Synthesis of some benzofurooxepines' derivatives via [3+2] cycloaddition of epoxide with tethered alkyne: A photochemical approach

Article abstract of DOI:10.1016/j.jphotochem.2013.12.017

A novel, environmentally benign and single-step synthesis of 8-chloro-2-arylbenzo[b]furo[2,3-e]oxepin-10(4H)-ones by the photochemical irradiation of 2-{5-chloro-2-(prop-2-ynyloxy)benzoyl}-3-aryloxiranes has been developed. Some of these substrates also f

Full text of DOI:10.1016/j.jphotochem.2013.12.017

Journal of Photochemistry and Photobiology A: Chemistry 278 (2014) 31–38
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Synthesis of some benzofurooxepines’ derivatives via [3+2]
cycloaddition of epoxide with tethered alkyne: A photochemical
approach
Ramesh C. Kamboja,∗, Pooja Jindala, Dinesh Kumara, Sadhika Khullarb, Sanjay K. Mandalb
a Department of Chemistry, Kurukshetra University, Kurukshetra 136119, Haryana, India
b Department of Chemical Sciences, Indian Institute of Science Education and Research, Sector 81, Manauli PO, S.A.S. Nagar, Mohali 140306, Punjab, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A
novel, environmentally benign and single-step synthesis of 8-chloro-2-arylbenzo[b]furo[2,3-
e]oxepin-10(4H)-ones by the photochemical irradiation of 2-{5-chloro-2-(prop-2-ynyloxy)benzoyl}-3-
aryloxiranes has been developed. Some of these substrates also furnished hydroxyalkenones alongside.
The formation of oxepinones as major products from these substrates has been envisioned to occur
through the heterolytic C C bond cleavage of epoxide, the oxirane ring giving carbonyl ylide intermedi-
ates followed by the furo-oxepinone ring formation via [3+2] cycloaddition while the hydroxyalkenones’
formation as minor products takes place through the initial ␤-H abstraction followed by oxirane ring
opening.
Received 10 November 2013
Received in revised form
10 December 2013
Accepted 19 December 2013
Available online 2 January 2014
Keywords:
Benzofurooxepinone
Tricyclics
© 2014 Elsevier B.V. All rights reserved.
Benzoyl oxiranes
Photochemical approach
1. Introduction
oxepine ring in their molecular architecture. The oxepines and
their derivatives (fused and substituted) constitute an important
Epoxy ketones are among the most versatile building blocks in
organic synthesis as both the ketone [1] and epoxide [2] moieties
can be further functionalized to afford interesting intermedi-
ates that are ultimate building blocks of numerous biomolecules.
This invoked an ever-growing interest in the chemistry of epoxy
ketones. A fascinating range of transformations has been devel-
oped and proved progressively more valuable for the synthesis
of natural products and biologically active compounds such
as the SK&F 104353 [3] (leukotriene antagonist), diltiazem [4]
(potent blood pressure lowering agent), taxol [5] (anticancer-
drug) and (+)-decursin [6] (novel protein kinase C activator), etc.
The epoxy ketones have also been transformed to the oxepines,
seven-membered heterocycles on photoirradiation [7] through ␥-
hydrogen abstraction. Seven-membered heterocyclic motifs are
frequently present in the wide array of biologically active molecules
[8]. An ample range of recent chemical review literature con-
tributes to synthesis and transformation of seven-membered rings
[9–12]. An incredible diversity of natural products such as janox-
epin [13], oxepinamide C [14], and bauhiniastatin [15] contains
class of heterocyclic compounds and are known to possess many
biological activities like antileishmanial [16], antiallergic [17], anti-
depressant [18], antipsychotic [19], anti-inflammatory [20] and
antifungal [21] activities. From a chemical perspective, the intrica-
cies of the structures have made them the objectives of enhanced
attention by synthetic chemists. Numerous methods have been
developed for their formation [22].
Keeping in view the motivating reactions and important uses
elicited by epoxy ketones and also by oxepines, herein, an attempt
has been made to photoirradiate the epoxy ketones (propynyloxy
benzoyloxiranes) which offered benzofurooxepinone derivatives.
To the best of our knowledge, there is no such method available
for the synthesis of this type of tricyclic compounds i.e. benzo-
furooxepinones. The structural constructs of these molecules may
be used in the development of medication for the treatment of
urinary-incontinence [23].
2. Results and discussion
The required epoxy ketones (benzoyl oxiranes) 4(a–f) were
synthesized from 5-chloro-2-hydroxyacetophenone through the
following sequence of reactions (Scheme 1):
∗
Corresponding author. Tel.: +91 9466650266; fax: +91 1744 238277.
E-mail address: rckamboj@hotmail.com (R.C. Kamboj).
1010-6030/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jphotochem.2013.12.017

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R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 278 (2014) 31–38
3'''
3'
3
6
3'
6'
3''
6''
1'''
2
1'
O
O
O
O
R
4'
4
OH
O
2''
(i)
(ii)
5''
Cl
Cl
Cl
3
3(a-f)
1
2
(iii)
3'''
3''
2''
3, 4a; R = H
3'
1'''
2
O
O
R
b; R = CH3
4'
c; R = OCH3
d; R = F
3
5''
Cl
e; R = Cl
f; R = Br
6''
6'
O
4(a-f)
Scheme 1. Synthesis of benzoyl oxiranes 4(a–f). (i) Dry acetone/K2CO3/Propargyl Bromide, heat (ii) ArCHO, KOH/MeOH (iii) THF/MeOH/KOH, 0 oC, 50% H2O2.
The structures of the chalcones 3(a–f) and benzoyl oxiranes
δ-hydrogen
abstraction
4(a–f) were ascertained from their spectral parameters (vide
experimental). The yields of all these compounds were in the
range of 82–89%.
