Photochemistry of 3-alkoxychromones: Photocyclisation of 2-Aryl-6-chloro-3-{(thiophen-2-yl)methoxy}chromones

Article abstract of DOI:10.1590/S0103-50532010000200012

1,4-Biradicals generated upon photo-irradiation of 2-aryl-3-{(thiophen-2- yl)methoxy} chromones produced angular tetracyclic products bearing the thienyl group. The dehydrogenation and ring contraction products were also observed depending upon the electr

Full text of DOI:10.1590/S0103-50532010000200012

J. Braz. Chem. Soc., Vol. 21, No. 2, 270-278, 2010.
Printed in Brazil - ©2010 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Photochemistry of 3-Alkoxychromones: Photocyclisation of
2-Aryl-6-chloro-3-{(thiophen-2-yl)methoxy}chromones
Ramesh C. Kamboj,*,a Urmila Berar,a Surinder Berar,a Zeba N. Siddiquib and Satish C. Guptaa
aDepartment of Chemistry, Kurukshetra University, Kurukshetra-136 119, India
bDepartment of Chemistry, Aligarh Muslim University, Aligarh, India
1,4-Biradicais gerados da fotoirradiação de cromonos 2-aril-3-[(tiofen-2-il)metóxi] produziram
compostos tetraciclicos angulares contendo grupos tienil. A dehidrogenação e contração do anel
dos produtos foram também observadas dependendo da densidade elétrica no anel 2-aril.
1,4-Biradicals generated upon photo-irradiation of 2-aryl-3-{(thiophen-2-yl)methoxy}
chromones produced angular tetracyclic products bearing the thienyl group. The dehydrogenation
and ring contraction products were also observed depending upon the electron density on the
2-aryl ring.
Keywords: alkoxychromone, type-II reaction, 1,4-biradical, ring contraction, angular
tetracyclic
Introduction
in this work we report the synthesis and the photolytic
behavior of the chromones 2(a-g).
Conjugated enones bearing the alkoxy and/or alkyl
group at C-3, on photoirradiation with UV light undergo
γ-hydrogen abstractions.1-4 The products obtained, depend
upon the nature of the substituents present in the substrates,
for example, 2-alkyl-3-arylcyclohex-2-enones5 and
3-alkoxy-2-phenyl-4-oxo-4H-1-benzopyran,6-8 afforded
the photocyclised angular products whereas 3-methoxy-
2-methylchromones9 have been found to furnish the
novel dimeric oxetanol. In 3-alkoxy-2-arylchromones,the
synthetic applications of these γ-hydrogen abstractions
include the formation of vinyl ethers,10 spiropyrans,11
pyranopyrones,12 pyranoalcohols,13 angular tetracyclics14
etc. In these phototransformations, the primary reaction
Results and Discussion
The 2-aryl-3-{(thiophen-2-yl)methoxy}chromones
2(a-g) were obtained by reacting 3-hydroxybenzopyrans16-17
1(a-g) with 2-(chloromethyl)thiophene18 using anhydrous
K2CO3/n-Bu4N+I- in anhydrous acetone as the solvent as
shown in Scheme 1.
The structures of the benzopyrans 2(a-g) were derived
1
from their spectral data (IR, H, 13C NMR, Experimental
section).
The photoirradiation of the methanolic solution of
2(a-d) with pyrex filtered UV light from a 125W Hg
vapour lamp under the nitrogen atmosphere (Scheme 2)
produced the photoproducts 3(a-d) and 4a, 4c. In spite of
our best efforts, the compound 4a could not be isolated in
the pure form and its structure was derived from the NMR
data of the reaction mixture enriched in 4a by the repeated
crystallization of 3a.
The other chromones 2e and 2f under the similar
photolytic conditions produced the photoproducts 3e,
4e and 3f, 3f’, 4f, 4f’ respectively in 10-35% yields
(Scheme 3).
*
is the n-π excitation of the C=O group that subsequently
abstracts hydrogen from the 3-alkoxy group leading to the
formation of the 1,4-biradical.5-8 The nature of the 3-alkoxy
group has been found to have a profound effect on the fate
of 1,4-biradical10,13 to form the mesomeric biradicals. To
examine the effect of (thiophen-2-yl)methoxy group at
3-position of the chromones with different 2-aryl groups
and also to study the possibility of photo-transposition15
reactions of the thiophene when tied to the chromones,
The photoirradiation of 2g, a regio-isomer of 2e,
in the methanolic solution (0.001mol L-1) with pyrex
*e-mail: rckamboj@rediffmail.com

Vol. 21, No. 2, 2010
Kamboj et al.
271
O
Ar
O
O
Ar
K2CO3/Dry acetone
Cl
Cl
OH
O
S
O
S
1 (a-g)
2 (a-g)
Cl
R1
R2
R3
O
Ar =
X
g
a, R1 = R2 = R3 = H;
e, X = S; f, X = O
b, R1 = R3 = H, R2 = CH3;
c, R1 = R3 = H, R2 = OCH3;
d, R1 = R2 = R3 = OCH3;
Scheme 1. Synthesis of 2-aryl-3-{(thiophen-2-yl)methoxy}chromones 2(a-g).
R1
H
R1
R2
R3
R2
R3
1
1
4
O
O
4
hν
H
2 (a-d)
5
+
5
CH3OH/pyrex
Cl
O
Cl
O
H
H
S
O
S
O
4 (a,c)
3 (a-d)
a, R1 = R2 = R3 = H;
c, R1 = R3 = H, R2 = OCH3
a, R1 = R2 = R3 = H;
b, R1 = R3 = H, R2 = CH3;
c, R1 = R3 = H, R2 = OCH3;
d, R1 = R2 = R3 = OCH3
Scheme 2. Photolysis of compounds 2(a-d).
X
X
H
H
10
7
D
D
O
O
O
11b
C
11b
3a
C3a
4 H
H
4
Cl
O
Cl
O
H
H
S
O
S
hν
2e, 2f
3e, X = S
3f, X = O
3f', X = O
CH3OH/pyrex
H
H
1
H
1
1
CHO
CHO
H
S
H
8
O
1a H
O
O
9b
1a
2
O
O
9b
2
C
O
C
C
O
4
Cl
Cl
Cl
O
5
H
S
H
H
S
O
S
4f'
4e, X = S
4f
Scheme 3. Photolysis of compounds 2e and 2f.
2
1
H
O
11b O
3a
O
O
hν/ MeOH
H
H
C
O
4
40 min
Cl
O
Cl
O
O
S
3'
S
5'
2g
3g
Scheme 4. Photolysis of compound 2g.

272
Photochemistry of 3-Alkoxychromones
J. Braz. Chem. Soc.
filtered UV light for 40 min gave 3g (50%, Scheme 4).
