Photocyclisation of 3-alkoxy-6-chloro-2-(3-methylthiophen-2-yl)-4H-chromen- 4-ones

Article abstract of DOI:10.1016/j.crci.2011.11.005

Photocyclisation of 3-alkoxy-6-chloro-2-(3-methylthiophen-2-yl)-4H-chromen- 4-ones in methanol with pyrex filtered UV-light lead to the formation of tetracyclic compounds through intramolecular γ-hydrogen abstraction. The methyl group on the thiophenyl ri

Full text of DOI:10.1016/j.crci.2011.11.005

C. R. Chimie 15 (2012) 311–316
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´
Full paper/Memoire
Photocyclisation of 3-alkoxy-6-chloro-2-(3-methylthiophen-2-yl)-
4H-chromen-4-ones
*
Ramesh C. Kamboj , Geeta Sharma, Dinesh Kumar, Rita Arora
Department of Chemistry, Kurukshetra University, Kurukshetra, 136119, India
A R T I C L E I N F O
A B S T R A C T
Article history:
Photocyclisation of 3-alkoxy-6-chloro-2-(3-methylthiophen-2-yl)-4H-chromen-4-ones in
Received 1 June 2011
methanol with pyrex filtered UV-light lead to the formation of tetracyclic compounds
Accepted after revision 9 November 2011
Available online 16 December 2011
through intramolecular
g-hydrogen abstraction. The methyl group on the thiophenyl ring
does not interfere in the photocyclisation although it does effect the product formation.
´
ß 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Keywords:
Photochemistry
Thiophenylchromenone
Tetracyclic compounds
Hydrogen transfer
[1,5]-H Sigmatropic rearrangement
Radical reactions
Substituent effects
1. Introduction
3-alkoxy group. The 3-alkoxy-2-thiophenyl-4H-chromen-
4-ones on photo-irradiation produced cyclized dihydro
Chromones [1] and their derivatives are the naturally
occurring compounds ubiquitously found in the plant
kingdom, and therefore are present in representative
amounts in normal human diet. These phytochemicals
possess a wide spectrum of biological activities such as
anti-inflammatory [2], antimicrobial [3], anticancer and
antitumour [4] and antioxidant [5] properties. In fact, the
chromone moiety is an important element of the
pharmacophores of many biologically active molecules
displaying diverse medicinal applications [2].
and dehydrogenated photoproducts [10,11]. From these,
the cyclized dihydro photoproducts were formed via 1,5-
sigmatropic H-shift whereas the cyclized dehydrogenated
products are formed by the expulsion of H2 during
ketonisation directly. In the present study, we report the
results of our investigation on the photoreactions of 3-
alkoxy-6-chloro-2-(3-methylthiophen-2-yl)-4H-chro-
men-4-ones. The main objectives are:
ꢀ
ꢀ
how does the methyl group at 3’-position effect the
product formation through its steric/inductive effect;
does the demethylation occurs leading to the formation
of cyclized aromatic products as represented earlier or
simple cyclisation occurs without its expulsion giving
cyclized photoproducts analogous to dihydro-photo-
product having angular methyl group during photo-
cyclisation;
Intramolecular H-abstraction [6–9] in 3-alkoxy-2-
arylchromones is of considerable significance. These
chromones on photo-irradiation undergo cyclisation via
g
-H abstraction to yield the angular tetracyclic products
and the product formation depends upon the nature of
ꢀ
to unravel the effect of different groups at C-3 on the
product formation/distribution.
* Corresponding author.
E-mail address: rckamboj@rediffmail.com (R.C. Kamboj).
1631-0748/$ – see front matter ß 2011 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2011.11.005

312
R.C. Kamboj et al. / C. R. Chimie 15 (2012) 311–316
2. Results and discussion
these photoproducts (Scheme 2) were confirmed by their
spectral data (IR, 1H/13C-NMR) and elemental analysis.
In all these photoproducts, the ring C has half chair
conformation and evidently, the C/D ring fusion is cis. For
example in 4c, the trans-fusion of five-membered ring will
result in higher conformational strain as calculated by
MM2 energy minimizations programme [14] than the cis-
fusion and this is in accordance with the earlier findings in
case of the naturally occurring pterocarpans [15–18] and
N-heterocycles [19]. Now assuming the C/D ring fusion as
cis, the orientation of H-4 can be cis or trans with respect to
–CH3 at C-3a. So, four possible 3D conformations I, II (H-4
cis to CH3-3a) and III, IV (H-4 trans to CH3-3a) were derived
from MM2 energy minimizations programme which are
shown in Fig. 1.