Intermolecular
cycloaddition
Regarding the structure of compound 3b (mp 81–83 ◦C), its IR
spectrum showed the strong absorption band at 1643 cm−1 and a
weak absorption band at 2127 cm−1 due to C O and C C groups,
respectively. In the 1H NMR spectrum of 3b, three benzenoid pro-
tons appeared at ı 7.608 (1H, d, Jm = 2.7 Hz, H-6ꢀ), ı 7.456 (1H, dd,
J0 = 8.7 Hz, Jm = 2.7 Hz, H-4ꢀ) and ı 7.103 (1H, d, J0 = 8.7 Hz, H-3ꢀ). The
two-alkenyl protons had trans relationship as they showed reso-
nances at ı 7.646 (1H, d, H-3) and ı 7.344 (1H, d, H-2) with coupling
constant of 15.3 Hz. The NMR spectrum also exhibited two doublets
at ı 7.531 (2H, d, J0 = 7.5 Hz, H-2ꢀꢀ, 6ꢀꢀ) and ı 7.240 (2H, d, J0 = 7.5 Hz,
H-3ꢀꢀ, 5ꢀꢀ), respectively. The propargyl group protons H-1ꢀꢀꢀ and H-3ꢀꢀꢀ
were present as doublets at ı 4.784 and ı 2.467, respectively, with
Jallylic = 2.1 Hz. The NMR spectrum also displayed a sharp singlet at
ı 2.408 for methyl group protons.
H
O
R
H
Cl
O
O
β-hydrogen
abstraction
Oxirane
photochemistry
Fig. 1. Probable photochemical pathways of the substrates 4(a–f).
substrates in THF furnished the photoproducts 5(a–f) in 35–40%
yields while in methanol no photoproduct was obtained.
The structures of all the photoproducts formed were confirmed
by the support of their spectral data (IR, 1H NMR, 13C NMR and mass,
etc.). The compound 5b (mp 218–219 ◦C) was white crystalline solid
and showed IR absorption at 1612 cm−1 that may be assigned to the
The IR spectrum of compound 4b (mp 140–142 ◦C) exhibited a
strong absorption band at 1674 cm−1 due to C O stretch and at
2129 cm−1 due to C C stretch. In the NMR spectrum of the 4b,
was seen a doublet at ı 7.814 (Jm = 2.4 Hz) for H-6ꢀ. The other two-
benzenoid protons of benzoyl group showed the resonances at ı
7.504 (1H, dd, J0 = 8.4 Hz, Jm = 2.4 Hz, H-4ꢀ) and at ı 7.056 (1H, d,
J0 = 8.4 Hz, H-3ꢀ). The NMR spectrum also showed two doublets at ı
7.352 (2H, J0 = 8.4 Hz, H-2ꢀꢀ, 6ꢀꢀ) and at ı 6.945 (2H, J0 = 8.4 Hz, H-3ꢀꢀ,
5ꢀꢀ), respectively. The two protons of oxirane ring were appeared
as two distinct singlets at ı 4.332 (1H, s, H-2) and at ı 4.003 (1H,
s, H-3). The propargyl group protons resonated at ı 4.489 (2H, d,
Jallylic = 2.1 Hz, H-1ꢀꢀꢀ) and ı 2.516 (1H, d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ). The
methyl group protons appeared as a sharp singlet at ı 2.394.
The structural scaffolding (Fig. 1) of these molecules 4(a–f)
inherently has propensity to offer the varied type of photochem-
istry through the ı- and ␤-hydrogen abstractions [24], direct
cleavage of the oxirane ring [25] and inter-molecular cycloaddition
reactions [26]. The electronic absorption spectra of these benzoyl
oxiranes 4(a–f) showed ␭
in the range of 315–320 nm (Fig. 2).
max
Therefore, the photolysis (Scheme 2) of the benzoyl oxiranes
4(a–f) in dry benzene with pyrex filtered UV-light from 125W Hg
lamp under nitrogen atmosphere was carried out which furnished
the novel benzofurooxepinones 5(a–f) in 67–81% yields. Also in
some cases the hydroxyalkenones’ derivatives 6(a, b, d, f) were pro-
duced but the similar photoproducts from 4c and 4e could not be
realized for these may have been produced in such minute amounts
which escaped isolation in our hands. The photolysis of these
Fig. 2. Electronic absorption spectra of the substrates 4(a–f).

R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 278 (2014) 31–38
33
3'''
3'''
6
9
4
3'
6'
O
3''
6''
1'''
2
3
'
'
3''
6''
O
O
R
7
1'''
2
4'
2''
O
O
R
h
ν
3
4'
2''
+
6'
3'
Dry
3
Cl
5'
3
5''
Cl
benzene
5''
Cl
O
O
6
O
1
OH
R
2'
4(a-f)
6(a,b,d,f)
5(a-f)
Scheme 2. Photolysis of benzoyl oxiranes 4(a–f).
Fig. 3. Crystal structure of 5b as determined by single crystal X-ray crystallography.
C
C
O group of benzofurooxepinones. The peak due to absorption for
of benzoyl moiety competes with C C bond scission of the oxirane
ring and generates the 1,3-biradical, C. This 1,3-biradical undergoes
epoxide ring opening and affords 1,4-biradical, D which ultimately
endowed us with the hydroxyalkenones 6(a, c, d, f).
The photolysis of these benzoyl oxiranes 4(a–f) did not furnish
the benzofurans and its derivatives like 7 and 8 expected through
␦-hydrogen abstraction (Scheme 4) as were obtained from the pho-
tolysis of 1,5-bis(alkoxy)-2,4-dibenzoylbenzenes [29].
