Photo-reorganization of 3-alkoxy-6-chloro-2-(thiophen-3-yl)-4H-chromen-4- ones: Regioselective cyclization via γ-hydrogen abstraction

Article abstract of DOI:10.1016/j.jphotochem.2011.04.002

Regioselective photocyclization of 3-alkoxy-6-chloro-4H-chromen-4-ones bearing thiophen-3-yl moiety at 2-position has been described. These chromenones on irradiation by the pyrex filtered UV-light produced a diverse array of novel angular tetracyclic pho

Full text of DOI:10.1016/j.jphotochem.2011.04.002

Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 124–133
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Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Photo-reorganization of
3-alkoxy-6-chloro-2-(thiophen-3-yl)-4H-chromen-4-ones: Regioselective
cyclization via ␥-hydrogen abstraction
Ramesh C. Kamboj∗, Rita Arora, Dinesh Kumar, Geeta Sharma
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:
Regioselective photocyclization of 3-alkoxy-6-chloro-4H-chromen-4-ones bearing thiophen-3-yl moi-
ety at 2-position has been described. These chromenones on irradiation by the pyrex filtered UV-light
produced a diverse array of novel angular tetracyclic photoproducts. Of these, mostly the cyclic dihydro
and dehydrogenated photoproducts had the gem-dihydro functionality and exocyclic double bonds onto
the fused pyran ring respectively, which is unprecedent in these chromenones.
Received 23 November 2010
Received in revised form 1 March 2011
Accepted 2 April 2011
Available online 12 April 2011
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Photoirradiation
Thienylchromenones
Cyclization reaction
1,7-H shift
1. Introduction
the photoreactions of 3-alkoxy/allyloxy-6-chloro-4H-chromen-4-
ones bearing thiophen-3-yl moiety at 2-position in place of furan
Intramolecular H-abstractions [1–7] by the excited carbonyl
group are the interesting tools for the synthesis of many exotic
molecules, that are usually unobtainable through thermal modes.
The spirocyclics [1,2], polycyclics [4–7] (both linear and angu-
lar), vinyl ethers [3], lactams [8,9] etc. have been synthesized by
using this method. 3-Alkoxy-2-(phenyl/thienyl/furyl)chromones
[4–7] and 2-alkoxy/alkyl-3-aryl-2-cyclohexenones [10] on photoir-
radiation lead to angular polycyclic products. Although the basic
skeleton of the substrates is same, the products formed are quite
different as well as interesting and their distribution has been
found to depend upon the nature of substituents at C-2 and C-
3 in chromones [4–7]. Many research efforts have been directed
to obtain regioselective photocyclized products [11–13]. In most
cases, since several types of photoproducts were produced, control-
ling the selectivity of the product is very hard. In our earlier study,
an attempt was made to study the regioselective photocyclization
of 3-alkoxy-chromones bearing a 3-furyl [14] group at C-2, pos-
sessing two sites (C-2ꢀ and C-4ꢀ) for clipping of the initially formed
1,4-biradical, the photoproducts were afforded only by clipping at
C-2ꢀ with no photoproducts by clipping at C-4ꢀ (Fig. 1).
moiety. Our objectives are: (i) how a thiophene moiety tethered
to the chromenone through its C-3 position instead of C-2 posi-
tion [15] effects the product formation/distribution, (ii) whether
phototranspositions [16] – a route common in the photolysis of sub-
stituted thiophenes will occur in these photoreactions, (iii) whether
photoproduct formation involves the Dewar thiophene [17,18], a
valence bond isomer that may be formed in situ through the pho-
toisomerization of thiophene and (iv) the prospect of the oxetane
[19] – the cyclobutyl product formation.
2. Results and discussion
The targets, 2-(thiophen-3-yl)-4H-chromen-4-ones 3(a–f)
were synthesized by the condensation of 5-chloro-2-
hydroxyacetophenone with thiophene-3-carbaldehyde in the
presence of NaOH/EtOH, followed by reacting the resulting
chalcones with 50% H2O2/OH− under AFO conditions [20] and
subsequent alkylation (Scheme 1) of the 3-hydroxychromenones
with suitable alkyl halide in the presence of dry acetone, freshly
dried K2CO3 and n-Bu4N+I−.
To further explore the possibility of regioselective photocy-
clisation, in the present study, we report our investigations on
The structures of these photo-labile substrates 3(a–f) were
found to be consistent with their spectral parameters (IR, 1H/13
NMR, vide experimental).
C
In electronic absorption spectra, the chromenones 3(a–f)
showed ꢀmax in the range of 244–358 nm (Fig. 2), thus, a pyrex
filtered UV-light was used for their photoirradiation.
∗
Corresponding author. Tel.: +91 174 423 8466; fax: +91 174 423 8277.
E-mail address: rckamboj@rediffmail.com (R.C. Kamboj).
1010-6030/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2011.04.002

R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 124–133
125
2'
S
S
S
1
O
OH
CH3
8
5
OH
O
i
ii
iii
4'
Cl
3
Cl
Cl
OH
Cl
OR
O
O
O
O
1
3(a-f)
2
i; Thiophene-3-carbaldehyde/C2H5OH/NaOH/room temp.
ii; 50%H2O2/OH-/0oC; iii; K2CO3/CH3COCH3/Bu4N+I-/RX
3a, R =
3b, R =
-CH3
a H
(CH3)2SO4
80%
81%
RX =
CH2
-
-
H
CH2Br
C
C
C
C
b H
H
H
H
H
a H
CH2
CH2Cl
C
C
C
C
88%
72%
3c, R =
3d, R =
b H
CH3
H
CH3
H3Ca
CH2
H
-
H3C
H3C
CH2Br
C
H
C
C
C
H3C
b
H
C
Ph
CH2
H
-
H
C
Ph
CH2Cl
C
H
85%
86%
3e, R =
3f, R =
C
HC
C
CH2Br
HC C CH2 -
Scheme 1. Synthesis of thienylchromenones 3(a–f).
by their spectral parameters (IR, 1H/13C NMR) and elemental
analysis.
4'
O
4'
O
O
R
O
O
2
3
O
O
The compound 4b in its IR spectrum exhibited a strong absorp-
tion band at 1628 cm−1 that may be assigned to the C O of
pyrone moiety. The two diastereotopic protons (Hx and Hy) at C-
3 resonated at different ı values (Fig. 3) with Jgem = 16.5 Hz (bond
angle = 109.66◦). The proton Hx-3 appeared downfield as it falls in
deshielding zone of vinyl group and showed resonance at ı 4.04 (1H,
ddd, Jgem = 16.5 Hz, J3Hx,3a = 4.7 Hz, J3Hx,1 = 2.4 Hz) with gauche con-
formation giving approximately a cis-disposition with respect to
the H-3a (dihedral angle = 54.97◦). The Hy-3 resonated at ı 3.86 (1H,
ddd, Jgem = 16.5 Hz, J3Hy,3a = 5.0 Hz, J3Hy,1 = 3.7 Hz) indicating a near
trans-disposition to H-3a with the dihedral angle of 120◦. The pro-
ton H-1 was located at ı 6.62 (dt/ddd, J1,3Hy = 3.6 Hz, J1,3Hx = 2.4 Hz,
J1,3a = 2.4 Hz). The protons H-1, Hx-3 and Hy-3 belonging to the
modified thiophene moiety in 4b were found to be up-field as com-
pared to H-2ꢀ and H-5ꢀ in 3b, which indicated the loss of aromatic
character of the thiophene moiety in 4b. The ring junction proton
H-3a was seen at ı 4.49 (dtd/dddd, J3a,4 = 10.8 Hz, J3a,3Hy = 5.0 Hz,
J3a,3Hx = 4.7 Hz, J3a,1 = 2.2 Hz). The pyran proton H-4 gave a dd at ı
4.37 (J4,3a = 10.8 Hz, Jvic = 6.9 Hz).
hν
2'
2'
Cl
Cl
R
OH
1,4-biradical
Fig. 1. Possible sites for clipping at furyl group with 1,4-biradical.
