Iron-catalyzed synthesis of functionalized 2H-chromenes via intramolecular alkyne-carbonyl metathesis

Article abstract of DOI:10.1021/jo2000012

An iron-catalyzed intramolecular alkyne-aldehyde metathesis strategy of the alkynyl ether of salicylaldehyde derivatives has been developed which works under mild reaction conditions to produce the functionalized 2H-chromene derivatives. This protocol is compatible toward a wide range of functional groups, such as methoxy, fluoro, chloro, bromo, and phenyl groups. This method provides an atom-economical and environmentally friendly approach for the synthesis of a series of substituted 2H-chromenes.

Full text of DOI:10.1021/jo2000012

NOTE
pubs.acs.org/joc
Iron-Catalyzed Synthesis of Functionalized 2H-Chromenes via
Intramolecular AlkyneꢀCarbonyl Metathesis
Krishnendu Bera, Soumen Sarkar, Srijit Biswas, Sukhendu Maiti, and Umasish Jana*
Department of Chemistry, Jadavpur University, Kolkata 700032, West Bengal, India
S Supporting Information
b
ABSTRACT: An iron-catalyzed intramolecular alkyneꢀaldehyde metath-
esis strategy of the alkynyl ether of salicylaldehyde derivatives has been
developed which works under mild reaction conditions to produce the
functionalized 2H-chromene derivatives. This protocol is compatible
toward a wide range of functional groups, such as methoxy, fluoro, chloro,
bromo, and phenyl groups. This method provides an atom-economical
and environmentally friendly approach for the synthesis of a series of
substituted 2H-chromenes.
Scheme 1. AlkyneꢀCarbonyl Metathesis Reaction
ubstituted 2H-chromenes (2H-1-benzopyran derivatives) are
an important class of structural motif found in many natural
S
products.1 These also have very important medicinal qualities as
anti-HIV,2 antitumor,3 antibacterial/antimicrobial,4 fungicidal,5
and insecticidal agents.6 Moreover, 2H-chromene motifs are also
present in various health-promoting agents like antioxidants7 and
polyphenols.8 In addition to their biological applications, they
have also been widely used as photochromic materials.9 Conse-
quently, significant efforts have been made toward the synthesis
of substituted 2H-chromene motifs.10 However, many of the
reported methods suffer from low yields of the products, non-
availability of the substrates, use of a stoichiometric amount of
reagents, and limitations of the specific substitution pattern. Very
recently, a few catalytic methods have been developed using
transition-metal complexes such as Pt,11 Pd,12 Au,13 and Ru14 to
synthesize 2H-chromene derivatives. Among them, Pt- and Au-
catalyzed hydroarylation reactions of the terminal alkyne are the
most studied protocols; unfortunately, cyclization via a hydro-
arylation reaction often leads to mixture of products. Very
recently, another alternative approach has been described by
Aponick et al. involving a Au(I)-catalyzed dehydrative cyclization
of salicylaldehyde-derived diols in the presence of AgOTf as a
cocatalyst.15 We noted, however, that many of the above-
described approaches are associated with the use of toxic,
moisture-sensitive, and expensive transition-metal complexes as
catalyst. Considering these, the development of less expensive
and environmentally benign CꢀC bond-forming approaches
toward the synthesis of library of functionalized 2H-chromenes
is therefore highly desirable.
A few Lewis and Brønsted acid catalyzed inter- and intramole-
cular versions of this reaction have been investigated recently.
The intramolecular version of this reaction is very attractive
because proper design of the substrates could lead to complex
carbo- and heterocylic compounds.16 However, few studies
toward the synthesis of heterocyclic compounds have achieved
to date.16a,b,g Therefore, the construction of heterocycles using
the alkyneꢀaldehyde metathesis reaction in the presence of an
environmentally friendly and inexpensive catalyst would be of
significant importance in organic synthesis.