C stretch at 2129 cm−1 present in the IR spectrum of 4b was not
be seen in IR spectrum of 5b which indicates the involvement of
the acetylene group in the photoproduct formation. In the 1H NMR
spectrum, three benzenoid protons were appeared at ı 8.185 (1H,
d, Jm = 2.4 Hz, H-9), ı 7.471 (1H, dd, J0 = 8.1 Hz, Jm = 2.4 Hz, H-7) and
at ı 7.156 (1H, d, J0 = 8.1 Hz, H-6). The two-oxepinone ring protons
resonated at ı 5.140 (2H, s, H-4). The NMR spectrum also showed
two doublets at ı 7.793 (2H, d, J0 = 7.8 Hz, H-2ꢀ, 6ꢀ) and at ı 7.022 (2H,
d, J0 = 7.8 Hz, H-3ꢀ, 5ꢀ). A singlet at ı 6.703 may be well ascribed to the
H-3 furyl proton. A three protons sharp singlet appeared at ı 2.422
for methyl group. The 13C NMR spectrum of this photoproduct also
corroborated the structure proposed. In order to firmly establish
the structure of 5b, it was further examined through single crystal
X-ray crystallography [27]. There are two independent molecules
in the asymmetric unit (Fig. 3).
This may be because of the fact that the ␦-hydrogen in 4(a–f)
˚
is far away (5.078 A, the average distance as R H, CH3, OCH3, F,
Cl, Br) from the carbonyl oxygen as is shown in energy-minimized
MM2 structure (Fig. 4) and does not fall in the nodal plane of the
carbonyl group, a prerequisite for H-abstraction. The products of
inter-molecular cycloadditions were not obtained either.
This single-step process of benzofurooxepinones’ synthesis
appears to be very interesting as these products are obtained in
good yields without the use of additional reagent (catalysts, etc.)
and is thus novel and environmentally benign. The involvement of
ethynyl in such an act of 7-membered heterocyclic ring formation
is unprecedented. Our study shows the substantial complexity
of the mechanism yielding different products. This process and
its further exploration can lay a foundation for a clean route to
synthesize many heterocyclic compounds which may simulate
[23] the pharmaceutical activities.
The compound 6b (mp 128–129 ◦C) was white crystalline solid
and showed IR absorption at 3432 ( OH), 2150 (C C), 1713 (C O)
and 1605 (C C). The acetylenic group remained intact during pho-
tolysis which was ascertained by the peak at 2150 cm−1. The 1H
NMR spectrum showed three benzenoid protons at ı 7.900 (1H, d,
Jm = 2.4 Hz, H-6ꢀ), ı 7.446 (1H, dd, J0 = 8.7 Hz, Jm = 2.4 Hz, H-4ꢀ) and
ı 7.184 (1H, d, J0 = 8.7 Hz, H-3ꢀ). Two doublets were appeared at ı
7.959 (2H, d, J0 = 8.7 Hz, H-2ꢀꢀ, 6ꢀꢀ) and ı 7.061 (2H, d, J0 = 8.7 Hz, H-
3ꢀꢀ, 5ꢀꢀ). The propargyl group protons resonated at ı 4.829 (2H, d,
Jallylic = 2.1 Hz, H-1ꢀꢀꢀ) and ı 2.448 (1H, d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ). The
alkenyl proton H-2 exhibited a singlet at ı 7.308. The methyl group
protons appeared as a sharp singlet at ı 2.379.
The oxirane ring being 3-membered is highly strained and its
photochemical cleavage has been observed earlier [28]. Therefore,
its participation has been envisioned for the formation of photo-
products 5 and 6 from 2-{5-chloro-2-(prop-2-ynyloxy)benzoyl}-
3-aryloxiranes. In the formation of 5, it has been envisioned that
the heterolytic C C bond cleavage of the oxirane ring produces the
carbonyl ylide intermediate A (see Scheme 3) that then cyclizes
through [3+2] cycloaddition with ethynyl group to furnish B. Dehy-
drogenation of B in situ furnishes the oxepinones, the driving force
being the formation of aromatic furan ring system. For the hydrox-
yalkenones 6, the ␤-hydrogen abstraction by the carbonyl group
Fig. 4. Energy-minimized MM2 structure of benzoyl oxirane.

34
R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 278 (2014) 31–38
*
O
O
R
O
O
O
R
C-C cleavage
hν
Cl
Cl
O
Cl
Cl
O
O
O
A
4(a-f)
R
β-H abstraction
[3+2]
O
R
cycloadditon
.
O
.
O
OH
C
H
Cl
C-O cleavage
R
H
O
O
O
B
.
R
Cl
OH
O
.
D
O
O
O
R
O
O
R
1,5-H shift
Cl
O
Cl
Cl
O
OH
O
R
H
6(a,c,d,f)
5(a-f)
Scheme 3. Mechanism of photoproducts formation from benzoyl oxiranes.
O
R
O
R
O
hν
H
O
Cl
Cl
δ-H
Cl
O
O
O
abstraction
HO
7
OH
4(a-f)
-H2O
O
Cl
O
R
8
Scheme 4.
3. Conclusion
4. Experimental
In conclusion, the 2-{5-chloro-2-(prop-2-ynyloxy)benzoyl}-3-
aryloxiranes were synthesized in high chemical yields and their
photochemistry was investigated. Irradiation of these benzoyl oxi-
ranes resulted in the development of a facile and new efficient
synthesis of benzofurooxepine derivatives, which are structurally
similar to some known pharmaceutically important compounds
and thus may contribute immensely to the chemistry of hetero-
cyclic compounds.
4.1. General
The nuclear magnetic resonance 1H NMR (300 MHz) and proton-
decoupled 13C NMR (75.4 MHz) spectra were recorded on Bruker
spectrometer using TMS as internal standard. The infrared (IR)
spectra were scanned in KBr pellets on a MB3000 FT-IR with
HORIZON MBTM FTIR software from ABB Bomen. The mass spec-
tral data were obtained on WATERS, Q-TOF MICROMASS (LC–MS)

R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 278 (2014) 31–38
35
spectrometer. Melting points were determined in open capillar-
ies and are uncorrected. The photoirradiation of the deaerated
solution of substrates was carried out using a pyrex filter under
nitrogen atmosphere from 125 W Hg lamp. The columns for chro-
matographic separation were packed in pet. ether with silica gel
and were eluted with pet. ether and ethyl acetate mixture (99:1).