The photoirradiation of methanolic solution of the chromenones
3(a–f) with pyrex filtered UV-light using a 125 W Hg lamp, under
nitrogen atmosphere produced the photoproducts 4(a–f) and
4(aꢀ–fꢀ). The photoproducts 4(a–f) were obtained in the single
stereoisomeric forms. In addition to these, photolysis of 3a pro-
duced 4aꢀꢀ and that of 3b, 3c and 3f produced 4bꢀꢀ, 4cꢀꢀ and 4fꢀꢀ,
respectively; no such products were obtained on irradiation of 3d.
The structures of these photoproducts (Scheme 2) were confirmed
The glaring spectrum of proton H-1 in 4b described above was
also supported by its 2D NOESY spectrum where three spots below
H-1 corresponds to the H-3a, Hx-3 and Hy-3 protons confirmed
that the H-1 shows allylic coupling with H-3a and through space
coupling with Hx-3 and Hy-3.
Moreover, the 2D HSQC spectra further confirmed the presence
of the C-3 bearing two hydrogens in the structure of 4b as the spots
aroused below Hx-3 and Hy-3 corresponds to the negative signal at
ı 39.03 which became available due to C-3 (Fig. 4).
Likewise, the structures of other cyclic dihydro photoproducts
4a and 4(c–f) were confirmed by their spectral data.
Another feature worth revealing in the photoproducts isolated is
the stereochemistry of ring C; which is in half-chair conformation.
Regarding the relative stereochemical disposition of H-3a and H-4,
which can be cis or trans, the use of J/˚ relationship [21–23] and
MM2 programme [12] adequately indicated these to be in trans
(˚3a,4 = 152.80◦) relationship, thus placing the bulkier groups, i.e.
vinyl and acetylenyl groups in a pseudo-equatorial position. Such
Fig. 2. Electronic absorption spectra of the substrate 3b.

126
R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 124–133
1
1
S
D
S
3
10
7
10
7
Hx
Hy
O
B
3
H
R
O
C3a
O
4 H
R
4
Cl
Cl
O
H
O
O
4(a'-f')
4(a-f)
hν/MeOH
3(a-f)
2
4'
1
10
S
S
O
O
H
2'
4
3
Cl
O
R
Cl
7
5
O
O
4a''
4(b''-c''), 4f''
-R
Photoproduct Yield (%)
Photoproduct
Yield (%) Photoproduct
Yield (%)
4a
4b
4a''
30
29
4a'
-H
35
20
a H
C C
4b'
4c'
36
38
4b''
4c''
10
12
b H
a H
H
4c
4d
35
20
C C
b H
CH3
H3Ca
H3Cb
4d'
C C
21
45
H
H
10#
36
4e'
4f'
4e
4f
C C
Ph
H
(Ε)
8#
10#
4f''
HC C
# yield caculated from1 H NMR
Scheme 2. Photoirradiation of thienylchromenones 3(a–f) and distribution of the photoproducts.
Fig. 3. Partial 400MHz 1H NMR spectrum of H-3a, H-4, Hx-3 and Hy-3 in 4b.
Table 1
a contention was further corroborated from the observation that
H-3a in 4(b–f) appeared down field than the equivalent proton in
4a (R = –H) by 0.45–0.83 ppm (Table 1).
Chemical shift of proton H-3a in 4(a-f).
Compound
4a
4b
4c
4d
4e
4f
It may be argued that in 4b the only pseudo-equatorially placed
vinyl group at C-4 would deshield the H-3a in conformation I
(Fig. 5). The proton H-3a would not experience such deshielding in
the other possible conformation II. This has made the stereocentre
C-4 to have R-configuration and stereocentre C-3a to have S config-
uration. The steric energy (Ekcal) calculations [24] also showed that
ıH-3a
3.92
4.52
4.64
4.37
4.51
4.75

R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 124–133
127
Fig. 4. 1H/13C 2D HSQC spectrum of 4b.
Fig. 5. MM2 energy minimized structures of expected conformations of compound 4b.
the lower energy conformation (conformation I) is the one that
explain the observed J/ꢁ relationship (Table 2).
The mass spectrum of third photoproduct 4bꢀꢀ also showed the
m/z 317 as base peak as that of 4bꢀ but in its 1H NMR spectrum the
two thienyl protons appeared as doublets at ı 7.44 (J2,1 = 5.1 Hz,
H-2) and ı 7.35 (J1,2 = 5.1 Hz, H-1) that made it differ from 4bꢀ. Like-
wise, the structures of 4cꢀꢀ and 4fꢀꢀ were confirmed by their spectral
data.
The observed 3J values found in the present case for 4b are in
accordance with the J† values calculated for the conformation I,
in which the protons H-3a and H-4 are trans to each other and
dihydrothiophene ring is exo to the ␺-chair pyran ring.
In the 1H NMR of photoproduct 4bꢀ, the two thienyl protons H-1
and H-3 showed no coupling with each other and were located as
singlet at ı 7.44. The pyran proton H-4 appeared as doublet at ı 6.05
(J4,1ꢀ = 6.3 Hz) which illustrate the absence of proton corresponding
to H-3a. The structure of photoproduct 4bꢀ has been further corrob-
orated by its mass spectrum, which showed retro-Diels Alder (rDA)
fragmentation mode (Scheme 3), thereby indicating the presence
of chromenone moiety in the 4bꢀ. The structures of the other pho-
toproducts 4aꢀ and 4(cꢀ–fꢀ) were also confirmed by their spectral
data.
The demethoxylated product 4aꢀꢀ showed in its 1H NMR spec-
trum a signal at ı 6.69, characteristic of H-3 proton in chromones
[25]. The identity of photoproduct 4aꢀꢀ was further confirmed by
the synthesizing an authentic sample of the compound through
the cyclization of compound 1.
The photocyclization of 3(a–f), to furnish the dehydro-
genated photoproducts 4(bꢀꢀ–cꢀꢀ) and 4fꢀꢀ, takes place simply
through the coupling of 1,4-biradical 5X with C-2ꢀ-position
of the thiophene ring as reported in our earlier studies
[1–3,14] (Scheme 4).
Table 2
Expected coupling constants for the two conformations of 4b.
Coupling protons
Conformation I
Conformation II
Observed
˚
J†
E(kcal/mol)
˚
J†
E(kcal/mol)
J
H-3a and H-4
−175.17
12.9 Hz
16.616
−56.09
4.7 Hz
18.123
10.8 Hz
†
Expected value.

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R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 124–133
.
O
.
Cl
C
S
O
m/z 155/ 157
O
O
rDA
H
S
S
.
Cl
O
.
−H
H
O
4b'
m/z 317/ 319
O
m/z 161
Scheme 3. Mass fragmentation pattern of 4bꢀ.
S
2'
S
S
2'
O
.
O
O
.
4'
4'
.
.
O
O
O
HO
OH
OH
1,4-biradical
1,6-biradical
8
D
C
Fig. 6. Resonance in 1,4-biradical of 3b.
