Phototransformations of some 3-alkoxy-2-styrylchromones: Type II cyclisations of 1,4- and 1,6-biradicals

Article abstract of DOI:10.1016/j.tet.2004.07.003

3-Alkoxy-2-styrylchromones on photo-irradiation with UV-light transform into oxetanopyrananones, pyranopyrones, pyranopyrananones and pyranoalcohols. The products formed have been found to depend upon the structure of alkoxy group (methyl, benzyl and ally

Full text of DOI:10.1016/j.tet.2004.07.003

Tetrahedron 60 (2004) 8445–8454
Phototransformations of some 3-alkoxy-2-styrylchromones:
type II cyclisations of 1,4- and 1,6-biradicals
*
Satish C. Gupta, Mohamad Yusuf, Somesh Sharma, Ashok Saini, Surinder Arora
and Ramesh C. Kamboj
Department of Chemistry, Kurukshetra University, Kurukshetra 136 119, India
Received 20 February 2004; revised 14 June 2004; accepted 1 July 2004
Available online 3 August 2004
Abstract—3-Alkoxy-2-styrylchromones on photo-irradiation with UV-light transform into oxetanopyrananones, pyranopyrones,
pyranopyrananones and pyranoalcohols. The products formed have been found to depend upon the structure of alkoxy group (methyl,
benzyl and allyls). Alkoxychromones containing a heterocyclic ring (thiophene, furan) in place of phenyl in the styryl group produced only
pyranoalcohols as the photoproducts. The photo-conversions have been rationalized through an initial H-abstraction by the C]O group
producing a 1,4-biradical. In allyloxy derivatives, cyclisations involve both 1,4- and 1,6-biradicals.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
between the aryl group at C-2 and the chromone moiety
affect the reaction pathway, we present herein the results of
detailed investigations on the various 3-alkoxy derivatives
of 2-styrylchromones. The possibilities are:
3-Alkoxy-2-aryl(furan, thiophene or phenyl)chromones1
and 2-alkoxy/alkyl-3-aryl-2-cyclohexenones2 on photo-
irradiation undergo cyclisations to angular cyclic products,
with the involvement of the alkoxy chain and the aryl group.
a-Alkoxy acyclic enones3 with aryl substituents at the
b-position have been found to photo-convert into cyclobutyl
products without the involvement of the aryl group. The
reason for this diversity between cyclic and acyclic
compounds has been attributed to steric and conformational
effects.3 In a related study on 2-methyl-3-methoxychro-
mones,4,5 photo-irradiations have led to the formation of
dimeric-oxetanols. Evidently, although the basic premise of
the substrates is the same, the products formed are quite
different and have been found to depend upon the
substituents at the b-position of the enone moiety 1.1 In
all these transformations, the primary reaction is the
excitation of the C]O group that subsequently abstracts
hydrogen from the a-substituents with the formation of 1,4-
biradical1,2 2 (Scheme 1).
(a) H-abstraction by C]O from O–CH2 leading to
products as reported earlier.6
(b) Styryl bond undergoes cis–trans isomerisation.
(c) The ethers, that can be considered as triene systems
(styryl group coupled to the 2,3-double bond of
chromone), undergo conrotatory photocyclisations to
phenanthrenes.7
The substrates in the present study may undergo all these
competing reactions or some may take preference over the
others.
2. Results
The 3-alkoxy-2-styrylchromones were synthesised as fol-
lows. 5-Chloro-2-hydroxyacetophenone on condensation
with cinnamaldehyde in the presence of NaOH/EtOH gave 3
Earlier in a preliminary study, we reported the synthesis of
some linear tricyclic pyranopyrones from the photolysis of
3-benzyloxy-2-styrylchromones.6 With a view to better
understanding how the interposing of a double bond
Keywords: 3-Alkoxy-2-styrylchromones; Type II cyclisations; 1,4- and 1,6-
biradicals.
* Corresponding author. Tel.: C91-1744-292203; fax: C91-1744-238277;
e-mail: scguptaku@rediffmail.com
Scheme 1.
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.07.003

8446
S. C. Gupta et al. / Tetrahedron 60 (2004) 8445–8454
Scheme 2.
which under Algar-Flynn-Oyamada (H2O2/KOH) con-
ditions8 was converted into 3-hydroxy-2-styrylchromone 4
that subsequently was alkylated to obtain ethers 5–9
(Scheme 2).
by MM2 also showed that 10 is 2 Kcal more stable than
10a.
The oxetane 11 (C]O, 1693 cmK1) exhibited H-3 at d
5.05(s) and H-20/H-200 at d 4.82 and 5.05 (JZ7.0 Hz). The
loss of 30 mass units (CH2O) from the molecular ion m/z
312, further confirmed the presence of an oxetane ring in
compound 11. The demethoxylated product 12 showed in its
1H NMR spectrum a signal at d 6.30, characteristic5 of the
C-3 proton in chromones. The identity of the photoproduct
12 was further confirmed by synthesising an authentic
sample of the compound through cyclisation of 3.
The 6-chloro-3-methoxy-2-styrylchromone 5 on photo-
irradiation with pyrex filtered UV light furnished three
products 10, 11 and 12 (Scheme 3).
That the photoproduct 10 is a cis isomer of 5 became
evident from Ja,bZ12.0 Hz (cf. 5, Ja,bZ16.0 Hz). The
chromone 10 could have two conformations 10 and 10a
(Scheme 3). Our preference for expression 10 over 10a
stems from the observation that H-8 in 10 appeared at d
6.75 as compared to H-8 in 5 that was located at d 7.40;
such upfield shifting could be the result of shielding of
H-8 by the phenyl of styryl group. An energy calculation9
The photoirradiation of 3-benzyloxy-2-styrylchromone 6
produced a linear tricyclic pyranopyrone 13 in 10% yield
(Scheme 4) and no other compound could be isolated
although TLC analysis of the photolysate showed some
polymeric products. The reaction, here followed the same
Scheme 3.

S. C. Gupta et al. / Tetrahedron 60 (2004) 8445–8454
8447
Scheme 4.
route as reported by us previously on a chromone similar to
6.6 The trans disposition of two benzylic protons in 13 was
confirmed by the observation of J2,3Z7.0 Hz.
Next in the study were included the allyloxy derivatives 7, 8
and 9. The photoirradiation of a methanolic solution of 7
with UV light (pyrex) furnished three tricyclic products, two
linear 14, 16 and one angular 15 (Scheme 5).
