and tetrabutylammonium
1
2
persulfate in aprotic solvent, acetonitrile (20 °C, 30 h).
a
Time Yieldb
(h) (%)
Entry Ratio KI/Solvent
Additive
5
j
Whereas iodine–thallium(I) acetate allowed ortho-selec-
tive iodination of phenols, the present method constitutes
a metal-free ortho-selective iodinating system for phe-
nols. For selective monoiodination, a stoichiometric ratio
of substrate/iodide/oxidizer 1:1:2.5 was found to be re-
warding from an iodine atom economy standpoint. Here-
in, we report the results of the iodination of a wide array
of activated aromatics and coumarins using this reagent
combination (Table 2). In view of the importance of poly-
iodinated phenols in medical diagnostics, we explored tri-
iodination of phenol with 3.3 molar equivalents of
potassium iodide along with 7 molar equivalents of am-
monium peroxodisulfate at room temperature for ten
hours and to our satisfaction, 2,4,6-triiodophenol (1c) was
isolated as the exclusive product in 88% yield (entry 1).
Notably, no mineral acid was added for the iodination of
phenols. Previously, a combination of molecular iodine
(
NH )S O
4 2 8
1
a
0
8
1b
0
1
2
3
4
5
6
7
8
9
1:2
1:2
1:2
MeOH
MeCN
–
–
–
–
–
–
–
–
–
10
10
0
MeOH–H O (4:1)
20 55 10
2
1:1.5
1:2
MeOH–H O (2:1)
30 45
20 60
6
8
2
MeOH–H O (6:1)
2
1:2.5
1: 2
1:2
MeOH–H O (6:1)
20 65 10
2
MeCN–H O (4:1)
20 35
48 30
40 20
8
5
8
2
H O
2
1:2
H O
2
13
and potassium peroxodisulfate (0.5:2.2 molar ratio) was 10 1:2
utilized for the synthesis of iodoarenes, but this is effec-
H
O
SDS (10 cmc) 40 30 10
t-BuOH–H O (6:1) – 12 32
10 40 15c
2
1
1
1:2
5
2
tive only in the presence of concentrated sulfuric acid (3
mmol) or trifluoroacetic acid in dichloromethane as an ac- 12 1:2
AcOH–H O (1:3)
–
2
tivator; formation of resinous products and over-oxidation
for electron-rich oxidation-prone aromatics are some of
the serious limitations of this protocol. Successful iodina-
a
Ratio = mol equiv ratio of KI/(NH )S O per mmol of substrate; the
4
2
8
iodination of phenol was carried on a 1-mmol scale.
b
2
-Iodophenol (1a) and 2,6-diiodophenol (1b) were products of iodi-
tion of anisole with potassium iodide and 30% hydrogen nation of phenol.
1
4
c
peroxide in methanol also required one equivalent of
concentrated sulfuric acid to arrest the decomposition of
hydrogen peroxide to oxygen. We envisaged that the key
to the efficacy of the present combination was the in situ
generation of sulfuric acid upon hydrolysis of the acidic
salt ammonium peroxodisulfate. Subsequent release of
peroxomonosulfuric acid (Caro’s acid) by way of hydrol-
ysis of peroxodisulfuric acid and oxidation of iodide to io-
dine by either of the peracids under the acidic conditions
follow. Oxidation of iodide to iodine with peroxodisulfu-
ric acid and Caro’s acid are not mutually exclusive and
may compete with each other (Scheme 2). To support our
contention, a solution of ammonium peroxodisulfate (2
mmol) in methanol–water (6:1, 4 mL) was found to exhib-
it a pH of 1.19 at 33 °C; addition of potassium iodide (1
mmol) to it sharply increased its pH to 6.43. These obser-
vations coupled with the fact that this combination proved
ineffective in dry methanol strongly suggest the crucial
role of water in the iodination process. The actual iodinat-
ing species involved is not clear to us. The facilitating role
Several other products were formed in addition.