No secondary photoproducts corresponding to 4f and 4f’
were furnished.31
at C-4 to have a R configuration in the compounds 3e,
3f and 3g and a S configuration in the compound 3f’.
The absolute configuration at C-11b and C-3a is R and
S respectively in 3f, 3e, 3g and 3f’. The MM2 energy
minimized structures of the compounds 3f and 3f’ are
shown in Figure 1 and their J/Φ data has been given in
Table 1 which also confirms the above findings about the
stereochemistry of the photoproducts.
The structures of all the photoproducts were confirmed
1
by the comparison of their spectral parameters (IR, H,
13C NMR) with those of the starting substrates 2(a-g) and
also from their elemental analysis. The photoproducts
3(a-d) showed the IR absorption between 1630-1650 cm-1
for the pyrone C=O group. In their 1H NMR spectra, the
proton H-5 was found almost in the aromatic region of
spectrum between d 6.58-6.80 whereas in 4a and 4c it had
the upfield resonance at d ca. 5.00.
Table 1. Relationship between coupling constant and dihedral angle (Φ)
Compound
J11b,3a (Hz)
10.5
8.1
Φ11b,3a
4.01o
J3a,4 (Hz)
8.4
Φ3a,4
3f
27.76o
91.58o
30.63o
37.26o
Regarding the stereochemistry of photoproducts 3f,
3f’, 3e and 3g, the conformation of ring C is a half-chair.
The protons H-11b and H-3a are in the cis-disposition
(cis C/D ring junction) which has been derived from
the observation that the J3a,11b = 8.1-10.5 Hz which is
in accordance with J/Φ relationships19,20(karplus rule)
and the earlier studies.21 In compounds 3f, 3e and 3g,
the coupling constant J3a,4 ca. 8.4 Hz for H-3a and H-4
protons places them in a cis-orientation, which finds
support from the literature studies16 thus positioning the
4-thienyl group in Ψ-equatorial position on the half-chair
conformation of the ring C (Figure 1). Further, in the
photoproduct 3f’ (stereoisomer of 3f), the orientation of
H-3a and H-4 is trans (J3a,4 = 2.1 Hz) with thienyl group
in Ψ-axial conformation. This has made the stereocentre
3f’
3e
3g
29.70o
12.60o
11.60o
2.1
9.6
8.1
9.6
6.6
In the secondary photoproducts 4f and 4f’ obtained
from the photolysis of 2f, the cyclopropyl protons22 H-1a
and H-9b are cis (J = 9.0 Hz) placed to each other and the
H-1 is trans to both H-1a (J1,1a = 4.2/3.3 Hz) and H-9b (J1,9b
= 3.6/3.9 Hz); the –CHO group is exo to the pyran ring C.
In 4f, the H-2 has been observed as doublet (J2,1a = 2.4 Hz),
inferring that the plane containing H-1a and H-2 possesses
Φ
2,1a ca. 50o (Figure 2) whereas its isomeric compound 4f’
has been found to possess different stereochemistry at C-2
with Φ2,1a ca. 75o (J 1.2 Hz). The thienyl group at C-2 is
Figure 1. MM2 energy minimized structure of compounds 3f and 3f’.
Figure 2. MM2 energy minimized structure of compounds 4f and 4f’.

Vol. 21, No. 2, 2010
Kamboj et al.
273
below the plane in 4f and above the plane in 4f’(Figure 2).
The difference in chemical shift of H-1 (0.4 ppm) in 4f and
4f’is because of the proximity to the pyran oxygen (ring C).
The distance between H-1 and one of the sp3 orbital of pyran
oxygen is 2.25 Ao in 4f whereas in 4f’ it is 2.35Ao leading
to extra deshielding in the former. A similar explanation
can be given to explain the observed downfield shift in d
value of H-1 (ca. 0.65 ppm) as compared to that reported
in literature23 for cyclopropane carboxaldehyde (d 2.60)
fused to the cyclohexane ring.
The carbon skeleton of photoproducts 3b, 4c, 3c, 3d,
3e, 4e and 3g was further confirmed from their fully proton
decoupled 13C NMR spectra (Experimental section).
Regarding the effect of substituent at 2-position of the
chromones 2(a-g) on the product formation/distribution,
it has been observed that in the case of furyl chromones
2f and 2g only the cyclised products are obtained. From
the others substrates 2a-2e (phenyl, thiophene), the
photodehydrogenated cyclised products along with the
cyclised products are also formed. For such difference,
the assignable reason could be the different degree
of aromaticity of the C-2 ring moiety. The aromatic
character increases from furan via thiophene to benzene.
So, the gain in energy by dehydrogenation is higher in
3a-3d leading to the predominant formation of these
aromatized photoproducts. The dehydrogenation re-
establishes aromaticity. Since the aromatic character is less
expressed in the case of thiophene, the dehydrogenation
is less dominant here (4e). Obviously, the low aromatic
character of furan is insufficient to favour formation of
dehydrogenation products and hence only the cyclised
products are furnished.
A possible mechanism involving the 1,4-biradical
intermediate (Scheme 5) formed by the γ-hydrogen
abstraction from –OCH2– by the photo-excited C=O
akin to some earlier reports6-8 may be envisioned for
these phototransformations. The 1,4-biradical expectedly
undergoes bond formation between the –CH– and the
carbon atom of aryl ring at C-2 followed by product
formation 3f, 3f’, 3e, 3g and 4a, 4c through 1,5- and
1,7-H-shifts respectively. The dehydrogenated products
3a-3d and 4e are formed directly by the expulsion of H2
during the cyclisation and not by the dehydrogenation of
their respective dihydroderivatives6,8 as confirmed by the
photolysis of pure isolated dihydrocompounds when no
aromatization could be detected; only polymeric products
7
R
O
Ar
R
O
O
Ar = Phenyl
H
H
O
O
Th
O
Th
H
1 O
OH
S
H
5
O1
H
H
Ar = heteroaryl
1,7-H shift
-H2
X
O
H
X = S
4a,4c
4e
3a-3d
-H2
Th
O
H
O1
H
X
O
O
5
H
O
H
O
O
O
X = S, O
hν
X = O
H
H
1,5-H shift
Th
O
H
O
Th
O
O
Th
O1
H
H
O
H
3e, 3f, 3f'
6
H
O
4f, 4f'
H
O
Th
H
O
7
Scheme 5. Mechanism of photoproduct formation.