But the formation of photoproducts 4(a–f) and 4(aꢀ–fꢀ) can not
intermediacy of Dewar type moiety in the phoirradiation of the
thienylchromenones has been invoked. Since the energy of Dewar
thiophene (So energy = 65 kcal mol−1) is lower than that of Dewar
furan (So energy = 78 kcal mol−1) [29]. Therefore, it may be safely
concluded that the formation of products 4(a–f) and 4(aꢀ–fꢀ) occurs
via the low energy Dewar type intermediate 7 and the high level of
regioselectivity achieved over here may be credited to some hidden
electronic factors.
The chromenones 3(a–f) can also undergo phototransposition
reactions, but no products originating through such mode were
realized. This observation is supported by the fact that carbonyl and
olefinic substituents inhibit this type of rearrangement [30–38].
In case of 3a (R = –CH3), the formation of demethoxylated prod-
be explained by the above route and there is no other favorable path
except one (Scheme 5). According to this path the initially formed
1,4-biradical [1–3,26–28] 5Y may mesomerizes to C-4ꢀ position and
then clipped to give Dewar type structure 7 which furnished the
photoproducts consequently.
The photocyclised products 4(a–f) were formed from 7 via
ketonisation and 1,7-H shift (Scheme 5). The cyclodehydrogenated
photoproducts 4(aꢀ–fꢀ) formed independently from 7 through the
expulsion of H2 not via dihydro photoproduct 4(a–f). This was con-
firmed by the fact that further irradiation of isolated 4(a–f) yielded
no product corresponding to 4(aꢀ–fꢀ).
Even though we have not isolated any Dewar type moiety but
the proposed mechanism (Scheme 5) can also be supported by
the fact that the photoirradiation of the chromenones, substituted
with the 3-furyl group [14] at C-2 which have the same possi-
bility (i.e. two possible sites (C-2ꢀ and C-4ꢀ) for clipping of the
initially formed 1,4-biradical) as that of the chromenones under
study, afforded photoproducts only by clipping at C-2ꢀ. No photo-
products similar to 4(a–f) and 4(aꢀ–fꢀ) were produced by clipping
at C-4ꢀ as they need the involvement of the Dewar furan type
structure which could not have been possible in those furan-3-yl
chromenones probably due to high energy requirements. So, the
ꢀꢀ
˙
uct 4a can be explained as earlier due to the cyclisation of –O–CH–
radical at C-2 followed by the ketonisation and then ejection of
HCHO from the oxetane [25,39,40]. No such type of photoproduct
has been isolated when R = allyls. The only assignable reason to this
behavior could be the steric factor which disfavors cyclization [19]
of the bulky allyl radicals at C-2.
In the photolysis of allyloxy ethers 3(b–e), the allyl radical C
at C-1ꢀꢀ may also mesomerises to give 1,6-biradical D [41] (Fig. 6)
which may cyclise to give angular tricyclic photoproducts 8. Such
photoproducts were not obtained in the present study.
H
S
O
t
f
H
i
h
s
H
H
4'
-
O
O
]
5
,
R
R
S
S
H
1
[
O
O
O
O
O
hν
2'
3(a-f)
.
.
O
H
O
R
-H2
S
R
OH
H
(
5X)
1,4-biradical
H
(6)
O
4(b"-c"), 4f"
Scheme 4. Photocyclization through coupling at C-2ꢀ position of thienylchromenones.

R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 124–133
129
S
Hx
Hy
O
H
H
O
R
O
t
f
i
h
S
s
4(a-f)
S
H
-
]
7
,
O
O
1
4'
[
O
.
H
H
hν
3(a-f)
.
O
-H2
O
R
R
S
OH
H
O
(7)
1,4-biradical (5Y
)
H
O
R
O
4(a'-f')
Scheme 5. Photocyclization through coupling at C-4ꢀ position of thienylchromenones.
from the Dewar type moiety generated in situ through the pho-
tocyclization. No phototransposition, secondary ring contraction
of thiophene and oxetane formation occurred in these substrates
upon photoirradiation.
2
1
2
1
O
.
D
.
D
S
.
O
O
.
11b
3a
B
B
R
R
O
O
4. Experimental
H
H
O
O
4.1. General
9
10
Melting points were determined in open capillaries and are
thus uncorrected. The photoirradiation was carried out with a
125 W Hg lamp using a pyrex filter. The 1H NMR were recorded
on 400 MHz Bruker spectrometer and 300 MHz (75.4 MHz for
13C NMR) 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 3500 eV as (ESI +Q1 mode). Elemental analysis
was carried on Perkin Elmer 2400 instrument. TLC plates were
coated with silica gel G (suspended in CHCl3–MeOH) and iodine
vapours were used as visualizing agent. The columns for purifi-
cation 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 photo-
products and are calculated by excluding the recovered starting
substrates.
Fig. 7. Structures of proposed radicals.
The secondary ring contraction products observed by cleavage
of ring D as isolated in our earlier work on 3-alkoxy-2-(2ꢀ-furyl)
chromones [42–44], are altogether absent here and were not even
observed by further photolysis of pure photoproducts. The reason
attributed to such diversity may be the stabilty of biradicals (9 and
10) formed by cleavage of ring D which determines the ease of C–O
bond cleavage (Fig. 7).
The radical at C-11b in 9 (obtained in photolysis of 2ꢀ-furyl
chromones) is stabilized by pyrone moiety and thus C–O bond
becomes prone to cleavage. But there is no such stabilization avail-
able to radical at C-3a in 10 (possible intermediate which can be
formed from photoproduct obtained here) for its formation and
hence no ring contracted secondary photoproducts were formed.
These findings correlate well with the studies made by Maurizio
D’Auria [29] on the photochemical isomerization reactions of furan
and thiophene derivatives. On the basis of semiempirical calcula-
tions it has been shown that furan can give ring contraction product,
i.e. the cyclopropenyl derivative because its triplet state can give the
biradical intermediate, whereas thiophene can not be converted
into the biradical intermediate as this intermediate is of higher
4.2. Synthesis of chromones 3(a–f)
4.2.1. 1-(5-Chloro-2-hydroxyphenyl)-3-(thiophen-3-yl)prop-2-
en-1-one,
1
energy (69 kcal mol−1) than the excited triplet state (62 kcal mol−1
of thiophene, thus preventing the formation of the cyclopropenyl
derivatives.
)
To the well-stirred suspension of powdered NaOH
(0.8 g, 0.02 mol) in EtOH at 0 ◦C were added 5-
chloro-2-hydroxyacetophenone
(1.71 g,
0.01 mol)
and
thiophene-3-carbaldehyde (1.24 g, 0.011 mol). The reaction
mixture, which became deep red in color after 30 min, was stirred
further for 3 h. Thereafter, it was poured over ice and was neutral-
ized with dil. HCl to obtain acrylophenone, which was crystallized
3. Conclusion
3-Alkoxy-6-chloro-4H-chromen-4-ones bearing thiophen-3-yl
moiety at 2-position on irradiation with the pyrex filtered UV
light produced many novel dihydro and dehydrogenated angular
tetracyclic photoproducts via 1,4-biradical furnished through ␥-H
abstraction. Most of these photoproducts were probably originated
from EtOH to give yellow needles (86%), mp 90 ◦C; ꢂmax (cm−1
)
1643.0 (C O), 3405 (OH); ıH (CDCl3) 7.96 (1H, d, J3,2 = 15.3 Hz,
H-3), 7.86 (1H, d,ꢀꢀ Jm = 2.7 Hz, H-6ꢀ), 7.73 (1H, dd, J2
= 3.0 Hz,
= 1.2 Hz,
ꢀꢀ ꢀꢀ
,4
ꢀꢀ ꢀꢀ
ꢀꢀ ꢀꢀ
ꢀꢀ ꢀꢀ
J2
= 1.2 Hz, H-2 ), 7.50 (1H, dd, J5
= 5.1 Hz, J5
,5
,4
,2

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R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 124–133
H-5ꢀꢀ), 7.46 (1H, dd, Jo = 9.0 Hzꢀ,ꢀ Jm = 2.7 Hz, H-4ꢀ), 7.44 (1H, dd,
7.01 (1H, d, Jo = 9.0 Hz, H-3ꢀ).