(
NH4)2S2O8 + H2O
(NH4)2SO5 + H2SO4
H2S2O8 + (NH4)2SO4
H2SO5 + H2SO4
(
NH4)2S2O8 + H2SO4
H S O + H O
2
2
8
2
2 KI + H2SO5 + H2SO4
KI + H2S2O8
2
I2 + 2 KHSO4 + H O
2
2 KHSO4 + I2
Scheme 2
ortho-Iodination of phenol is tentatively due to the hydro-
gen-bonding interaction of the phenolic OH with MeOI
through a six-membered transition state thereby promot-
ing delivery of iodine at C2 (Scheme 3). However, this is
a purely hypothetical suggestion at this stage of the inves-
tigation. In case of 3-methylphenol the mono/diiodinated
product ratio (3a/3b) was almost identical to that for 1a/
1
b, ortho-monoiodinated product, 2-iodo-5-methylphe-
nol, predominating in 60% yield (Table 2, entry 3).
Synthesis 2010, No. 9, 1467–1472 © Thieme Stuttgart · New York

PAPER
Iodination of Activated Aromatics and Coumarins
1469
Table 2 Oxidative Iodination of Activated Aromatics and Coumarins with Potassium Iodide and Ammonium Peroxodisulfate
a
b
Entry
1
Substrate
Time (h)
Product(s) [yield (%)]
OH
OH
OH
I
I
(i) 20
1
a (65)
1b (10) I
OH
I
I
(
(
ii) 10c
iii) 10
1
b (40)
1c (8)
I
d
1
c (88)
OH
OH
OH
I
I
I
2
3
16
12
2
a (70)
OH
2b (8)
OH
OH
OH
I
I
I
3
a (60)
3b (10)
OH
OH
I
4
5
6
12
12
15
OH
I
OH
OH
I
a (65)
4
4b (15)
OH
OH
5
a (95)
OH
OH
I
6
a (92)
OH
OH
OH
I
I
I
7
8
20
12
CHO
CHO
CHO
OH
7
a (80)
7b (5)
OH
I
OMe
OMe
CHO
CHO
8
a (80)
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1
470
N. C. Ganguly et al.
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Table 2 Oxidative Iodination of Activated Aromatics and Coumarins with Potassium Iodide and Ammonium Peroxodisulfate (continued)
a
b
Entry
9
Substrate
Time (h)
Product(s) [yield (%)]
OH
OH
I
6
CH2OH
CH2OH
OMe
9
a (92)
OMe
1
0
16
I
1
0a (92)
OMe
OMe
1
1
1
1
2
3
10
OMe
OMe
I
1
1a (90)
12
I
1
2a (94)
NH2
NH2
NH2
NH2
I
16e
I
I
1
3a (55)
13b (8)
NH2
NH2
I
I
I
1
1
4
5
10
10
1
4a (68)
14b (10)
NMe2
NMe2
I
5a (58)
1
I
HO
O
O
O
O
HO
O
O
O
1
1
6
7
20
24
1
6a (85)
I
HO
HO
O
1
7a (87)
Synthesis 2010, No. 9, 1467–1472 © Thieme Stuttgart · New York

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Iodination of Activated Aromatics and Coumarins
1471
Table 2 Oxidative Iodination of Activated Aromatics and Coumarins with Potassium Iodide and Ammonium Peroxodisulfate (continued)
a
b
Entry
Substrate
Time (h)
Product(s) [yield (%)]
O
O
O
O
1
8
18c
H2N
H2N
I
1
8a (75)
I
1
9
12c
O
O
O
HO
O
O
1
9a (66)
I
2
0
HO
O
O
12c
O
O
O
2
0a (68)
a
b
c
d
e
Reaction conditions: substrate/KI/(NH ) S O 1:1:2.5, MeOH–H O (6:1), r.t.
4
2
2
8
2
Yields refer to the chromatographically pure products characterized by spectral data (FT-IR, H and 13C NMR, and EIMS).
1
Reaction conditions: substrate/KI/(NH ) S O 1:1:2:5, MeOH–H O (6:1), 50–60 °C.
4
2
2
8
2
Reaction conditions: substrate/KI/(NH ) S O 1:3.3:7, MeOH–H O, r.t.
4
2
2
8
2
Reaction conditions: substrate/KI/(NH) S O 1:1:1.5, MeOH–H O, r.t.
