Photochemistry of 3-alkoxychromones I - Photocyclisation of 6-chloro-3-alkoxy-2-(furan-3-yl)-4H-chromen-4-ones

Article abstract of DOI:10.1139/V08-177

3-Alkoxy/allyloxy-6-chloro-2-(furan-3-yl)-4H-chromen-4-ones yield angular tetracyclic products involving the 2- furyl group on photoirradiation through the intermediacy of 1,4-biradicals. The nature of the 3-alkoxy/allyloxy group influenced the photoprodu

Full text of DOI:10.1139/V08-177

422
Photochemistry of 3-alkoxychromones I —
Photocyclisation of 6-chloro-3-alkoxy-2-(furan-3-
yl)-4H-chromen-4-ones
Ramesh C. Kamboj, Urmila Berar, Surinder Berar, Mandeep Thakur, Rita Arora,
and Satish C. Gupta
Abstract: 3-Alkoxy/allyloxy-6-chloro-2-(furan-3-yl)-4H-chromen-4-ones yield angular tetracyclic products involving the 2-
furyl group on photoirradiation through the intermediacy of 1,4-biradicals. The nature of the 3-alkoxy/allyloxy group influ-
enced the photoproduct distribution. The stereochemical dispositions of the products have been established using the J/F
relationship and were corroborated by MM2 calculations.
Key words: furylchromone, type-II reaction, 1,5-sigmatropic shift.
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Resume : La photoirradiation des 3-alkoxy/allyloxy-6-chloro-2-(furan-3-yl)-4H-chromenones conduit a des produits tetra-
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cycliques angulaires impliquant le groupe 2-furyle par l’intermediaire de biradicaux-1,4. La nature du groupe 3-alkoxy/al-
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lyloxy influence la distribution des photoproduits. Les dispositions stereochimiques des produits ont ete determinees a
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l’aide de la relation J/F et elles ont ete corroborees par des calculs theoriques MM2.
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Mots-cles : furylchromone, reaction de type II, deplacement sigmatropique 1,5.
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[Traduit par la Redaction]
The structures of compounds 3a–3j were found to be con-
Introduction
1
sistent with their spectral parameters (IR, H-13C NMR, Ex-
In photochemical transformations of 3-alkoxy-2-aryl-4H-
chromen-4-one,1 the products formed depend upon the na-
ture of substituents at C-2 and C-3. The 2-methyl-3-methoxy
derivatives produced dimeric oxetanols and underwent de-
methoxylation.2 The photolysis of 3-alkoxy-2-(phenyl/furyl/
thienyl)-4H-chromen-4-one3 produced angular tetracyclics,
whereas 2-styryl4 derivatives provided linear tricyclics. The
photochemical reaction in these substrates are basically g-H
abstractions1,5 and have provided interesting mechanistic and
structural studies as well as synthetic utility.6 We now report
the results of our investigations on the photoreactions of 3-
alkoxy/allyloxy-6-chloro-2-(furan-3-yl)-4H-chromen-4-ones.
The study was aimed at the effect of different 3-alkoxy
groups on the product distribution and stereochemistry
when the furyl group is tethered to the chromone through
its 3-position instead of 2-position.3
perimental secion).
The photolysis of the methanolic solution of 3a–3j with
pyrex filtered UV light, under nitrogen atmosphere produced
the photoproducts 4a–4j, 4b’, 4h’, 5g, and 6g. The structures
of these photoproducts (Fig. 1) were confirmed by their
spectral parameters(IR,1H-13C NMR) and elemental analysis.
Here, the interesting feature in the photoproducts isolated
is the stereochemistry of ring C, which is in a half chair
conformation (Fig. 2). In the photoproducts, 4a–4j, 4b’, 5g,
and 4h’, the stereochemistry of the C/D ring junction is cis,
as the trans-fusion of a five-membered ring will result in
higher conformational strain as calculated by the MM2 en-
ergy minimizations program.7 This is further borne out by
the fact that J3a,11b = *9.0 Hz, which correlates with calcu-
lated values of F3a,11b (karplus rule) with cis-fusion of these
protons (Table 1) and also from literature references.8 Now
assuming the C/D ring fusion as cis, the orientation of H-4
can be cis to H-3a or trans to H-3a. Here again, regarding
the relative stereochemical disposition of H-3a and H-4, the
use of the J/F relationship9 and MM2 program has been in-
voked. The correlation of F3a,4 values obtained from two
possible MM2 energy minimized 3D conformations,7 A (H-
4 trans to H-3a) and B (H-4 cis to H-3a), with J3a,4 observed
Results and discussion
The targets, 2-(furan-3-yl)-4H-chromen-4-ones (3a–3j),
were synthesized commencing with the condensation of 5-
chloro-2-hydroxyacetophenone with furan-3-carbaldehyde as
per Scheme 1.
1
from H NMR is shown in Table 1. In compound 4a and 4c
Received 16 July 2008. Accepted 10 November 2008. Published
on the NRC Research Press Web site at canjchem.nrc.ca on
7 January 2009.
both conformation are equivalent as substituents at C-4 are
the same. A look at Table 1 demonstrates the trans disposi-
tion of H-3a and H-4 in compounds 4b, 4d–4f, and 4h,
whereas it is a cis disposition in compounds 4g, 4i, 4j, 4b’,
4h’, and 5g, which are in accordance with karplus rule.9 This
has given the stereocentre at C-4 - a R configuration in com-
pounds 4b, 4d–4f, and 4h and a S configuration in com-
R.C. Kamboj,1 U. Berar, S. Berar, M. Thakur, R. Arora, and
S.C. Gupta. Department of Chemistry, Kurukshetra University,
Kurukshetra 136 119, India.
1Corresponding author (e-mail: rckamboj@rediffmail.com).
Can. J. Chem. 87: 422–429 (2009)
doi:10.1139/V08-177
Published by NRC Research Press

Kamboj et al.
423
Scheme 1. Synthesis of furylchromones 3a–3j.
Fig. 1. Structures of photoproducts.
Fig. 2. MM2 energy minimized structures of compound 4h and 4h’.
pounds 4g, 4i, 4j, 4b’, 4h’, and 5g. A correlation of steric
energy (Ekcal) also shows that in most cases the lower
energy conformations are the ones that explain the observed
J/F relationship (Table 1).
Here it is worth mentioning that in photolysis of chro-
mones 3b and 3h, both photoproducts with conformation A
and B were isolated, whereas in all other chromones only
one product was isolated (either conformation A or B). The
reason for this behaviour could be from the steric influence
of the C-4 substituent, where the second isomer is either not
formed or formed in such low concentrations that it escaped
isolation. The 3-cinnamyloxychromone, 3g, along with cyc-
lisation to yield 4g also underwent isomerization of the cin-
namyl double bond to yield two new products, 5g and 6g,
where the cinnamyl double bond is cis (J = 11.7 Hz).
The phototransformations (Scheme 2) described above
can be visualized as having occurred through the formation
of the 1,4 biradical intermediate1 7. The products have been
expected to be formed through
a
bond formation
between the -CH- and the C-2 atom of the furan ring, which
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424
Can. J. Chem. Vol. 87, 2009
Table 1. J/F correlation of conformations of photoproducts.
Comp.