(C-4), 153.18, 152.51, 141.15, 138.86, 133.53, 131.76, 130.60,
129.37, 127.07, 125.97, 125.16, 125.08, 119.59, 113.90, 75.38 (C-1ꢀꢀ),
19.82 (2ꢀꢀ-CH3); Mass (m/z, +Q1): 333 (M+, 100%).
ꢀꢀ ꢀꢀ
ꢀꢀ ꢀꢀ
= 3.0 Hz, H-4 ), 7.40 (1H, d, J2,3 = 15.3 Hz, H-2),
,5
J4
= 5.1 Hz, J4
,5
4.2.2.
4.2.6. 6-Chloro-3-(3-methylbut-2-enyloxy)-2-(thiophen-3-yl)-
6-Chloro-3-hydroxy-2-(thiophen-3-yl)-4H-chromen-4-one, 2
To the well stirred suspension of compound 1 (2.64 g, 0.01 mol)
in methanol was added 10.0 ml of 20% aq. KOH and cooled to 0 ◦C.
To this dark red solution was added H2O2 (30%) drop-wise till the
color changed to yellow and the stirring was continued for 4 h. The
reaction mixture was neutralized with ice–HCl to give light yellow
precipitates which were crystallized (CHCl3–MeOH) to light yellow
4H-chromen-4-one,
3d
Yield 72%, white solid; mp 103 ◦C (MeOH); ꢀmax MeOH 357,
300, 246nm; ꢂmax (cm−1) 1643 (C O), 1605 (C C); ıH (CDCl3) 8.36
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(1H, dd, J2 ,4 = 3.0 Hz, J2 ,5 = 1.2 Hz, H-2 ), 8.21 (1H, d, Jm = 2.4 Hz,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
H-5), 7.85 (1H, dd, J5 ,4 = 5.1 Hz, J5 ,2 = 1.2 Hz, H-5 ), 7.61 (1H, dd,
Jo = 9.0 Hz, Jm = 2.4 Hz, H-7), 7.49 (ꢀ1H, d, Jo = 9.0 Hz, H-8), 7.45 (1H,
crystals (81%), mp 208–210 ◦C; ꢂmax (cm−1) 1605.0 (C O), 3248
dd, J4 ,5 = 5.1 Hz, J4 ,2 = 3.0 Hz, H-4 ), 5.53 (1H, t, Jvic = 7.2 Hz, H-2ꢀꢀ),
4.75 (1H, d, Jvic = 7.2 Hz, H-1ꢀꢀ), 1.75 (3H, s, C3ꢀꢀ-CH3a), 1.72 (3H,
s, C3ꢀꢀ-CH3b); ␦13C (CDCl3) 173.85 (C-4), 153.22, 152.71, 139.71,
138.96, 133.46, 132.01, 130.54, 129.28, 127.11, 125.79, 125.14,
125.10, 119.74, 119.58, 68.63 (C-1ꢀꢀ), 25.81 (3ꢀꢀ-CH3a), 18.11 (3ꢀꢀ-
CH3b); Mass (m/z, +Q1): 347 (M+, 100%).
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(OH); ıH (CDCl3) 8.34 (1H, dd, J2 ,4 = 3.0 Hz, J2 ,5 = 1.2 Hz, H-2 ), 8.23
ꢀ
ꢀ
ꢀ
ꢀ
(1H, d, Jm = 2.4 Hz, H-5), 7.88 (1H, dd, J5 ,4 = 5.1 Hz, J5 ,2 = 1.2 Hz, H-
5ꢀ), 7.66 (1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-7), 7.55ꢀ(1H, d, Jo = 9.0 Hz,
ꢀ
ꢀ
ꢀ
ꢀ
H-8), 7.49 (1H, dd, J4 ,5 = 5.1 Hz, J4 ,2 = 3.0 Hz, H-4 ), 6.9 (1H, s, OH);
Mass (m/z, +Q1): 279 (M+, 100%).
4.2.3.
4.2.7. 6-Chloro-3-(3-phenylallyloxy)-2-(thiophen-3-yl)-4H-
6-Chloro-3-methoxy-2-(thiophen-3-yl)-4H-chromen-4-one, 3a
To a suspension of compound, 2 (0.556 g, 0.002 mol) and freshly
ignited K2CO3 (1.38 g, 0.01 mol) in dry acetone was added dimethyl
sulphate (0.277 g, 0.002 mol), and tetra-n-butylammonium iodide
(0.050 g). The reaction mixture was refluxed for 4 h and the color
of reaction mixture change from orange red to white. Filtration,
evaporation of solvent and crystallization of the residue (MeOH)
gave 3a (80%), white solid/colourless crystals, mp 142–143 ◦C;
chromen-4-one,
3e
Yield 85%, creamish solid; mp 102–104 ◦C (EtOH); ꢀmax MeOH
354, 308, 252nm; ꢂmax (cm−1) 1643 (C O), 1605 (C C); ␦H
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(CDCl3) 8.38 (1H, dd, J2 ,4 = 3.0 Hz, J2 ,5 = 1.2 Hz, H-2 ), 8.24 (1H,
d, Jm = 2.4 Hz, H-5), 7.87 (1H, dd, J5 ,4 = 5.1 Hz, J5 ,2 = 1.2 Hz, H-5 ),
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
7.62 (1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-7), 7.51–7.47 ꢀꢀ(2H, m, H-8,
H-4ꢀ), 7.33–7.29 (5H,ꢀꢀm, H-2ꢀꢀꢀ–6ꢀꢀꢀ), 6.69 (1H, d, J3 ꢀꢀ = 15.6 Hz,
,2
ꢀmax MeOH 351, 300, 252nm; ꢂmax (cm−1) 1636.0 (C O); ıH
H-3ꢀꢀ), 6.41 (1H, dt, J2 ꢀꢀ = 15.6 Hz, J2 ꢀꢀ = 6.6 Hz, H-2ꢀꢀ), 4.94 (2H,
ꢀꢀ
,3
,1
ꢀ
ꢀꢀ
(CDCl3) 8.33 (1H, dd, J2 ,4 = 3.0 Hz, J2 ,5 = 1.2 Hz, H-2 ), 8.24 (1H, d,
d, J1 ꢀꢀ = 6.6 Hz, H-1ꢀꢀ); ı13C (CDCl3) 173.74 (C-4), 153.24, 152.90,
ꢀ
ꢀ
ꢀ
ꢀ
,2
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Jm = 2.4 Hz, H-5), 7.83 (1H, dd, J5 ,4 = 5.1 Hz, J5 ,2 = 1.2 Hz, H-5 ), 7.63
139.23, 138.58, 136.31, 134.49, 133.59, 131.91, 130.64, 129.48,
128.57, 128.02, 127.19, 126.69, 126.03, 125.11, 124.40, 119.64,
72.73 (C-1ꢀꢀ); Mass (m/z, +Q1): 395 (M+, 100%).