The structure of the linear tricyclic pyranopyrone 14 was
confirmed as it is similar to the photoproduct 13 obtained from
6; H-2 and H-3 are trans to each other, J2,3Z6.8 Hz. The
angular tricyclic alcohol 15 did not exhibit any C]O
absorption in its ir spectrum. The trans configuration of Ha
and Hb was confirmed from Ja,bZ16.0 Hz; a D2O shake
confirmed the presence of the OH (1H NMR spectra). The
salient spectral features of linear pyranopyrananone (C]O,
1700 cmK1) 16 are that Ha and Hb possess a cis configuration
with Ja,bZ12.0 Hz (cf. 7 and 15 Ja,bZ16.0 Hz) and out of the
three protons belonging to benzenoid ring A, H-9 appears at d
5.95 (cf. 7, H-8 d 7.40). This latter observation could be due to
a cis disposition of Ha and Hb so that the styryl group is
disposed to shield H-9 (Fig. 1), a situation similar to that
observed in 10.
Figure 1. Energy minimized structure of 16.
19 (trace amount) and 20, 21 (yield 10–11%), 22 (yield 5%),
respectively. It is rather intriguing to mention here that H-9
in 22 appeared at d 7.07 and the styryl protons exhibited
Ja,bZ16.0 Hz (cf. 16, JZ12.0 Hz H-9). For this diverse
behaviour of pyranopyranones 19 and 22, we are unable to
offer any explanation. From the photolysate of 8, the
photoproduct 19 could not be isolated due to its extremely
low yield although its formation could be seen from the 1H
NMR and ir spectra of the reaction mixture.
The other styryl chromones 8 and 9 behaved in a similar
manner and furnished the products 17–18 (yield 10–12%),
To seek further information on the photo-transformations
occurring in allyloxystyrylchromones, the investigations
Scheme 5.

8448
S. C. Gupta et al. / Tetrahedron 60 (2004) 8445–8454
Scheme 6.
were extended to include the substrates 27–30 that were
synthesised by following the sequence of reactions shown in
Scheme 6. The purpose here was to investigate how the
replacement of the phenyl ring by electron rich heterocyclic
five-membered rings, furan and thiophene, affect the course
of the reaction.
The 1,4-biradical 35 resulting from the photolysis of 5 may
cyclise to give oxetanol 39 (RZH) that subsequently may
cleave to furnish demethoxylated product 12. Alternatively,
the chromone 12 may be obtained through the extrusion of
HCHO from oxetane5,10 11 that is formed from ketonisation
of 38 (RZH).
From the photolysate of the chromones 27–30, the only
compounds that could be isolated were angular tricyclic
alcohols 31, 32 (yield 10%), 30, 34(yield w5%); inspiteof our
best efforts, no other products could be isolated (Scheme 7).
Our preference for the formation of 12 from 11 rests on the
following: (a) the oxetane 11 has been isolated and its
photolysis led to its conversion into 12, (b) envisaged
instability of 39 where oxetanol is part of the fused system
carrying an sp2-hybridized carbon; 38 is only an enolic form
of 11. The formation of oxetane 11 finds corroboration from
an earlier report where such intermediates have been
isolated in the photolytic demethoxylation of 3-methoxy-
2-cholesten-4-one.11 In a previous report on the photolysis
of 3-methoxy-2-methylchromones,5 such demethoxylation
has been rationalised through photoaddition of CH3OH to
the 2,3-double bond of pyrone, but no addition products
whatsoever were isolated. In all probability the photoreac-
tion there also might have occurred through the formation of
oxetane followed by cleavage. It may be added here that the
probability of the formation of products similar to 13 from
5, and 12 from 6 can not altogether be excluded; perhaps
these were formed in such small quantities that we were
unable to isolate them.
3. Discussion
The photo conversions described above may be explained
through an initial H-abstraction from the 3-alkoxy group by
the photo excited C]O of the pyrone moiety that then
results in the formation of a 1,4-biradical (Scheme 8).1,2 In
the photolysis of 5 and 6, the diversity in the product
formation may be rationalised on the basis of radical
stability. The photolysis of 6 (RZC6H5) produces the
benzyloxy radical 36 (RZC6H5) that consequently cyclises
to produce 37 (RZC6H5), which by 1,5-hydrogen shift
finally culminates in the formation of linear product 13.
Such a situation may not occur in the photolysis of 5
(RZH) where the alkoxy radical 35 (RZH) lacks the
inherent stability of the benzyloxy radical 36 (RZC6H5).
The photo conversions of allyloxychromones 7, 8 and 9
Scheme 7.

S. C. Gupta et al. / Tetrahedron 60 (2004) 8445–8454
8449
Scheme 8.
offer an interesting proposition where the reaction followed
a different course; here the photolysis produced two linear
tricyclic pyranes and one angular tricyclic alcohol
(Scheme 9). The reaction once again is envisaged to initiate
through the formation of 1,4-biradical 40 which could
undergo cyclisation to produce linear tricyclic pyrano-
pyrone products: 7/14 (RZR0ZH), 8/17 (RZH, R0Z
CH3) and 9/20 (RZR0]CH3); these are similar to 13 as
obtained from the photolysis of 6. Such similarity could
very well be rationalised on the basis of almost equal
stability12 of allyl and benzyl radicals. Regarding the
realisation of tricyclic alcohols (15, 18 and 21) and
pyranopyranones (16, 19 and 22) it is understandable that
these are formed (Scheme 9) by delocalisation in allyloxy
radical 40 (1,4-biradical)440a (1,6-biradical)440b (1,6-
biradical). Such behaviour of allyloxy radicals has not been
observed in the past in our laboratory during the photolytic
experiments on 3-allyloxy-2-arylchromones where instead
of styryl group an aryl (phenyl, furyl, thiophene) moiety is
present.13 Although in 2-arylchromones where the allyloxy
chain carries an electron-captive group (RZCOOCH3)14 at
the distal end, products are known to arise through
delocalisation of initially formed allyloxy radicals. But, in
these compounds no cyclisation similar to the one
experienced by allyloxychromones 7–9 was observed. In a
related study on 3-allyloxy-1,2-naphthaquinones,15 the
formation of a 1,6-biradical from the initially produced
1,4-biradical has been reported but no products similar to
alcohol (15, 18 and 21) as obtained in the present case were
reported. In some other studies pertaining to photocyclisa-
tions involving 1,n-biradicals where the substrates did
possess allylic moieties, no products involving isomerisa-
tions have been reported.16
product similar to 14 and 16 were available. It is possible
that some electronic factors may be operating that do not
allow the formation of such products; or it may be the steric
bulk of furan or thiophene rings as compared to phenyl ring
that pushes the allyloxy group towards the C]O for
instantaneous cyclisation leading to photoproducts 31–34.