Coupling constant
Conformation A
Conformation B
J3a,11b (Hz) J3a,4 (Hz)
F3a,11b
16.84
15.00
F3a,4
Ekcal
11.40
11.66
F3a,11b
F3a,4
Ekcal
11.40
4a
4b*
4b’
4c
4d
4e
10.2
7.8
9.9
9.3
9.6
9.3
9.0
9.6
9.9
9.9
9.6
9.9
9.0
9.0
8.4
1.2
—
6.9
7.5
7.2
7.2
6.9
2.7
8.1
8.4
7.2
167.0
167.0
16.84
167.0
13.75
13.77
15.47
8.12
14.10
13.81
43.24
—
44.35
32.63
43.01
14.28
11.91
12.38
12.18
13.56
14.05
14.24
13.77
15.30
19.36
13.96
1.90
—
12.38
11.67
12.90
12.89
13.93
11.13
169.0
175.0
171.0
90.50
167.0
4f
4g
4h*
4h’
4i
4j
5g
16.33
16.51
3.60
8.72
48.21
19.70
3.65
8.0
11.17
15.19
16.67
14.44
3.97
5.40
19.97
85.59
86.51
66.97
15.87
20.47
13.88
15.98
*Isomeric compounds with both conformations were isolated.
is followed by ketonisation and H-migration to C-11b (1,5-H
migration). The furyl group at C-2 also possesses a 5-carbon
for clipping of the 3-alkoxy radical but here, the 1,5-sigma-
tropic shift is not feasible.
Fig. 3. Structures of proposed radicals.
The secondary ring contraction products observed by
cleavage of ring D, as isolated in our earlier work on 3-al-
koxy-2-(2’-furyl) chromones,3,10 are altogether absent here
and were not even observed by further photolysis of pure
photoproducts. The reason attributed to such diversity may
be the difference in stabilization of radicals (Fig. 3) formed
by the cleavage of ring D, which determines the ease of C–
O bond cleavage.
benzene in the petroleum ether–benzene mixture. The yields
reported are based on the amount of isolated photoproducts
and are calculated by excluding the recovered substrates.
The radical at C-11b in 8 (obtained in photolysis of 2’-
furyl chromones) is stabilized by pyrone moiety and thus
the C–O bond becomes prone to cleavage. There is no such
stabilization available to the radical (at C-3a) in 9 for its for-
mation and for the formation of ring contracted secondary
photoproducts.
Synthesis of chromones 3a–3j
1-(5-Chloro-2-hydroxyphenyl)-3-(furan-3-yl)prop-2-en-1-
one (1)
A solution of 5-chloro-2-hydroxyacetophenone (17.0 g,
0.1 mol) and 3-furaldehyde (9.6 g, 0.1 mol) in absolute etha-
nol and dehydrated S-200 barium hydroxide (dried at 200 8C
for 2 h, 20.0 g) were refluxed in a water bath for 20 min.
The dark red mixture was cooled and poured on ice-HCl to
obtain 1 (17.36 g, 70%) as a yellow solid, crystallized from
EtOH, mp 110–113 8C. IR nmax (cm–1): 1648.0 (C=O),
Conclusion
3-Alkoxy/allyloxy-6-chloro-2-(furan-3-yl)-4H-chromen-4-
ones upon photoirradiation yielded angular tetracyclic prod-
ucts through the 1,4-biradical furnished through g-H abstrac-
tion. No ring contracted secondary photoproduct formation
was observed.
1
3405(OH). H NMR (CDCl3) d: 12.72 (1H, s, OH), 7.85
(1H, d, J3,2 = 15.0 Hz, H-3), 7.80 (1H, d, Jm = 2.7 Hz, H-
6’), 7.79 (1H, br s, H-2@), 7.49 (1H, d, J5@,4@ = 2.4 Hz, H-
5@), 7.42 (1H, dd, Jm = 2.7 Hz, Jo = 9.0 Hz, H-4’), 7.25
(1H, d, J2,3 = 15.0 Hz, H-2), 6.96 (1H, d, Jo = 9.0 Hz, H-
3’), 6.75 (1H, d, J4@,5@ = 2.4 Hz, H-4@). Anal. calcd. for
C13H9ClO3: C 62.79, H 3.65; found: C 62.70, H 3.61.
Experimental
General
Melting points were determined in open capillaries and
1
are thus uncorrected. H NMR spectra were recorded on a
6-Chloro-3-hydroxy-2-(furan-3-yl)-4H-chromen-4-one (2)
A solution of compound 1 (2.48 g, 0.01 mol) in EtOH at
0 8C was mixed with 12.0 mL 20% aq. NaOH by stirring.
To this dark red solution was added H2O2 (30%) dropwise
until the colour changed to yellow and the stirring was con-
tinued for 4 h. The reaction mixture was neutralized with
ice-HCl to give creamy white precipitates, crystallized
(chloroform-ethanol) to creamy white crystals (2.37 g,
90%), mp 206–208 8C. IR nmax (cm–1): 1615.0 (C=O),
300 MHz Bruker spectrometer using TMS as the internal
standard. IR spectra were recorded on a Buck Scientific 500
spectrophotometer using KBr pellets. Mass spectra were re-
corded at 70 eV. Elemental analysis was carried out on a
Perkin Elmer 2400 instrument. TLC plates were coated with
silica gel G (suspended in CHCl3-MeOH) and iodine va-
pours were used as the visualizing agent. The columns for
purification were packed with Silica gel 100–200 mesh in
petroleum ether/benzene (9:1) and left overnight before use.
The elution was carried out with increasing proportions of
1
3400(OH). H NMR (CDCl3) d: 8.31 (1H, br s, H-2’), 8.21
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Kamboj et al.
425
Scheme 2. Cyclisation and 1,5-H shift of 1,4-biradical.
(1H, d, Jm = 2.4 Hz, H-5), 7.63 (1H, dd, Jm = 2.4 Hz, Jo =
9.0 Hz, H-7), 7.58 (1H, t, J5’,2’ = 1.5 Hz, J5’,4’ = 1.8 Hz, H-
7.04 (1H, d, J4’,5’ = 1.8 Hz, H-4’), 5.15 (1H, septet, Jvic
=
6.3 Hz, H-1@), 1.32 (6H, d, Jvic = 6.3 Hz, C1@-CH3). 13C
NMR (CDCl3) d: 173.07 (C-4), 153.12 (C-8a), 151.79 (C-
2), 145.73 (C-5’), 143.32 (C-2’), 137.00 (C-4a), 133.26 (C-
7), 130.49 (C-6), 125.13 (C-5), 125.00 (C-3), 119.44 (C-8),
118.13 (C-1’), 108.92 (C-4’), 73.98 (C-1@), 22.49 (C1@-CH3).
Anal. calcd. for C16H13ClO4: C 63.06, H 4.30; found: C
62.97, H 4.27.
5’), 7.51 (1H, d, Jo = 9.0 Hz, H-8), 7.05 (1H, dd, J4’,2’
=
0.3 Hz, J4’,5’ = 1.8 Hz, H-4’). Anal. calcd. for C13H7ClO4: C
59.45, H 2.69; found: C 59.31, H 2.69.