2
2
8
2
ortho-Selectivity was further demonstrated in the iodina- 4-methyl group. Notably, exclusive bromination at C3 of
tion of benzene-1,3-diol which furnished 2-iodobenzene- 7-hydroxycourmarin was accomplished by us with N-bro-
1
,3-diol (4b) in 15% yield despite unfavorable steric situ- mosuccinimide in molten tetrabutylammonium bro-
17
ation (entry 4). Oxidation-prone aromatic aldehydes and mide, a hydrogen-bond base that discourages hydrogen
benzylic alcohol remained intact during the iodination bond formation of N-bromosuccinimide with the 7-OH
(
entries 7–9). However, in case of aniline, the use of 2.5 group thereby preventing ortho-selective bromination.
equivalents of oxidizer led to substantial formation of in- For substrates 8-allyl-7-hydroxycoumarin and 8-allyl-7-
tractable colored oxidized products and successful para hydroxy-4-methylcoumarin bearing an allyl moiety ortho
iodination was achieved only by its careful dropwise ad- to the 7-OH group, iodolactonization took precedence
dition to a stoichiometric combination of potassium io- over slower ring iodination process furnishing angular
dide and ammonium peroxodisulfate in 1:1.5 molar ratio furanocoumarins (entries 19 and 20).
(
entry 13). Iodination of N,N-dimethylaniline led to 4-
In conclusion, a mild ecofriendly protocol for the monoio-
dination of activated aromatics and coumarins using po-
tassium iodide and ammonium peroxodisulfate has been
developed. Use of commercially available, inexpensive
reagents, simple procedure, good to acceptable yields and
ortho-selective iodination for phenols and hydroxycou-
marins without use of metal salts are key attractive fea-
tures of the protocol.
iodo-N,N-dimethylaniline (15a) as the only isolable prod-
uct (entry 15). However, formation of the violet coloration
characteristic of Methyl Violet dye was observed upon ad-
dition of N,N-dimethylaniline to the reagent system. Pre-
vious attempted of iodination of N,N-dimethylaniline with
5
j
iodine–thallium(I) acetate resulted in the formation of
1
5a, but the reaction was complicated due to the oxidation
of N,N-dimethylaniline to 4,4¢-methylenebis(N,N-dimeth-
ylaniline) and Methyl Violet. Analogous oxidation of
N,N-dimethylaniline with iodine–silver(I) trifluoroace-
H
O
O
O
Me
1
6
H
I
tate–dichloromethane gave N,N,N¢,N¢-tetramethylbenzi-
dine.
I
+ MeOH
Iodination of 7-hydroxycoumarins (entries 16 and 17) was
sluggish as expected due to the deactivating effect of the
a-pyrone moiety, but it is remarkable that ortho-monoio-
dination occurred exclusively in the benzenoid ring de-
spite substantial electron withdrawal to the vinylogous C3
position from the 7-OH group and this is so particularly
for 7-hydroxy-4-methylcoumarin where C3 becomes fur-
ther electron-rich due to the presence of electron-releasing
OH
I
Scheme 3
Synthesis 2010, No. 9, 1467–1472 © Thieme Stuttgart · New York

1
472
N. C. Ganguly et al.
PAPER
KI and (NH ) S O were procured from Merck, Germany and SRL, References
4
2
2
8
India respectively. IR spectra were recorded on a Perkin-Elmer
FTIR L120-000A. NMR spectra were measured on Bruker AM-
(
1) (a) Seevers, R. H.; Counsell, R. E. Chem. Rev. 1982, 82,
75. (b) Levin, R. H. React. Intermed. (Wiley) 1985, 3, 1.
c) Merkushev, E. B. Synthesis 1988, 923. (d) Metal-
5
(
3
00L (300 MHz) and Bruker DPX-400 (400 MHz). Applied Bio-
systems MDS Sciex API 3200 were used for recording mass spectra
of the compounds. Silica gel (60–120 mesh, Spectrochem, India)
was used for column chromatographic separations and purification
of regioisomeric and polyiodinated byproducts. PE = petroleum
ether bp 60–80 °C. All products were known compounds unless oth-
erwise given below, and their spectroscopic data were identical to
Catalyzed Cross-Coupling Reactions; Diederich, F.; Stang,
P. J., Eds.; Wiley-VCH: New York, 1998. (e) Beletskaya, I.
P.; Cheprakov, A. V. Coord. Chem. Rev. 2004, 248, 2337.