The energy minimised structures9 of chromones 7 and 27
(Fig. 2) show that the distance between one of the hydrogens
belonging to –O–CH2– and O of C]O group in 27 is
˚
˚
2.887 A and in 7 is 2.987 A. This observation supports the
notion that the allyloxy group in 27 is being pushed closer to
the C]O facilitating the formation of angular products.
It is evident from the photo-products reported here that the
alkoxychromones 5–9 and 27–30 did not undergo any
conrotatory cyclisations; may be conrotatory ring closure of
the type dominant in the triene systems,7 here, is suppressed
due to the blockade of the point of cyclisation in preference
to more facile H-abstractions. Although a literature survey
reveals that photocyclisations do take place even in
those triene systems where the point of cyclisation
carries a substituent17 that is extruded during the reaction;
2-styrylchromones18 have also been reported to undergo
photocyclisations to angular tetracyclics.
4. Conclusions
From the above study it may be concluded that 3-alkoxy-2-
styrylchromones undergo reactions through H-abstractions
and no conrotatory ring closures were observed. The
initially generated allyloxy radicals in the photolysis of
3-allyloxchromones produce mesomeric biradicals en
route to products.
In the photocyclisation of chromones 27–30 carrying
5-membered heterocyclic rings (furan and thiophene), only
angular tricyclic alcohols 31–34 could be isolated and no

8450
S. C. Gupta et al. / Tetrahedron 60 (2004) 8445–8454
Scheme 9.
5. Experimental
The percent yields reported in the photochemical reactions
are calculated by excluding the recovered starting
substrates.
Melting points reported are uncorrected. IR spectra were
recorded on a Buck Scientific IR spectrophotometer using
KBr pellets and UV spectra were recorded on U-2000
spectrophotometer. 1H NMR spectra were recorded on a 300
or 90 MHz spectrometer using Me4Si as internal standard.
Mass spectra were recorded at 70 eV. TLC plates were
coated with silica gel G suspended in MeOH–CHCl3 silica
gel (60–120 mesh) was used for column chromatography.
5.1. Synthesis of chromones 5–9 and 27–30
5.1.1. 1-(5-Chloro-2-hydroxy-phenyl)-5-phenyl-penta-
2,4-dien-1-one, 3. A solution of 5-chloro-2-hydroxyaceto-
phenone (10.0 g, 59 mmol) and cinnamaldehyde (7.8 g,
58 mmol) in EtOH was mixed with powdered NaOH (3.0 g,
75 mmol) at 0 8C and the resulting dark red mixture was
stirred for 12 h and thereafter was poured on ice-HCl to
obtain 3 (15.35 g, 92%) as yellow solid, crystallised
from EtOH, mp 151–152 8C; [Found: C, 71.48; H, 4.79.
C17H13ClO2 requires C, 71.71; H, 4.60]; nmax (cmK1) 3400
(–OH), 1640 (C]O). 1H NMR (300 MHz, CDCl3): d 12.68
(s, 1H), 7.76 (d, JZ2.0 Hz, 1H), 7.60–6.80 (m, 11H).
5.1.2. 1-(5-Chloro-2-hydroxy-phenyl)-5-thiophen-2-yl-
penta-2,4-dien-1-one, 23. Prepared using a procedure
similar to above by taking 5-chloro-2-hydroxyacetophenone
(5.0 g, 29.5 mmol).
Yellow solid (6.40 g, 75%), mp 125–127 8C; [Found: C,
61.69; H, 3.68. C15H11ClO2S requires C, 61.96; H, 3.81];
nmax (cmK1) 3254 (OH), 1639 (C]O). 1H NMR (300 MHz,
CDCl3): d 12.80 (s, 1H), 7.79 (d, JZ2.4 Hz, 1H), 7.70 (d,
JZ14.6 Hz, 1H), 7.66 (d, JZ14.6 Hz, 1H), 7.41 (dd, JZ2.4,
8.9 Hz, 1H), 7.36 (d, JZ5.1 Hz, 1H), 7.20 (d, JZ3.4 Hz, 1H),
7.06 (dd, JZ3.7, 5.1 Hz, 1H), 6.97 (d, JZ8.9 Hz, 1H), 6.88
(d, JZ15.2 Hz, 1H), 6.83 (d, JZ15.2 Hz, 1H).
5.1.3. 1-(5-Chloro-2-hydroxy-phenyl)-5-furan-2-yl-
penta-2,4-dien-1-one, 24. Prepared using a procedure
similar to above by taking 5-chloro-2-hydroxyacetophenone
(5.0 g, 29.5 mmol).
Figure 2. Energy minimized structures of 7 and 27.

S. C. Gupta et al. / Tetrahedron 60 (2004) 8445–8454
8451
Yellow solid (7.25 g, 90%), mp 150–152 8C; [Found: C,
65.35; H, 4.29. C15H11ClO3 requires C, 65.58; H, 4.04];
nmax (cmK1) 3400 (OH), 1640 (C]O). 1H NMR (CDCl3): d
12.16 (s, 1H), 7.78 (d, JZ2.4 Hz, 1H), 7.70 (d, JZ11.0 Hz,
1H), 7.65 (d, JZ11.0 Hz, 1H), 7.50 (d, JZ1.8 Hz, 1H), 7.42
(dd, JZ2.4, 8.7 Hz, 1H), 7.11 (d, JZ14.6 Hz, 1H), 6.96 (d,
JZ8.7 Hz, 1H), 6.84 (d, JZ14.6 Hz, 1H), 6.57 (d, JZ
3.6 Hz, 1H), 6.49 (dd, JZ3.6, 1.8 Hz, 1H).
chloride, allyl chloride, methyl allyl chloride and dimethyl
allyl chloride by the procedure as used for compound 5.
5.1.8. 3-Benzyloxy-6-chloro-2-styryl-chromen-4-one, 6.