The required substrates, 3-alkoxy-2-(3-methylthio-
phen-2-yl)-4H-chromen-4-ones 3(a–e) were synthesized
by the alkylation of 3-hydroxychromen-4-one 2 that was
obtained by the condensation of 5-chloro-2-hydroxyace-
tophenone with 3-methylthiophene-2-carboxaldehyde in
the presence of NaOH/EtOH [12] to give chalcone 1,
followed by the treatment with H2O2/ÀOH under AFO
conditions [13] (Scheme 1).
The structures of compounds 3(a–e) were found to be
consistent with their spectral parameters (IR, 1H/13C NMR).
The yields of all these compounds were in the range of 80–
98%.
The photolysis of methanolic solution of 3(a–e) with
pyrex filtered UV-light, under nitrogen atmosphere
produced photoproducts 4(a–e), and the structures of
From the above four conformations, the one which has
minimum energy i.e. conformation I, could be the possible
1S'
5'
S
8
2
3
OH
O
O
O
OH
7
3'
ii
i
CH3
OH
CH3
CH3
Cl
Cl
Cl
5
O
1
2
iii
5'
1S
2
S
2'
11b
H
10
A
7
D
3
2
O
O
B
9
7
3Ca H3
R
h
3'
CH3
OCH2R
C
O
4
3
Cl
Cl
MeOH
5
H
O
O
3(a-e)
4(a-e)
a, R = -H; b, R = -CCH; c, R = -CHCH2; d, R = -C(CH3 )CH2; e, R = -C6H5
i) 3-Methyl thiophene-2-carboxaldehyde/C H5OH/NaOH; ii) KOH/H2O2(30%)/ 0oC
2
iii) K2CO3/dry CH3COCH3/Bu4N+I-/RCH2X
Scheme 1. Synthesis and photolysis of chromenones 3(a–e).
S
D
O
C
O
R
H
O
5'
S
S
S
-CH4
5
O
O
O
O
2
3'
CH3
CHR
CH3
h
4
.
CH3
OCH2R
[1, 5]-H shift
Cl
O
O
R
H
OH
1
O
H
1
S
1,4-biradicals
3(a-e)
H
D
O
11b
C
O
3aCH3
R
B
H
O
4(a-e)
Scheme 2. Mechanism of photocyclisation of 3(a–e).

R.C. Kamboj et al. / C. R. Chimie 15 (2012) 311–316
313
Fig. 1. Possible energy minimized conformations of photoproduct 4c.
conformation for the photoproduct 4c in which H-4 is cis to
3a-CH3 group and bulkier vinyl group is at -equatorial
position. Such a view is in conformity with the literature
[20] where the heavier group at equatorial position in
cyclohexane is always preferred.
The thiophen-2-yl chromenones having same basic
skeleton similar to 3(a–e) with no 3–CH3 group at
thiophenyl group furnished cyclised dihydro and cyclised
dehydrogenated aromatic photoproducts [10,11]. The
cyclised dihydro photoproducts were formed via 1,5-
sigmatropic H-shift whereas the cyclised dehyderogenated
aromatic products were formed by the expulsion of H2
during ketonisation directly. But, in the present study, the
thiophen-2-yl chromenones 3(a–e) having a –CH3 group as
a substituent at C-3 of thiophenyl, the formation of only
cyclised dihydro type photoproducts 4(a–e) through 1,5-
sigmatropic H-shift is favored. No demethylation leading
to the formation of aromatic photoproducts was observed
as the energy required to break C–C bond is higher than
that required to break a C–H bond.
The phototransformations (Scheme 2) described above
can be visualized to occur through the formation of 1,4-
biradical intermediate. The products have been expected
c
˙
to be formed through a bond formation between –CH–
radical and the C-3 atom of thiophene ring followed by
ketonisation and H-migration to C-11b (1,5-H shift). The
thiophenyl moiety at C-2 possesses only 3’-carbon
available for clipping of 1,4-biradical.