274
Photochemistry of 3-Alkoxychromones
J. Braz. Chem. Soc.
O
O
5
O
H
O
O
O
O
hν
O
O
Th
O
H
S
S
O1
OH
H
2g
5
1,5-H shift
H
H
O
O
H
O
O
O
O
O
Th
O
Th
H
H
3g
9
Scheme 6. Mechanism of photoproduct 3g formation
were formed. In the chromone 2f, when the 2-aryl group
is the furyl moiety, in addition to the dihydro products
3f and 3f’, the other photoproducts 4f and 4f’ were also
realized from the further photoisomerisation of 3f and 3f’
where the dihydrofuran ring D undergoes ring contraction
mechanism24-27 to provide the cyclopropylaldehyde moiety.
That the fused cyclopropylaldehyde 4f and 4f’are furnished
from 3f and 3f’ was confirmed by the observation that these
on further irradiation under identical conditions provided
4f and 4f’ along with some other minor products which
escaped isolation. In this ring contraction mechanism, the
biradical intermediate 6 is stabilized by the double bond
of the pyrone moiety making the C-O bond amenable to
cleavage. A similar ring contraction mechanism could not
be observed in photolysis of 2g which only yielded 3g
(Scheme 6).
Experimental
General
Melting points were determined in open capillaries and
are thus uncorrected. 1H NMR and 13C NMR spectra were
recorded on a 300 MHz (for 13C frequency = 75 MHz)
Bruker spectrophotometer using TMS as the internal
standard. IR spectra were recorded on a Buck Scientific
500 spectrophotometer using KBr pellets. Mass spectra
recorded are either EI or FAB+. 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 vapours were used as the visualizing agent.
The columns for purification were packed with silica gel
100-200 mesh in petroleum ether-benzene (9:2) and left
overnight before use. The elution was carried out with
increasing proportion of benzene in the petroleum ether-
benzene mixture. The compounds 3f, 3f’ and 4f, 4f’ were
separated by using silica gel of 200-400 mesh (ACROS
Organics) for column chromatography. All photochemical
reactions were conducted under a nitrogen (99.9%)
atmosphere. Any trace of oxygen and moisture from the
procured nitrogen was removed by passing through the
alkaline pyragallol solution and concentrated sulfuric acid
respectively.
Also, 3g on further photoirradiation did not furnish
any ring-contracted product similar to 4f. This is probably
due to the lack of stabilization of possible biradical31
9
(Scheme 6), which is not in conjugation with the double
bond of the pyrone ring.
In all these chromones 2(a-g), the often occurring
phototransposition15,28-30 reactions of alkyl/aryl thiophenes
were not observed though they bear alkyl thiophene or both
aryl and alkyl thiophene groups (2e).
Conclusions
Synthesis of benzopyrans 2(a-g)
Hydrogen abstraction from the 3-alkoxy group by the
excited C=O is the preferred reaction pathway for the
formation of photoproducts. The (thiophen-2-yl)methoxy
radical generated undergoes cyclisation only similar to
the allyl and benzyl radicals. No photo-transposition
reactions of the thiophene ring were observed in these
compounds.
6-Chloro-2-phenyl-3-{(thiophen-2-yl)methoxy}-4-oxo-
4H-1-benzopyran, 2a:The 3-hydroxychromone, 1a (2.72 g,
0.01 mol), 2-(chloromethyl)thiophene (1.32 g, 0.01 mol),
anhydrous K2CO3 (1.0 g) and tetra-n-butylammonium
iodide (100 mg) were refluxed in anhydrous acetone
(50 mL) for 3 h. Filtration, evaporation of the solvent and

Vol. 21, No. 2, 2010
Kamboj et al.
275
crystallization of the residue from methanol gave 2a (2.40
g, 65%), light brown solid; mp 86-89 oC; IR nmax/cm-1: 1645
(C=O); 1H NMR (CDCl3) d 8.26 (1H, d, Jm = 2.4 Hz, H-5),
8.00 (2H, m, H-2’, H-6’), 7.63 (1H, dd, Jm = 2.4 Hz, Jo =
8.7 Hz, H-7), 7.49 (4H, m, H-8, H-3’, H-4’, H-5’), 7.22
(1H, dd, J5’’,3’’= 1.2 Hz, J5’’,4’’=5.1 Hz, H-5″), 6.95 (1H, dd,
H-5), 7.55 (1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz, H-7), 7.42
(1H, d, Jo = 9.0 Hz, H-8), 7.15 (1H, dd, J5’’,4’’ = 5.1 Hz,
H-5”), 6.90 (1H, d, J3”,4” = 3.3 Hz, H-3”), 6.81 (1H, dd,
J4”,3” = 3.3 Hz, J4”,5” = 5.1 Hz, H-4”), 5.27 (2H, s, –CH2–),
3.86 (3H, s, C4’–OCH3), 3.77 (6H, s, C3’ & C5’–OCH3);
13C NMR (CDCl3) d 173.8 (C-4), 156.4 (C-8a), 153.5 (C-2),
152.9 (C-3′, C-5′), 140.6 (C-4′), 139.3 (C-2″), 138.6 (C-3),
133.7 (C-7), 130.8 (C-5), 128.3 (C-6), 127.0 (C-4″), 126.6
(C-5″), 125.5 (C-1′), 125.2 (C-3″), 125.0 (C-4a), 119.7
(C-8), 106.7 (C-2′, C-6′), 68.0 (–OCH2–), 61.0 (4′–OCH3),
56.3 (3′, 5′–OCH3);Anal. Calc. for C23H19ClO6S: C, 60.20;
H, 4.17. Found: C, 60.12; H, 4.18.
J3’’,4’’ = 3.6 Hz, H-3”), 6.87 (1H, dd, J4’’,3’’ = 3.6 Hz, J4’’,5”
=
13
5.1 Hz, H-4”), 5.38 (2H, s, –OCH2–); C NMR (CDCl3)
d 174.0 (C-4), 156.9 (C-8a), 153.6 (C-2), 139.1 (C-2″),
138.4 (C-3), 133.7 (C-7), 130.8 (C-5), 130.6 (C-1′), 128.9
(C-3′, C-5′), 128.5 (C-4′), 128.4 (C-6), 128.3 (C-2′, C-6′),
126.9 (C-4a), 126.5 (C-4″), 126.1 (C-3″), 125.1 (C-5′′),
119.8 (C-8), 67.6 (–OCH2–); Anal. Calc. for C20H13ClO3S:
C, 65.13; H, 3.55. Found: C, 65.02; H, 3.57.
6-Chloro-2-(2’-thienyl)-3-{(thiophen-2-yl)methoxy}-
The other ethers 2b-2g were synthesized by using the
above described procedure starting from the compounds
1b-1g (0.01 mol each) respectively.