(
f) Hassan, J.; Sévignon, M.; Gozzi, C.; Schulz, E.; Lemaire,
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1
8
those given in the literature.
(
Experimental Pharmacology; Springer: Berlin, 1993.
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Hönigmann, H.; Edelson, R. L. In Psoralen DNA
Photobiology, Vol. II; Gasparro, F. P., Ed.; CRC Press: Boca
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Larock, R. C.; Armstrong, D. W. Org. Biomol. Chem. 2003,
6
-Amino-5-iodocoumarin (18a); Typical Procedure
(
To a stirred soln of (NH ) S O (570 mg, 2.5 mmol) in MeOH–H O
4
2
2
8
2
(
1
6:1, 7 mL) was added sequentially in small portions KOH (166 mg,
mmol) and 6-aminocoumarin (160 mg, 1 mmol). When the addi-
tion was complete the resulting mixture was heated at 50–60 °C for
8 h (TLC monitoring). MeOH was removed from the mixture un-
1
der reduced pressure and the remaining material was extracted with
EtOAc (3 × 5 mL). The combined organic extracts were washed
successively with 5% aq Na S O soln (3 mL), H O (3 mL) and then
dried (Na SO ). Concentration of the dried extract followed by
chromatography of the residue (silica gel, PE–EtOAc, 1:3) gave
2
2
3
2
(
(
2
4
1, 186; and references cited therein.
pure 18a (215 mg, 75%); mp 138 °C.
5) (a) Orito, K.; Hatakeyama, T.; Takeo, M.; Suginome, H.
Synthesis 1995, 1273. (b) Krishna Mohan, K. V. V.;
Narender, N.; Kulkarni, S. J. Tetrahedron Lett. 2004, 45,
8015. (c) Sy, W. W. Tetrahedron Lett. 1993, 34, 6223.
IR (KBr): 3441, 3328, 2962, 2924, 1699, 1556, 1466, 1261, 1102,
1
–1
018, 802 cm .
1
H NMR (300 MHz, CDCl ): d = 8.17 (d, J = 9.6 Hz, 1 H), 7.18 (d,
3
(
9
d) Lulinski, P.; Skulski, L. Bull. Chem. Soc. Jpn. 2000, 73,
51. (e) Sujuki, H. Org. Synth. Coll. Vol. VI; John Wiley &
J = 9 Hz, 1 H), 6.96 (d, J = 9 Hz, 1 H), 6.45 (d, J = 9.6 Hz, 1 H).
LC-MS: m/z = 288 (M + 1).
Sons: London, 1988, 700. (f) Lulinski, P.; Skulski, L. Bull.
Chem. Soc. Jpn. 1997, 70, 1665. (g) Krassowska-
Swiebocka, B.; Lulinski, P.; Skulski, L. Synthesis 1995,
8
-(Iodomethyl)-8,9-dihydro-2H-furo[2,3-h]chromen-2-one
(
19a)
926. (h) Brazdil, L. C.; Cutlar, C. J. J. Org. Chem. 1996, 61,
White solid; mp 164–166 °C.
9621. (i) Alexander, V. M.; Khandekar, A. C.; Samant, S. D.
IR (KBr): 3079, 3027, 1725, 1617, 1449, 1263, 1113, 1059, 836,
7
Synlett 2003, 1895. (j) Cambie, R. C.; Rutledge, P. S.;
Smith-Palmer, T.; Woodgate, P. D. J. Chem. Soc., Perkin
Trans. 1 1976, 1161.
–
1
57 cm .