Moreover, the yields of the photoproducts 4(a–e)
formed depended upon the nature of the alkoxy group
at C-3 position of the substrates (3a–3e). As the stability of
the 1,4-biradicals generated in situ from 3a (R = –H) to 3e
(R = –C6H5) increases (Scheme 2), yield of the correspond-
ing photoproduct also increases (Table 1).
Table 1
Yields of the photoproducts (4a–4e).
Photoproduct
R
4a
–H
24
4b
4c
4d
4e
–CCH
38
–CHCH2
46
–C(CH3)CH2
71
C6H5
87
Yield (%)

314
R.C. Kamboj et al. / C. R. Chimie 15 (2012) 311–316
3. Conclusion
(1H, d, J5,7 = 2.4 Hz, H-5), 7.66 (1H, dd, J7,5 = 2.4 Hz, J7,8
= 9.0 Hz, H-7), 7.56 (1H, d, J5’,4’ = 5.1 Hz, H-5’), 7.51 (1H, d,
J8,7 = 9.0 Hz, H-8), 7.01 (1H, d, J4’,5’ = 5.1 Hz, H-4’), 2.60 (3H,
s, 3’–CH3); 13C NMR (CDCl3):
d 172.23 (C-3), 153.52,
The 3-alkoxy-6-chloro-2-(3-methylthiophen-2-yl)-4H-
chromen-4-ones upon photo-irradiation yielded angular
tetracyclic products through 1,4-biradical furnished by
H abstraction, no demethylation occurred and therefore no
cyclised aromatic photoproduct was realized.
g
-
144.02, 140.84, 137.12, 133.70, 131.44, 130.57, 129.44,
125.39, 124.72, 121.94, 119.73, 16.79 (3’–CH3);
Anal. Calcd. for C14H9ClO3S: C, 57.44; H, 3.10. Found: C,
57.39; H, 3.07.
4. Experimental
6-Chloro-3-methoxy-2-(3-methylthiophen-2-yl)-4H-
chromen-4-one (3a)
4.1. Materials and methods
The compound, 2 (2.92 g, 1.0 eq.), (CH3)2SO4 (1.38 g, 1.1
eq.), dry K2CO3 (1.1 eq.) and tetra-n-butylammonium
iodide (100 mg, 3.0 mol%) were refluxed in dry acetone
(20 ml) for 4 h. Filtration, evaporation of solvent and
crystallization of the residue (EtOH) gave 3a (80%) as a
creamish solid, m.p. 136–138 8C; lmax (MeOH) 297,
264 nm; IR nmax (cmÀ1): 1643.0 (C = O); 1H NMR (CDCl3,
Melting points were determined in open capillaries and
are thus uncorrected. 1H/13C NMR spectra were recorded at
300 MHz (75.4 MHz for 13C NMR) on a Bruker spectrometer
using TMS as internal standard. IR spectra were recorded
on a MB3000 FT-IR with HORIZON MBTM FTIR software
from ABB Bomen using KBr pellets. Mass spectra were
recorded at 2500 eV (ESI-Source) using a Water’s Q-TOF
micro instrument. Elemental analysis was carried on
Perkin Elmer 2400 instrument. TLC plates were coated
with silica gel G (suspended in CHCl3–MeOH) and iodine
vapors were used as visualizing agent. The columns for
purification were packed with Silica gel 100–200 mesh in
pet.ether and left overnight before use. The elution was
carried out with increasing proportion of benzene in
pet.ether-benzene mixture. The yields reported are based
on the amount of isolated photoproducts and are
calculated by excluding the recovered substrates.
300 MHz):
d 8.24 (1H, d, J5,7 = 2.4 Hz, H-5), 7.62 (1H, dd,
J7,5 = 2.4 Hz, J7,8 = 9.0 Hz, H-7), 7.53 (1H, d, J5’,4’ = 5.1 Hz, H-
5’), 7.46 (1H, d, J8,7 = 9.0 Hz, H-8), 7.00 (1H, d, J4’,5’ = 5.1 Hz,
H-4’), 3.99 (3H, s, –OCH3), 2.66 (3H, s, 3’–CH3); 13C NMR
(CDCl3):
d 172.84 (C-4), 153.14, 141.83, 139.46, 133.46,
131.66, 130.74, 130.12, 125.33, 125.16, 124.57, 119.28,
77.19, 59.96 (3-OCH3), 17.33 (3’–CH3); Mass (m/z): 307
(M + 1, 88%); Anal. Calcd. for C15H11ClO3S: C, 58.73; H, 3.61.