(1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-7), 7.51 (1H, d, Jo = 9.0 Hz, H-8),
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
7.47 (1H, dd, J4 ,5 = 5.1 Hz, J4 ,2 = 3.0 Hz, H-4 ), 4.01 (3H, s, OCH3);
ı
13C (CDCl3) 173.62 (C-4), 153.23, 152.39, 140.16, 133.56, 131.72,
130.64, 129.26, 126.93, 126.13, 125.21, 125.10, 119.57, 59.75 (3-
4.2.8.
OCH3); Mass (m/z, +Q1): 293 (M+).
6-Chloro-3-propargyloxy-2-(thiophen-3-yl)-4H-chromen-4-one,
3f
The other ethers 3(b–f) were synthesized by reacting 3-
hydroxychromenone 2 with allyl bromide, methyl allyl chloride,
dimethyl allyl bromide, cinnamyl chloride and propargyl bromide
respectively by the procedure as used for compound 3a.
Yield 86%, white solid; mp 148–150 ◦C (MeOH); ꢀmax MeOH 347,
306, 249 nm; ꢂmax (cm−1) 1638 (C O), 2ꢀ135 (C C); ıH (CDCl3) 8.42
ꢀ
ꢀ
ꢀ
ꢀ
(1H, dd, J2 ,4 = 3.0 Hz, J2 ,5 = 1.2 Hz, H-2 ), 8.22 (1H, d, Jm = 2.4 Hz,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
H-5), 7.89 (1H, dd, J5 ,4 = 5.1 Hz, J5 ,2 = 1.2 Hz, H-5 ), 7.64 (1H, dd,
4.2.4. 3-Allyloxy-6-chloro-2-(thiophen-3-yl)-4H-chromen-4-one,
Jo = 9.0 Hz, Jm = 2.4 Hz, H-7), 7.52 (1H, d, Jo = 9.0 Hz, H-8), 7.46 (1H,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀꢀ ꢀꢀ
= 2.4 Hz, H-
,3
3b
d, J4 ,5 = 5.1 Hz, J4 ,2 = 3.0 Hz, H-4 ),ꢀꢀ5.10 (2H, d, J1
Yield 81%, white solid; mp 102–104 ◦C (MeOH); ꢀmax MeOH
1ꢀꢀ), 2.42 (1H, t, J3
= 2.4 Hz, H-3 ); ı13C (CDCl3) 173.66 (C-4),
ꢀꢀ ꢀꢀ
,1
348, 302, 251 nm; ꢂmax (cm−1) 1636 (C O), 1605 (C = C); ıH
(CDCl3) 8.37 (1H, dd, J2 ,4 = 3.0 Hz, J2 ,5 = 1.2 Hz, H-2 ), 8.23 (1H,
153.21, 152.71, 138.62, 133.57, 133.35, 131.84, 130.63, 129.44,
127.09, 125.97, 125.10, 119.59, 119.10, 77.23, 72.92 (C-1ꢀꢀ); Mass
(m/z, +Q1): 317 (M+, 100%).
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
d, Jm = 2.4 Hz, H-5), 7.86 (1H, dd, J5 ,4 = 5.1 Hz, J5 ,2 = 1.2 Hz, H-5 ),
7.63 (1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-7), 7.51 (1H, d, Jo = 9.0 Hz,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
H-8), 7.47 (1H, dd, J4 ,5 = 5.1 Hz, J4 ,2 = 3.0 Hz, H-4 ), 6.08 (1H,
ddt, Jtrans = 17.1 Hz, Jcis = 10.5 Hz, Jvic = 6.0 Hz, H-2ꢀꢀ), 5.39 (1H, dt,
Jtrans = 17.1 Hz, Jallyl = 1.2 Hz, Ha-3ꢀꢀ), 5.26(1H, d, Jcis = 10.5 Hz, Hb-3ꢀꢀ),
4.78 (2H, dd, Jvic = 6.0 Hz, Jallyl = 1.2 Hz, H-1ꢀꢀ); ı13C (CDCl3) 173.66
(C-4), 153.21, 152.71, 140.15, 138.62, 133.57, 133.35, 131.83,
130.63, 129.44, 127.09, 125.97, 125.10, 119.59, 119.10 (C-3ꢀꢀ), 72.92
(C-1ꢀꢀ); Mass (m/z, +Q1): 318.96 (M+, 100%).
4.3. Photoirradiation of chromones 3(a-f)
4.3.1. Photolysis of
6-chloro-3-methoxy-2-(thiophen-3-yl)-4H-chromen-4-one, 3a
A 1.0 mM methanolic solution of chromone 3a contained in a
pyrex glass vessel was purged with nitrogen for 30 min and then
irradiated under nitrogen with light from a 125 W Hg vapor lamp
for 50 min. The removal of solvent left a gummy solid which was
chromatographed to yield 4a, 4aꢀ and 4aꢀꢀ.
4.2.5. 6-Chloro-3-(2-methylallyloxy)-2-(thiophen-3-yl)-4H-
chromen-4-one,
Compound 4a.Yield 30%, light yellow solid; mp 224–226 ◦C; ꢂmax
(cm−1) 1636 (C O); ıH (CDCl3/400MHz) 8.22 (1H, d, Jm = 2.6 Hz, H-
7), 7.58 (1H, dd, Jo = 9.0 Hz, Jm = 2.6 Hz, H-9), 7.41 (1H, d, Jo = 9.0 Hz,
H-10), 6.59 (1H, dt/ddd, J1,3Hx = 3.6 Hz, J1,3Hy = 2.4 Hz, J1,3a = 2.4 Hz,
H-1), 4.71–4.64 (2H, m, Ha-4, Hb-4), 4.09 (1H, ddd, J3Hx,3Hy = 16.4 Hz,
J3Hx,3a = 4.6 Hz, J3Hx,1 = 2.4 Hz, Hx-3), 3.96-3.88 (2H, m, Hy-3, H-3a);
3c
Yield 88%, white solid; mp 108–110 ◦C (MeOH); ꢀmax MeOH 358,
301, 244 nm; ꢂmax (cm−1) 1636 (C O), 1ꢀ605 (C C); ıH (CDCl3) 8.36
ꢀ
ꢀ
ꢀ
ꢀ
(1H, dd, J2 ,4 = 3.0 Hz, J2 ,5 = 1.2 Hz, H-2 ), 8.22 (1H, d, Jm = 2.7 Hz,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
H-5), 7.84 (1H, dd, J5 ,4 = 5.1 Hz, J5 ,2 = 1.2 Hz, H-5 ), 7.63 (1H, dd,
Jo = 9.0 Hz, Jm = 2.7 Hz, H-7), 7.56 (1H, d, Jo = 9.0 Hz, H-8), 7.50 (1H,
ı
13C (CDCl3) 170.76 (C-6), 152.95, 142.80, 138.07, 133.82 (C-9),
ꢀ
ꢀꢀ
ꢀ
ꢀ
ꢀ
ꢀ
dd, J4 ,5 = 5.1 Hz, J4 ,2 = 3.0 Hz, H-4 ), 5.15 (1H, s, Ha-3 ), 5.01 (1H, s,
131.99, 130.49, 128.30 (C-1), 125.35 (C-7), 124.63, 119.51 (C-10),
71.75 (C-4), 48.09 (C-3a), 39.27 (C-3). Anal. Calcd. for C14H9ClO3S:
Hb-3ꢀꢀ), 4.66 (2H, s, H-1ꢀꢀ), 1.86 (3H, s, 2ꢀꢀ-CH3); ı13C (CDCl3): 173.58

R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 124–133
131
C, 57.44; H, 3.10. Found: C, 57.04; H, 3.10; Mass (m/z, +Q1): 293/295
(M+, 100%).