4-oxo-4H-1-benzopyran, 2e: Yield 2.98 g (80%), pale
o
yellow solid; mp 122-124 C; IR nmax/cm-1: 1639 (C=O);
1H NMR (CDCl3) d 8.24 (1H, d, Jm = 2.4 Hz, H-5), 7.96
(1H, dd, J3’,5’ = 0.9 Hz, J3’,4’ = 3.6 Hz, H-3’), 7.65 (1H, dd,
J5’,3’= 0.9 Hz, J5’,4’=4.8 Hz, H-5’), 7.63 (1H, dd, Jm = 2.4 Hz,
Jo = 9.0 Hz, H-7), 7.47 (1H, d, Jo = 9.0 Hz, H-8), 7.29
(1H, dd, J3”,5” = 0.9 Hz, H-3”), 7.20 (1H, dd, J4’,3’ =3.9 Hz,
J4’,5’ = 4.8 Hz, H-4’), 7.17 (1H, d, H-5”), 6.95 (1H, dd,
J4”,3” = 3.3 Hz, J4”,5” = 5.1 Hz, H-4”), 5.64 (2H, s, –OCH2–);
13CNMR (CDCl3) d 174.1 (C-4), 153.0 (C-8a), 149.8 (C-2),
138.0 (C-4a), 133.5 (C-7), 132.5 (C-2′), 131.8 (C-2″), 130.1
(C-6), 129.9 (C-5′), 129.1 (C-4″), 127.9 (C-4′), 127.4
(C-3″), 126.6 (C-5″), 125.6 (C-3), 125.1 (C-5), 124.5 (C-3′),
119.5 (C-8), 67.0 (–OCH2–);Anal. Calc. for C18H11ClO3S2:
C, 57.67; H, 2.96. Found: C, 57.48; H, 2.92.
6-Chloro-2-(4’-methylphenyl)-3-{(thiophen-2-yl)
methoxy}-4-oxo-4H-1-benzo-pyran, 2b: Yield 2.30 g
o
(60%), light brown solid; mp 128-131 C; IR nmax/cm-1:
1641 (C=O); 1H NMR (CDCl3) d 8.24 (1H, d, Jm = 2.4 Hz,
H-5), 7.92 (2H, d, Jo = 8.4 Hz, H-2’, H-6’), 7.60 (1H, dd,
Jm = 2.4 Hz, Jo = 9.0 Hz, H-7), 7.47 (1H, d, Jo = 9.0 Hz,
H-8), 7.35 (2H, d, Jo = 8.4 Hz, H-3’, H-5’), 7.22 (1H, dd,
J5’’,4’’ = 4.8 Hz, H-5”), 6.97 (1H, dd, J3’’,4’’ = 3.0 Hz, H-3”),
6.87 (1H, m, H-4”), 5.36 (2H, s, –OCH2–), 2.44 (3H,
s, –CH3); 13C NMR (CDCl3) d 173.9 (C-4), 153.6 (C-8a),
141.4 (C-2), 138.6 (C-2”), 135.4 (C-4′), 133.8 (C-3), 133.6
(C-7), 130.7 (C-5), 129.4 (C-6), 129.1 (C-3′, C-5′), 128.8
(C-4″), 128.4 (C-5″), 127.7 (C-1′), 126.9 (C-3″), 126.5 (C-
2′, C-6′), 125.1 (C-4a), 119.7 (C-8), 67.5 (–OCH2–), 21.6
(4′–CH3); Anal. Calc. for C21H15ClO3S: C, 65.88; H, 3.95.
Found: C, 65.73; H, 3.90.
6-Chloro-2-(2’-furyl)-3-{(thiophen-2-yl)methoxy}-4-
oxo-4H-1-benzopyran, 2f:Yield 2.15 g (60%), pale yellow
solid; mp 114-115 oC; IR nmax/cm-1: 1640 (C=O); 1H NMR
(CDCl3) d 8.22 (1H, d, Jm = 2.4 Hz, H-5), 7.67 (1H, m,
H-5’), 7.61 (1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz, H-7), 7.50
6-Chloro-2-(4’-methoxyphenyl)-3-{(thiophen-2-yl)
(1H, d, Jo = 9.0 Hz, H-8), 7.36 (1H, dd, J3’,5’= 1.8 Hz, J3’,4’=
methoxy}-4-oxo-4H-1-benzopyran, 2c:Yield 2.57 g (65%),
3.3 Hz, H-3’), 7.28 (1H, dd, J5’’,3’’ = 1.8 Hz, J5’’,4’’ = 5.1 Hz,
H-5’’), 7.11 (1H, dd, J3”,5” = 1.8 Hz, J3’’,4’’ = 3.0 Hz, H-3”),
6.93 (1H, dd, J4”,3” = 3.0 Hz, J4”,5” = 5.1 Hz, H-4”), 6.60
(1H, dd, J4’,5’ = 1.8 Hz, J4’,3’ = 3.3 Hz, H-4’), 5.57 (2H, s,
–OCH2–); 13CNMR (CDCl3) d 172.2 (C-4), 154.2 (C-8a),
151.5 (C-2), 145.3 (C-5′), 144.2 (C-2’), 138.4 (C-4a), 137.1
(C-2”), 132.9 (C-7), 130.5 (C-6), 127.8 (C-4”), 127.0 (C-
3”), 126.3 (C-5’’), 125.2 (C-5), 124.9 (C-3), 119.7 (C-8),
110.1 (C-4’), 109.2 (C-3’), 67.2 (–OCH2–);Anal. Calc. for
C18H11ClO4S: C, 60.26; H, 3.09. Found: C, 60.11; H, 3.11.
o
light brown solid; mp 118-120 C; IR nmax/cm-1: 1639
(C=O); 1H NMR (CDCl3) d 8.24 (1H, d, Jm = 2.7 Hz, H-5),
8.02 (2H, d, Jo = 9.0 Hz, H-2’, H-6’), 7.60 (1H, dd, Jm = 2.7
Hz, Jo = 9.0 Hz, H-7), 7.46 (1H, d, Jo = 9.0 Hz, H-8), 7.35
(2H, d, Jo = 8.4 Hz, H-3’, H-5’), 7.22 (1H, dd, J5’’,4’’ = 5.1
Hz, H-5”), 6.97 (3H, m, H-3”, H-3’, H-5’), 6.88 (1H, dd,
J4”,3” = 3.6 Hz, J4”,5” = 5.1 Hz, H-4”), 5.36 (2H, s, –OCH2–),
3.89 (3H, s, –OCH3);Anal. Calc. for C21H15ClO4S: C, 63.24;
H, 3.79. Found: C, 63.13; H, 3.74.