Iron is one of the most abundant metals on the earth. Recently,
it has received much attention as an alternative and promising
catalyst for many organic transformations because of its easy
availability, low price, sustainability, and environmentally friendly
characteristics. As a consequence, a series of novel iron-catalyzed
organic transformations including cross-couplings, oxidations,
reductions, etc. have been developed.17 Recently, iron salt has
also been employed for the synthesis of 2H-chromenes via
intramolecular hydroarylation of alkynes;18 however, this meth-
od generally required 2ꢀ4 equiv of aniline as additives, and it
works at high temperature in DMF solvent. In addition, it also
suffers from concomitant formation of benzofuran derivatives.
In continuation of our interests in the development of various iron-
catalyzed transformations,19 we would report herein our findings of
an iron-catalyzed intramolecular alkyneꢀaldehyde metathesis reac-
tion for the regioselective synthesis of substituted 2H-chromenes
On the other hand, alkyneꢀcarbonyl metathesis is a very
useful reaction for the construction of the carbonꢀcarbon
double bond as this transformation represents a completely
atom-economical alternative to the use of stabilized Wittig
reagents in carbonyl olefination reactions. This reaction generally
proceeds via a formal [2 þ 2] cycloaddition and cycloreversion
pathway and produces conjugated carbonyl compounds (Scheme 1).
Received: January 6, 2011
Published: March 18, 2011
r
2011 American Chemical Society
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|

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NOTE
Table 1. Optimization of Fe-Catalyzed Intramolecular
Scheme 2. Design of Intramolecular AlkyneꢀAldehyde
Metathesis for the Synthesis of 2H-Chromenes
AldehydeꢀAlkyne Metathesis Reactiona
time
T
yieldb
Scheme 3. Preparation of the Propargylic Ether of
Salicylaldehydea
entry
solvent
catalyst
(h) (°C]) (%)
1
2
dichloromethane FeCl3 (10 mol %)
dichloromethane FeCl3 (10 mol %)
12 r.t 15
12 reflux 20
3
dichloroethane
toluene
FeCl3 (10 mol %)
FeCl3 (10 mol %)
FeCl3 (10 mol %)
FeCl3 (15 mol %)
FeCl3 (10 mol %)
FeBr3 (15 mol %)
Fe(OTf)3 (15 mol %)
5
4
5
4
7
6
4
9
9
9
9
reflux 35
reflux 25
reflux 60
reflux 70
reflux 50
reflux 55
reflux 35
reflux 50
reflux n.r.
reflux 30
reflux trace
4
5
acetonitrile
acetonitrile
nitromethane
acetonitrile
acetonitrile
acetonitrile
acetonitrile
acetonitrile
acetonitrile
a Reaction conditions: (i) K2CO3, propargyl bromide, CH3CN, reflux;
6
(ii) R2X, Pd(PPh3)4, CuI, Et3N, DMSO.
7
8
9
(Scheme 2). This protocol is found to work well for a wide variety of
substrates in high yields.
10
11
12
13
FeCl3 6H2O(15 mol %)
3
Fe(acac)3 (10 mol %)
InCl3 (15 mol %)
AlCl3 (15 mol %)
The required starting materials for this transformation could
easily be obtained from salicylaldehyde or its derivatives. Salicy-
laldehyde is readily alkylated with substituted propargylic bro-
mide to obtain propargylic ether derivatives. A majority of
substrates have been prepared following this method in high
yields (Scheme 3). Aryl-substituted alkynyl ether could also be
prepared from easily available unsubstituted propargylic ether
derivatives of salicylaldehyde by the Sonogashira coupling
reaction.
a Reaction conditions: substrate 1a (0.5 mmol) and solvent (3 mL).
b Yield after column chromatography.
are summarized in Table 2. The reaction appeared to be quite
general with respect to a wide variety of functional groups such as ꢀ
Cl, ꢀBr, ꢀOMe, and ꢀPh in salicylaldehyde. In general, good
yields were obtained with the substrates having weakly electron-
withdrawing halides such as 4-Cl (1b), 2,4-Cl( 1c and 1h), and
4-Br (1d) as substituents of the aromatic ring of the salicylalde-
hyde. Interestingly, dichloro-substituted salicylaldehyde deriva-
tives 1c and 1h produced the desired products 2c and 2h in 89%
and 74% yields (Table 2, entries 3 and 8), respectively.