Pale yellow solid (3.12 g, 80%), mp 144–146 8C; [Found: C,
74.33; H, 4.71. C24H17ClO3 requires C, 74.13; H, 4.41];
lmax MeOH 351, 261 nm; nmax (cmK1) 1640 (C]O), 1615
(C]C). 1H NMR (300 MHz, CDCl3): d 8.15 (d, JZ2.0 Hz,
1H), 7.70–7.50 (m, 13H), 7.35 (d, JZ9.0 Hz, 1H), 5.26 (s,
2H); m/z 388 (MC, 100%).
5.1.4. 6-Chloro-3-hydroxy-2-styryl-chromen-4-one, 4. To
a solution of 3 (2.0 g, 1 mmol) in MeOH (30 mL) mixed
with powdered KOH (1.0 g, 25 mmol) 0 8C, was added
H2O2 (30%, 5 mL) dropwise. The solution after stirring for
5 h was poured on ice-HCl to give light yellow precipitates,
crystallised (CHCl3–EtOH) to yellow needles (6.30 g,
30%), mp 225–227 8C; [Found: C, 68.59; H, 3.54.
5.1.9. 3-Allyloxy-6-chloro-2-styryl-chromen-4-one, 7.
Pale yellow solid (2.72 g, 80%), mp 134 8C; [Found: C,
70.69; H, 4.76. C20H15ClO3 requires C, 70.90; H, 4.46];
lmax MeOH 352, 264 nm; nmax (cmK1) 1640 (C]O), 1615
(C]C). 1H NMR (300 MHz, CDCl3): d 8.10 (d, JZ2.0 Hz,
1H), 7.60–7.20 (m, 9H), 6.20–5.80 (m, 1H), 5.40–5.10 (m,
2H), 4.70 (d, JZ6.0 Hz, 2H); m/z 338 (MC, 100%).
C17H11ClO3 requires C, 68.35; H, 3.71]; nmax (cmK1
)
1
3400 (OH), 1638 (C]O). H NMR (300 MHz, CDCl3): d
12.25 (s, 1H, –OH), 8.10 (d, JZ2.0 Hz, 1H), 7.60–7.50 (dd,
JZ9.0, 2.0 Hz, 1H), 7.46–7.20 (m, 7H), 6.80 (d, JZ
17.0 Hz, 1H).
5.1.10. 3-(2-Methyl)-allyloxy-6-chloro-2-styryl-chromen-
4-one, 8. Pale yellow solid (2.66 g, 75%), mp 110 8C;
[Found: C, 71.89; H, 4.46. C21H17ClO3 requires C, 71.49; H,
4.86]; lmax MeOH 351, 264 nm; nmax (cmK1) 1640 (C]O),
5.1.5. 6-Chloro-3-hydroxy-2-(2-thiophen-2-yl-vinyl)-
chromen-4-one, 25. Prepared using a procedure similar to
above.
1
1615 (C]C). H NMR (300 MHz, CDCl3): d 8.15 (d, JZ
2.0 Hz, 1H), 7.70–7.30 (m, 9H), 5.10–4.95 (m, 2H), 4.65 (s,
2H),1.90 (s, 3H); m/z 352 (MC, 100%).
Yellow needles (1.05 g, 50%), mp 238–240 8C; [Found: C,
59.38; H, 3.22. C15H9ClO3S requires C, 59.12; H, 2.98];
nmax (cmK1) 3271 (OH), 1632 (C]O). 1H NMR (300 MHz,
CDCl3): d 12.10 (s, 1H), 8.18 (d, JZ2.5 Hz, 1H), 7.58 (dd,
JZ8.9, 2.5 Hz, 1H), 7.60 (d, JZ15.9 Hz, 1H), 7.50 (d, JZ
8.9 Hz, 1H), 7.37 (d, JZ5.1 Hz, 1H), 7.28 (d, JZ3.6 Hz,
1H), 7.11 (d, JZ15.9 Hz, 1H), 7.07 (dd, JZ3.6, 5.1 Hz,
1H).
5.1.11. 3-(3-Methyl)-allyloxy-6-chloro-2-styryl-chromen-
4-one, 9. Pale yellow solid (2.87 g, 78%), mp 116–117 8C;
[Found: C, 72.25; H, 5.54. C22H19ClO3 requires C, 72.03; H,
5.22]; lmax MeOH 351, 264 nm; nmax (cmK1) 1640 (C]O),
1
1615 (C]C). H NMR (300 MHz, CDCl3): d 8.10 (d, JZ
2.0 Hz, 1H), 7.65 (dd, J0Z9.0 Hz, 1H), 7.60–7.40 (m, 8H),
5.50 (m, 1H), 4.70 (d, JZ7.0 Hz, 2H), 1.80 (s, 6H); m/z 366
(MC, 100%).
5.1.6. 6-Chloro-3-hydroxy-2-(2-furan-2-yl-vinyl)-chro-
men-4-one, 26. Prepared using a procedure similar to
above.
5.1.12. 3-Allyloxy-6-chloro-2-(2-thiophen-2-yl-vinyl)-
chromen-4-one, 27. Pale yellow solid (2.71 g, 80%), mp
123–125 8C; [Found: C, 62.97; H, 3.58. C18H13ClO3S
requires C, 62.70; H, 3.80]; lmax THF 390, 374, 271 nm;
nmax (cmK1) 1640 (C]O), 1615 (C]C). 1H NMR
(300 MHz, CDCl3): 8.18 (d, JZ2.7 Hz, 1H), 7.65 (d, JZ
15.8 Hz, 1H), 7.60 (dd, JZ2.7, 8.9 Hz, 1H), 7.46 (d, JZ
8.9 Hz, 1H), 7.38 (d, JZ5.1 Hz, 1H), 7.29 (d, JZ3.6 Hz,
1H), 7.15 (d, JZ15.9 Hz, 1H), 7.09 (dd, JZ3.6, 5.1 Hz,
1H), 6.08 (t{dd} JZ6.0, 10.2, 16.5 Hz, 1H), 5.38 (t{dd} JZ
1.4, 2.7, 16.5 Hz, 1H), 5.28 (dd JZ1.0, 10.2 Hz, 1H), 4.75
(dd, JZ1.2, 6.0 Hz, 2H).