6-Chloro-3-{(thiophen-2-yl)methoxy}-2-(3’,4’,5’-
trimethoxyphenyl)-4-oxo-4H-1-benzopyran, 2d:Yield 2.60
g (57%), pale yellow solid; mp 129-131 oC; IR nmax/cm-1:
1643 (C=O); 1H NMR (CDCl3) d 8.17 (1H, d, Jm = 2.4 Hz,
6-Chloro-2-(3’-furyl)-3-{(thiophen-2-yl)methoxy}-4-
oxo-4H-1-benzopyran, 2g:Yield 2.43 g (68%), light brown
solid; mp 126-128 oC; IR nmax/cm-1: 1646 (C=O); 1H NMR
(CDCl3) d 8.27 (1H, t, J2’,4’ = 0.6 Hz, H-2’), 8.24 (1H, d,

276
Photochemistry of 3-Alkoxychromones
J. Braz. Chem. Soc.
Jm = 2.4 Hz, H-5), 7.61 (1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz,
H-7), 7.52 (1H, t, J5’,2’ = 1.5 Hz, J5’,4’ = 1.8 Hz, H-5’), 7.45
(1H, d, Jo = 9.0 Hz, H-8), 7.29 (1H, dd, J5’’,3’’ = 1.2 Hz,
J5’’,4’’=5.1 Hz, H-5”), 7.12 (1H, d, J3”,4” = 3.3 Hz, H-3”), 6.96
(2H,m,H-4”,H-4’),5.58(2H,s,–OCH2–);13CNMR(CDCl3)
d 172.8 (C-4), 153.2 (C-8a), 152.0 (C-2), 145.7 (C-5′),
143.4 (C-2’), 138.5 (C-4a), 138.0 (C-2”), 133.4 (C-7), 130.7
(C-6), 128.6 (C-4”), 127.0 (C-3”), 126.8 (C-5”), 125.2 (C-
3), 125.1 (C-5), 119.5 (C-8), 117.7 (C-3’), 108.7 (C-4’),
67.2 (–OCH2–); Anal. Calc. for C18H11ClO4S: C, 60.26; H,
3.09. Found: C, 60.21; H, 3.05.
1635 (C=O); 1H NMR (CDCl3) d 8.23 (1H, d, Jm = 2.4 Hz,
H-8), 7.82 (1H, d, Jo = 7.8 Hz, H-1), 7.58 (1H, dd, Jm = 2.4
Hz, Jo = 9.0 Hz, H-10), 7.49 (1H, d, Jo = 9.0 Hz, H-11),
7.36 (2H, m, H-3’, H-5’), 7.08 (1H, dd, H-2), 6.88 (2H, m,
H-4’, H-4), 6.58 (1H, s, H-5), 2.45 (3H, s, –CH3); 13C NMR
(CDCl3) d 173.0 (C-7), 153.5 (C-11a), 151.0 (C-13), 149.8
(C-2′), 135.3 (C-3), 134.0 (C-6a), 133.0 (C-10), 130.0
(C-8), 127.9 (C-4), 127.3 (C-2), 126.9 (C-4′), 126.6 (C-11),
125.9 (C-9), 125.7 (C-3′), 125.2 (C-5′), 124.0 (C-4a), 122.3
(C-12b), 119.6 (C-11), 74.7 (C-5), 22.0 (3–CH3); m/z 380
(M+, 100%); Anal. Calc. for C21H13ClO3S: C, 66.23; H,
3.44. Found: C, 66.25; H, 3.36.
Photolysis of benzopyrans 2a-2g
Compound 3c: Yield 44 mg (22%), light brown solid;
General procedure: A deoxygenated solution of
chromone 2a (200 mg) in magnesium dried methanol
(150 mL) was refluxed for 5 min. The solution was degassed
with nitrogen for 1 h and then irradiated in a pyrex vessel
under nitrogen atmosphere for 40 min with a 125W Hg
vapour lamp. The removal of the solvent under reduced
pressure left a red gummy mass that was chromatographed
over a column of silica gel to yield 3a and 4a.
Other compounds 2b-2g (200 mg each) were also
photolysed by following the same procedure to yield the
respective products. In all these cases the yield of the
photoproducts ranges between 20-50%. The rest of the
material was a mixture of unidentifiable polymeric products
and starting chromone.
mp 140-142 oC; Rf 0.54 (5% ethyl acetate in benzene); IR
1
n
max/cm-1: 1637 (C=O); H NMR (CDCl3) d 8.25 (1H, d,
Jm = 2.4 Hz, H-8), 7.89 (1H, d, Jo = 8.4 Hz, H-1), 7.58 (1H,
dd, Jm = 2.4 Hz, Jo = 9.0 Hz, H-10), 7.49 (1H, d, Jo = 9.0
Hz, H-11), 7.37 (1H, s, H-5’), 7.09 (1H, dd, J2,4 = 2.1 Hz,
J2,1 = 8.4 Hz, H-2), 6.90 (2H, m, H-3’, H-4’), 6.79 (1H, d,
J4,2 = 2.4 Hz, H-4), 6.58 (1H, s, H-5), 3.97 (3H, s, –OCH3);
13C NMR (CDCl3) d 170.3 (C-7), 162.6 (C-3), 154.0
(C-11a), 152.0 (C-12a), 148.7 (C-2′), 135.8 (C-6a), 133.1
(C-10), 130.6 (C-8), 128.3 (C-9), 128.0 (C-7a), 127.3 (C-1),
126.9 (C-4″), 126.6 (C-3″), 125.4 (C-5″), 125.0 (C-4a),
124.3 (C-12b), 119.5 (C-11), 114.8 (C-2), 111.7 (C-4), 74.8
(C-5), 55.7 (3–OCH3); m/z 396 (M+, 100%);Anal. Calc. for
C21H13ClO4S: C, 63.56; H, 3.30. Found: C, 63.21; H, 3.34.
Compound 3a: Yield 52 mg (26%), off-white solid;
Compound 4c:Yield 59 mg (30%),white solid; mp 163-
166 oC; Rf 0.58 (5% ethyl acetate in benzene); IR nmax/cm-1:
1648 (C=O); 1H NMR (CDCl3) d 8.22 (1H, d, Jm = 2.7 Hz,
H-8), 7.56 (1H, dd, Jm = 2.7 Hz, Jo = 8.7 Hz, H-10), 7.39
(2H, m, H-11, H-5’), 7.14 (1H, d, H-3’), 7.02 (1H, m,
H-4’), 6.86 (1H, br s, H-1), 5.20 (2H, m, H-4, H-5), 3.67
(3H, s, –OCH3), 3.38 (1H, m, H-4a), 2.38 (1H, m, H-2a),
1.98 (1H, m, H-2b); 13CNMR (CDCl3) d 170.6 (C-7), 152.9
(C-11a), 144.6 (C-3), 139.4 (C-6a), 138.4 (C-2′), 133.9
(C-10), 133.0 (C-12b), 130.5 (C-8), 128.8 (C-12a), 127.9
(C-9), 127.1 (C-7a), 126.8 (C-4′), 125.5 (C-3′), 124.7 (C-
5′), 123.9 (C-1), 120.2 (C-4), 119.4 (C-11), 79.0 (C-5), 40.9
(4–OCH3), 40.8 (C-4a), 39.9 (C-2); m/z 398 (M+, 100%);
Anal. Calc. for C21H15ClO4S: C, 63.24; H, 3.79. Found: C,
63.19; H, 3.78.
