Highly stereoselective formation of 1,3-dioxolanes by photocatalytic ring opening reacrions of α-epoxyketones in acetone solution using 1-benzyl-2,4,6-triphenylpyridinium tetrafluoroborate (NBTPT)

Article abstract of DOI:10.3987/COM-06-10767

Highly stereoselective formation of 1,3-dioxolanes has been observed on photoinduced electron transfer ring opening of α-epoxyketones by 1-benzyl-2,4,6-triphenylpyridinium tetrafluoroborate (NBTPT) in acetone solution. The presence of various substituents on the donor molecule has not affected the rate of the ring opening and also stereoselectivity of the reaction too much. Stepwise addition of the photocatalyst leads to decreasing of irradiation time and increasing of the yield of products. Photoinduced electron transfer deoxygenation and isomerization of some α-epoxyketones has also been observed. Cyclic voltammetric study of the photocatalyst shows a greater tendency of NBTPT for accepting an electron in the excited state.{A figure is presented}.

Full text of DOI:10.3987/COM-06-10767

HETEROCYCLES, Vol. 68, No. 9, 2006
1861
Heterocycles, Vol. 68, No. 9, 2006, pp. 1861 - 1874. © The Japan Institute of Heterocyclic Chemistry
Received, 18th April, 2006, Accepted, 27th June, 2006, Published online, 29th June, 2006. COM-06-10767
HIGHLY STEREOSELECTIVE FORMATION OF 1,3-DIOXOLANES
BY PHOTOCATALYTIC RING OPENING REACRIONS OF ꢀ-
EPOXYKETONES IN ACETONE SOLUTION USING 1-BENZYL-2,4,6-
TRIPHENYLPYRIDINIUM TETRAFLUOROBORATE (NBTPT)
Hamid Reza Memarian,* Ali Saffar-Teluri, and Mohammad Kazem Amini
Department of Chemistry, Faculty of Science, University of Isfahan,
81746-73441, Isfahan, Iran. E-mail:memarian@sci.ui.ac.ir
Abstract - Highly stereoselective formation of 1,3-dioxolanes has been
observed on photoinduced electron transfer ring opening of ꢀ-epoxyketones by
1-benzyl-2,4,6-triphenylpyridinium tetrafluoroborate (NBTPT) in acetone
solution. The presence of various substituents on the donor molecule has not
affected the rate of the ring opening and also stereoselectivity of the reaction too
much. Stepwise addition of the photocatalyst leads to decreasing of irradiation
time and increasing of the yield of products. Photoinduced electron transfer
deoxygenation and isomerization of some ꢀ-epoxyketones has also been
observed. Cyclic voltammetric study of the photocatalyst shows a greater
tendency of NBTPT for accepting an electron in the excited state.
Photoinduced single electron transfer (SET) ring opening reactions of epoxides and ꢀ-epoxyketones have
attracted considerable interest from both synthetic and mechanistic standpoints.1-33 Such reactions have
been recognized as important processes not only in thermal but also in photochemical transformations.
Single electron transfer induced ring opening reactions of epoxides and ꢀ-epoxyketones have
demonstrated C-C, and C-O bond cleavages through photoinduced electron transfer by various electron
donors such as 1,4-dihydropyridines,2 triethylamine (TEA),3 tribenzylamine (TBA),3 1,3-dimethyl-2-
phenylbenzimidazoline (DMPBI)4-6 and 2-hydroxyphenyl-1,3-dimethylbenzimidazoline7 or thermally
induced single electron transfer by electron donating compounds such as samarium diiodide,8
tributyltinhydride9 and bis(cyclopentadienyl)titanium(III) chloride.10 Ring opening of these compounds
have also occurred thermally or photochemically by the presence of various electron acceptors. These
reactions have been observed thermally by ceric ammonium nitrate,11,12 2,3-dichloro-5,6-dicyano-p-
benzoquinone13 and iron(III) chloride14 or photoinduced electron transfer reactions by
dicyanoanthracene,15,16 tetracyanoethylene17,18 and 2,4,6-triphenylpyrilium tetrafluoroborate.19-23 In the
case of C-C bond cleavage, the generated carbonyl ylides from epoxide radical cations have been trapped
by molecular oxygen to form trioxolane derivatives15-17 or by dipolarophiles to form various
tetrahydrofurans and dihydrofurans.24 In the absence of appropriate dipolarophiles, cis/trans