Found: C, 58.78; H, 3.63.
The other ethers 3(b–e) were synthesized by reacting 3-
hydroxychromenone
2 with propargyl bromide, allyl
bromide, methyl allyl chloride, and benzyl chloride
respectively by the procedure as used for compound 3a.
6-Chloro-2-(3-methylthiophen-2-yl)-3-propargyloxy-
4H-chromen-4-one (3b)
4.2. Synthesis of chromones 3(a–e)
1-(5-Chloro-2-hydroxyphenyl)-3-(3-methylthiophen-2-
yl)prop-2-en-1-one (1)
Yield 88%, light yellow solid; m.p. 156–158 8C; lmax
(MeOH) 294, 263 nm; IR nmax (cmÀ1): 1636.3 (C = O); 1H
A solution of 5-chloro-2-hydroxyacetophenone (1.70 g,
1.0 eq.) and 3-methylthiophene-2-carboxaldehyde (1.38 g,
1.1 eq.) in absolute ethanol and sodium hydroxide (2.0 eq.)
were stirred for 4 h. The dark red mixture was poured on
ice-HCl to obtain 1 as yellow solid, crystallized from EtOH
(1.90 g, 68.44%), m.p. 110–112 8C; IR nmax (cmÀ1): 1628.0
NMR (CDCl3, 300 MHz): d 8.23 (1H, d, J5,7 = 2.7 Hz, H-5),
7.63 (1H, dd, J7,5 = 2.7 Hz, J7,8 = 9.0 Hz, H-7), 7.55 (1H, d,
J5’,4’ = 5.1 Hz, H-5’), 7.48 (1H, d, J8,7 = 9.0 Hz, H-8), 7.00 (1H,
d, J4’,5’ = 5.1 Hz, H-4’), 5.07 (2H, d, J1’’,3’’ = 2.4 Hz, H-1’’), 2.65
(3H, s, 3’–CH3), 2.40 (1H, t, J3’’,1’’ = 2.4 Hz, H-3’’); 13C NMR
(CDCl3):
d 172.50 (C-4), 153.22, 152.10, 142.10, 141.00,
(C = O), 3405 (OH); 1H NMR (CDCl3, 300 MHz):
d
12.90 (1H,
133.62, 131.47, 130.87, 130.27, 129.80, 125.15, 124.78,
119.36, 76.59, 76.33, 59.03 (C-1’’), 17.39 (3’’–CH3); Mass
(m/z): 331 (M + 1, 36%); Anal. Calcd. for C17H11ClO3S: C,
61.73; H, 3.35. Found: C, 61.78; H, 3.37.
3-Allyloxy-6-chloro-2-(3-methylthiophen-2-yl)-4H-chro-
men-4-one (3c)
s, OH), 8.19 (1H, d, J3,2 = 15.0 Hz, H-3), 7.84 (1H, d,
J6’,4’ = 2.4 Hz, H-6’), 7.45 (1H, dd, J4’,6’ = 2.4 Hz, J4’,3’ = 9.0 Hz,
H-4’), 7.42 (1H, d, J5’’,4’’ = 5.4 Hz, H-5’’), 7.28 (1H, d,
J2,3 = 15.0 Hz, H-2), 7.00 (1H, d, J3’,4’ = 9.0 Hz, H-3’), 6.97
(1H, d, J4’’,5’’ = 5.4 Hz, H-4’’), 2.46 (3H, s, 3’’–CH3); 13C NMR
(CDCl3):