6-Chloro-3-methoxy-2-(furan-3-yl)-4H-chromen-4-one (3a)
The compound 2 (2.50 g, 0.01 mol), CH3I (1.2 g,
0.01 mol), dry K2CO3 (1.0 g), and tetra-n-butylammonium
iodide (100 mg) were refluxed in dry acetone (50 mL) for 2
h. Filtration, evaporation of the solvent, and crystallization
of the residue (MeOH) gave 3a (80%), a light brown solid,
3-Allyloxy-6-chloro-2-(furan-3-yl)-4H-chromen-4-one (3d)
Yield 85%, light brown solid; mp 93–95 8C(MeOH). IR
1
nmax (cm–1): 1641 (C=O), 1613 (C=C). H NMR (CDCl3) d:
1
mp 114–117 8C. IR nmax (cm–1): 1655.0 (C=O). H NMR
8.33 (1H, br s, H-2’), 8.20 (1H, d, Jm = 2.4 Hz, H-5), 7.60
(1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz, H-7), 7.56 (1H, dd, J5’,2’
= 0.9 Hz, J5’,4’ = 1.8 Hz, H-5’), 7.47 (1H, d, Jo = 9.0 Hz, H-
8), 7.02 (1H, dd, J4’,2’ = 0.3 Hz, J4’,5’ = 1.8 Hz, H-4’), 6.08
(1H, tdd, Jvic = 6.3 Hz, Jtrans = 17.4 Hz, Jcis = 10.2 Hz, H-
2@), 5.39 (1H, td, Jallyl = 1.5 Hz, Jtrans = 17.4 Hz, H-3@b),
(CDCl3) d: 8.30 (1H, br s, H-2’), 8.23 (1H, d, Jm = 2.4 Hz,
H-5), 7.62 (1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz, H-7), 7.59
(1H, dd, J5’,2’ = 1.2 Hz, J5’,4’ = 1.5 Hz, H-5’), 7.48 (1H, d, Jo
= 9.0 Hz, H-8), 7.02 (1H, dd, J4’,2’ = 0.3 Hz, J4’,5’ = 1.5 Hz,
H-4’), 4.03 (3H, s, OCH3). 13C NMR (CDCl3) d: 172.83 (C-
4), 153.24 (C-8a), 151.74 (C-2), 145.37 (C-5’), 143.75 (C-
2’), 139.31 (C-4a), 133.44 (C-7), 130.67 (C-6), 125.33 (C-
3), 125.15 (C-5), 119.50 (C-8), 117.71 (C-3’), 108.61 (C-4’),
59.53 (3-OCH3). Anal. calcd. for C14H9ClO4: C 60.78, H
3.28; found: C 63.65, H 3.31.
The other ethers (3b–3j) were synthesized by reacting 3-
hydroxychromone (2) with ethyl iodide, isopropyl bromide,
allyl bromide, methyl allyl chloride, dimethyl allyl bromide,
cinnamyl chloride, propargyl bromide, benzyl chloride, and
para methoxy benzyl chloride, respectively, by the proce-
dure as described for compound 3a.
5.26 (1H, d, Jcis = 10.2 Hz, H-3@a), 4.80 (2H, dd, Jvic
=
6.3 Hz, Jallyl = 1.5 Hz, H-1@). 13C NMR (CDCl3) d: 171.00
(C-4), 153.10 (C-8a), 153.00 (C-2), 145.50 (C-5’), 143.62
(C-2’), 139.09 (C-4a), 133.45 (C-7), 133.30(C-2@), 130.60
(C-6), 123.14 (C-3), 123.34 (C-5), 119.83(C-3@), 119.10 (C-
8), 117.84 (C-3’), 108.70 (C-4’), 72.69 (C-1@). Anal. calcd.
for C16H11ClO4: C 63.48, H 3.66; found: C 63.33, H 3.65.
6-Chloro-2-(furan-3-yl)-3-(2-methylallyloxy)-4H-chromen-
4-one (3e)
Yield 72%, creamy white solid; mp 90–92 8C (MeOH).
IR nmax (cm–1): 1637 (C=O), 1619 (C=C). 1H NMR
(CDCl3) d: 8.32 (1H, dd, Jm = 0.9 Hz, H-2’), 8.20 (1H, d,
Jm = 2.7 Hz, H-5), 7.59 (1H, dd, Jm = 2.7 Hz, Jo = 9.0 Hz,
H-7), 7.56 (1H, t, J5’,2’ = 0.9 Hz, J5’,4’ = 1.8 Hz, H-5’), 7.46
(1H, d, Jo = 9.0 Hz, H-8), 7.01 (1H, dd, J4’,2’ = 0.9 Hz, J4’,5’
= 1.8 Hz, H-4’), 5.15 (1H, s, H-3@b), 5.01 (1H, s, H-3@a),
4.67 (2H, s, H-1@), 1.87 (3H, s, 2@-CH3). 13C NMR (CDCl3)
d: 172.78 (C-4), 153.18 (C-8a), 151.65 (C-2), 145.44 (C-5’),
143.64 (C-2’),141.18 (C-2@), 138.80 (C-4a), 133.37 (C-7),
130.63 (C-6), 125.29 (C-3), 125.12 (C-5), 119.48 (C-8),
117.76 (C-1’),113.80 (C-3@), 108.68 (C-4’), 75.13 (C-1@),
19.79 (2@-CH3). Anal. calcd. for C17H13ClO4: C 64.46, H
4.14; found: C 64.30, H 4.11.
6-Chloro-3-ethoxy-2-(furan-3-yl)-4H-chromen-4-one (3b)
Yield 82%, colourless solid; mp 104–106 8C (MeOH). IR
1
nmax (cm–1): 1635.0 (C=O). H NMR (CDCl3) d: 8.33 (1H,
br s, H-2’), 8.20 (1H, d, Jm = 2.1 Hz, H-5), 7.60 (1H, dd,
Jm = 2.1 Hz, Jo = 9.0 Hz, H-7), 7.57 (1H, t, J5’,2’ = 1.2 Hz,
J5’,4’ = 1.5 Hz, H-5’), 7.46 (1H, d, Jo = 9.0 Hz, H-8), 7.02
(1H, dd, J4’,2’ = 0.3 Hz, J4’,5’ = 1.5 Hz, H-4’), 4.31 (2H, q,
Jvic = 7.2 Hz, H-1@), 1.44 (3H, t, Jvic = 7.2 Hz, H-2@). 13C
NMR (CDCl3) d: 172.98 (C-4), 153.19 (C-8a), 151.70 (C-
2), 145.27 (C-5’), 143.62 (C-2’), 139.09 (C-4a), 133.38 (C-
7), 130.59 (C-6), 125.29 (C-3), 125.15 (C-5), 119.50 (C-8),
117.91 (C-1’), 108.71 (C-4’), 67.89 (C-1@), 15.71 (C-2@).
Anal. calcd. for C15H11ClO4: C 61.98, H 3.81; found: C
61.88, H 3.78.