Yellow needles (0.42 g, 20%), mp 225–228 8C; [Found: C,
62.19; H, 2.92. C15H9ClO4 requires C, 62.41; H, 3.14]; nmax
(cmK1) 3400 (OH), 1641 (C]O). 1H NMR (300 MHz,
CDCl3): d 11.99 (s, 1H), 8.14 (d, JZ2.7 Hz, 1H), 7.58 (dd,
JZ8.7, 2.7 Hz, 1H), 7.52 (d, JZ1.5 Hz, 1H), 7.44 (d, JZ
8.7 Hz, 1H), 7.35 (d, JZ16.0 Hz, 1H), 7.28 (d, JZ16.0 Hz,
1H), 6.64 (d, JZ3.4 Hz, 1H), 6.50 (dd, JZ1.5, 3.4 Hz, 1H).
5.1.7. 6-Chloro-3-methoxy-2-styryl-chromen-4-one, 5. A
suspension of 4 (3.0 g, 10 mmol), CH3I (2.1 g, 15 mmol),
Bu4NCIK (2.0 g), freshly fused K2CO3 (2.0 g in dry acetone
(25 mL) was refluxed for 1 h with continuous stirring. The
colour of the solution changed from dark red to yellow. The
reaction mixture was poured in HCl–H2O. Subsequent
filtration and evaporation of the solvent provided ether 5
(2.45 g, 78%) as pale yellow solid that was purified by
percolating through a column of silica gel with pet. ether as
eluent, mp 168 8C; [Found: C, 69.15; H, 4.29. C18H13ClO3
requires C, 69.13; H, 4.19]; lmax MeOH 351, 262 nm; nmax
5.1.13. 3-(2-Methyl)-allyloxy-6-chloro-2-(2-thiophen-2-
yl-vinyl)-chromen-4-one, 28. Pale yellow solid (2.54 g,
72%), mp 121–123 8C; [Found: C, 63.79; H, 3.91.
C19H15ClO3S requires C, 63.59; H, 4.21]; lmaxTHF 393,
1
376, 269 nm; nmax(cmK1) 1643 (C]O), 1620 (C]C). H
NMR (300 MHz, CDCl3): 8.18 (d, JZ2.4 Hz, 1H), 7.66 (d,
JZ16.0 Hz, 1H), 7.60 (dd, JZ2.4, 9.0 Hz, 1H), 7.47 (d, JZ
9.0 Hz, 1H), 7.38 (d, JZ5.0 Hz, 1H), 7.29 (d, JZ3.6 Hz, 1H),
7.19 (d, JZ16.0 Hz, 1H), 7.09 (dd, JZ3.6, 5.0 Hz, 1H), 5.11
(s, 1H), 5.02 (d, JZ1.1 Hz, 1H), 4.66 (s, 2H), 1.94 (s, 3H).
1
(cmK1) 1640 (C]O), 1615 (C]C). H NMR (300 MHz,
CDCl3): d 8.15 (d, JZ2.0 Hz, 1H), 7.55 (dd, JZ9.0, 2.0 Hz,
1H), 7.50–7.20 (m, 8H), 4.00 (s, 3H); m/z 312 (MC, 100%).
5.1.14. 3-Allyloxy-6-chloro-2-(2-furan-2-yl-vinyl)-chromen-
4-one, 29. Pale yellow solid (2.22 g, 65%), mp 125–127 8C;
[Found: C, 65.36; H, 3.49. C18H13ClO4 requires C, 65.76; H,
The chromones 6–9, 27–30 were synthesised using benzyl

8452
S. C. Gupta et al. / Tetrahedron 60 (2004) 8445–8454
3.99]; lmax MeOH 343, 275 nm; nmax (cmK1) 1641 (C]O),
1624 (C]C). H NMR (300 MHz, CDCl3): d 8.15 (d, JZ
JZ7.0 Hz, 1H), 3.35 (m, 1H), 3.15 (d, JZ8.0 Hz, 2H); m/z
1
388 (MC 18%).
2.4 Hz 1H), 7.58 (dd, JZ9.0, 2.4 Hz, 1H), 7.52 (d, JZ
1.2 Hz, 1H), 7.3 (d, JZ9.0 Hz, 1H), 7.30 (d, JZ15.9 Hz
1H), 7.23 (d, JZ15.9 Hz, 1H), 6.63 (d, JZ3.3 Hz, 1H), 6.50
(dd, JZ1.8, 3.3 Hz, 1H), 6.11 (m, 1H), 5.38 (br d, JZ
18.0 Hz, 1H), 5.26 (br d, JZ10.2 Hz, 1H), 4.76 (br d, JZ
6.3 Hz, 2H).
5.2.3. Photoirradiation of 3-allyloxy-6-chloro-2-styryl-
chromen-4-one, 7. A methanolic solution of 7 (1.0 g) on
photolysis for 1 h furnished 14, 15 and 16.
Compound 14. White solid (105 mg, 15%), mp 118–120 8C;
[Found: C, 70.48; H, 4.18. C20H15ClO3 requires C, 70.90; H,
4.46]; nmax (cmK1) 1642 (C]O). 1H NMR (300 MHz,
CDCl3): d 8.19 (d, JZ2.6 Hz, 1H), 7.49 (dd, JZ2.6, 9.0 Hz,
1H), 7.33–7.17 (m, 6H), 5.76–5.57 (m, 1H), 5.24 (d, JZ
17.2 Hz, 1H), 5.08 (d, JZ10.6 Hz, 1H), 4.53 (t, JZ6.8,
7.2 Hz, 1H), 3.26–3.11 (m, 1H), 3.09–2.99 (m, 2H); m/z 338
(MC, 100%).
5.1.15. 3-(2-Methyl)-allyloxy-6-chloro-2-(2-furan-2-yl-
vinyl)-chromen-4-one, 30. Pale yellow solid (2.31 g,
65%), mp 125–126 8C; [Found: C, 66.29; H, 4.17.
C19H15ClO4 requires C, 66.58; H, 4.41]; lmax MeOH 342,
258 nm; nmax (cmK1) 1642 (C]O), 1626 (C]C). 1H NMR
(300 MHz, CDCl3): d 8.14 (d, JZ2.4 Hz, 1H), 7.56 (dd, JZ
8.8, 2.4 Hz, 1H), 7.48 (d, JZ1.6 Hz, 1H), 7.41 (d, JZ
8.8 Hz 1H), 7.26 (d, JZ15.6 Hz, 1H), 7.17 (d, JZ15.6 Hz,
1H), 6.63 (d, JZ3.6 Hz, 1H), 6.51 (dd, JZ1.6, 3.6 Hz, 1H),
5.09 (s, 1H), 4.97 (s, 1H), 4.63 (s, 2H), 1.90 (s, 3H).