d
192.24 (C-1), 162.02, 144.24, 137.26, 135.96,
Yield 95%, creamish solid; m.p. 130–132 8C; lmax
(MeOH) 296, 266 nm; IR nmax (cmÀ1): 1643 (C = O), 1605
134.25, 131.66, 128.75, 128.62, 123.47, 120.62, 120.17,
117.06, 14.38; Anal. Calcd. for C14H11ClO2S: C, 60.32; H,
3.98. Found: C, 60.30; H, 3.94.
6-Chloro-3-hydroxy-2-(3-methylthiophen-2-yl)-4H-
chromen-4-one (2)
(C = C); 1H NMR (CDCl3, 300 MHz):
d 8.23 (1H, d,
J5,7 = 2.4 Hz, H-5), 7.61 (1H, dd, J7,5 = 2.4 Hz, J7,8 = 9.0 Hz,
H-7), 7.52 (1H, d, J5’,4’ = 5.1 Hz, H-5’), 7.46 (1H, d,
J8,7 = 9.0 Hz, H-8), 7.00 (1H, d, J4’,5’= 5.1 Hz, H-4’), 6.07
(1H, ddt, J2’’,1’’ = 6.6 Hz, J2’’,3’’a = 17.4 Hz, J2’’,3’’b = 10.8 Hz, H-
2’’), 5.37 (1H, dd, J3’’a,1’’ = 1.5 Hz, J3’’a,2’’ = 17.4 Hz, H-3’’a),
5.23 (1H, dd, J3’’b,2’’ = 10.5 Hz, J3’’b,1’’ = 1.2 Hz, H-3’’b), 4.76
(2H, d, J1’’,2’’ = 6.6 Hz, H-1’’), 2.64 (3H, s, 3’–CH3); 13C NMR
To a well stirred suspension of compound 1 (1.0 g,
0.003 mol) in MeOH was added aq. KOH (10 ml, 20%). This
mixture was cooled to 0 8C. To this dark red solution was
added H2O2 (30%) drop-wise till the colour changed to
yellow and the stirring was continued for 4 h. The reaction
mixture was neutralized with ice-HCl to give light yellow
precipitates, crystallized (chloroform-ethanol) to light
yellow solid (0.74 g, 70%), m.p. 190 8C; IR nmax (cmÀ1):
(CDCl3):
d 172.87 (C-4), 154.07, 153.12, 141.83, 137.87,
133.44, 133.21, 131.54, 130.69, 129.99, 125.20, 125.12,
124.76, 119.31, 119.18, 72.99, 17.36 (3’–CH3); Mass (m/z):
333 (M + 1, 3%); Anal. Calcd. for C17H13ClO3S: C, 61.35; H,
3.94. Found: C, 61.33; H, 3.92.
1597 (C = O), 3232 (OH); 1H NMR (CDCl3, 300 MHz):
d 8.23

R.C. Kamboj et al. / C. R. Chimie 15 (2012) 311–316
315
6-Chloro-2-(3-methylthiophen-2-yl)-3-(2-methylally-
loxy)-4H-chromen-4-one (3d)
3a–CH3); 13C (CDCl3):
137.21, 133.81, 130.67, 127.51, 127.11, 125.43, 124.55,
119.65, 76.63, 76.52, 68.40, 53.71, 51.54, 18.93 (3a–CH3);
Mass (m/z): 331 (M + 1, 100%); Anal. Calcd. for
d
170.39 (C-6), 153.66, 148.85,
Yield 95%, light yellow solid; m.p. 98–100 8C; lmax
(MeOH) 297, 263 nm; IR nmax (cmÀ1): 1636 (C = O), 1605
(C = C); 1H NMR (CDCl3, 300 MHz):
d
8.19 (1H, d,
C17H11ClO3S: C, 61.73; H, 3.35. Found: C, 61.78; H, 3.31.
J5,7 = 2.7 Hz, H-5), 7.62 (1H, dd, J7,5 = 2.7 Hz, J7,8 = 7.8 Hz,
H-7), 7.52 (1H, d, J5’,4’ = 4.8 Hz, H-5’), 7.46 (1H, d,
J8,7 = 7.8 Hz, H-8), 6.98 (1H, d, J4’,5’ = 4.8 Hz, H-4’), 5.09
(1H, s, H-3’’b), 5.03 (1H, s, H-3’’a), 4.72 (2H, s, H-1’’), 1.80
4.3.3. Photolysis of compound (3c)
A methanolic solution of 3c (500 mg, 1.5 mmol) on
photolysis for 45 min furnished 4c.
Compound (4c): yield 46%, creamish solid; m.p. 176–
178 8C; IR nmax (cmÀ1): 1651(C = O); 1H NMR (CDCl3,
(3H, s, 2’’–CH3), 1.58 (3H, s, 3’–CH3); 13C (CDCl3):
d
172.88
(C-4), 154.02, 153.21, 141.76, 141.00, 138.46, 133.45,
131.33, 130.69, 129.87, 125.30, 125.15, 124.86, 119.35,
114.08, 75.67 (C-1’’), 19.67, 17.10 (3’–CH3); Mass (m/z):