6-Chloro-2-(furan-3-yl)-3-(3-methylbut-2-enyloxy)-4H-
chromen-4-one (3f)
6-Chloro-3-isopropyloxy-2-(furan-3-yl)-4H-chromen-4-one
(3c)
Yield 70%, off-white solid; mp 81–84 8C (MeOH). IR
nmax (cm–1): 1637.2 (C=O), 1608.6 (C=C). 1H NMR
(CDCl3) d: 8.33 (1H, d, J2’,5’ = 1.2 Hz, H-2’), 8.21 (1H, d,
Jm = 2.4 Hz, H-5), 7.59 (1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz,
H-7), 7.55 (1H, t, J5’,2’ = 1.2 Hz, J5’,4’ = 1.8 Hz, H-5’), 7.46
(1H, d, Jo = 9.0 Hz, H-8), 7.01 (1H, d, J4’,5’ = 1.8 Hz, H-4’),
5.53 (1H, tt, Jvic = 7.2 Hz, Jallyl = 1.5 Hz, H-2@), 4.78 (1H, d,
Yield 70%, colourless solid; mp 95–97 8C (MeOH); IR
1
nmax (cm–1): 1639.2 (C=O). H NMR (CDCl3) d: 8.36 (1H,
d, J = 0.9 Hz, H-2’), 8.19 (1H, d, Jm = 2.7 Hz, H-5), 7.59
(1H, dd, Jm = 2.7 Hz, Jo = 9.0 Hz, H-7), 7.55 (1H, t, J5’,2’
=
1.5 Hz, J5’,4’ = 1.8 Hz, H-5’), 7.46 (1H, d, Jo = 9.0 Hz, H-8),
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Can. J. Chem. Vol. 87, 2009
Jvic = 7.2 Hz, H-1@), 1.75 (3H, d, Jallyl = 1.5 Hz, H-4@), 1.73
(3H, s, C3@-CH3). 13C NMR (CDCl3) d: 172.17 (C-4), 153.18
(C-8a), 152.79 (C-2), 145.63 (C-5’), 143.82 (C-2’), 137.90
(C-4a), 132.96 (C-7), 131.85 (C-3@), 130.42 (C-6), 124.23
(C-5), 123.50 (C-3), 120.80 (C-2@), 119.02 (C-8), 118.13
(C-3’), 108.62 (C-4’), 68.99 (C-1@), 18.05 (C-4@), 25.86 (3@-
CH3). Anal. calcd. for C18H15ClO4: C 65.36, H 4.57; found:
C 65.24, H 4.52.
6-Chloro-2-(furan-3-yl)-3-(4-methoxybenzyloxy)-4H-
chromen-4-one (3j)
Yield 58%, light yellow solid; mp 89–92 8C (MeOH). IR
1
nmax (cm–1): 1650.4 (C=O). H NMR (CDCl3) d: 8.16 (1H,
d, Jm = 2.7 Hz, H-5), 8.13 (1H, br s, H-2’), 7.52 (1H, dd,
Jm = 2.7 Hz, Jo = 9.0 Hz, H-7), 7.44 (1H, t, J5’,2’ = 1.5 Hz,
J5’,4’ = 1.8 Hz, H-5’), 7.38 (1H, d, Jo = 9.0 Hz, H-8), 7.33
(2H, d, Jo = 8.4 Hz, H-2@, H-6@), 6.87 (1H, d, J4’,5’
=
1.8 Hz, H-4’), 6.79 (2H, d, Jo = 8.4 Hz, H-3@, H-5@), 5.18
(2H, s, -OCH2-), 3.73 (3H, s, C4@-OCH3). 13C NMR(CDCl3)
d: 171.49 (C-4), 158.31 (C-4@), 151.71 (C-8a), 150.39 (C-2),
144.12 (C-5’), 142.00 (C-2’), 137.19 (C-1@), 131.90 (C-7),
129.19 (C-2@, C-6@), 129.00 (C-3), 126.26 (C-6), 123.79 (C-
4a), 123.65 (C-5), 118.06 (C-8), 116.31 (C-1’), 112.39 (C-3@,
C-5@), 107.25 (C-4’), 72.00 (OCH2), 53.79 (C4@-OCH3).
Anal. calcd. for C21H15ClO4: C 65.89, H 3.95; found: C
65.68, H 3.91.
6-Chloro-2-(furan-3-yl)-3-(3-phenylallyloxy)-4H-chromen-
4-one (3g)
Yield 68%, light brown solid; mp 91–94 8C (EtOH). IR
1
nmax (cm–1): 1648.4 (C=O), 1617(C=C). H NMR (CDCl3)
d: 8.36 (1H, t/dd, J2’,5’ = 1.5 Hz, J2’,4’ = 1.8 Hz, H-2’), 8.22
(1H, d, Jm = 2.4 Hz, H-5), 7.60 (1H, dd, Jm = 2.4 Hz, Jo =
9.0 Hz, H-7), 7.56 (1H, t, J5’,2’ = 1.5 Hz, J5’,4’ = 1.8 Hz, H-
5’), 7.46 (1H, d, Jo = 9.0 Hz, H-8), 7.29–7.35 (5H, m, H-2@’-
6@’), 7.03 (1H, t, J4’,2’ = 1.8 Hz, J4’,5’ = 1.8 Hz, H-4’), 6.70
(1H, d, J3’,2’ = 15.9 Hz, H-3@), 6.44 (1H, td, J2’,3’ = 15.9 Hz,
J2’,1’ = 6.6 Hz, H-2@), 4.96 (2H, d, J1’,2’ = 6.6 Hz, H-1@). 13C
NMR (CDCl3) d: 172.94 (C-4), 153.21 (C-8a), 152.03 (C-2),
145.50 (C-5’), 143.67 (C-2’), 136.26 (C-1@’), 134.61 (C-7),
133.44 (C-3@), 130.66(C-4@’), 128.57 (C-2’@, C-6@’), 128.05
(C-3), 126.70 (C-3’@, C-5’@), 125.26 (C-6), 125.14 (C-2@),
125.14 (C-4a), 124.29 (C-5), 119.54 (C-8), 117.91 (C-1’),
108.77 (C-4’), 72.48 (C-1@). Anal. calcd. for C22H15ClO4: C
69.75, H 3.99; found: C 69.68, H 3.97.
Photoirradiation of chromones 3a–3j
Photolysis of 6-chloro-2-(furan-3-yl)-3-methoxy-4H-
chromen-4-one (3a)
A methanolic solution (150 mL) of chromone 3a
(200 mg, 0.72 mmol) was irradiated with light from a 125
W Hg vapor lamp in a pyrex reactor under nitrogen atmos-
phere for 45 min. The removal of the solvent left a gummy
solid, which was chromatographed to yield 4a.
Compound 4a
Yield 45%, white solid; mp 185–188 8C (EtOH). IR nmax
6-Chloro-2-(furan-3-yl)-3-propargyloxy-4H-chromen-4-one
(3h)
Yield 88%, light brown solid; mp 121–123 8C (MeOH).