Compound 15. Pale yellow solid (42 mg, 6%), mp 98–
100 8C; [Found: C, 70.57; H, 4.72. C20H15ClO3 requires C,
70.90; H, 4.46]; lmax MeOH 367, 294 nm; nmax (cmK1
)
1
1610 (C]C). H NMR (300 MHz, CDCl3): d 7.69 (d, JZ
2.0 Hz, 1H), 7.44 (dd, JZ2.0, 9.0 Hz, 1H), 7.20–7.10 (m,
6H), 6.95 (d, JZ9.0 Hz, 1H), 6.50 (d, JZ16.0 Hz, 1H), 6.45
(d{t}, JZ6.0{1.5}Hz, 1H), 5.10 (m, 1H), 3.90 (s, 1H), 3.10
(br d, JZ1.5 Hz, 2H); m/z338 (MC, 100%).
5.2. Photoirradiation of chromones 5–9 and 27–30
5.2.1. Photoirradiation of 6-chloro-3-methoxy-2-styryl-
chromen-4-one, 5. A deoxygenated solution of 5 (600 mg)
in dry MeOH (75 mL) was irradiated in a pyrex reactor
under N2 atmosphere for 90 min. The removal of solvent
under reduced pressure yielded a red gummy viscous mass
that was chromatographed over silica gel. The column was
eluted with increasing proportion of benzene in pet. ether–
benzene mixture yielding 10, 11 and 12.
Compound 16. White solid (28 mg, 4%), mp 118–120 8C;
[Found: C, 70.62; H, 4.18. C20H15ClO3 requires C, 70.90; H,
4.46]; lmax MeOH 339 nm; nmax (cmK1) 1700 (C]O), 1615
(C]C). 1H NMR (300 MHz, CDCl3): d 7.70 (d, JZ2.0 Hz,
1H), 7.30 (s, 5H), 7.05 (dd, JZ2.0, 9.0 Hz, 1H), 6.50 (d, JZ
12.0 Hz, 1H), 6.45 (d{t}, JZ6.0, 1.5 Hz, 1H), 5.95 (d, JZ
9.0 Hz, 1H), 5.70 (d, JZ12.0 Hz, 1H), 4.85 (m, 1H), 4.70 (s,
1H), 2.90 (m, 2H).
Compound 10. Pale yellow solid (63 mg, 14%), mp 152 8C.
[Found: C, 68.83; H, 4.48. C18H13ClO3 requires C, 69.13; H,
1
4.19]; nmax (cmK1) 1640 (C]O), 1620 (C]C). H NMR
(300 MHz, CDCl3): d 8.20 (d, JZ2.7 Hz, 1H), 7.43 (dd, JZ
2.7, 9.0 Hz, 1H), 7.35 (m, 5H), 6.73 (d, JZ9.0 Hz, 1H), 6.76
(d, JZ12.0 Hz, 1H), 7.04 (d, JZ12.0 Hz, 1H), 3.98 (s, 3H);
m/z 312 (MC, 100%).
5.2.4. Photoirradiation of 3-(2-methyl)-allyloxy-6-
chloro-2-styryl-chromen-4-one, 8. A methanolic solution
of 8 (1.0 g) on photolysis for 1 h furnished 17 and 18.
Compound 17. White solid (71 mg, 12%), mp 190–192 8C;
[Found: C, 71.01; H, 4.48. C21H17ClO3 requires C, 71.49; H,
4.86]; nmax (cmK1) 1642 (C]O). 1H NMR (300 MHz,
CDCl3): d 8.19 (d, JZ2.6 Hz, 1H), 7.48 (dd, JZ2.6, 9.0 Hz,
1H), 7.31–7.13 (m, 6H), 4.79 (d, JZ4.0 Hz, 2H), 4.47 (d,
JZ9.2 Hz, 1H), 3.33–3.12 (m, 1H), 3.01 (dd, JZ2.8,
8.2 Hz, 2H), 1.64 (s, 3H); m/z 352 (MC, 100%).
Compound 11. Creamy solid (32 mg, 7%), mp 112–114 8C;
[Found: C, 69.43; H, 4.48. C18H13ClO3 requires C, 69.13; H,
4.19]; lmax MeOH 338, 253 nm; nmax (cmK1) 1693 (C]O),
1
1618 (C]C). H NMR (300 MHz, CDCl3): d 7.85 (d, JZ
2.0 Hz, 1H), 7.65–7.20 (m, 8H), 6.87 (d, JZ16.0 Hz, 1H),
5.05 (s, 1H), 5.02 (d, JZ7.0 Hz, 1H), 4.82 (d, JZ7.0 Hz,
1H); m/z 312 (MC, 23%).
Compound 18. Pale yellow solid (73 mg, 12%), mp 88–
90 8C; [Found: C, 71.19; H, 5.24. C21H17ClO3 requires C,
Compound 12. Pale yellow solid (41 mg, 10%), mp 145–
146 8C; [Found: C, 72.62; H, 3.48. C17H11ClO2 requires C,
72.22; H, 3.92]; lmax MeOH 334 nm; nmax (cmK1) 1640
(C]O), 1615 (C]C). 1H NMR (300 MHz, CDCl3): d 815 (d,
JZ2.0 Hz, 1H), 7.74 (d, JZ15.0 Hz, 1H), 7.65 (m, 8H), 6.30 (s,
1H).
71.49; H, 4.86]; lmax MeOH 297, 265 nm; nmax (cmK1
)
1
1615 (C]C). H NMR (300 MHz, CDCl3): d 7.69 (d, JZ
2.0 Hz, 1H), 7.44 (dd, JZ2.0, 9.0 Hz, 1H), 7.20–7.10 (m,
6H), 6.95 (d, JZ9.0 Hz, 1H), 6.50 (d, JZ16.0 Hz, 1H), 6.35
(m, 1H), 3.90 (s, 1H), 3.10 (s, 2H), 1.72 (s, 3H); m/z 352
(MC, 100%).
5.2.2. Photoirradiation of 3-benzyloxy-6-chloro-2-styryl-
chromen-4-one, 6. A benzene solution of 6 (600 mg,
22 mmol) on photolysis for 3 h furnished 13.
5.2.5. Photoirradiation of 3-(3-methyl)-allyloxy-6-
chloro-2-styryl-chromen-4-one, 9. A methanolic solution
of 9 (1.0 g) on photolysis for 1 h furnished 20, 21and 22.