mp 180-182 oC; Rf 0.68 (5% ethyl acetate in benzene); IR
n
1
max/cm-1: 1640 (C=O); H NMR (CDCl3) d 8.26 (1H, d,
Jm = 2.1 Hz, H-8), 7.97 (1H, m, H-1), 7.64 (1H, dd, Jm =
2.1 Hz, Jo = 9.0 Hz, H-10), 7.57 (2H, m, H-2, H-3), 7.52
(1H, d, Jo = 9.0 Hz, H-11), 7.42 (1H, m, H-4), 7.23 (1H, d,
J5’,4’ = 5.1 Hz, H-5’), 6.90 (2H, m, H-4’, H-3’), 6.65 (1H,
s, H-5); m/z 366 (M+, 100%);Anal. Calc. for C20H11ClO3S:
C, 65.49; H, 3.02. Found: C, 65.31; H, 2.99.
1
Compound 4a: Yield 20% (calculated from H NMR
spectrum of mixture); Rf 0.68 (5% ethyl acetate in benzene);
1H NMR (CDCl3) d 8.24 (1H, d, Jm = 2.4 Hz, H-8), 7.60
(1H, dd, Jm = 2.4 Hz, Jo = 8.7 Hz, H-10), 7.44 (1H, d, Jo =
8.7 Hz, H-11), 7.18 (1H, d, J5’,4’= 3.3 Hz, H-5’), 7.06 (1H,
d, J4’,3’ = 3.6 Hz, H-4’), 6.90 (1H, d, J3’,4’ = 3.6 Hz, H-3’),
6.80 (1H, br s, H-1), 5.88 (1H, m, H-3), 5.39 (1H, d, J =
9.9 Hz, H-4), 5.00 (1H, d, J5,4a = 11.1 Hz, H-5), 3.46 (1H,
m, H-4a), 3.03 (2H, m, H-2).
Compound 3d: Yield 40 mg (20%), light brown solid;
mp 200-203 oC; Rf 0.47 (5% ethyl acetate in benzene); IR
n
max/cm-1: 1636 (C=O);1H NMR (CDCl3) d 8.15 (1H, d, Jm =
2.1 Hz, H-8), 7.50 (1H, dd, Jm = 2.1 Hz, Jo = 9.0 Hz, H-10),
7.43 (1H, d, Jo = 9.0 Hz, H-11), 7.11 (2H, m, H-1, H-5’),
6.78 (3H, m, H-3’, H-4’, H-5), 3.95 (3H, s, C4–OCH3),
Compound 3b:Yield 60mg (30%), off-white solid; mp
207-209oC;Rf0.67(5%ethylacetateinbenzene);IRnmax/cm-1:

Vol. 21, No. 2, 2010
Kamboj et al.
277
3.88 (3H, s, C3–OCH3), 3.77 (3H, s, C2–OCH3); 13CNMR
(CDCl3) d 172.8 (C-7), 154.6 (C-11a), 152.9 (C-12a), 149.4
(C-2′), 145.0 (C-4), 142.8 (C-2), 136.2 (C-3), 134.4 (C-6a),
133.2 (C-10), 130.6 (C-8), 126.8 (C-9), 126.6 (C-4′),
126.4 (C-5′), 125.4 (C-3′), 125.3 (C-7a), 121.0 (C-12b),
119.5 (C-4a), 119.5 (C-11), 101.1 (C-1), 69.7 (C-50), 61.1
(4–OCH3), 61.1 (3–OCH3), 56.4 (2–OCH3); m/z 456 (M+,
100%); Anal. Calc. for C23H17ClO6S: C, 60.46; H, 3.75.
Found: C, 66.31; H, 3.74.
J3,3a = 2.7 Hz, H-3), 4.70 (1H, d, J11b,3a = 10.5 Hz, H-11b),
3.43 (1H, d{t}, J3a,3 = 2.1 Hz, J3a,4 = 8.4 Hz, J3a,11b = 10.5 Hz,
H-3a). m/z 358 (M+, 100%); Anal. Calc. for C18H11ClO4S:
C, 60.26; H, 3.09. Found: C, 60.10; H, 3.05.
Compound 3f′: Yield 34 mg (17%), pale yellow solid;
mp 165-170 oC; Rf 0.56 (5% ethyl acetate in benzene); IR
1
n
max/cm-1: 1652 (C=O); H NMR (CDCl3) d 8.23 (1H, d,
Jm = 2.4 Hz, H-7), 7.61 (1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz,
H-9), 7.48 (1H, d, Jo = 9.0 Hz, H-10), 7.36 (1H, dd, J5’,4’
=
Compound 3e:Yield 42 mg (21%),off-white solid; mp
179-182oC;Rf0.48(5%ethylacetateinbenzene);IRnmax/cm-1:
1655 (C=O); 1H NMR (CDCl3) d 8.16 (1H, d, Jm = 2.4 Hz,
H-7), 7.52 (1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz, H-9), 7.34 (1H,
5.1 Hz, H-5’), 7.17 (1H, d, J3’,4’ = 3.0 Hz, H-3’), 7.04 (1H,
dd, J4’,3’= 3.0 Hz, J4’,5’= 5.1 Hz, H-4’), 6.39 (1H, br s, H-2),
5.66 (1H, d, J11b,3a = 8.1 Hz, H-11b), 5.43 (1H, d, J4,3a = 2.1
Hz, H-4 ), 5.10 (1H, t, J3,3a = 2.1 Hz, J3,2 = 2.1 Hz, H-3),
4.11 (1H, d{t}, J3a,3 = 2.1 Hz, J3a,4 = 2.1 Hz, J3a,11b = 8.1 Hz,
H-3a). m/z 358 (M+, 100%); Anal. Calc. for C18H11ClO4S:
C, 60.26; H, 3.09. Found: C, 60.02; H, 3.02.