IR nmax (cm–1): 1634.3 (C=O), 2135(C:C). 1H NMR
(CDCl3) d: 8.40 (1H, dd/t, J2’,5’ = 1.2 Hz, J2’,4’ = 0.6 Hz, H-
1
(cm–1): 1649.7 (C=O). H NMR (CDCl3) d: 8.23 (1H, d, Jm
= 2.4 Hz, H-7), 7.58 (1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz, H-
9), 7.40 (1H, d, Jo = 9.0 Hz, H-10), 6.46 (1H, dd/t, J2,11b
=
2.1 Hz, J2,1 = 2.4 Hz, H-2), 5.28 (1H, dd/t, J1,2 = 2.4 Hz,
J1,11b = 2.7 Hz, H-1), 5.10 (1H, d{dd}, J3a,4a = 2.4 Hz, J3a,4b
2’), 8.20 (1H, d, Jm = 2.4 Hz, H-5), 7.61 (1H, dd, Jm
=
= 9.0 Hz, J3a,11b = 10.2 Hz, H-3a), 4.34 (1H, dd, J11b,1
=
2.4 Hz, Jo = 9.0 Hz, H-7), 7.56 (1H, t, J5’,2’ = 1.2 Hz, J5’,4’
= 1.8 Hz, H-5’), 7.48 (1H, d, Jo = 9.0 Hz, H-8), 7.05 (1H,
2.7 Hz, J11b,3a = 10.2 Hz, H-11b), 4.14–4.07 (2H, m, H-4a,
H-4b). 13C NMR (CDCl3) d: 170.52 (C-6), 153.58 (C-10a),
151.94 (C-11a), 148.39 (C-2), 138.83 (C-6a), 133.47 (C-9),
130.57 (C-8), 125.45 (C-7), 124.73 (C-5a), 119.48 (C-10),
100.60 (C-1), 78.73 (C-4), 65.88 (C-3a), 40.83 (C-11b).
Anal. calcd. for C14H9ClO4: C 60.78, H 3.28; found: C
63.58, H 3.34. Mass (m/z): 276 (M+, 100%).
d, J4’,5’ = 1.8 Hz, J4’,2’ = 0.6 Hz, H-4’), 5.09 (2H, d, J1’,3’
=
2.4 Hz, H-1@), 2.44 (1H, d, J3’,1’ = 2.4 Hz, H-3@). 13C NMR
(CDCl3) d: 172.50 (C-4), 153.22 (C-2), 152.10 (C-8a),
145.96 (C-5’), 143.55 (C-2’), 138.50 (C-7), 133.60 (C-3),
130.82 (C-5), 128.42 (C-6), 125.11 (C-4a), 119.51 (C-8),
117.62 (C-1’), 108.83 (C-4’), 78.45 (C-2@), 76.27 (C-3@),
59.08 (C-1@). Anal. calcd. for C16H9ClO4: C 63.91, H 3.02;
found: C 63.72, H 3.00.
Photolysis of 6-chloro-3-ethoxy-2-(furan-3-yl)-4H-
chromen-4-one (3b)
A methanolic solution of 3b (0.20 g, 0.7 mmol) on pho-
tolysis for 45 min furnished 4b and 4b’. These isomeric pho-
toproducts were separated from the starting substrate 3b by
column chromatography. They were further separated from
each other by preparative TLC.
3-Benzyloxy-6-chloro-2-(furan-3-yl)-4H-chromen-4-one (3i)
Yield 70%, light yellow solid; mp 86–89 8C (MeOH). IR
1
nmax (cm–1): 1643.3 (C=O). H NMR (CDCl3) d: 8.23 (1H,
d, Jm = 2.7 Hz, H-5), 8.20 (1H, d, J2’,5’ = 1.2 Hz, H-2’),
7.60 (1H, dd, Jm = 2.7 Hz, Jo = 9.0 Hz, H-7), 7.50 (1H, t,
Compound 4b
J5’,2’ = 1.2 Hz, J5’,4’ = 1.5 Hz, H-5’), 7.49 (1H, d, Jo
=
9.0 Hz, H-8), 7.39–7.26 (5H, m, H-2@, 3@, 4@, 5@, 6@), 6.94
(1H, d, J4’,5’ = 1.5 Hz, H-4’), 5.30 (2H, s, -OCH2-). 13C
NMR (CDCl3) d: 172.87 (C-4), 153.19 (C-2), 151.83 (C-
8a), 145.57 (C-5’), 143.51 (C-2’), 138.74 (C-1@), 136.59 (C-
7), 133.40 (C-3), 130.66 (C-4@), 128.85 (C-3@, C-5@), 128.50
(C-2@, C-6@), 128.42 (C-6), 125.28 (C-4a), 125.15 (C-5),
119.51 (C-8), 117.71 (C-1’), 108.69 (C-4’), 73.79 (-OCH2-).
Anal. calcd. for C20H13ClO4: C 68.09, H 3.71; found: C
62.95, H 3.66.
Yield 22%, white solid; mp 174–176 8C (EtOH). IR nmax
1
(cm–1): 1651.0 (C=O). H NMR (CDCl3) d: 8.24 (1H, d, Jm
= 2.4 Hz, H-7), 7.58 (1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz, H-
9), 7. 41 (1H, d, Jo = 9.0 Hz, H-10), 6.44 (1H, d, J2,1
=
2.7 Hz, H-2), 5.36 (1H, dd/t, J1,2 = 2.7 Hz, J1,11b = 2.7 Hz,
H-1), 4.63 (1H, dd, J3a,11b = 7.8 Hz, J3a,4 = 8.4 Hz, H-3a),
4.23 (1H, dd, J11b,1 = 2.7 Hz, J11b,3a = 7.8 Hz, H-11b), 3.88
(1H, q{d}, Jvic = 6.6 Hz, J4,3a = 8.4 Hz, H-4), 1.65 (3H, d,
Jvic = 6.6 Hz, C4-CH3). 13C NMR (CDCl3) d: 171.10 (C-6),
Published by NRC Research Press

Kamboj et al.
427
153.63 (C-10a), 151.11 (C-11a), 147.27 (C-2), 138.22 (C-
6a), 133.43 (C-9), 130.51 (C-8), 125.49 (C-7), 124.79 (C-
5a), 119.46 (C-10), 100.69 (C-1), 80.69 (C-4), 71.72 (C-3a),
41.78 (C-11b), 17.69 (C4-CH3). Anal. calcd. for C15H11ClO4:
C 61.98, H 3.81; found: C 61.90, H 3.80. Mass (m/z): 290
(M+, 100%).
C 63.48, H 3.66; Found: C 63.46, H 3.60. Mass (m/z): 302
(M+, 100%).
Photolysis of 6-chloro-2-(furan-3-yl)-3-(2-methylallyloxy)-
4H-chromen-4-one (3e)
A methanolic solution of 3e (0.20 g, 0.63 mmol) on pho-
tolysis for 45 min furnished 4e.
Compound 4b’
Compound 4e
Yield 11%, white solid; mp 160–162 8C (EtOH). IR nmax.
1
(cm–1): 1652.0 (C=O). H NMR (CDCl3) d: 8.22 (1H, d, Jm
Yield 24%, white solid; mp 196–200 8C (CHCl3-EtOH).
1
IR nmax (cm–1): 1641 (C=O). H NMR (CDCl3) d: 8.22 (1H,
= 2.4 Hz, H-7), 7.56 (1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz, H-
d, Jm = 2.4 Hz, H-7), 7.59 (1H, dd, Jm = 2.4 Hz, Jo
=
9), 7.38 (1H, d, Jo = 9.0 Hz, H-10), 6.44 (1H, d, J2,1
=
9.0 Hz, H-9), 7. 41 (1H, d, Jo = 9.0 Hz, H-10), 6.47 (1H, d,
J2,1 = 2.7 Hz, H-2), 5.37 (1H, s, H-2’b), 5.17 (1H, s, H-2’a),
5.13 (1H, dd/t, J1,2 = 2.7 Hz, J1,11b = 2.7 Hz, H-1), 4.63 (1H,
dd, J3a,11b = 9.3 Hz, J3a,4 = 7.5 Hz, H-3a), 4.31 (1H, q{d},
2.7 Hz, H-2), 5.25 (1H, d, J1,2 = 2.7 Hz, H-1), 4.91 (1H, d,
J3a,11b = 9.9 Hz, H-3a), 4.15 (1H, q, Jvic = 6.3 Hz, H-4), 4.05
(1H, d, J11b,3a = 9.9 Hz, H-11b), 1.55 (3H, d, Jvic = 6.3 Hz,
C4-CH3). Anal. calcd. for C15H11ClO4: C 61.98, H 3.81;
found: C 61.87, H 3.78. Mass (m/z): 290 (M+, 100%).