At first, we screened the various iron salts to determine their
catalytic efficiency toward the intramolecular alkyneꢀaldehyde
metathesis reaction. For this purpose, the easily accessible
alkynyl ether of salicylaldehyde 1a was chosen as a model
substrate to develop appropriate reaction conditions for this
transformation. We were pleased to find that treating 1a with a
catalytic amount of anhydrous FeCl3 (15 mol %) in acetonitrile
under refluxing conditions gave the desired cyclization product
2a exclusively in 70% yield after 4 h (Table 1, entry 6). Further
increasing the amount of catalyst loading did not increase the
yield, whereas reducing the amount of the catalyst led to a lower
yield of the desired product (Table 1, entry 5), even after
prolonged heating. It was also observed that anhydrous FeCl3
was a more effective catalyst than hydrated FeCl3 (Table 1, entry 10).
Other iron salts such as FeBr3 and Fe(OTf)3 were also found to
catalyze the reaction, albeit affording the desired product with
lower yields (Table 1, entries 8 and 9). Fe(acac)3 did not have
any catalytic activity in this reaction (Table 1, entry 11). The
Lewis acidity of the various iron salts may play a crucial role. In
order to determine the high catalytic activity of FeCl3, we have
also studied the same reaction using other Lewis acid catalysts
such as InCl3 and AlCl3. It was found that InCl3 gave 30% yield
and AlCl3 gave only a trace amount of the desired product under
similar reaction conditions. The reaction was also investigated
using various common organic solvents, such as dichloro-
methane, 1,2-dichloroethane, acetonitrile, toluene, and nitro-
methane, at different temperatures, and acetonitrile was found
to be optimal among them in terms of the yield. In order to avoid
any photoisomerization the reaction was studied in the dark.
Under the optimized reaction conditions, we explored the
feasibility of the reaction with a variety of substrates. The results
Along these lines, it is noteworthy to mention that halide-
substituted chromenes are very attractive for further synthetic
transformations through various cross-coupling reactions. Simi-
larly, electron-donating groups such ꢀOMe on the salicylalde-
hyde unit also underwent a smooth intramolecular alkyneꢀ
aldehyde metathesis reaction in the presence of catalytic FeCl3
to yield the desired products 2e and 2g in 76% and 68% yields,
respectively (Table 2, entries 5 and 7). The result was also
consistent for naphthalene system 1f, which gave the desired
tricyclic 2H-chromene derivative 2f in 68% yield at 60 °C
(Table 2, entry 6). Moreover, biphenyl system 1j also underwent
smooth conversion to the desired chromene derivative 2j in 68%
yield (Table 2, entry 10). Likewise, the variations of substituents
on the aromatic ring attached to alkyne were also well-tolerated
for this protocol, which provides good yields for electron-
donating groups such as 4-OMe 1i (Table 2, entry 9) and for
electron-withdrawing substituents such as 4-F (2g) and 4-Br
(2h) (Table 2, entries 7 and 8). Thus, these results demonstrated
the potential usefulness of this process for the synthesis of
complex 2H-chromene derivatives. The electronic nature of
the substituents on the aromatic rings of 1 has little influence
in this process, since good yields were obtained with both
electron-rich and weakly electron-deficient molecules.
Next, alkyl groups at the alkynyl terminus (Table 2, entries 2k
and 2l) were also examined to prove the generality of this
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NOTE
Table 2. FeCl3-Catalyzed Intramolecular Alkyne-Aldehyde
Metathesis for the Synthesis of Functionalized
2H-Chromenesa
Scheme 4. Proposed Mechanism for the IronꢀSalt Cata-
lyzed Intramolecular AlkyneꢀAldehyde Metathesis
functional groups which could be useful for further synthetic
transformations. Unfortunately, when propargylic ether 1m with-
out any substituents at the alkyne terminus (Table 2, entry 13)
was employed, no reaction occurred.