Compound 13. White solid (45 mg, 10%), mp 210–211 8C;
[Found: C, 74.43; H, 4.68. C24H17ClO3 requires C, 74.13; H,
4.41]; lmax MeOH 333, 287, 237 nm; nmax (cmK1) 1640
(C]O). 1H NMR (300 MHz, CDCl3): d 8.20 (d, JZ2.0 Hz,
1H), 7.65 (dd, JZ8.0, 2.0 Hz, 1H), 7.20 (m, 11H), 5.05 (d,
Compound 20. White solid (66 mg, 11%), mp 187–189 8C;
[Found: C, 71.73; H, 5.63. C22H19ClO3 requires C, 72.03; H,
5.22]; nmax (cmK1) 1640 (C]O). 1H NMR (300 MHz,
CDCl3): d 8.19 (d, JZ2.0 Hz, 1H), 7.64 (dd, JZ2.0, 9.0 Hz,

S. C. Gupta et al. / Tetrahedron 60 (2004) 8445–8454
8453
1H), 7.50–7.30 (m, 6H), 5.25 (d, 1H), 4.85–4.83 (m, 1H),
3.10–3.00 (m, 3H), 1.55 (s, 3H), 1.45 (s, 3H); m/z 366 (MC,
100%).
1H), 7.43 (dd, JZ2.7, 9.0 Hz, 1H), 7.43 (d, JZ1.2 Hz, 1H),
7.01 (d, JZ15.9 Hz, 1H), 6.98 (d, JZ9.0 Hz, 1H), 6.50
(d{t}, JZ6.0{1.5} Hz, 1H), 6.36 (dd, JZ1.8, 3.6 Hz, 1H),
6.32 (d, JZ15.9 Hz, 1H), 6.30 (d, JZ3.3 Hz, 1H), 5.14–
5.12 (m, 1H), 3.90 (br s, 1H), 3.07 (br s, 2H); m/z 328 (MC,
100%).
Compound 21. Pale yellow solid (60 mg, 10%), mp 80–
82 8C; [Found: C, 71.92; H, 5.03. C22H19ClO3 requires C,
72.03; H, 5.22]; lmax MeOH 295, 268 nm; nmax (cmK1
)
1
1612 (C]C). H NMR (300 MHz, CDCl3): d 7.61 (d, JZ
2.0 Hz, 1H), 7.29 (dd, JZ2.0, 9.0 Hz, 1H), 7.16 (m, 6H),
6.80 (d, JZ9.0 Hz, 1H), 6.50 (d, JZ16.0 Hz, 1H), 6.35 (d,
JZ6.0 Hz, 1H), 4.73 (d, JZ6.0 Hz, 1H), 3.85 (s, 1H), 1.45
(s, 3H), 1.32 (s, 3H); m/z 366 (MC, 100%).
5.2.9. Photoirradiation of 3-(2-methyl)-allyloxy-6-
chloro-2-(2-furan-2-yl-vinyl)-chromen-4-one, 30. A ben-
zene solution of 30 (1.0 g) on photolysis for 1 h furnished 34.
Compound 34. Pale yellow solid (30 mg, 5%), mp 118–
120 8C; [Found: C, 66.29; H, 4.19. C19H15ClO4 requires C,
66.58; H, 4.41]; lmax MeOH 307 nm; nmax (cmK1) 3428
(OH), 1629(C]C). 1H NMR (300 MHz, CDCl3): d 7.67 (d,
JZ2.7 Hz, 1H), 7.44 (dd, JZ2.7, 9.0 Hz, 1H), 7.35 (d, JZ
0.9 Hz, 1H), 7.05 (d, JZ15.9 Hz, 1H), 6.97 (d, JZ9.0 Hz,
1H), 6.38–6.37 (m, 2H), 6.37 (d, JZ15.9 Hz, 1H), 6.31 (d,
JZ3.0 Hz, 1H), 3.90 (s, 1H), 2.96 (br s, 2H), 1.72 (s, 3H);
m/z 342 (MC, 100%).
Compound 22. White solid (31 mg, 5%), mp 115–117 8C;
[Found: C, 71.73; H, 5.56. C22H19ClO3 requires C, 72.03; H,
5.22]; nmax (cmK1) 1698 (C]O). 1H NMR (300 MHz, CDCl3):
d 7.77 (d, JZ2.0 Hz, 1H), 7.46 (dd, JZ2.0, 9.0 Hz, 1H), 7.24–
7.20 (m, 5H), 7.07 (d, JZ8.7 1H), 6.48 (d, JZ16.2 Hz, 1H),
6.12 (d, JZ16.2 Hz, 1H), 6.42 (d, JZ6.0 Hz, 1H), 5.07 (s, 1H),
4.73 (d, JZ6.0 Hz, 1H), 1.42 (s, 3H), 1.27 (s, 3H).
5.2.6. Photoirradiation of 3-allyloxy-6-chloro-2-(2-thio-
phen-2-yl-vinyl)-chromen-4-one, 27. A benzene solution
of 27 (1.0 g) on photolysis for 1 h furnished 31
Acknowledgements
Financial assistance from DST and UGC for the accom-
plishment of this work is gratefully acknowledged. M.Y.
and S.S. thank CSIR and DAE for SRF.
Compound 31. Pale yellow solid (61 mg, 10%), mp 128–
30 8C; [Found: C, 62.27; H, 3.38. C18H13ClO3S requires C,
62.70; H, 3.80]; lmax THF (3) 407 nm (11700), 379 nm
(14300), 315 nm (21400), 229 nm (25500); nmax (cmK1
)
1
3630 (OH), 1633 (C]C). H NMR (300 MHz, CDCl3): d
11.68 (s, 1H), 7.70 (d, JZ2.4 Hz, 1H), 7.43 (dd, JZ2.4,
8.9 Hz, 1H), 7.17 (d, JZ4.8, 1.0 Hz, 1H), 7.01 (d, JZ1.0,
3.4 Hz, 1H), 6.98 (d, JZ8.9 Hz, 1H), 6.95 (dd, JZ4.8,
3.4 Hz, 1H), 6.93 (d, JZ15.8 Hz, 1H), 6.65 (d, JZ15.8 Hz,
1H), 6.51 (t{d}, JZ1.2, 5.4 Hz, 1H), 5.12 (t{d}, JZ3.0,
5.4 Hz, 1H), 3.11 (dd, JZ1.2, 3.0 Hz, 2H); m/z 344 (MC,
100%).