Jvic = 6.6 Hz, J4,3a = 7.5 Hz, H-4), 3.88 (1H, dd, J11b,1
=
2.7 Hz, J11b,3a = 9.3 Hz, H-11b), 1.85 (3H, s, C1’-CH3). 13C
NMR (CDCl3) d: 171.80 (C-6), 152.68 (C-10a), 149.05 (C-
11a), 146.27 (C-2), 135.82 (C-6a), 133.40 (C-9), 140.28 (C-
1’), 129.51 (C-8), 126.49 (C-7), 122.70 (C-5a), 118.06 (C-
10), 108.45 (C-2’), 99.69 (C-1), 80.10 (C-4), 72.70 (C-3a),
40.15 (C-11b), 18.69 (1’-CH3). Anal. calcd. for C17H13ClO4:
C 64.46, H 4.14; found: C 64.34, H 4.12. Mass (m/z): 316
(M+, 100%).
Photolysis of 6-chloro-2-(furan-3-yl)-3-isopropyloxy-4H-
chromen-4-one (3c)
A methanolic solution of 3c (0.20 g, 0.66 mmol) on pho-
tolysis for 45 min furnished 4c.
Compound 4c
Yield 48%, white solid; mp 165–167 8C (CHCl3-EtOH).
1
IR nmax (cm–1): 1655.8 (C=O). H NMR (CDCl3) d: 8.23
Photolysis of 6-chloro-2-(furan-3-yl)-3-(3-methylbut-2-
enyloxy)-4H-chromen-4-one (3f)
A methanolic solution of 3f (0.20 g, 0.6 mmol) on photol-
ysis for 45 min furnished 4f.
(1H, d, Jm = 2.7 Hz, H-7), 7.56 (1H, dd, Jm = 2.7 Hz, Jo =
9.0 Hz, H-9), 7.38 (1H, d, Jo = 9.0 Hz, H-10), 6.43 (1H, dd,
J2,11b = 1.8 Hz, J2,1 = 3.0 Hz, H-2), 5.30 (1H, dd/t, J1,2
=
3.0 Hz, J1,11b = 3.0 Hz, H-1), 4.64 (1H, d, J3a,11b = 9.3 Hz,
H-3a), 3.95 (1H, dd{d}/m, J11b,2 = 1.8 Hz, J11b,1 = 3.0 Hz,
J11b,3a = 9.3 Hz, H-11b), 1.62 (3H, s, C4-CH3b), 1.39 (3H, s,
C4-CH3a). 13C NMR (CDCl3) d: 173.00 (C-6), 159.00 (C-
10a), 152.00 (C-11a), 148.20 (C-2), 135.00 (C-6a), 133.18
(C-9), 130.00 (C-8), 125.47 (C-7), 125.00 (C-5a), 119.39
(C-10), 100.49 (C-1), 85.99 (C-3a), 75.37 (C-4), 39.73 (C-
11b), 23.94 (C4-CH3b), 23.38 (C4-CH3a). Anal. calcd. for
C16H13ClO4: C 63.06, H 4.30; found: C 63.01, H 4.25.
Mass (m/z): 304/306 (M+, 100%).
Compound 4f
Yield 31%, light brown solid; mp 99–102 8C (CHCl3-
1
EtOH). IR nmax (cm–1): 1637.2 (C=O). H NMR (CDCl3) d:
8.23 (1H, d, Jm = 2.4 Hz, H-7), 7.58 (1H, dd, Jm = 2.4 Hz,
Jo = 9.0 Hz, H-9), 7.44 (1H, d, Jo = 9.0 Hz, H-10), 6.45 (1H,
d, J2,1 = 2.7 Hz, H-2), 5.49 (1H, dd/t, J1,2 = 2.7 Hz, J1,11b
=
3.0 Hz, H-1), 5.37 (1H, dd, J1’,4 = 5.7 Hz, Jallyl = 1.5 Hz, H-
1’), 4.75 (1H, dd, J3a,11b = 9.0 Hz, J3a,4 = 7.8 Hz, H-3a), 4.58
(1H, dd, J4,3a = 7.8 Hz, J4,1’ = 5.7 Hz, H-4), 4.21 (1H, dd,
J11b,1 = 3.0 Hz, J11b,3a = 9.0 Hz, H-11b), 1.80 (3H, d, Jallyl
=
Photolysis of 3-allyloxy-6-chloro-2-(furan-3-yl)-4H-
chromen-4-one (3d)
A methanolic solution of 3d (0.20 g, 0.66 mmol) on pho-
tolysis for 45 min furnished 4d.
1.5 Hz, C2’-CH3b), 1.76 (3H, s, C2’-CH3a). 13C NMR
(CDCl3) d: 172.50 (C-6), 153.41 (C-10a), 150.30 (C-11a),
144.28 (C-2), 135.00 (C-6a), 132.78 (C-9), 132.70 (C-2’),
128.00 (C-8), 123.20 (C-1’), 123.50 (C-7), 123.05 (C-5a),
119.19 (C-10), 101.79 (C-1), 79.80 (C-3a), 70.37 (C-4),
39.97 (C-11b), 25.20 (2’-CH3b), 19.20 (2’-CH3a). Anal.
calcd. for C18H15ClO4: C 65.36, H 4.57; found: C 65.28, H
4.51. Mass (m/z): 330 (M+, 100%).
Compound 4d
Yield 29%, white solid; mp 145–146 8C (EtOH). IR nmax
1
(cm–1): 1637(C=O). H NMR (CDCl3) d: 8.17 (1H, d, Jm
=
2.4 Hz, H-7), 7.51 (1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz, H-9),
7.34 (1H, d, Jo = 9.0 Hz, H-10), 6.40 (1H, d, J2,1 = 2.7 Hz,
Photolysis of 6-chloro-2-(furan-3-yl)-3-(3-phenylallyloxy)-
4H-chromen-4-one (3g)
A methanolic solution of 3g (0.20 g, 0.53 mmol) on pho-
tolysis for 45 min furnished three photoproducts: 4g, 5g, and
6g.