Compound 4c. Yield 35%, light yellow solid; mp 210 ◦C; ꢂmax
(cm−1) 1636 (C O); ıH (CDCl3/400MHz) 8.23 (1H, d, Jm = 2.6 Hz,
H-7), 7.59 (1H, dd, Jo = 9.0 Hz, Jm = 2.6 Hz, H-9), 7.41 (1H, d,
Jo = 9.0 Hz, H-10), 6.61 (1H, dt/ddd, J1,3Hy = 3.6 Hz, J1,3Hx = 2.4 Hz,
J1,3a = 2.4 Hz, H-1), 5.19 (1H, s, H-2ꢀb), 5.15 (1H, t, J = 1.4 Hz, H-2ꢀa),
4.63 (1H, dtd/dddd, J3a,4 = 10.8 Hz, J3a,3Hy = 5.0 Hz, J3a,3Hx = 4.8 Hz,
J3a,1 = 2.2 Hz, H-3a), 4.32 (1H, d, J4,3a = 10.8 Hz, H-4), 4.03 (1H, ddd,
Jgem = 16.5 Hz, J3Hx,3a = 4.8 Hz, J3Hx,1 = 2.4 Hz, Hx-3), 3.85 (1H, ddd,
Compound 4aꢀ.Yield35%, light yellow solid; mp240–242 ◦C; ꢂmax
(cm−1) 1636 (C O); ıH (CDCl3) 8.30 (1H, d, Jm = 2.4 Hz, H-7), 7.61
(1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-9), 7.50 (1H, d, Jo = 9.0 Hz, H-10),
7.42 (2H, s, H-1, H-3), 5.51 (2H, s, Ha-4, Hb-4); ı13C (CDCl3) 169.82
(C-6), 152.59, 147.17, 135.92, 134.90, 133.24 (C-9), 130.80, 127.60,
126.20, 125.57 (C-7), 125.41, 121.70, 119.57 (C-10), 65.56 (C-4).
Anal. Calcd. for C14H7ClO3S: C, 57.84; H, 2.83. Found: C, 57.95; H,
2.86; Mass (m/z, +Q1): 291/293 (M+, 100%).
ꢀ
Jgem = 16.5 Hz, J3Hy,3a = 5.0 Hz, J3Hy,1 = 3.7 Hz, Hy-3), 1.91 (3H, s, C1
-
CH3); ı13C (CDCl3) 170.63 (C-6), 152.92, 142.82, 139.67 (C-1ꢀ),
138.63, 133.74 (C-9), 132.33, 130.41, 128.71 (C-1), 125.45 (C-7),
124.83, 119.48 (C-10), 117.54 (C-2ꢀ), 86.38 (C-4), 51.62 (C-3a), 38.97
(C-3), 17.52 (1ꢀ-CH3). Anal. Calcd. for C17H13ClO3S: C, 61.35; H, 3.94.
Found: C, 60.84; H, 4.02; Mass (m/z, +Q1): 333/335 (M+, 100%).
Compound 4cꢀ. Yield 38%, light yellow solid; mp 184 ◦C; ꢂmax
(cm−1) 1627 (C O); ıH (CDCl3) 8.30 (1H, d, Jm = 2.4 Hz, H-7), 7.61
(1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-9), 7.50 (1H, d, Jo = 9.0 Hz, H-
10), 7.43 (2H, s, H-1,3), 6.04 (1H, s, H-4), 5.17 (1H, s, H-2ꢀa),
Compound 4aꢀꢀ.Yield 20%, white solid; mp 160 ◦C; ꢂmax (cm−1
)
1651 (C O); ıH (CDCl3) 8.19 (1H, d, Jm = 2.7 Hz, H-5), 8.04 (1H, dd,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
J2 ,4 = 2.4 Hz, J2 ,5 = 1.5 Hz, H-2 ), 7.64 (1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz,
H-7), 7.50 (3H, m, H-8, 4ꢀ, 5ꢀ), 6.69 (1H, s, H-3); ı13C (CDCl3)
177.11 (C-4), 159.77, 154.37, 133.86 (C-7), 131.15, 127.54, 127.15,
125.48 (C-5), 125.19, 125.02, 124.97, 119.66 (C-8), 107.04 (C-3).
Anal. Calcd. for C13H7ClO2S: C, 59.43; H, 2.69. Found: C, 59.43; H,
2.67; Mass (m/z, +Q1): 263/265 (M+, 100%).
5.02 (1H, s, H-2ꢀb), 1.95 (3H, s, C1 -CH3); ı13C (CDCl3) 169.88 (C-
ꢀ
6), 152.52, 146.56, 141.90, 138.98, 134.38, 133.14 (C-9), 130.69,
127.54, 126.88, 125.61, 125.43 (C-7), 121.82, 119.57 (C-10), 116.26,
79.75 (C-4), 18.09 (1ꢀ-CH3). Anal. Calcd. for C17H11ClO3S: C, 61.73;
H, 3.35. Found: C, 61.73; H, 3.39; Mass (m/z, +Q1): 331/333(M+,
100%).
4.3.2. Photolysis of
3-allyloxy-6-chloro-2-(thiophen-3-yl)-4H-chromen-4-one, 3b
A 1.0 mM methanolic solution of 3b on photolysis for 50 min
furnished 4b, 4bꢀ and 4bꢀꢀ.
Compound 4b. Yield 29%, white solid; mp 210–212 ◦C; ꢂmax
(cm−1) 1628 (C O); ıH (CDCl3/400MHz) 8.23 (1H, d, Jm = 2.6 Hz,
H-7), 7.59 (1H, dd, Jo = 9.0 Hz, Jm = 2.6 Hz, H-9), 7.41 (1H, d,
Jo = 9.0 Hz, H-10), 6.62 (1H, dt/ddd, J1,3Hy = 3.6 Hz, J1,3Hx = 2.4 Hz,
J1,3a = 2.4 Hz, H-1), 5.99 (1H, ddd, Jtrans = 17.2 Hz, Jcis = 10.6 Hz,
Compound 4cꢀꢀ. Yield 12%, off-white solid; mp 190–192 ◦C; ꢂmax
(cm−1) 1643 (C O); ıH (CDCl3) 8.26 (1H, d, Jm = 2.4 Hz, H-7), 7.63
(1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-9), 7.47 (1H, d, Jo = 9.0 Hz, H-10),
7.37 (1H, d, J2,1 = 5.4 Hz, H-2), 7.31 (1H, d, J1,2 = 5.4 Hz, H-1), 6.44 (1H,
s, H-4), 4.89 (2H, s, H-2ꢀa, 2ꢀb), 1.85 (3H, s, C1 -CH3); ı13C (CDCl3)
ꢀ
Jvic = 6.9 Hz, H-1ꢀ), 5.58 (1H, dd, Jtrans = 17.2 Hz, J2 a,4 = 0.9 Hz, H-2ꢀa),
ꢀ
171.80 (C-6), 153.93, 143.41, 141.68, 138.98, 133.78 (C-9), 130.81,
129.21, 126.91, 126.05, 125.56 (C-7), 125.14, 124.95, 119.87 (C-10),
115.64, 74.79 (C-4), 21.61 (1ꢀ-CH3). Anal. Calcd. for C17H11ClO3S: C,
61.73; H, 3.35. Found: C, 61.34; H, 3.12; Mass (m/z, +Q1): 331/333
(M+, 100%).