References
1. Waiss, A. C.; Lundin, R. E.; Lee, A.; Corse, J. J. Am. Chem.
Soc. 1967, 89, 6213. Matsuura, T.; Matsushima, T. Tetra-
hedron 1968, 24, 6615. Gupta, S. C.; Mukerjee, S. K. Ind.
J. Chem. 1973, 11, 1263. Gupta, S. C.; Yadav, N. S.; Dhawan,
S. N. J. Ind. Chem. Soc. 1990, 67, 770. 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. Gupta, S. C.; Saini,
A.; Sharma, S.; Kapoor, M.; Dhawan, S. N. Tetrahedron Lett.
1996, 37, 8913. Gupta, S. C.; Sharma, S.; Saini, A.; Dhawan,
S. N. J. Chem. Soc., Perkin Trans 1 1999, 2391.
2. Feigenbaum, A.; Fort, Y.; Pete, J. P.; Scholler, D. J. Org.
Chem. 1986, 51, 4424.
5.2.7. Photoirradiation of 3-(2-methyl)-allyloxy-6-
chloro-2-(2-thiophen-2-yl-vinyl)-chromen-4-one, 28. A
benzene solution of 28 (1.0 g) on photolysis for 1 h
furnished 32.
Compound 32. Pale yellow solid (55 mg, 10%), mp 118–
20 8C; [Found: C, 63.27; H, 4.47. C19H15ClO3S requires C,
63.59; H, 4.21]; lmax THF (3) 410 nm (11900), 380 nm
3. Cormier, R. A.; Schreiber, W. L.; Agosta, W. C. J. Chem. Soc.,
Chem. Commun. 1972, 729. Cormier, R. A.; Schreiber, W. L.;
Agosta, W. C. J. Am. Chem. Soc. 1973, 95, 4873. Cormier,
R. A.; Agosta, W. C. J. Am. Chem. Soc. 1974, 96, 618 see also
1867. Arnould, J. C.; Enger, A.; Feigenbaum, A.; Pete, J. P.
Tetrahedron 1979, 35, 2501.
(11400), 318 nm (28000), 228 nm (26900). nmax (cmK1
)
1
3610 (OH), 1630 (C]C). H NMR (300 MHz, CDCl3): d
11.71 (s, 1H), 7.68 (d, JZ2.6 Hz, 1H), 7.43 (dd, JZ2.6,
8.9 Hz, 1H), 7.17 (d, JZ4.9 Hz, 1H), 7.01 (d, JZ3.3 Hz,
1H), 6.99 (d, JZ15.9 Hz, 1H), 6.97 (d, JZ8.9 Hz, 1H), 6.95
(dd, JZ4.9, 3.3 Hz, 1H), 6.70 (d, JZ15.9 Hz, 1H), 6.39 (d,
JZ1.4 Hz, 1H), 2.99 (br s, 2H), 1.73 (s, 3H); m/z 358 (MC,
100%).
4. Gupta, S. C.; Mukerjee, S. K. Tetrahedron Lett. 1973, 14,
5073.
5. Mandal, P.; Nath, A.; Venkateswaran, R. V. Tetrahedron
1996, 52, 7855.
5.2.8. Photoirradiation of 3-allyloxy-6-chloro-2-(2-
furan-2-yl-vinyl)-chromen-4-one, 29. A benzene solution
of 29 (1.0 g) on photolysis for 1 h furnished 33.
6. Gupta, S. C.; Yadav, N. S. Tetrahedron Lett. 1987, 28, 2039.
Gupta, S. C.; Yadav, N. S.; Dhawan, S. N. Ind. J. Chem. 1991,
33B, 790.
7. Mazzucato, U. Pure Appl. Chem. 1982, 54, 1705; Laarhoven,
W.H. Rec. J. R. Neth. Chem. Soc. 1983, 185 and 241; Mallory,
F. B.; Mallory, C. W. Organic Reactions 1984, 30, 1; John
Wiley and Sons: New York.
Compound 33. Pale yellow solid (24 mg, 4%), mp 130 8C;
[Found: C, 65.38; H, 3.59. C18H13ClO4 requires C, 65.76; H,
3.99]; lmax MeOH 310 nm; nmax (cmK1) 3434 (OH), 1628
(C]C). 1H NMR (300 MHz, CDCl3): d 7.69 (d, JZ2.7 Hz,
8. Oyamada, T. J. Chem. Soc. Jpn. 1934, 55, 1256. Algar, J.;

8454
S. C. Gupta et al. / Tetrahedron 60 (2004) 8445–8454
Flynn, J. P. Proc. R. Irish Acad. 1934, 42B, 1. Dean, F. M.;
Podimuang, V. J. Chem. Soc. 1965, 3978.
15. Ellis, J. V.; Jones, J. E. J. Org. Chem. 1975, 40, 485.
16. Carless, H. A. J.; Mwesigye-Kibende, S. J. Chem. Soc. Chem.
Commun. 1987, 1673. Kraus, G. A.; Zhang, W.; Wu, Y.
J. Chem. Soc. Chem. Commun. 1996, 2439.
9. Chem office 6.0 Chem 3D Pro 6.0 Ink.
10. Collins, P. M.; Gupta, P. J. Chem. Soc. Chem. Commun. 1969,
90.
17. Gilbert, A. Synthetic Organic Chemistry; Plenum Press: New
York, 1984, Coyle, J. D. Photochemistry in Organic Synthesis,
The Chemical Royal Society: London, Special Publication No.
57, 1986; Tominango, Y.; Castle, R. N. J. Heterocyclic
Chemistry 1996 33, 523.
11. Enger, A.; Feigenbaum, A.; Pete, J. P.; Wolfhugel, J. L.
Tetrahedron 1978, 34, 1509.
12. Leroy, C.; Peeters, D.; Wilante, C. THEOCHEM 1982, 5, 217.
13. Sharma, S., PhD Thesis. Kurukshetra University, Kurukshetra,
Hryana, 1999.
18. Kumar, K. A.; Srimannarayana, G. Ind. J. Chem. 1980, 19B,
615. Maliah, B. V.; Krupadanam, G. L. D.; Srimannarayana,
G. Ind. J. Chem. 1985, 862.
14. Gupta, S. C.; Yusuf, M.; Sharma, S.; Arora, S. Tetrahedron
Lett. 2002, 43, 6875.