H-2), 5.93 (1H, ddd, Jvic = 5.1 Hz, Jtrans = 17.4 Hz, Jcis
=
10.8 Hz, H-1’), 5.47 (1H, d, Jtrans = 17.4 Hz, H-2’b), 5.35
(1H, d, Jcis = 10.8 Hz, H-2’a), 5.30 (1H, t, J1,2 = 2.7 Hz,
J1,11b = 2.7 Hz, H-1), 4.77 (1H, dd J3a,4 = 6.9 Hz, J3a,11b
9.6 Hz, H-3a), 4.10 (1H, dd, J11b,1 = 2.7 Hz, J11b,3a
=
=
Compound 4g
9.6 Hz, H-11b), 4.40 (1H, dd, J4,3a= 6.9 Hz, J4,1’ = 5.1 Hz,
H-4). 13C NMR (CDCl3) d: 172.00 (C-6), 151.61 (C-10a),
149.35 (C-11a), 145.57 (C-2), 135.47 (C-6a), 131.49 (C-9),
130.76 (C-1’), 128.59 (C-8), 123.51 (C-7), 122.79 (C-5a),
117.67 (C-10), 117.50 (C-2’), 98.77 (C-1), 77.91 (C-4),
73.23 (C-3a), 39.11 (C-11b). Anal. calcd. for C16H11ClO4:
Yield 16%, light yellow solid; mp 155–157 8C (CHCl3-
1
EtOH). IR nmax (cm–1): 1639.6 (C=O). H NMR (CDCl3) d:
8.25 (1H, d, Jm = 2.7 Hz, H-7), 7.58 (1H, dd, Jm = 2.7 Hz,
Jo = 9.0 Hz, H-9), 7.41 (1H, d, Jo = 9.0 Hz, H-10), 7.28–
7.36 (5H, m, H-2@-6@), 6.85 (1H, d, J2’,1’ = 16.5 Hz, H-2’),
Published by NRC Research Press

428
Can. J. Chem. Vol. 87, 2009
6.50 (1H, dd/t, J2,11b = 2.1 Hz, J2,1 = 2.4 Hz, H-2), 6.33 (1H,
dd, J1’,4 = 6.0 Hz, J1’,2’ = 16.5 Hz, H-1’), 5.40 (1H, dd/t,
2.7 Hz, J4,2’ = 2.1 Hz, H-4), 4.16 (1H, t, J11b,1 = 2.1 Hz,
J11b,2 = 1.5 Hz, J11b,3a = 9.9 Hz, H-11b), 2.63 (1H, d, J2’,4
=
J1,11b = 2.4 Hz, J1,2 = 2.4 Hz, H-1), 4.91 (1H, dd, J3a,4
7.2 Hz, J3a,11b = 9.6 Hz, H-3a), 4.58 (1H, t, J4,3a = 7.2 Hz,
J4,1’ = 6.0 Hz, H-4), 4.25 (1H, t{d}, J11b,2 = 2.1 Hz, J11b,1
=
2.1 Hz, H-2’). 13C NMR (CDCl3) d: 172.08 (C-6), 153.06
(C-10a), 151.22 (C-11a), 145.32 (C-2), 136.12 (C-6a),
134.02 (C-9), 130.11 (C-8), 127.24 (C-7), 124.30 (C-5a),
119.00 (C-10), 101.68 (C-1), 77.44 (C-1’), 74.50 (C-3a),
73.78 (C-2’), 68.98 (C-4), 40.45 (C-11b). Anal. calcd. for
C16H9ClO4: C 63.91, H 3.02; found: C 63.83, H 3.06. Mass
(m/z): 300 (M+, 100%).
=
2.4 Hz, J11b,3a = 9.6 Hz, H-11b). 13C NMR (CDCl3) d:
172.13 (C-6), 154.05 (C-10a), 151.91 (C-11a), 144.50 (C-2),
138.44 (C-6a), 137.20 (C-1@), 130.78 (C-2’), 129.65 (C-9),
129.06 (C-3@, C-5@), 128.00 (C-4@), 127.77 (C-2@, C-6@),
126.02 (C-1’), 125.81 (C-7), 125.54 (C-8), 124.37 (C-5a),
118.06 (C-10), 98.88 (C-1), 77.56 (C-3a), 75.00 (C-4),
38.75 (C-11b). Anal. calcd. for C22H15ClO4: C 69.75, H
3.99; found: C 69.60, H 3.95. Mass (m/z): 378 (M+, 100%).
Compound 4h’
Yield 20%, white solid; mp 121–122 8C (CHCl3-EtOH).
IR nmax. (cm–1): 1645 (C=O), 2128 (C:C). 1H NMR
(CDCl3) d: 8.21 (1H, d, Jm = 2.4 Hz, H-7), 7.58 (1H, dd, Jm
= 2.4 Hz, Jo = 9.0 Hz, H-9), 7.40 (1H, d, Jo = 9.0 Hz, H-10),
6.46 (1H, d, J2,1 = 3.0 Hz, H-2), 5.31 (1H, d, J1,2 = 3.0 Hz,
H-1), 5.09 (1H, d, J3a,11b = 9.9 Hz, J3a,4 = 6.9 Hz, H-3a),
4.86 (1H, q, J4,3a = 6.9 Hz, J4,2’ = 2.1 Hz, H-4), 4.12 (1H,
d, J11b,3a = 9.9 Hz, H-11b), 2.49 (1H, d, J2’,4 = 1.8 Hz, H-
2’). 13C NMR (CDCl3) d: 171.68 (C-6), 152.56 (C-10a),
152.92 (C-11a), 145.60 (C-2), 135.98 (C-6a), 134.44 (C-9),
130.19 (C-8), 127.22 (C-7), 124.54 (C-5a), 119.23 (C-10),
101.45 (C-1), 77.49 (C-1’), 74.67 (C-3a), 73.88 (C-2’),
68.38 (C-4), 40.15 (C-11b). Anal. calcd. for C16H9ClO4: C
63.91, H 3.02; found: C 63.80, H 2.99. Mass (m/z): 300
(M+, 100%).
Compound 5g
Yield 10%, light yellow solid; mp 181–182 8C (CHCl3-
EtOH). IR nmax (cm–1): 1642 (C=O). 1H NMR (CDCl3):
8.23 (1H, d, Jm = 2.7 Hz, H-7), 7.58 (1H, dd, Jm = 2.7 Hz,
Jo = 9.0 Hz, H-9), 7.41 (1H, d, Jo = 9.0 Hz, H-10), 7.28–
7.36 (5H, m, H-2@-6@), 6.93 (1H, d, J2’,1’ = 11.7 Hz, H-2’),
6.39 (1H, dd/t, J2,11b = 2.4 Hz, J2,1 = 2.4 Hz, H-2), 5.83
(1H, dd, J1’,4 = 6.0 Hz, J1’,2’ = 11.7 Hz, H-1’), 5.35 (1H, dd/
t, J1,11b = 2.4 Hz, J1,2 = 2.4 Hz, H-1), 4.72 (1H, dd, J3a,4
7.2 Hz, J3a,11b = 9.0 Hz, H-3a), 4.58 (1H, t, J4,3a = 7.2 Hz,
J4,1’ = 6.0 Hz, H-4), 4.25 (1H, t{d}, J11b,2 = 2.4 Hz, J11b,1
=
=
2.4 Hz, J11b,3a = 9.6 Hz, H-11b). 13C NMR (CDCl3) d:
172.92 (C-6), 154.56 (C-10a), 151.21 (C-11a), 144.59 (C-2),
137.94 (C-6a), 138.88 (C-1@), 132.05 (C-2’), 129.42 (C-9),
129.86 (C-3@, C-5@), 128.05 (C-4@), 127.95 (C-2@, C-6@),
126.22 (C-1’), 126.01 (C-7), 125.54 (C-8), 124.72 (C-5a),
119.08 (C-10), 98.76 (C-1), 77.25 (C-3a), 75.84 (C-4),
39.08(C-11b). Anal. calcd. for C22H15ClO4: C 69.75, H
3.99; found: C 69.65, H 3.93. Mass (m/z): 378 (M+, 100%).