5.44 (1H, dd, Jcis = 10.6 Hz, J2 b,4 = 0.9 Hz, H-2ꢀb), 4.49 (1H, dtd/dddd,
ꢀ
J3a,4 = 10.8 Hz, J3a,3Hy = 5.0 Hz, J3a,3Hx = 4.8 Hz, J3a,1 = 2.2 Hz, H-3a),
4.37 (1H, dd, J4,3a = 10.8 Hz, J4,1 = 6.9 Hz, H-4), 4.04 (1H, ddd,
ꢀ
Jgem = 16.5 Hz, J3x,3a = 4.8 Hz, J3x,1 = 2.4 Hz, Hx-3), 3.86 (1H, ddd,
Jgem = 16.5 Hz, J3Hy,3a = 5.0 Hz, J3Hy,1 = 3.7 Hz, Hy-3); ı13C (CDCl3)
170.66 (C-6), 152.96, 142.92, 138.33, 133.80 (C-9), 133.00(C-1ꢀ),
132.03, 130.48, 128.90 (C-1), 125.48 (C-7), 124.81, 120.75 (C-2ꢀ),
119.50 (C-10), 83.02 (C-4), 53.44 (C-3a), 39.02 (C-3). Anal. Calcd.
for C16H11ClO3S: C, 60.28; H, 3.48. Found: C, 60.46; H, 3.60; Mass
(m/z, +Q1): 319/321 (M+, 100%).
4.3.4. Photolysis of 6-chloro-3-(3-methylbut-2-enyloxy)-2-
(thiophen-3-yl)-4H-chromen-4-one,
3d
A 1.0 mM methanolic solution of 3d on photolysis for 50 min
Compound 4bꢀ. Yield 36%, light yellow solid; mp 198–200 ◦C;
ꢂmax (cm−1) 1643 (C O); ıH (CDCl3) 8.30 (1H, d, Jm = 2.4 Hz, H-7),
7.61 (1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-9), 7.50 (1H, d, Jo = 9.0 Hz,
H-10), 7.44 (2H, s, H-1, H-3), 6.18 (1H, ddd, Jtrans = 17.1 Hz,
Jcis = 10.5 Hz, Jvic = 6.3 Hz, H-1ꢀ), 6.05 (1H, d, Jvic = 6.3 Hz, H-4), 5.45-
5.39 (2H, m, H-2ꢀa, H-2ꢀb); ı13C (CDCl3) 170.01 (C-6), 152.56,
146.74, 138.81, 134.02, 133.21 (C-9), 130.75, 128.34, 127.13,
126.89, 125.59, 125.45 (C-7), 121.96, 119.92, 119.58 (C-10), 76.30
(C-4). Anal. Calcd. for C16H9ClO3S: C, 60.67; H, 2.86. Found: C, 61.46;
H, 2.72; Mass (m/z, +Q1): 317/319 (M+, 100%).
furnished 4d and 4dꢀ.
Compound 4d. Yield 20%, light brown solid; mp 212–214 ◦C; ꢂmax
(cm−1) 1637 (C O); ıH (CDCl3) 8.23 (1H, d, Jm = 2.4 Hz, H-7), 7.59
(1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-9), 7.41 (1H, d, Jo = 9.0 Hz, H-10),
ꢀ
6.64-6.61 (1H, m, H-1), 5.82 (1H, dd, J1 ,4 = 6.6 Hz, Jallyl = 1.5 Hz, H-
1ꢀ), 4.56 (1H, dtd/dddd, J3a,4 = 10.8 Hz, J3a,3Hy = 5.0 Hz, J3a,3Hx = 4.8 Hz,
ꢀ
J3a,1 = 2.2 Hz, H-3a), 4.37 (1H, dd, J4,3a = 10.8 Hz, J4,1 = 6.6 Hz, H-4),
4.05 (1H, ddd, Jgem = 16.5 Hz, J3Hx,3a = 4.8 Hz, J3Hx,1 = 2.4 Hz, Hx-3),
3.87 (1H, ddd, Jgem = 16.5 Hz, J3Hy,3a = 5.0 Hz, J3Hy,1 = 3.7 Hz, Hy-3),
1.80 (3H, d, Jallyl = 1.5 Hz, C2 -CH3a), 1.76 (3H, s, C2 -CH3b); ı13C
(CDCl3) 170.65 (C-6), 152.94, 142.86, 139.82, 138.00, 133.98 (C-9),
133.70, 130.42, 128.20 (C-1), 125.50 (C-7), 124.82, 121.52, 119.46
(C-10), 85.80(C-4), 50.37 (C-3a), 39.97 (C-3), 25.20 (2ꢀ-CH3a), 19.20
(2ꢀ-CH3b). Anal. Calcd. for C18H15ClO3S: C, 62.33; H, 4.36. Found: C,
62.33; H, 4.36; Mass (m/z, +Q1): 347/349 (M+, 100%).
ꢀ
ꢀ
Compound 4bꢀꢀ. Yield 10%, white solid; mp 178–180 ◦C; ꢂmax
(cm−1) 1637 (C O); ıH (CDCl3) 8.26 (1H, d, Jm = 2.4 Hz, H-7), 7.63
(1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-9), 7.47 (1H, d, Jo = 9.0 Hz, H-10),
7.44 (1H, d, J2,1 = 5.1 Hz, H-2), 7.35 (1H, d, J1,2 = 5.1 Hz, H-1), 6.60
(1H, ddd, Jtrans = 17.1 Hz, Jcis = 10.5 Hz, Jvic = 6.3 Hz, H-1ꢀ), 6.03 (1H,
d, Jvic = 6.3 Hz, H-4), 5.15–5.03 (2H, m, H-2ꢀa, H-2ꢀb); ı13C (CDCl3)
171.21 (C-6), 153.65, 143.74, 138.78, 133.78 (C-9), 133.01, 130.86,
129.34, 127.13, 126.94, 125.67, 125.51 (C-7), 125.04, 123.87, 119.85
(C-10), 74.30 (C-4). Anal. Calcd. for C16H9ClO3S: C, 60.67; H, 2.86.
Found: C, 60.67; H, 2.78; Mass (m/z, +Q1): 317/319 (M+, 100%).
Compound 4dꢀ. Yield 21%, light brown solid; mp 188 ◦C; ꢂmax
(cm−1) 1641 (C O); ıH (CDCl3) 8.28 (1H, d, Jm = 2.4 Hz, H-7), 7.60
(1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-9), 7.49 (1H, d, Jo = 9.0 Hz, H-10),
7.44 (2H, s, H-1, H-3), 6.01 (1H, dd, J1 ,4 = 6.3 Hz, Jallyl = 1.5 Hz, H-1ꢀ),
ꢀ
ꢀ
ꢀ
5.86 (1H, d, J4,1 = 6.3 Hz, H-4), 1.81 (3H, d, Jallyl = 1.5 Hz, C2 -CH3a),
1.78 (3H, s, C2 -CH3b); ı13C (CDCl3) 170.23 (C-6), 152.54, 146.50,
ꢀ
138.87, 134.22, 133.16 (C-9), 130.71, 129.56, 127.34, 126.87,
125.60, 125.49 (C-7), 121.89, 119.58 (C-10), 118.65, 76.42 (C-4),
24.20 (2ꢀ-CH3a), 18.09 (2ꢀ-CH3b). Anal. Calcd. for C18H13ClO3S: C,
62.70; H, 3.80. Found: C, 62.58; H, 3.80; Mass (m/z, +Q1): 345/347
(M+, 100%).
4.3.3. Photolysis of 6-chloro-3-(2-methylallyloxy)-2-(thiophen-
3-yl)-4H-chromen-4-one,
3c
A 1.0 mM methanolic solution of 3c on photolysis for 50 min
furnished 4c, 4cꢀ and 4cꢀꢀ.