The X-ray crystallographic structure was collected on a Bruker
Kappa APEX II diffractometer equipped with CCDC detector and
sealed-tube monochromated MoK␣ radiation using the program
APEX2.
J23 = 15.9 Hz, H-2), 7.099 (1H, d, J0 = 8.7 Hz, H-3ꢀ), 6.952 (2H, d,
J0 = 8.7 Hz, H-3ꢀꢀ, 5ꢀꢀ), 4.787 (2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 3.870 (3H,
s, OCH3), 2.555 (1H, d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ).
4.3.4. 1-{5-Chloro-2-(prop-2-ynyloxy)phenyl}-3-(4-
fluorophenyl)prop-2-en-1-one
3d
Yield 89%, white solid, mp 104–105 ◦C; ꢀmax(cm−1): 2150 (C C),
1651 (C O); ıH(CDCl3): 7.631 (1H, d, J32 = 15.9 Hz, H-3), 7.592 (1H,
d, Jm = 2.7 Hz, H-6ꢀ), 7.502 (2H, d, J0 = 8.7 Hz, H-2ꢀꢀ, 6ꢀꢀ), 7.471 (1H, dd,
J0 = 8.7 Hz, Jm = 2.7 Hz, H-4ꢀ), 7.335 (1H, d, J23 = 15.9 Hz, H-2), 7.137
(1H, d, J0 = 8.7 Hz, H-3ꢀ), 7.104 (2H, d, J0 = 8.7 Hz, H-3ꢀꢀ, 5ꢀꢀ), 4.797
(2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 2.568 (1H, d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ).
4.2. General method for the synthesis of
5-chloro-2-(prop-2-ynyloxy)acetophenone 2
The 5-chloro-2-hydroxyacetophenone 1 (0.01 mol), propargyl-
bromide (0.01 mol), dry K2CO3 (1.0 g) and tetra-n-butylammonium
iodide (50 mg) were refluxed in dry acetone (25 ml) for 3 h during
which the color of reaction mixture changed from yellowish-brown
to white. Filtration, evaporation of solvent and crystallization of the
residue (MeOH) delivered 2.
4.3.5. 1-{5-Chloro-2-(prop-2-ynyloxy)phenyl}-3-(4-
chlorophenyl)prop-2-en-1-one
3e
Yield 87%, white solid, mp 101–103 ◦C; ꢀmax(cm−1): 2129
(C C),1643 (C O); ıH(CDCl3): 7.634 (1H, d, J32 = 15.9 Hz, H-3), 7.568
(1H, d, Jm = 2.7 Hz, H-6ꢀ), 7.540 (2H, d, J0 = 8.7 Hz, H-2ꢀꢀ, 6ꢀꢀ), 7.473
(1H, dd, J0 = 8.7 Hz, Jm = 2.7 Hz, H-4ꢀ), 7.407 (1H, d, J23 = 15.9 Hz, H-
2), 7.335 (1H, d, J0 = 8.7 Hz, H-3ꢀ), 7.098 (2H, d, J0 = 8.7 Hz, H-3ꢀꢀ,
5ꢀꢀ), 4.793 (2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 2.570 (1H, d, Jallylic = 2.1 Hz,
H-3ꢀꢀꢀ).
4.2.1. 5-Chloro-2-(prop-2-ynyloxy)acetophenone 2
Yield 87%, white solid, mp 58–60 ◦C; ꢀmax(cm−1): 2122 (C C),
1674 (C O); ıH(CDCl3): 7.734 (1H, d, Jm = 2.4 Hz, H-6), 7.455 (1H,
dd, J0 = 8.7 Hz, Jm = 2.4 Hz, H-4), 7.061 (1H, d, J0 = 8.7 Hz, H-3), 4.819
(2H, d, Jallylic = 2.1 Hz, H-1ꢀ), 2.579 (1H, d, Jallylic = 2.1 Hz, H-3ꢀ), 2.645
(3H, s, CH3).
4.3.6. 1-{5-Chloro-2-(prop-2-ynyloxy)phenyl}-3-(4-
bromophenyl)prop-2-en-1-one
3f
4.3. General method for the synthesis of chalcones 3(a–f)
Yield 89%, white solid, mp 110–112 ◦C; ꢀmax(cm−1): 2150 (C C),
1651 (C O); ıH(CDCl3): 7.637 (1H, d, J32 = 15.9 Hz, H-3), 7.562 (1H,
d, Jm = 2.7 Hz, H-6ꢀ), 7.493 (1H, dd, J0 = 8.7 Hz, Jm = 2.7 Hz, H-4ꢀ),
7.474 (2H, d, J0 = 7.8 Hz, H-2ꢀꢀ, 6ꢀꢀ), 7.406 (1H, d, J23 = 15.9 Hz, H-
2), 7.354 (1H, d, J0 = 8.7 Hz, H-3ꢀ), 7.093 (2H, d, J0 = 7.8 Hz, H-3ꢀꢀ,
5ꢀꢀ), 4.795 (2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 2.571 (1H, d, Jallylic = 2.1 Hz,
H-3ꢀꢀꢀ).
To the well-stirred suspension of KOH (0.02 mol) in MeOH
at 0 ◦C were added 5-chloro-2(prop-2-ynyloxy)acetophenone 2
(0.01 mol) and appropriate aldehyde (0.011 mol). The reaction mix-
ture turned deep red in color after 30 min, and allowed to stir
further for 3 h. Thereafter, it was poured over ice and neutralized
with diluted HCl to obtain corresponding chalcone, which was crys-
tallized from EtOH to give the shining needles.