d, Jo = 9.0 Hz, H-10), 7.28 (1H, m, H-5’), 7.07 (1H, d, J3’,4’
3.3 Hz, H-3’), 6.94 (1H, dd, J4’,3’ = 3.3 Hz, J4’,5’ = 4.8 Hz,
H-4’), 6.33 (1H, d, J2,3 = 6.3 Hz, H-2), 5.30 (1H, dd, J3,3a
=
=
3.0 Hz, J3,2 = 6.3 Hz, H-3), 5.08 (1H, d, J4,3a = 9.6 Hz, H-4),
4.98 (1H, d, J11b,3a = 8.1 Hz, H-11b), 3.60 (1H, m, J3a,3 = 3.0
Hz, J3a,4 = 9.6 Hz, H-3a); 13CNMR (CDCl3) d 170.4 (C-6),
153.5 (C-10a), 148.6 (C-11a), 139.6 (C-2′), 138.6 (C-6a),
134.7 (C-9), 130.6 (C-8), 128.3 (C-2), 127.4 (C-4′), 126.8
(C-3′), 126.4 (C-4), 125.5 (C-7), 124.7 (C-5a), 121.6 (C-5′),
119.6 (C-10), 72.5 (C-4), 51.5 (C-3a), 46.2 (C-11b);
m/z 374 (M+, 100%), 320 (M+-54, 39%); Anal. Calc. for
C18H11ClO3S2: C, 57.67; H, 2.96. Found: C, 57.45; H, 2.94.
Compound 4f:Yield 40 mg (20%), brown solid; mp 190-
193 oC; Rf 0.41 (5% ethyl acetate in benzene); IR nmax/cm-1:
1707 (–CHO), 1660 (C=O); 1H NMR (CDCl3) d 9.79 (1H,
d, JCHO,1 = 2.4 Hz, –CHO), 8.23 (1H, d, Jm = 2.7 Hz, H-5),
7.59 (1H, dd, Jm = 2.7 Hz, Jo = 9.0 Hz, H-7), 7.43 (1H, d, Jo =
9.0 Hz, H-8), 7.39 (1H, dd, J5’,3’ = 2.1 Hz, J5’,4’ = 5.1 Hz,
H-5’), 7.22 (1H, dd, J3’,5’= 2.1 Hz, J3’,4’= 3.6 Hz, H-3’), 7.04
(1H, dd, J4’,3’ = 3.6 Hz, J4’,5’ = 5.1 Hz, H-4’), 5.27 (1H, d,
J2,1a = 2.4 Hz, H-2 ), 3.27 (1H, d{dd}, J1,CHO = 2.4 Hz, J1,9b
3.6 Hz, J1,1a = 4.2 Hz, H-1), 2.89 (1H, dd, J9b,1 = 3.6 Hz,
J9b,1a = 9.0 Hz, H-9b), 2.82 (1H, d{dd}, J1a,2 = 2.4 Hz, J1a,1
4.2 Hz, J1a,9b = 9.0 Hz, H-1a); m/z 358 (M+, 44%), 329
(M+-29, 100%); Anal. Calc. for C18H11ClO4S: C, 60.26; H,
3.09. Found: C, 60.30; H, 3.00.
=
Compound 4e: Yield 40 mg (20%), light brown solid;
mp 122-125 oC; Rf 0.34 (5% ethyl acetate in benzene); IR
n
=
1
max/cm-1: 1642 (C=O); H NMR (CDCl3) d 8.16 (1H, d,
Jm = 2.4 Hz, H-7), 7.56 (1H, d, J2,3 = 5.1 Hz, H-2), 7.50
(1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz, H-9), 7.39 (1H, d, Jo =
9.0 Hz, H-10), 7.28 (1H, m, H-5’), 7.22 (1H, dd, J3’,5’= 1.2
Hz, J3’,4’ = 5.1 Hz, H-3’), 6.91 (1H, d, J3,2 = 5.1 Hz, H-3),
6.86 (1H, dd, J4’,5’= 3.6 Hz, J4’,3’= 5.1 Hz, H-4’), 6.74 (1H,
s, H-4); 13C NMR (CDCl3) d 172.2 (C-6), 153.0 (C-10a),
147.9 (C-11a), 145.1 (C-3a), 139.4 (C-2′), 139.0 (C-6a),
134.9 (C-11b), 133.2 (C-9), 130.8 (C-8), 129.5 (C-2), 127.2
(C-4), 126.9 (C-3′), 126.8 (C-3), 125.7 (C-7), 125.5 (C-5a),
122.6 (C-5′), 119.4 (C-10), 74.0 (C-4); m/z 372 (M+, 100%);
Anal. Calc. for C18H11ClO3S2: C, 57.98; H, 2.43. Found:
C, 58.00; H, 2.40.
Compound 4f′: Yield 22mg (11%), light brown solid;
mp 168-170 oC; Rf 0.35 (5% ethyl acetate in benzene); IR
1
n
max/cm-1: 1705 (–CHO), 1657 (C=O); H NMR (CDCl3)
d 9.40 (1H, d, JCHO,1 = 5.7 Hz, –CHO), 8.23 (1H, d, Jm =
2.7 Hz, H-5), 7.59 (1H, dd, Jm = 2.7 Hz, Jo = 9.0 Hz, H-7),
7.43 (1H, d, Jo = 9.0 Hz, H-8), 7.39 (1H, dd, J5’,3’ = 2.1 Hz,
J5’,4’ = 5.1 Hz, H-5’), 7.22 (1H, dd, J3’,5’ = 2.1 Hz, J3’,4’ = 3.6
Hz, H-3’), 7.04 (1H, dd, J4’,3’= 3.6 Hz, J4’,5’= 5.1 Hz, H-4’),
5.46 (1H, d, J2,1a = 1.2 Hz, H-2), 2.87 (1H, d{dd}, J1,1a
3.3 Hz, J1,9b = 3.9 Hz, J1,CHO = 5.7 Hz, H-1), 2.75 (1H, dd,
J9b,1 = 3.9 Hz, J9b,1a = 9.0 Hz, H-9b), 2.53 (1H, d{dd}, J1a,2
=
Compound 3f: Yield 49 mg (25%), pale yellow solid;
=
mp 188-191 oC; Rf 0.60 (5% ethyl acetate in benzene); IR
1.2 Hz, J1a,1 = 3.3 Hz, J1a,9b = 9.0 Hz, H-1a); m/z 358 (M+,
38%), 329 (M+-29, 100%); Anal. Calc. for C18H11ClO4S:
C, 60.26; H, 3.09. Found: C, 60.08; H, 3.10.