347 (M + 1, 8%); Anal. Calcd. for C18H15ClO3S: C, 62.33; H,
4.36. Found: C, 62.30; H, 4.31.
3-Benzyloxy-6-chloro-2-(3-methylthiophen-2-yl)-4H-
chromen-4-one (3e)
Yield 95%, light yellow solid; m.p. 132–134 8C; lmax
(MeOH) 297, 263 nm; IR nmax (cmÀ1): 1628.0 (C = O); 1H
300 MHz):
d 8.26 (1H, d, J7,9 = 2.4 Hz, H-7), 7.60 (1H, dd,
J9,7 = 2.4 Hz, J9,10 = 9.0 Hz, H-9), 7.41 (1H, d, J10,9 = 9.0 Hz, H-
10), 6.37 (1H, d, J2,3 = 6.0 Hz, H-2), 5.99 (1H, ddd,
J1’,2’ = 6.6 Hz, J1’,2’a = 17.4 Hz, J1’,2’b = 10.8 Hz, H-1’), 5.47 (1H,
d, J2’a,1’ = 17.4 Hz,H-2’a), 5.35 (1H, d, J2’b,1’ = 10.8 Hz, H-2’b),
5.40 (1H, d, J2,3 = 6.0 Hz, H-3), 4.60(1H, s, H-11b), 4.54(1H, d,
J4,1’ = 6.6 Hz, H-4),1.26(3H, s, 3a–CH3);13C(CDCl3):
d171.00
(C-6), 153.61, 148.15, 139.57, 138.47, 133.49, 130.76,
128.59, 126.51, 125.79, 124.68, 119.67, 116.50, 78.7,
54.10, 52.06, 18.97 (3a–CH3); Mass (m/z): 333 (M + 1,
88%); Anal. Calcd. for C17H13ClO3S: C, 61.35; H, 3.94. Found:
C, 61.30; H, 3.91.
NMR (CDCl3, 300 MHz):
d 8.26 (1H, d, J5,7 = 2.4 Hz, H-5),
7.62 (1H, dd, J7,5 = 2.4 Hz, J7,8 = 8.7 Hz, H-7), 7.42–7.46 (3H,
m, H-8, 3’’, 7’’), 7.49 (1H, d, J5’,4’ = 5.1 Hz, H-5’), 7.39–7.28
(3H, m, H-4’’, 5’’, 6’’), 6.93 (1H, d, J4’,5’ = 5.1 Hz, H-4’), 5.22
(2H, s, –OCH2–), 2.55 (3H, s, 3’–CH3); 13C (CDCl3):
d 172.95
(C-4), 154.14, 153.21, 141.82, 138.13, 136.40, 133.48,
131.32, 130.73, 129.91, 128.95, 128.22, 125.27, 125.12,
124.83, 119.38, 73.75 (–OCH2–), 17.11 (3’–CH3); Mass (m/
z): 383 (M + 1, 4%); Anal. Calcd. for C21H15ClO3S: C, 65.88;
H, 3.95. Found: C, 65.79; H, 3.88.
4.3.4. Photolysis of compound (3d)
A methanolic solution of 3d (500 mg, 1.4 mmol) on
photolysis for 45 min furnished 4d.
Compound (4d): yield 71%, creamish solid; m.p. 214 8C;
IR n d
max (cmÀ1): 1659 (C = O); 1H NMR (CDCl3, 300 MHz):
8.24 (1H, d, J7,9 = 2.7 Hz, H-7), 7.59 (1H, dd,
J9,7 = 2.7 Hz, J9,10 = 9.0 Hz, H-9), 7.39 (1H, d, J10,9 = 9.0 Hz,
H-10), 6.36 (1H, d, J2,3 = 6.0 Hz, H-2), 5.44 (1H, d,
J2,3 = 6.0 Hz, H-3), 5.16 (2H, d, J4,3a = 2.1, 2’–CH2), 4.56
(1H, s, H-11b), 1.94 (3H, s, 1’–CH3), 1.28 (3H, s, 3a–CH3);
4.3. Photo-irradiation of chromenones 3(a–e)
4.3.1. Photolysis of compound (3a)
A methanolic solution (150 ml) of chromenone 3a
(500 mg, 1.6 mmol) was irradiated with light from a 125 W
13C (CDCl3):
d 170.51 (C-6), 153.62, 147.96, 139.87, 138.35,
Hg vapor lamp in
a
pyrex reactor under Nitrogen
133.61, 130.47, 128.56, 126.42, 125.39, 124.67, 119.62,
116.57, 78.34, 54.05, 52.01, 21.42, 18.78 (3a–CH3); Mass
(m/z): 347 (M + 1, 27%); Anal. Calcd. for C18H15ClO3S: C,
62.33; H, 4.36. Found: C, 62.28; H, 4.31.
atmosphere for 90 min. The removal of solvent left a
gummy solid which was chromatographed to yield 4a.