On the basis of the above results and the known chemistry of
the alkyneꢀcarbonyl methathesis reaction, we tentatively pro-
pose the mechanism depicted in Scheme 4. The reaction pro-
ceeds through a formal [2 þ 2] cycloaddition reaction; the exact
role of the ironꢀsalt is not known; however the reaction is
initiated by the coordination of the carbonyl group with the
ironꢀsalt through Lewis acidꢀbase interaction to form a reactive
species A. Then nucleophilic attack of the alkyne unit to the
activated aldehyde group generates a vinylic cation intermediate
B and subsequent cyclization by intramolecular nucleophilic
attack of the carbonyl oxygen at the vinylic carbocation center
leads to the formation of an oxetene intermediate C regenerating
the ironꢀsalt for next catalytic cycle. The oxetene intermediate
then undergoes formal (2 þ 2) cycloreversion producing the
desired 2H-chromene derivative with complete regioselectivity.
The generation of vinylic carbocation is supported by the fact
that terminal alkyne did not produce the product, and aryl-
substituted alkynes were more efficient compare to alkyl-sub-
stituted alkynes toward this transformation.
In summary, we have developed an FeCl3-catalyzed intramo-
lecular alkyneꢀaldehyde metathesis process for the library
synthesis of functionalized 2H-chromene from readily available
alkynyl ethers of salicylaldehyde derivatives. A number of func-
tional groups including methoxy, phenyl, chloro, fluoro, and
bromo groups are well-tolerated in this reaction conditions. The
attractive features of this procedure are the mild reaction condi-
tions, high atom-economy, use of inexpensive starting materials,
and environmentally friendly catalyst. Moreover, this protocol
can introduce carbonyl functionality in the chromene unit. Thus,
the present reaction represents a versatile access to functiona-
lized 2H-chromenes and would be a useful tool for the synthesis
of biologically and photochemically active molecules.
a Reaction conditions: Substrate 1a (0.5 mmol), acetonitrile (3 mL) and
FeCl3 (15 mol-%). b Yield after column chromatography. c Reaction was
performed in nitromethane (3 mL) at 60 °C. d Reaction was performed in
1,2-dichloroethane (3 mL) under refluxing condition. e N.R = No Reaction.
’ EXPERIMENTAL SECTION
1
transformation. It was also observed that the reaction proceeded
to produce the desired products in moderate yields and took a
longer time to reach completion compared to the aryl-substi-
tuted alkynes. These results indicate the aryl-substituted alkynes
to be more effective substrates compared to the alkyl-substituted
alkynes. Thus, the iron-catalyzed intramolecular alkyneꢀaldehyde
metathesis reaction has been well accommodated with various
General Methods. H NMR spectra were recorded in CDCl3
solutions. Chemical shifts are expressed in parts per million (ppm, δ)
and are referenced to CHCl3 (δ = 7.26 ppm) as an internal standard. All
coupling constants are absolute values and are expressed in hertz. Signal
description: s = singlet, d = doublet, t = triplet, m = multiplet, dd =
doublet of doublets, brs = broad singlet. 13C NMR spectra were recorded
in CDCl3 solutions with complete proton decoupling. Chemical shifts
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NOTE
are expressed in parts per million (ppm, δ) and are referenced to CDCl3
(δ = 77.0 ppm) as an internal standard. High-resolution mass spectra
(HRMS) were performed in dichloromethane solvent. The molecular
fragments are quoted as the relation between mass and charge (m/z).
The IR spectra were recorded as thin films with KBr. The routine
monitoring of reactions was performed with silica gel coated glass slides
and precoated Al plates, which were analyzed with iodine, UV light, and
alkaline KMnO4, respectively. All reactions involving moisture-sensitive
reactants were executed with oven-dried glassware.
General Procedure for FeCl3-Catalyzed Synthesis of 2H-Chromenes.