4.4. General method for the synthesis of benzoyl oxiranes 4(a–f)
4.3.1. 1-{5-Chloro-2-(prop-2-ynyloxy)phenyl}3-phenylprop-2-
en-1-one
3a
To the well stirred suspension of compound 3 (0.005 mol) in
methanol was added 10.0 ml of 20% aqueous KOH and cooled to
0 ◦C. To this mixture was added H2O2 (50%) drop-wise till a white
solid began to appear. The reaction mixture was neutralized with
ice-HCl to give white precipitates. The solid was filtered, dried and
crystallized (EtOH) to give creamish crystals of benzoyl oxirane 4.
Yield 88%, white solid, mp 92–93; ꢀmax(cm−1): 2126 (C C), 1643
(C O); ıH(CDCl3): 7.648 (1H, d, J32 = 15.3 Hz, H-3), 7.617 (1H, d,
Jm = 2.4 Hz, H-6ꢀ), 7.538 (2H, d, J0 = 7.5 Hz, H-2ꢀꢀ, 6ꢀꢀ), 7.461 (1H, dd,
J0 = 8.7 Hz, Jm = 2.4 Hz, H-4ꢀ), 7.349 (1H, d, J23 = 15.3 Hz, H-2), 7.246
(3H, m, H-3ꢀꢀ, 4ꢀꢀ, 5ꢀꢀ), 7.122 (1H, d, J0 = 8.7 Hz, H-3ꢀ), 4.792 (2H, d,
Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 2.473 (1H, d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ).
4.4.1. 2-{5-Chloro-2-(prop-2-ynyloxy)benzoyl}-3-phenyloxirane
4a
4.3.2. 1-{5-Chloro-2-(prop-2-ynyloxy)phenyl}-3-(p-tolyl)prop-
2-en-1-one
3b
Yield 84%, creamish white solid, mp 117–118; ꢀmax(cm−1): 2150
(C C), 1666 (C O); ıH(CDCl3): 7.830 (1H, d, Jm = 2.4 Hz, H-6ꢀ), 7.505
(1H, dd, J0 = 8.4 Hz, Jm = 2.4 Hz, H-4ꢀ), 7.236 (2H, d, J0 = 8.4 Hz, H-2ꢀꢀ,
6ꢀꢀ), 7.036 (1H, d, J0 = 8.4 Hz, H-3ꢀ), 7.019 (3H, m, H-3ꢀꢀ, 4ꢀꢀ, 5ꢀꢀ), 4.478
(2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 4.343 (1H, s, H-2), 4.039 (1H, s, H-3),
2.367 (1H, d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ); Anal. calcd. for C18H13ClO3: C,
69.13; H, 4.19. Found: C, 69.06; H, 4.12.
Yield 84%, white solid, mp 81–83 ◦C; ꢀmax(cm−1): 2127 (C C),
1643 (C O); ıH(CDCl3): 7.646 (1H, d, J32 = 15.3 Hz, H-3), 7.608 (1H,
d, Jm = 2.7 Hz, H-6ꢀ), 7.531 (2H, d, J0 = 7.5 Hz, H-2ꢀꢀ, 6ꢀꢀ), 7.456 (1H, dd,
J0 = 8.7 Hz, Jm = 2.7 Hz, H-4ꢀ), 7.344 (1H, d, J23 = 15.3 Hz, H-2), 7.240
(2H, d, J0 = 7.5 Hz, H-3ꢀꢀ, 5ꢀꢀ), 7.103 (1H, d, J0 = 8.7 Hz, H-3ꢀ), 4.784 (2H,
d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 2.467 (1H, d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ), 2.408
(3H, s, CH3).
4.4.2.
2-{5-Chloro-2-(prop-2-ynyloxy)benzoyl}-3-(p-tolyl)oxirane 4b
Yield 84%, white solid, mp 140–142 ◦C; ꢀmax(cm−1): 2129 (C C),
1674 (C O); ıH(CDCl3): 7.814 (1H, d, Jm = 2.4 Hz, H-6ꢀ), 7.504 (1H,
dd, J0 = 8.4 Hz, Jm = 2.4 Hz, H-4ꢀ), 7.352 (2H, d, J0 = 8.4 Hz, H-2ꢀꢀ, 6ꢀꢀ),
7.056 (1H, d, J0 = 8.4 Hz, H-3ꢀ), 6.945 (2H, d, J0 = 8.4 Hz, H-3ꢀꢀ, 5ꢀꢀ),
4.489 (2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ) 4.332 (1H, s, H-2), 4.003 (1H, s,
H-3), 2.516 (1H, d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ), 2.394 (3H, s, CH3); Anal.
calcd. for C19H15ClO3: C, 69.84; H, 4.63. Found: C, 69.81; H, 3.67.
4.3.3. 1-{5-Chloro-2-(prop-2-ynyloxy)phenyl}-3-(4-
methoxyphenyl)prop-2-en-1-one
3c
Yield 87%, creamish solid, mp 117–118 ◦C; ꢀmax(cm−1): 2126
(C C), 1643 (C O); ıH(CDCl3): 7.628 (1H, d, J32 = 15.9 Hz, H-3),
7.603 (1H, d, Jm = 2.7 Hz, H-6ꢀ), 7.576 (2H, d, J0 = 8.7 Hz, H-2ꢀꢀ,
6ꢀꢀ), 7.455 (1H, dd, J0 = 8.7 Hz, Jm = 2.7 Hz, H-4ꢀ), 7.258 (1H, d,

36
R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 278 (2014) 31–38
4.4.3. 2-{5-Chloro-2-(prop-2-ynyloxy)benzoyl}-3-(4-
methoxyphenyl)oxirane
160.35, 176.65. MS(ES+) m/z: 311, 313; Anal. calcd. for C18H11ClO3:
C, 69.58; H, 3.57. Found: C, 69.51; H, 3.52.