Compound (4a): yield 24%, light yellow solid; m.p. 174–
176 8C; IR nmax (cmÀ1): 1649.7 (C = O); 1H NMR (CDCl3,
300 MHz):
d
8.25 (1H, d, J7,9 = 2.1 Hz, H-7), 7.60 (1H, dd,
4.3.5. Photolysis of compound (3e)
J9,7 = 2.4 Hz, J9,10 = 9.0 Hz, H-9), 7.42 (1H, d, J10,9 = 9.0 Hz,
H-10), 6.27 (1H, d, J2,3 = 6.6 Hz, H-2), 5.43 (1H, d,
J3,2 = 6.6 Hz, H-3), 4.44 (1H, s, H-11b), 4.08 (1H, d, H-4a),
A methanolic solution of 3e (500 mg, 1.3 mmol) on
photolysis for 45 min furnished 4e.
Compound (4e): yield 87%, creamish solid; m.p. 186–
188 8C; IR nmax (cmÀ1): 1651 (C = O); 1H NMR (CDCl3,
3.88 (1H, d, H-4b), 1.36 (3H, s, 3a–CH3); 13C (CDCl3):
d
170.52 (C-6), 153.58, 151.94, 148.39, 138.83, 133.47,
130.57, 125.45, 124.73, 119.48, 100.60, 78.73, 65.88,
40.83, 17.90 (3a–CH3); Mass (m/z): 307 (M + 1, 3%); Anal.
Calcd. for C15H11ClO3S: C, 58.73; H, 3.61. Found: C, 58.78;
H, 3.64.
300 MHz): d 8.28 (1H, d, J7,9 = 2.4 Hz, H-7), 7.62 (1H, dd,
J9,7 = 2.4 Hz, J9,10 = 8.4 Hz, H-9), 7.28–7.47 (6H, m, H-10, 2’,
3’, 4’, 5’, 6’), 6.46 (1H, d, J2,3 = 6.0 Hz, H-2), 5.16 (1H, d,
J3,2 = 6.0 Hz, H-3), 5.12 (1H, s, H-4), 4.74 (1H, s, H-11b),
1.60 (3H, s, 3a–CH3); 13C (CDCl3):
d 170.51 (C-6), 153.68,
148.10, 138.72, 135.75, 133.70, 130.56, 128.23, 127.96,
127.85, 126.93, 125.48, 124.72, 119.64, 76.61, 53.57,
52.22, 17.77 (3a–CH3); Mass (m/z): 383 (M + 1, 44%); Anal.
Calcd. for C21H15ClO3S: C, 65.88; H, 3.95. Found: C, 65.91;
H, 3.96.
4.3.2. Photolysis of compound (3b)
A methanolic solution of 3b (500 mg, 1.5 mmol) on
photolysis for 45 min furnished 4b.
Compound (4b): yield 38%, creamish white solid; m.p.
202–204 8C; IR nmax (cmÀ1): 1643 (C = O), 2114 (CBC); 1H
Acknowledgements
NMR (CDCl3, 300 MHz):
d 8.25 (1H, d, J7,9 = 2.7 Hz, H-7),
7.60 (1H, dd, J9,7 = 2.7 Hz, J9,10 = 9.0 Hz, H-9), 7.42 (1H, d,
J10,9 = 9.0 Hz, H-10), 6.30 (1H, d, J2,3 = 6.0 Hz, H-2), 5.54 (1H,
d, J3,2 = 6.0 Hz, H-3), 4.83 (1H, d, J4,2’ = 2.1 Hz, H-4), 4.54
(1H, s, H-11b), 2.58 (1H, d, J2’,4 = 2.1 Hz, H-2’), 1.46 (3H, s,
Grateful acknowledgment is made to CSIR, New Delhi
for generous financial support for accomplishing this
work.

316
R.C. Kamboj et al. / C. R. Chimie 15 (2012) 311–316
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