132
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4.3.5. Photolysis of 6-chloro-3-(3-phenylallyloxy)-2-(thiophen-3-
yl)-4H-chromen-4-one,
3e
A 1.0 mM methanolic solution of 3e on photolysis for 50 min
furnished three photoproducts 4e and 4eꢀ.
Compound 4e. (Data from mixture 1H NMR/IR of 2 and 4e) Yield
10%; ꢂmax (cm−1) 1638 (C O); ıH (CDCl3) 8.27 (1H, d, Jm = 2.4 Hz, H-
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7), 7.61 (1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-9), 7.43 (1H, d, Jo = 9.0 Hz,
ꢀ
H-10), 7.36–7.28 (5H, m, H-2ꢀꢀ-6ꢀꢀ), 6.84 (1H, d, J2 ,1 = 16.2 Hz, H-2 ),
ꢀ
ꢀ
6.64 (1H, brs, H-1), 6.31 (1H, dd, J1 ,2 = 16.2 Hz, J1 ,4 = 6.9 Hz, H-1ꢀ),
ꢀ
ꢀ
ꢀ
[8] D. Donati, S. Fusi, F. Ponticelli, Photochemical synthesis of
a 4,5-
4.51 (1H, dtd/dddd, J3a,4 = 10.8 Hz, J3a,3Hy = 5.0 Hz, J3a,3Hx = 4.8 Hz,
dihydrofuroazetidinone, a novel ␤-lactam system, Tetrahedron Lett. 44 (2003)
9247–9250.
ꢀ
J3a,1 = 2.2 Hz, H-3a), 4.37 (1H, dd, J4,3a = 10.8 Hz, J4,1 = 6.9 Hz, H-4),
4.16 (1H, ddd, Jgem = 16.5 Hz, J3Hx,3a = 4.8 Hz, J3Hx,1 = 2.4 Hz, Hx-3),
3.88 (1H, ddd, Jgem = 16.5 Hz, J3Hy,3a = 5.0 Hz, J3Hy,1 = 3.7 Hz, Hy-3).
Compound 4eꢀ Yield 45%, off white solid; mp 176–178 ◦C; ꢂmax
(cm−1) 1643 (C O); ıH (CDCl3) 8.15 (1H, d, Jm = 2.1 Hz, H-7), 7.61
(1H, dd, Jo = 9.0 Hz, Jm = 2.1 Hz, H-9), 7.51 (1H, d, Jo = 9.0 Hz, H-
10), 7.46 (2H, s, H-1,ꢀ H-3), 7.42-7.31 (5H, m, H-2ꢀꢀ-6ꢀꢀ), 6.71 (1H,
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a new synthesis of cepham analogues,
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(2010) 872–874.
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
d, J2 ,1 = 15.9 Hz, H-2 ), 6.51 (1H, dd, J1 ,2 = 15.9 Hz, J1 ,4 = 6.6 Hz,
H-1ꢀ), 6.23 (1H, d, J4,1 = 6.6 Hz, H-4); ␦13C (CDCl3) 170.06 (C-
ꢀ
6), 152.58, 146.72, 139.21, 135.36, 135.02, 134.20, 133.21 (C-9),
130.75, 128.66, 128.34, 127.19, 127.07, 126.99, 125.67, 125.47
(C-7), 124.83, 122.03, 119.58 (C-10), 75.76(C-4). Anal. Calcd. for
C
22H13ClO3S: C, 67.26; H, 3.34. Found: C, 67.68; H, 3.23; Mass (m/z,
+Q1): 393/395 (M+, 100%).
[14] R.C. Kamboj, U. Berar, S. Berar, M. Thakur, R. Arora, S.C. Gupta, Photochemistry of
3-alkoxychromones I—photocyclisation of 6-chloro-3-alkoxy-2-(furan-3-yl)-
4H-chromen-4-ones, Can. J. Chem. 87 (2009) 422–429.
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Chem. Soc. Perkin Trans. I (1999) 2391–2395.
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some 3-alkoxy-6-chloro-2-{(E)-1’-methyl-2’-phenylvinyl}chromones: A study
of type-II and triene bichromophoric system, J. Photochem. Photobiol. A: Chem.
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4.3.6. Photolysis of
6-chloro-3-propargyloxy-2-(thiophen-3-yl)-4H-chromen-4-one,
3f
A 1.0 mM methanolic solution of 3f on photolysis for 50 min
furnished 4f, 4fꢀ and 4fꢀꢀ. These photoproducts were separated from
the starting substrate by column chromatography.
Compound 4f. Yield 36%, light brown solid; mp 228–230 ◦C;
ꢂmax (cm−1) 1636 (C O), 2129 (C C); ıH (CDCl3) 8.25 (1H, d,
Jm = 2.4 Hz, H-7), 7.62 (1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-9), 7.43
(1H, d, Jo = 9.0 Hz, H-10), 6.66 (1H, brs, H-1), 4.75 (1H, dtd/dddd,
J3a,4 = 10.8 Hz, J3a,3Hy = 5.0 Hz, J3a,3Hx = 4.8 Hz, J3a,1 = 2.2 Hz, H-3a),
ꢀ
4.63 (1H, dd, J4,3a = 10.8 Hz, J4,2 = 1.8 Hz, H-4), 4.11 (1H, ddd,
Jgem = 16.5 Hz, J3Hx,3a = 4.8 Hz, J3Hx,1 = 2.4 Hz, Hx-3), 3.92 (1H, ddd,
Jgem = 16.5 Hz, J3Hy,3a = 5.0 Hz, J3Hy,1 = 3.7 Hz, Hy-3), 2.74 (1H, d,
J2 ,4 = 1.8 Hz, H-2ꢀ); ı13C (CDCl3) 170.15 (C-6), 152.95, 142.73,
ꢀ
137.70, 133.98 (C-9), 131.19, 130.70, 130.06 (C-1), 125.53 (C-7),
124.77, 119.48 (C-10), 90.82, 77.75 (C-2ꢀ), 72.72 (C-4), 54.27 (C-3a),
39.02 (C-3). Anal. Calcd. for C16H9ClO3S: C, 60.67; H, 2.86. Found:
C, 60.67; H, 2.89; Mass (m/z, +Q1): 317/319 (M+, 100%).
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Compound 4fꢀ. (Data from mixture 1H NMR/IR of 4fꢀ and 4fꢀꢀ)
Yield 8%; ꢂmax (cm−1) 1628 (C O), 2128 (C C); ıH (CDCl3) 8.27 (1H,
d, Jm = 2.4 Hz, H-7), 7.63 (1H, dd, Jo = 9.0 Hz, Jm = 2.4 Hz, H-9), 7.52
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ꢀ
(1H, d, Jo = 9.0 Hz, H-10), 7.47 (2H, s, H-1,3), 6.76 (1H, d, J4,2 = 2.4 Hz,
H-4), 2.48 (1H, d, J2 ,4 = 2.4 Hz, H-2ꢀ).
ꢀ
Compound 4fꢀꢀ. Yield 10%; ꢂmax (cm−1) 1643 (C O), 2130
(C C); ıH (CDCl3) 8.32 (1H, d, Jm = 2.4 Hz, H-7), 7.63 (1H, dd,
Jo = 9.0 Hz, Jm = 2.4 Hz, H-9), 7.52 (1H, d, Jo = 9.0 Hz, H-10), 7.48 (1H,
d, J2,1 = 5.1 Hz, H-2), 7.44 (1H, d, J1,2 = 5.1 Hz, H-1), 6.30 (1H, d,
J4,2 = 2.4 Hz, H-4), 2.75 (1H, d, J2 ,4 = 2.4 Hz, H-2ꢀ).
ꢀ
ꢀ
Acknowledgements
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