4c
Yield 82%, white solid, mp 128–130 ◦C; ꢀmax(cm−1): 2129 (C C),
1674 (C O); ıH(CDCl3): 7.820 (1H, d, Jm = 2.4 Hz, H-6ꢀ), 7.510 (1H,
dd, J0 = 8.7 Hz, Jm = 2.4 Hz, H-4ꢀ), 7.336 (2H, d, J0 = 8.4 Hz, H-2ꢀꢀ, 6ꢀꢀ),
7.058 (1H, d, J0 = 8.7 Hz, H-3ꢀ), 6.953 (2H, d, J0 = 8.4 Hz, H-3ꢀꢀ, 5ꢀꢀ),
4.502 (2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 4.335 (1H, s, H-2), 3.990 (1H, s,
H-3), 3.851 (3H, s, OCH3), 2.410 (1H, d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ); Anal.
calcd. for C19H15ClO4: C, 66.58; H, 4.41. Found: C, 69.54; H, 4.38.
4.5.1.2. 1-{5-Chloro-2-(prop-2-ynyloxy)phenyl}-3-hydroxy-3-
phenylprop-2-en-1-one 6a. Yield 25%, white solid, mp 140–142 ◦C;
ꢀmax(cm−1): 3418 ( OH), 2150 (C C), 1713 (C O), 1605 (C = C);
ıH(CDCl3): 8.026 (2H, d, J0 = 8.1 Hz, H-2ꢀꢀ, 6ꢀꢀ), 7.973 (1H, d,
Jm = 2.4 Hz, H-6ꢀ), 7.520 (3H, m, H-3ꢀꢀ, 4ꢀꢀ, 5ꢀꢀ), 7.456 (1H, dd,
J0 = 8.4 Hz, Jm = 2.4 Hz, H-4ꢀ), 7.209 (1H, s, H-2), 7.071 (1H, d,
J0 = 8.4 Hz, H-3ꢀ), 4.841 (2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 2.630 (1H,
d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ). ıC(CDCl3): 57.13, 99.24, 115.09, 115.36,
121.89, 126.27, 127.42, 127.67, 129.58, 129.62, 130.12, 132.29,
133.54, 153.46, 154.87, 181.22, 186.64. MS (ES+) m/z: 313.1, 315.1.
Anal. calcd. for C18H13ClO3: C, 69.13; H, 4.19. Found: C, 69.08; H,
4.13.
4.4.4. 2-{5-Chloro-2-(prop-2-ynyloxy)benzoyl}-3-(4-
fluorophenyl)oxirane
4d
Yield 85%, white solid, mp 111–113 ◦C; ꢀmax(cm−1): 2129 (C C),
1674 (C O); ıH(CDCl3): 7.642 (1H, d, Jm = 2.4 Hz, H-6ꢀ), 7.464 (1H,
dd, J0 = 8.4 Hz, Jm = 2.4 Hz, H-4ꢀ), 7.379 (2H, d, J0 = 8.7 Hz, H-2ꢀ, 6ꢀ),
6.965 (1H, d, J0 = 8.4 Hz, H-3ꢀ), 6.940 (2H, d, J0 = 8.7 Hz, H-3ꢀ, 5ꢀ),
4.367 (2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 4.186 (1H, s, H-2), 3.865 (1H, s, H-
3), 2.556 (1H, d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ), Anal. calcd. for C18H12ClFO3:
C, 65.37; H, 3.66. Found: C, 65.43; H, 3.61.
4.5.2. Photolysis of
2-{5-chloro-2-(prop-2-ynyloxy)benzoyl}-3-(p-tolyl)oxirane 4b
A 1.0 mM solution of 4b in dry benzene on photolysis for 45 min
furnished 5b and 6b.
4.4.5. 2-{5-Chloro-2-(prop-2-ynyloxy)benzoyl}-3-(4-
chlorophenyl)oxirane
4e
4.5.2.1. 8-Chloro-2-(p-tolyl)benzo[b]furo[2,3-e]oxepin-10(4H)-one
5b. Yield 72%, white solid, mp 218–219 ◦C; ꢀmax(cm−1): 1612
(C O); ıH(CDCl3): 8.185 (1H, d, Jm = 2.4 Hz, H-9), 7.793 (2H, d,
J0 = 7.8 Hz, H-2ꢀ, 6ꢀ), 7.471 (1H, dd, J0 = 8.1 Hz, Jm = 2.4 Hz, H-7), 7.156
(1H, d, J0 = 8.1 Hz, H-6), 7.022 (2H, d, J0 = 7.8 Hz, H-3ꢀ, 5ꢀ), 6.703
(1H, s, H-3), 5.140 (2H, s, H-4), 2.422 (3H, s, CH3). ıC(CDCl3): 21.51,
66.94, 105.03, 123.93, 125.52, 126.01, 129.69, 130.10, 130.32,
130.67, 134.17, 136.58, 140.39, 148.50, 156.58, 160.53, 176.62. MS
(ES+) m/z: 325, 327; Anal. calcd. for C19H13ClO3: C, 70.27; H, 4.03.
Found: C, 70.19; H, 4.01.
Yield 85%, white solid, mp 118–120 ◦C; ꢀmax(cm−1): 2129 (C C),
1674 (C O); ıH(CDCl3): 7.708 (1H, d, Jm = 2.4 Hz, H-6ꢀ), 7.625 (1H,
dd, J0 = 8.4 Hz, Jm = 2.4 Hz, H-4ꢀ), 7.434 (2H, d, J0 = 8.7 Hz, H-2ꢀꢀ, 6ꢀꢀ),
7.218 (1H, d, J0 = 8.4 Hz, H-3ꢀ), 6.985 (2H, d, J0 = 8.7 Hz, H-3ꢀꢀ, 5ꢀꢀ),
4.433 (2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 4.229 (1H, s, H-2), 3.918 (1H, s, H-
3), 2.516 (1H, d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ); Anal. calcd. for C18H12Cl2O3:
C, 62.27; H, 3.48. Found: C, 62.25; H, 3.44.