Representative Experimental Procedure for the Synthesis of
(2H-Chromen-3-yl)methanone 2a (Table 2, Entry 1). Compound 1a
(118 mg, 0.5 mmol) was taken in a 25 mL round-bottom flask containing
3 mL of dry acetonitrile solvent. Anhydrous FeCl3 (12 mg, 0.08 mmol)
was added, and the reaction mixture was heated to reflux for 4 h under an
Ar atmosphere in the dark. After complete conversion of the starting
material (TLC), acetonitrile was distilled out under reduced pressure
and the residue was purified by silica gel (mess 60ꢀ120) column
chromatography to afford 2a (83 mg, 0.35 mmol, 70%) as a yellow
oil. IR (KBr): 3058, 1626, 1483, 1322, 1294, 1074, 708 cmꢀ1. 1H NMR
(300 MHz, CDCl3): δ = 5.16 (s, 2 H), 6.89ꢀ6.95 (m, 2 H), 7.09ꢀ7.12
(m, 2 H), 7.25ꢀ7.27 (m, 1 H), 7.49 (t, J = 7.5 Hz, 2 H), 7.58 (t,
J = 7.1 Hz, 1 H), 7.71ꢀ7.75 (m, 2 H). 13C NMR (75 MHz, CDCl3):
δ = 65.3, 116.4, 121.0, 121.9, 128.5, 129.0, 129.4, 129.9, 132.0, 132.6,
137.1, 137.6, 155.6, 194.1. HRMS: calcd for C16H13O2 [M þ 1]
237.0916, found 237.0912.
(6-Chloro-2H-chromen-3-yl)(phenyl)methanone 2b (Table 2, Entry 2).
Compound 1b (135 mg, 0.5 mmol) and anhydrous FeCl3 (12 mg,
0.08 mmol) were treated in acetonitrile solvent as described for the
synthesis of 2a for 6 h to afford 2b (92 mg, 0.34 mmol, 68%) as a yellow
solid. Mp: 88 °C. IR (KBr): 1627, 1339, 1261, 1036, 710 cmꢀ1. 1H NMR
(300 MHz, CDCl3): δ = 5.15 (s, 2 H), 6.84 (d, J = 8.6 Hz, 1 H), 7.03
(s, 1 H), 7.08 (s, 1 H), 7.18ꢀ7.22 (m, 1 H), 7.49 (t, J = 7.2 Hz, 2 H), 7.58
(t, J = 7.3 Hz, 1 H), 7.72 (d, J = 7.1 Hz, 2 H). 13C NMR (75 MHz, CDCl3):
δ = 65.5, 117.7, 122.2, 126.6, 128.5, 129.0, 130.8, 132.0, 132.3, 135.5,
137.2, 154.0, 193.9. HRMS: calcd for C16H12ClO2 [M þ 1] 271.0526,
found 271.0523.
Representative Experimental Procedure for the Prepara-
tion of Propargylic Bromide.
At first, propargylic alcohol 3 (1.50 g, 11.4 mmol) was taken in a
50 mL round-bottom flask. PBr3 (4.60 g, 17.1 mmol) was added
dropwise by a pressure equalizer funnel while the mixture was stirred
at 0 °C. After 0.5 h of stirring at the same temperature, the reaction
mixture was poured into iceꢀwater (150 mL), and the solution was
neutralized by addition of solid NaHCO3. After complete neutralization,
the aqueous solution was extracted with dichloromethane (2 ꢁ 50 mL)
followed by washing the organic layer by saturated NaCl solution
(50 mL). Finally, the dichloromethane part was dried over anhydrous
Na2SO4 and concentrated under reduced pressure. The residue was purified
by column chromatography through a short silica gel (mess 60ꢀ120)
column to afford compound 4 (1.90 g, 9.7 mmol, 85%) as a yellow oil.
Representative Experimental Procedure for the Synthesis
of Propargylic Ether 1a20.