1
n
max/cm-1: 1652 (C=O); H NMR (CDCl3) d 8.24 (1H, d,
Jm = 2.7 Hz, H-7), 7.63 (1H, dd, Jm = 2.7 Hz, Jo = 9.0 Hz,
H-9), 7.50 (1H, d, Jo = 9.0 Hz, H-10), 7.38 (1H, d, J5’,4’
=
5.1 Hz, H-5’), 7.17 (1H, d, J3’,4’ = 3.0 Hz, H-3’), 7.04 (1H,
dd, J4’,3’= 3.0 Hz, J4’,5’= 5.1 Hz, H-4’), 6.59 (1H, br s, H-2),
5.28 (1H, d, J4,3a = 8.4 Hz, H-4 ), 5.02 (1H, t, J3,2 = 2.7 Hz,
Compound 3g: Yield 100 mg (50%), off-white solid;
mp 142-144 oC; Rf 0.62 (5% ethyl acetate in benzene); IR
n
max/cm-1: 1645.0 (C=O); 1H NMR (CDCl3) d 8.23 (1H, d,

278
Photochemistry of 3-Alkoxychromones
J. Braz. Chem. Soc.
Jm = 2.4 Hz, H-7), 7.59 (1H, dd, Jm = 2.4 Hz, Jo = 9.0 Hz,
H-9), 7.42 (1H, d, Jo = 9.0 Hz, H-10), 7.33 (1H, d, J5’,4’
12. Gupta, S. C.; Yadav, N. S.; Dhawan, S. N.; Indian J. Chem.
1991, 30B, 790.
=
5.1 Hz, H-5’), 7.20 (1H, d, J3’,4’ = 3.0 Hz, H-3’), 7.02 (1H,
m, H-4’), 6.52 (1H, d, J2,1 = 2.4 Hz, H-2), 5.41 (1H, t, J1,2 =
2.4 Hz, J1,11b = 2.4 Hz, H-1), 5.30 (1H, d, J4,3a = 6.6 Hz, H-4),
5.20 (1H, dd, J3a,4 = 6.6 Hz, J3a,11b = 9.6 Hz, H-3a), 4.27
(1H, dd, J11b,3a = 9.6 Hz, H-11b); 13CNMR (CDCl3) d 170.4
(C-6), 153.6 (C-10a), 151.5 (C-11a), 147.7 (C-2), 138.9
(C-6a), 137.4 (C-2′), 133.5 (C-9), 130.6 (C-8), 126.9 (C-
4′), 126.9 (C-3′), 125.5 (C-7), 124.8 (C-5a), 124.3 (C-5′),
119.5 (C-10), 100.8 (C-1), 81.2 (C-4), 73.1 (C-3a), 41.4
(C-11b); m/z 358 (M+, 100%);Anal. Calc. for C18H11ClO4S:
C, 60.26; H, 3.09. Found: C, 60.35; H, 3.06.
13. Gupta, S. C.; Yusuf, M.; Sharma, S.; Saini, A.; Arora, S.;
Kamboj, R. C.; Tetrahedron 2004, 60, 8445.
14. Yadav, N. S.; Gupta, S. C.; Tetrahedron Lett. 1987, 28, 2049.
15. Kellogg, R. M.; Dik, J. K.; Van Driel, H.; Wynberg, Hans.;
J. Org. Chem. 1970, 35, 2737.
16. Gupta, S. C.; Saini, A.; Kumar, D.; Yadav, N. S.; Chand, K.;
Mor, S.; Dhawan, S. N.; J. Chem. Soc., Perkin Trans. 1 1995,
177.
17. Gupta, S. C.; Sharma, S.; Saini, A.; Dhawan, S. N.; J. Chem.
Soc., Perkin Trans. 1 1999, 2391.
18. Org. Synthesis - Collective vol. 3, 1955, pp. 197.
19. Pachler, K. G. R.; Underwood, W. G. E.; Tetrahedron 1967, 23,
1817; Karplus, M.; Grand, D. M.; Proc. Nat. Acad. Sci. USA
1969, 45, 1269.
Acknowledgment
Financial support from the Council of Scientific and
Industrial Research (CSIR), New Delhi for carrying out
this work is highly acknowledged.
20. Banks, S. W.; Steele, M. J.; Ward, D.; Dewick, P. M.; J. Chem.
Soc., Chem. Commun. 1982, 156.
21. Chavdarian, C. G.; Seeman J. I.; Wooten, J. B.; J. Org. Chem.
1983, 48, 492.
References
22. Dauben, W. G.; Wipke, W. T.; J. Org. Chem. 1967, 32, 2976.
23. Padwa, A.; Koehn, W.; J. Org. Chem. 1973, 38, 4007.
24. Tamelen, E. E.Van; Whitesides, T. H.; J. Am. Chem. Soc. 1971,
93, 6129.
1. Agosta, W. C.; Smith, A. B., III; J. Am. Chem. Soc. 1971, 93,
5513.
2. Smith, A. B.;Agosta, W. C.; J. Am. Chem. Soc. 1973, 95, 1961.
3. Cossy, J.; Pete, J. P.; Heterocycles 1984, 22, 97.
4. Arnould, J. C.; Enger, A.; Feigenbaum, A.; Pete, J. P.;
Tetrahedron 1979, 35, 2501.
25. Tamelen, E. E.Van; Whitesides, T. H.; J. Am. Chem. Soc. 1968,
90, 3894.
26. Francis, B.; Sherwood, A. G.; Can. J. Chem. 1970, 48, 25.
27. Scribe, P.; Nouet, C.; Wiemann, J.; Tetrahedron Lett. 1970, 11,
4375.
5. Feigenbaum,A.; Fort,Y.; Pete, J. P.; Scholler, D.; J. Org. Chem.
1986, 51, 4424.
28. Wynberg, Hans.; Van Driel, H.; Kellogg, R. M.; Buter, J.;
J. Am. Chem. Soc. 1967, 89, 3487.
6. Waiss, A. C.; Corse, J.; J. Am. Chem. Soc. 1965, 87, 2068.
7. Waiss, A. C.; Lundin, R.E.; Lee, A.; Corse, J.; J. Am. Chem.
Soc. 1967, 89, 6213.
29. Kellogg, R. M.; Wynberg, H.; Tetrahedron Lett. 1968, 9, 5895.
30. Wynberg, Hans.; Sinnige, H. J. M.; Creemers, H. M. J. C.;
J. Org. Chem. 1971, 36, 1011.
8. Matsuura, T.; Matsushima, H.; Tetrahedron 1968, 24, 6615.
9. Gupta, S. C.; Mukerjee, S. K.; Tetrahedron Lett. 1973, 14, 5073.
10. Gupta, S. C.; Yusuf, M.; Sharma, S.; Arora, S.; Tetrahedron
Lett. 2002, 43, 6875.
31. Kamboj, R. C.; Berar, U.; Berar, S.; Thakur, M.; Arora, R.;
Gupta, S. C.; Can. J. Chem. 2009, 87, 422.
11. Gupta, S. C.; Saini, A.; Sharma, S.; Kapoor, M.; Dhawan, S.
N.; Tetrahedron Lett. 1996, 37, 8913.
Received: March 29, 2009
Web Release Date: November 19, 2009