4.4.6. 2-{5-Chloro-2-(prop-2-ynyloxy)benzoyl}-3-(4-
bromophenyl)oxirane
4f
4.5.2.2. 1-{5-Chloro-2-(prop-2-ynyloxy)phenyl}-3-hydroxy-3-p-
tolylprop-2-en-1-one 6b. Yield 24%, white solid, mp 128–129 ◦C;
ꢀmax(cm−1): 3432 ( OH), 2150 (C C), 1713 (C O), 1605 (C = C);
ıH(CDCl3): 7.959 (2H, d, J0 = 8.7 Hz, H-2ꢀꢀ, 6ꢀꢀ), 7.900 (1H, d,
Jm = 2.4 Hz, H-6ꢀ), 7.446 (1H, dd, J0 = 8.7 Hz, Jm = 2.4 Hz, H-4ꢀ),
7.308 (1H, s, H-2), 7.184 (1H, d, J0 = 8.7 Hz, H-3ꢀ), 7.061 (2H, d,
J0 = 8.7 Hz, H-3ꢀꢀ, 5ꢀꢀ), 4.829 (2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 2.448 (1H,
d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ), 2.379 (3H, s, CH3). ıC(CDCl3): 21.61, 57.08,
98.42, 114.90, 122.53, 127.19, 127.38, 127.46, 129.33, 129.65,
130.13, 132.15, 133.00, 143.29, 154.84, 181.19, 186.56. MS (ES+)
m/z: 327.1, 329.1. Anal. calcd. for C19H15ClO3: C, 69.84; H, 4.63.
Found: C, 69.79; H, 4.58.
Yield 85%, white solid, mp 138–140 ◦C; ꢀmax(cm−1): 2127 (C C),
1682 (C O); ıH(CDCl3): 7.553 (1H, d, Jm = 2.4 Hz, H-6ꢀ), 7.340 (1H,
dd, J0 = 7.8 Hz, Jm = 2.4 Hz, H-4ꢀ), 7.314 (2H, d, J0 = 8.7 Hz, H-2ꢀꢀ, 6ꢀꢀ),
7.083 (1H, d, J0 = 7.8 Hz, H-3ꢀ), 6.882 (2H, d, J0 = 8.7 Hz, H-3ꢀꢀ, 5ꢀꢀ),
4.311 (2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 4.116 (1H, s, H-2), 3.772 (1H, s, H-
3), 2.381 (1H, d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ); Anal. calcd. for C18H12BrClO3:
C, 55.20; H, 3.09. Found: C, 55.16; H, 3.03.
4.5. Photolysis of benzoyl oxiranes 4(a–f)
4.5.1. Photolysis of
2-{5-chloro-2-(prop-2-ynyloxy)benzoyl}-3-phenyloxirane 4a
A deoxygenated 1.0 mM solution in dry benzene of the benzoyl
oxirane 4a contained in a pyrex glass vessel was purged with nitro-
gen for 30 min and then irradiated under nitrogen atmosphere with
light from a 125W Hg vapor lamp for 45 min. The removal of solvent
under reduced pressure yielded a gummy mass that was chro-
matographed over a column of silica gel. The column was eluted
with increasing proportion of ethyl-acetate in pet. ether–ethyl
acetate mixture to obtain photoproducts 5a and 6a.
4.5.3. Photolysis of 2-{5-chloro-2-(prop-2-ynyloxy)benzoyl}-3-
(4-methoxyphenyl)oxirane
4c
A 1.0 mM solution of 4c in dry benzene on photolysis for 45 min
furnished only one photoproduct 5c.
4.5.3.1. 8-Chloro-2-(4ꢀ-methoxyphenyl)benzo[b]furo[2,3-e]oxepin-
10(4H)-one 5c. Yield 79%, white solid, mp 194–196 ◦C; ꢀmax(cm−1):
1612 (C O); ıH(CDCl3): 8.189 (1H, d, Jm = 2.4 Hz, H-9), 7.846 (2H, d,
J0 = 8.7 Hz, H-2ꢀ, 6ꢀ), 7.467 (1H, dd, J0 = 8.7 Hz, Jm = 2.4 Hz, H-7), 7.155
(1H, d, J0 = 8.7 Hz, H-6), 7.050 (2H, d, J0 = 8.7 Hz, H-3ꢀ, 5ꢀ), 6.628 (1H,
s, H-3), 5.136 (2H, s, H-4), 3.890 (3H, s, OCH3). ıC(CDCl3): 55.42,
66.83, 105.52, 113.91, 114.47, 122.23, 123.28, 124.50, 127.25,
130.42, 130.66, 132.74, 139.80, 160.62, 161.21, 168.39, 173.98. MS
(ES+) m/z: 341, 343. Anal. calcd. for C19H13ClO4: C, 66.97; H, 3.85.
Found: C, 66.92; H, 3.76.