(6,8-Dichloro-2H-chromen-3-yl)(phenyl)methanone 2c (Table 2,
Entry 3). Compound 1c (152 mg, 0.5 mmol) and anhydrous FeCl3
(12 mg, 0.08 mmol) were treated in acetonitrile solvent as described for
the synthesis of 2a for 8 h to afford 2c (137 mg, 0.45 mmol, 89%) as a
brownish yellow solid. Mp: 130 °C. IR (KBr): 3066, 1629, 1463, 1337,
1212, 714 cmꢀ1. 1H NMR (300 MHz, CDCl3): δ = 5.25 (s, 2 H), 7.0
(s, 2 H), 7.30 (brs, 1 H), 7.48ꢀ7.52 (m, 2 H), 7.58ꢀ7.63 (m, 1 H), 7.72
(d, J = 7.2 Hz, 2 H). 13C NMR (75 MHz, CDCl3): δ = 66.2, 122.3, 123.0,
126.4, 127.0, 128.5, 128.6, 129.0, 131.3, 131.9, 132.5, 134.4, 136.9, 149.7,
193.5. HRMS: calcd for C16H10Cl2O2Na [M þ Na] 326.9956, found
326.9955.
(6-Bromo-2H-chromen-3-yl)(phenyl)methanone2d (Table 2, Entry 4).
Compound 1d (158 mg, 0.5 mmol) and anhydrous FeCl3 (12 mg,
0.08 mmol) were treated in acetonitrile solvent as described for the
synthesis of 2a for 7 h to afford 2d (114 mg, 0.36 mmol, 72%) as a
yellowish white solid. Mp: 120 °C. IR (KBr): 3448, 1646, 1627, 1476, 1338,
818 cmꢀ1. 1H NMR (300 MHz, CDCl3): δ = 5.16 (s, 2 H), 6.79 (d, J =
8.6 Hz, 1 H), 7.03 (s, 1 H), 7.23 (d, J = 2.35 Hz, 1 H), 7.35
(dd, J = 8.6, 2.4 Hz, 1 H), 7.47ꢀ7.52 (m, 2 H), 7.57ꢀ7.62 (m, 1 H),
7.72 (d, J = 7.0 Hz, 2 H). 13C NMR (75 MHz, CDCl3): δ = 58.7, 107.0,
111.5, 116.0, 121.8, 122.3, 124.0, 124.7, 125.6, 128.1, 128.6, 130.5, 147.7,
187.1. HRMS: calcd for C16H11BrO2Na [M þ Na] 336.9840, found
336.9835.
Salicylaldehyde 5 (626 mg, 5.13 mmol) was dissolved in dry aceto-
nitrile (15 mL) in a 50 mL round-bottom flask. To this solution was
added propargylic bromide 4 (1.00 g, 5.13 mmol) followed by anhy-
drous K2CO3 (3.50 g, 25.7 mmol), and the reaction mixture was refluxed
under an Ar atmosphere for 4 h. The mixture was cooled to room
temperature and filtered through the sintered glass crucible. After that,
the solvent acetonitrile was removed under reduced pressure, and the
residue was purified by silica gel (mess 60ꢀ120) column chromatogra-
phy to obtain the product 1a (875 mg, 3.71 mmol, 72%) as a white solid.
Compounds 1bꢀh,jꢀm were also synthesized by similar procedure.
Scheme 5. Representative Experimental Procedure for the
Synthesis of Propargyl Ether 1i:21
(8-Methoxy-2H-chromen-3-yl)(phenyl)methanone 2e (Table 2,
Entry 5). Compound 1e (133 mg, 0.5 mmol) and anhydrous FeCl3 (12 mg,
0.08 mmol) were treated in acetonitrile solvent as described for the synthesis of
2a for 8 h to afford 2e (96 mg, 0.36 mmol, 76%) as a yellow solid. Mp: 94 °C.
To a mixture of compound 6 (950 mg, 5.0 mmol), 4-iodoanisole
(1.17 g, 5 mmol), and triethylamine (0.759 g, 7.5 mmol) in dry DMSO
(10 mL) under an Ar atmoshphere were added Pd (PPh3)4 (58 mg, 0.05
mmol) and CuI (0.029 g, 0.15 mmol) successively. The reaction mixture
was stirred at room temperature for 8 h. Then the mixture was dissolved
in water and extracted with EtOAc. The compound was purified using
silica gel column chromatography to afford the propargylic ether 1i as a
white solid (953 mg, 68%).