Photolysis of 3-benzyloxy-6-chloro-2-(furan-3-yl)-4H-
chromen-4-one (3i)
A methanolic solution of 3i (0.20 g, 0.57 mmol) on pho-
tolysis for 45 min furnished 4i.
Compound 4i
Yield 50%, white solid; mp 116–118 8C (CHCl3-EtOH).
1
1
IR nmax (cm–1): 1647.2 (C=O). H NMR (CDCl3) d: 8.25
Compound 6g (data from a mixture of H NMR/IR of 3g and
6g)
(1H, d, Jm = 2.4 Hz, H-7), 7.59 (1H, dd, Jm = 2.4 Hz, Jo =
9.0 Hz, H-9), 7.49–7.36 (6H, m, H-10, 2’, 3’, 4’, 5’, 6’), 6.51
(1H, dd, J2,11b = 1.8 Hz, J2,1 = 2.4 Hz, H-2), 5.44 (1H, t,
Yield 25%. IR nmax (cm–1): 1653 (C=O). 1H NMR
(CDCl3) d: 8.32 (1H, t, J2’,5’ = 1.8 Hz, J2’,4’ = 1.8 Hz, H-2’),
8.23 (1H, d, Jm = 2.4 Hz, H-5), 7.55 (1H, dd, Jm = 2.4 Hz,
Jo = 9.0 Hz, H-7), 7.55 (1H, t, J5’,2’ = 1.8 Hz, J5’,4’ = 1.8 Hz,
H-5’), 7.44 (1H, d, Jo = 9.0 Hz, H-8), 7.20–7.28 (5H, m, H-
2@’-6@’), 7.00 (1H, t, J4’,2’ = 1.8 Hz, J4’,5’ = 1.8 Hz, H-4’),
J1,11b = 2.1 Hz, J1,2 = 2.4 Hz, H-1), 5.08 (1H, dd, J3a,4
8.1 Hz, J3a,11b = 9.6 Hz, H-3a), 4.80 (1H, d, J4,3a = 8.1 Hz,
H-4), 4.30 (1H, t, J11b,1 = 2.1 Hz, J11b,2 = 2.4 Hz, J11b,3a
=
=
9.6 Hz, H-11b). 13C NMR (CDCl3) d: 171.00 (C-6), 153.00
(C-10a), 150.78 (C-11a), 146.96 (C-2), 138.00 (C-6a),
136.42 (C-1’), 133.08 (C-9), 130.31 (C-8), 128.34 (C-4’),
128.20 (C-3’, C-5’), 126.83 (C-2’, C-6’) 125.14 (C-7),
124.00 (C-5a), 119.07 (C-10), 100.45 (C-1), 79.99 (C-4),
76.38 (C-3a), 41.75 (C-11b). Anal. calcd. for C20H13ClO4:
C 68.09, H 3.71; found: C 63.15, H 3.66. Mass (m/z): 352
(M+, 100%).
6.65 (1H, d, J3’,2’ = 11.4 Hz, H-3@), 6.35 (1H, td, J2’,3’
=
11.4 Hz, J2’,1’ = 6.6 Hz, H-2@), 4.93 (2H, d, J1’,2’ = 6.6 Hz,
H-1@).
Photolysis of 6-chloro-2-(furan-3-yl)-3-propargyloxy-4H-
chromen-4-one (3h)
A methanolic solution of 3h (0.20 g, 0.66 mmol) on pho-
tolysis for 45 min furnished two isomeric products: 4h and
4h’. These photoproducts were separated from the starting
substrate by column chromatography. They were further
separated from each other by preparative TLC.
Photolysis of 6-chloro-2-(furan-3-yl)-3-(4@-
methoxybenzyloxy)-4H-chromen-4-one (3j)
A methanolic solution of 3j (0.20 g, 0.52 mol) on photol-
ysis for 45 min furnished 4j.
Compound 4h
Compound 4j
Yield 21%, white solid; mp 140–145 8C (CHCl3-EtOH).
IR nmax (cm–1): 1641.2 (C=O), 2130 (C:C). 1H NMR
(CDCl3): 8.24 (1H, d, Jm = 2.4 Hz, H-7), 7.58 (1H, dd, Jm
= 2.4 Hz, Jo = 9.0 Hz, H-9), 7.42 (1H, d, Jo = 9.0 Hz, H-
10), 6.51 (1H, dd, J2,11b = 1.5 Hz, J2,1 = 2.4 Hz, H-2), 5.31
(1H, t, J1,11b = 2.1 Hz, J1,2 = 2.4 Hz, H-1), 5.17 (1H, dd,
Yield 37%, white solid; mp 172–174 8C (CHCl3-EtOH).
IR nmax (cm–1): 1644.6 (C=O). H NMR (CDCl3) d: 8.17
1
(1H, d, Jm = 2.4 Hz, H-7), 7.52 (1H, dd, Jm = 2.4 Hz, Jo =
9.0 Hz, H-9), 7.35 (1H, d, Jo = 9.0 Hz, H-10), 7.34 (2H, d,
Jo = 8.7 Hz, H-2’, H-6’), 6.86 (2H, d, Jo = 8.7 Hz, H-3’, H-
5’), 6.43 (1H, dd, J2,11b = 2.1 Hz, J2,1 = 3.6 Hz, H-2), 5.36
J3a,4 = 2.7 Hz, J3a,11b = 9.9 Hz, H-3a), 5.06 (1H, t, J4,3a
=
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Kamboj et al.
429
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MM2 incorporated in Chem office 8.0 Chem 3D ultra 8.0.
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(1H, dd, J1,11b = 2.4 Hz, J1,2 = 3.6 Hz, H-1), 5.00 (1H, dd,
J3a,4 = 8.4 Hz, J3a,11b = 9.9 Hz, H-3a), 4.75 (1H, d, J4,3a
8.4 Hz, H-4), 4.24 (1H, t{d}, J11b,2 = 2.1 Hz, J11b,1
=
=
2.4 Hz, J11b,3a = 9.9 Hz, H-11b), 3.74 (3H, s, C4’-OCH3).
13C NMR (CDCl3) d: 171.00 (C-6), 156.96 (C-4’), 154.00
(C-10a), 151.00 (C-11a), 144.37 (C-2), 138.00 (C-6a),
135.55 (C-1’), 130.47 (C-9), 125.84 (C-8), 125.66 (C-2’, C-
6’), 124.00 (C-5a), 122.54 (C-7), 116.49 (C-10), 111.06 (C-
3’, C-5’), 97.83 (C-1), 77.29 (C-3a), 74.00 (C-4), 39.25(C-
11b), 52.31 (C4’-OCH3). Anal. calcd. for C21H15ClO4: C
65.89, H 3.95; found: C 65.93, H 3.96. Mass (m/z): 382
(M+, 100%).
Acknowledgements
We thank the University Grants Commission (UGC) and
the Council of Scientific and Industrial Research (CSIR),
New Delhi, for generous financial support of this work.
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