4.5.1.1. 8-Chloro-2-phenylbenzo[b]furo[2,3-e]oxepin-10(4H)-one
5a. Yield 73%, white solid, mp 183–185; ꢀmax(cm−1): 1612 (C O);
ıH(CDCl3): 8.194 (1H, d, Jm = 2.4 Hz, H-9), 7.899 (2H, d, J0 = 8.7 Hz,
H-2ꢀ, 6ꢀ), 7.481 (1H, dd, J0 = 8.7 Hz, Jm = 2.4 Hz, H-7), 7.162 (1H,
d, J0 = 8.7 Hz, H-6), 7.456 (3H, m, H-3ꢀ, 4ꢀ, 5ꢀ), 6.757 (1H, s, H-3),
5.153 (2H, s, H-4). ıC(CDCl3): 66.87, 105.02, 123.82, 125.55, 129.68,
130.33, 130.52, 130.59, 134.06, 136.46, 140.21, 148.68, 156.43,

R.C. Kamboj et al. / Journal of Photochemistry and Photobiology A: Chemistry 278 (2014) 31–38
37
4.5.4. Photolysis of 2-{5-chloro-2-(prop-2-ynyloxy)benzoyl}-3-
(C C); ıH(CDCl3): 7.604 (2H, d, J0 = 8.1 Hz, H-2ꢀꢀ, 6ꢀꢀ), 7.500 (1H,
d, Jm = 2.4 Hz, H-6ꢀ), 7.472 (2H, d, J0 = 8.1 Hz, H-3ꢀꢀ, 5ꢀꢀ), 7.168 (1H,
s, H-2), 6.938 (1H, dd, J0 = 8.4 Hz, Jm = 2.4 Hz, H-4ꢀ), 6.721 (1H, d,
J0 = 8.4 Hz, H-3ꢀ), 4.787 (2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 2.591 (1H,
d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ). ıC(CDCl3): 57.13, 99.24, 115.09, 115.36,
121.89, 126.27, 127.42, 127.67, 129.58, 129.62, 130.12, 132.29,
133.54, 153.46, 154.87, 181.22, 186.64. MS (ES+) m/z: 391.0, 393.0,
395.0. Anal. calcd. for C18H12BrClO3: C, 55.20; H, 3.09. Found: C,
55.16; H, 3.03.
(4-fluorophenyl)oxirane
4d
A 1.0 mM solution of 4d in dry benzene on photolysis for 45 min
yielded 5d and 6d.
4.5.4.1. 8-Chloro-2-(4ꢀ-fluorophenyl)benzo[b]furo[2,3-e]oxepin-
10(4H)-one 5d. Yield 67%, white solid, mp 178–180 ◦C; ꢀmax(cm−1):
1612 (C O) ıH(CDCl3): 8.189 (1H, d, Jm = 2.7 Hz, H-9), 7.969 (2H,
d, J0 = 8.4 Hz, H-2ꢀ, 6ꢀ), 7.872 (2H, d, J0 = 8.4 Hz, H-3ꢀ, 5ꢀ), 7.487 (1H,
dd, J0 = 8.4 Hz, Jm = 2.4 Hz, H-7), 7.202 (1H, d, J0 = 8.4 Hz, H-6), 6.765
(1H, s, H-3), 5.154 (2H, s, H-4). ıC(CDCl3): 66.91, 105.13, 123.15,
125.33, 126.21, 129.48, 129.57, 130.03, 130.58, 134.17, 136.58,
149.67, 149.22, 156.32, 160.33, 176.54. MS (ES+) m/z: 329, 331.
Anal. calcd. for C18H10ClFO3: C, 65.77; H, 3.07. Found: C, 65.71; H,
3.00.
Acknowledgement
One of the authors (P.J.) wishes to express her gratitude to the
University Grant commission (UGC), New Delhi for the financial
assistance as JRF for the accomplishment of this work.
4.5.4.2. 1-{5-Chloro-2-(prop-2-ynyloxy)phenyl}-3-hydroxy-3-(4ꢀ-
fluorophenyl)prop-2-en-1-one 6d. Yield 29%, white solid, mp
121–122 ◦C; ꢀmax(cm−1): 3418 (-OH), 2150 (C C), 1713 (C O),
1605 (C = C); ıH(CDCl3): 8.029 (2H, d, J0 = 8.7 Hz, H-2ꢀꢀ, 6ꢀꢀ), 7.972
(1H, d, Jm = 2.4 Hz, H-6ꢀ), 7.456 (1H, dd, J0 = 8.4 Hz, Jm = 2.4 Hz, H-4ꢀ),
7.355 (1H, s, H-2), 7.176 (2H, d, J0 = 8.7 Hz, H-3ꢀꢀ, 5ꢀꢀ), 7.064 (1H,
d, J0 = 8.4 Hz, H-3ꢀ), 4.839 (2H, d, Jallylic = 2.1 Hz, H-1ꢀꢀꢀ), 2.637 (1H,
d, Jallylic = 2.1 Hz, H-3ꢀꢀꢀ). ıC(CDCl3): 57.21, 99.33, 115.34, 115.82,
127.22, 127.44, 127.78, 129.82, 129.91, 130.25, 132.32, 133.56,
154.35, 155.02, 181.47, 186.71. MS (ES+) m/z: 331.1, 333.1. Anal.
calcd. for C18H12ClFO3: C, 65.37; H, 3.66. Found: C, 65.32; H, 3.63.
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(4-chlorophenyl)oxirane
4e
A 1.0 mM solution of 4e in dry benzene on photolysis for 45 min
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4.5.5.1. 8-Chloro-2-(4ꢀ-chlorophenyl)benzo[b]furo[2,3-e]oxepin-
10(4H)-one 5e. Yield 81%, white solid, mp 240–242 ◦C; ꢀmax(cm−1):
1612 (C O); ıH(CDCl3): 8.179 (1H, d, Jm = 2.4 Hz, H-9), 7.830 (2H,
d, J0 = 8.1 Hz, H-2ꢀ, 6ꢀ), 7.465 (1H, dd, J0 = 8.4 Hz, Jm = 2.4 Hz, H-7),
7.444 (2H, d, J0 = 8.1 Hz, H-3ꢀ, 5ꢀ), 7.164 (1H, d, J0 = 8.4 Hz, H-6),
6.748 (1H, s, H-3), 5.148 (2H, s, H-4). ıC(CDCl3): 66.80, 105.90,
119.28, 123.97, 126.72, 126.87, 129.30, 129.62, 130.20, 130.53,
130.68, 134.37, 136.23, 159.13, 160.54, 177.47. MS (ES+) m/z: 345,
347, 349. Anal. calcd. for C18H10ClFO3: C, 65.77; H, 3.07. Found: C,
65.71; H, 3.02.
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124.57, 126.87, 127.65, 129.83, 130.02, 130.26, 131.12, 131.58,
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