1
IR (KBr): 1622, 1336, 1269, 1097, 775, 709 cmꢀ1. H NMR (300 MHz,
CDCl3): δ = 3.91 (s, 3 H), 5.22 (s, 2 H), 6.74 (d, J = 7.0 Hz, 1 H), 6.89 (d,
J = 7.7 Hz, 2 H), 7.11 (s, 1 H), 7.48 (t, J = 7.6 Hz, 2 H), 7.56 (d, J = 6.7 Hz,
1 H), 7.72 (d, J = 7.8 Hz, 2 H). 13C NMR (75 MHz, CDCl3): δ = 56.3, 65.7,
115.1, 121.4, 121.7, 121.8, 128.6, 129.1, 130.0, 132.2, 137.1, 137.6, 144.6, 148.2,
194.2. HRMS: calcd for C17H14O3Na [M þ Na] 289.0841, found 289.0835.
(3H-Benzo[f]chromen-2-yl)(phenyl)methanone 2f (Table 2, Entry 6).
Compound 1f (143 mg, 0.5 mmol) and anhydrous FeCl3 (12 mg,
0.08 mmol) were treated in nitromethane solvent at 60 °C for 5 h to
The experimental details and spectroscopic data (IR, 1H, 13C NMR
1
and HRMS for all unknown final compounds 2bꢀl and only H and
13C NMR spectroscopic data for known final compound 2a are
provided below.
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NOTE
afford 2f (97.4 mg, 0.34 mmol, 68%) as a sticky brown solid. IR (KBr):
3061, 1626, 1562, 133, 817, 750 cmꢀ1. 1H NMR (300 MHz, CDCl3):
δ = 5.26 (s, 2 H), 7.16 (d, J = 8.9 Hz, 1H), 7.36ꢀ7.42 (m, 1 H),
7.47ꢀ7.56 (m, 3 H), 7.61(d, J = 7.3 Hz, 1 H), 7.77ꢀ7.85 (m, 6 H).
13C NMR (75 MHz, CDCl3): δ = 65.2, 114.4, 117.7, 121.1, 124.4,
127.5, 127.7, 128.5, 128.9, 129.1, 129.4, 130.0, 130.1, 132.0, 133.4,
137.9,193.9. HRMS: calcd for C20H16O2 [M þ 1] 287.1072, found
287.1069.
for 15 h to afford 2l (52 mg, 0.23 mmol, 45%) as a yellow sticky liquid. IR
(KBr): 3286, 2968, 1658, 1632, 1489, 1238 cmꢀ1. 1H NMR (500 MHz,
CDCl3): δ = 0.98 (t, J = 7 Hz, 3 H), 1.66ꢀ1.74 (m, 2 H), 2.71 (t,
J = 7.5 Hz, 2 H), 5.0 (s, 2 H), 6.79 (d, J = 8.5 Hz, 1 H), 7.14(d, J = 2.5 Hz,
1 H), 7.18ꢀ7.22 (m, 1 H), 7.26 (s, 1 H). 13C NMR (125 MHz, CDCl3):
δ = 14.0, 18.1, 39.2, 64.8, 117.8, 126.6, 128.5, 131.6, 131.9, 154.2, 198.4.
HRMS: calcd for C22H17O2 [M þ 1] 237.0682, found 237.0676.