1
H NMR (400 MHz, CDCl ): d = 7.63 (d, J = 9.6 Hz, 1 H), 7.29 (d,
3
(
(
6) Fristad, W. E.; Peterson, J. R. Tetrahedron Lett. 1983, 24,
J = 8.4 Hz, 1 H), 6.75 (d, J = 8.4 Hz, 1 H), 6.23 (d, J = 9.6 Hz, 1 H),
4547.
5
.07–5.03 (m, 1 H), 3.58–3.97 (m, 3 H), 3.22, 3.18 (2 d, J = 6.4, 6.4
7) Gelbard, G. Polymer-Supported Reagents, In Handbook of
Green Chemistry and Technology; Clark, J. H.; Macquarrie,
D., Eds.; Blackwell Science: Oxford, 2002.
Hz, 1 H).
1
3
C NMR (100 MHz, CDCl ): d = 163.1, 160.9, 151.4, 143.9, 129.0,
3
1
13.3, 112.8, 112.5, 107.0, 83.4, 33.1, 8.2.
(
8) Clerici, A.; Porta, O. Can. J. Chem. 1980, 58, 2117.
LC-MS: m/z = 329 (M + 1).
(9) (a) Lakouraj, M. M.; Bahrami, K. J. J. Chem. Res., Synop.
002, 222. (b) Minghu, N.; Guichun, Y.; Zuxing, C. React.
2
8
2
-(Iodomethyl)-4-methyl-8,9-dihydro-2H-furo[2,3-h]chromen-
-one (20a)
Funct. Polym. 2000, 44, 49. (c) Verma, R. S.; Meshram, H.
M. Tetrahedron Lett. 1997, 38, 7973.
(10) Chen, F.-E.; Ling, X.-H.; He, Y.-P.; Peng, X.-H. Synthesis
White solid; mp 156–158 °C.
2001, 1772.
IR (KBr): 3031, 2968, 1735, 1615, 1456, 1382, 1365, 1249, 1068,
9
(
(
11) Ganguly, N. C.; Datta, M. Synlett 2004, 659.
12) Yang, S. G.; Kim, Y. H. Tetrahedron Lett. 1999, 40, 6051.
(13) Hossain, D. Md.; Oyamada, J.; Kitamura, T. Synthesis 2008,
690.
(14) Iskra, J.; Stavber, S.; Zupan, M. Synthesis 2004, 1869.
(15) Kajigaeshi, S.; Kakinami, T.; Yamasaki, H.; Fujisaki, S.;
Kondo, M.; Okamoto, T. Chem. Lett. 1987, 2109.
16) Ghosal, S.; Dutta, S. K. Indian J. Chem. 1968, 6, 301.
17) Ganguly, N. C.; De, P.; Dutta, S. Synthesis 2005, 1103.
18) (a) Dictionary of Organic Compounds; Buckingham, J., Ed.;
–
1
57, 840, 755 cm .
1
H NMR (400 MHz, CDCl ): d = 7.43 (d, J = 8.4 Hz, 1 H), 6.77 (d,
3
J = 8.4 Hz, 1 H), 6.11 (d, J = 0.8 Hz, 1 H), 5.07–5.02 (m, 1 H),
3
3
.58–3.39 (m, 3 H), 3.22, 3.18 (2 d, J = 6.8, 6.4 Hz, 1 H), 2.39 (s,
H).
1
3
C NMR (100 MHz, CDCl ): d = 162.9, 160.9, 153.0, 150.8, 125.7,
3
(
(
(
1
14.4, 112.9, 111.5, 106.5, 83.5, 33.2, 19.0, 8.4.
LC-MS: m/z = 343 (M + 1).
5th ed., Vol. III, Chapman and Hall: New York, 1982.
(
(
b) Kometani, T.; Watt, D. S. J. Org. Chem. 1985, 50, 5384.
c) Kajigaeshi, S.; Kakinami, T.; Yamasaki, H.; Fujisaki, S.;
Acknowledgment
S.K.B. thanks the University of Kalyani for financial assistance by
way of a research fellowship. Facilities provided by DST-FIST and
UGC-SAP Grant, Government of India are also acknowledged.
Kondo, M.; Okamoto, T. Chem. Lett. 1987, 2109.
Synthesis 2010, No. 9, 1467–1472 © Thieme Stuttgart · New York