(4-Fluorophenyl)(8-methoxy-2H-chromen-3-yl)methanone 2g
(Table 2, Entry 7). Compound 1g (142 mg, 0.5 mmol) and anhydrous
FeCl3 (12 mg, 0.08 mmol) were treated in acetonitrile solvent as
described for the synthesis of 2a for 6 h to afford 2g (97 mg, 0.34
mmol, 68%) as a yellow solid. Mp: 82 °C. IR (KBr): 3462, 1624, 1597,
1482, 1345, 1267, 1227 cmꢀ1. 1H NMR (300 MHz, CDCl3): δ = 3.89
(s, 3 H), 5.18 (s, 2 H), 6.74 (d, J = 6.9 Hz, 1 H), 6.86ꢀ6.93 (m, 2 H), 7.08
(s, 1 H), 7.16 (t, J = 8.5 Hz, 2 H), 7.73ꢀ7.78 (m, 2 H). 13C NMR
(75 MHz, CDCl3): δ = 56.3, 65.8, 115.2, 115.6, 115.9, 121.4, 121.7, 129.9,
131.6, 131.8, 133.8, 136.9, 144.7, 148.3, 163.6, 167.0 (d, JCꢀF = 255 Hz),
192.7. HRMS: calcd for C17H14FO3 [M þ 1] 285.0927, found 285.0922.
(4-Bromophenyl)(6,8-dichloro-2H-chromen-3-yl)methanone 2h
(Table 2, Entry 8). Compound 1h (192 mg, 0.5 mmol) and anhydrous
FeCl3 (12 mg, 0.08 mmol) were treated in acetonitrile solvent as
described for the synthesis of 2a for 7 h to afford 2h (142.1 mg, 0.37
mmol, 74%) as a yellow solid. Mp: 102 °C. IR (KBr): 3449, 1686, 1627,
1581, 1337, 1213, 826 cmꢀ1. 1H NMR (300 MHz, CDCl3): δ = 5.23
(s, 2 H), 7.0 (d, J = 7.5, 2 H), 7.32 (brs, 1 H), 7.62 (dd, J = 8.3, 17.3 Hz,
4 H).13 13C NMR (125 MHz, CDCl3): δ = 66.2, 122.6, 123.0, 126.7,
127.2, 127.7, 130.7, 131.3, 132.1, 132.3, 134.6, 135.8, 150.0, 192.5.
HRMS: calcd for C16H10BrCl2O2 [M þ 1] 382.9241, found 382.9236.
(2H-Chromen-3-yl)(4-methoxyphenyl)methanone 2i (Table 2, Entry 9).
Compound 1i (133 mg, 0.5 mmol) and anhydrous FeCl3 (12 mg,
0.08 mmol) were treated in acetonitrile solvent as described for the
synthesis of 2a for 4 h to afford 2i (85 mg, 0.32 mmol, 64%) as a yellow
solid. Mp: 85 °C. IR (KBr): 3447, 1616, 1599, 1570, 1256, 1171,
751 cmꢀ1. 1H NMR (300 MHz, CDCl3) δ: 3.80 (s, 3 H), 5.05 (s, 2 H),
6.80ꢀ6.85 (m, 1 H), 6.89 (d, J = 5.0 Hz, 2 H), 6.90ꢀ7.0 (m, 2 H), 7.68
(dd, J = 6.9, 2.0 Hz, 2 H). 13C NMR (75 MHz, CDCl3) δ: 55.6, 65.7,
113.9, 116.5, 121.3, 121.9, 129.3, 130.1, 130.2, 131.5, 132.3, 135.8,
155.6, 163.1, 192.9. HRMS: calcd for C17H14NaO3 [M þ Na]
289.0841, found 289.0836.
’ ASSOCIATED CONTENT
S
Supporting Information. Copies of NMR spectra. This
b
material is available free of charge via the Internet at http://pubs.
acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Tel: þ9133-2414-6152, þ91-9051230927. Fax: þ91-33-2414-
6584. E-mail: jumasish2004@yahoo.co.in.
’ ACKNOWLEDGMENT
We acknowledge the financial and infrastructural support
from the UGC-CAS program of the Department of Chemistry,
Jadavpur University. The DST-PURSE program is also gratefully
acknowledged. K.B. and S.S. are thankful to the CSIR, New
Delhi, India, for their fellowships. S.M. and S.B. are also thankful
to the UGC, Jadavpur University, New Delhi, India, for their
fellowships.
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1
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3543
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The Journal of Organic Chemistry
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