1862
HETEROCYCLES, Vol. 68, No. 9, 2006
isomerization of the epoxide ring has been observed. The cleavage of Cα-O and Cβ-O bonds has been
confirmed either by rearrangement to carbonyl compounds25-32 or by nucleophilic attack of appropriate
reagents.19, 30, 33
The use of the 2,4,6-triphenylpyridinium salt as intermediate for replacing amine by other functional
groups in the nucleophilic substitution reactions has been studied.34,35 Garcia and his co-workers have
recently used N-alkyl-2,4,6-triphenylpyridinium tetrafluoroborate as photosensitizer in the photochemical
cyclization of 5-methyl-4-hexenoic acid to the corresponding γ-lactone.36
Ph
O
O
H
400 nm
hv
+
H
O
Ph
O
Ph
R1
+
BF4-
CH3
O
H3C
R2
2
1
R2
R2
O
O
H
O
H
O
CH2OH
H
O
H
O
R
R1
R1
CH3
H3C
CH3
H3C
5
4
3
R2
O
O
OH
H
O
H
O
Ph
Ph
O
OH
R1
6
7
Scheme 1
Recently, we have reported on the photocatalytic ring opening of some α-epoxyketones (1) of our interest
with 2,4,6-triphenylpyrilium tetrafluoroborate (TPT) (2) as photocatalyst in methanol,20 cyclohexanone,21
acetone22 and acetic acid solutions.23 The interesting point in our studies was especially to compare the
results obtained in acetone solution with those obtained in cyclohexanone solution. Whereas irradiation of
various α-epoxyketones in the presence of 2 in dry acetone resulted in the formation of cis- and trans-1,3-
dioxolanes (3) and (4) and also in the formation of alcoholic by-products (5) and (6), only the formation
of cis-1,3-dioxolane (7) has been observed on irradiation in cyclohexanone solution (Scheme 1).
As noted therein, the rate of the ring opening was affected by the nature of substituents and their location
on the α-epoxyketones, but the steric hindrance of the nucleophile (cyclohexanone compared with
acetone) has also a great effect on the formation of the stereoisomeric 1,3-dioxolanes. On the basis of the
observed stereoselectivity of the reaction and also the influence of the nature of the substituent on the rate
of the ring opening, we have proposed the involvement of the intermediates (8-10) for the nucleophilic

HETEROCYCLES, Vol. 68, No. 9, 2006
1863
attack in these reactions (Scheme 2).21, 22
.
δ+
O
.
O
+
O
.
O
O
δ+
O
H
H
H
+
H
H
H
R2
R1
R2
R2
R1
R1
8
10
9
Scheme 2
Since the extent of electron transfer from α-epoxyketones to the excited photocatalyst is the key step in
these reactions, we decided to use the photocatalyst 1-benzyl-2,4,6-triphenylpyridinium tetrafluoroborate
(NBTPT) (11) which we thought to be a weaker electron acceptor (nitrogen vs. oxygen), and therefore,
higher stereoselectivity of reactions should be expected. Now we wish to report on the photocatalytic ring
opening of α-epoxyketones (1a-1l) by using of 11 in acetone solution.
RESULTS AND DISCUSSION
Irradiation (λ ≥ 280 nm) of α-epoxyketones (1a-1l) with 11 in a 10:1 molar ratio in dry acetone solution
by bubbling of argon through the solution under irradiation resulted in the formation of different products
(3, 4, 13, 14) besides 2,4,6-triphenylpyridine (12) (Scheme 3).
Ph
O
O
280 nm
acetone
hv
H
+
H
Ph
N
Ph
R1
+
-
BF4
Ph
1
R2
11
Ph
R2
R1
1
3
+
4
+
a
b
c
d
e
f
g
h
i
H
H
H
CH3
H
OCH3
H
Br
Ph
N
Ph
CH3
H
OCH3
H
Br
H
Br
CH3
H
12
O
O
Cl
H
O
H
R1
R2
CCH=CH-
+
CH3
Br
Cl
H
13
14
j
k
l
a: R1=Br, R2=CH3
b: R1=H, R2=Cl
c: R1=Br, R2=Cl
Cl
Cl
Br
Scheme 3
The results obtained in the present work show that substituted α-epoxyketones (1a-1l) behave totally
different in this reaction. Whereas ring opening of α-epoxyketones (1a-1h) resulted in the formation of
cis-1,3-dioxolanes (3a-3h) as major products besides smaller amount of trans-1,3-dioxolanes (4a-4h)

1864
HETEROCYCLES, Vol. 68, No. 9, 2006
(according to TLC observation) as minor products, α-epoxyketones (1i), (1k) and (1l) were converted to
their corresponding precursor, namely, chalcones (13a-13c). The compound (1j) was isomerized to its
cis-isomer (14). The results are summarized in Table 1.
Table1. Photochemical reactions of 1a-1l catalyzed by 11 in acetone solution
Product (%)c
1
Conversion(%)a,b 12 (mg) Dioxolanes
Chalcones
Cis
3
4
a
b
c
d
e
f
g
h
i
90
92
88
85
89
79
81
80
82
89
83
81
23
22
23
23
23
21
23
23
22
23
23
23
a (68)
b (70)
c (69)
d (72)
e (68)
f (67)
g (66)
h (68)
-
a (trace)
b (trace)
c (trace)
d (trace)
e (trace)
f (trace)
g (trace)
h (trace)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
13a (76)
-
13b (71)
13c (67)
-
j
k
l
-
-
-
-
-
-
14 (81)
-
-
aIrradiation time for all compounds was 9 hours. b[1a-1l] = 0.04 M, [11] = 0.004 M, corresponding to molar ratio of
10:1, cIsolated yield, the amounts of unconsumed 1a-1l are determined and given in the experimental part.
1
IR, H NMR and MS spectral data gave useful information for the structural assignment of the
photoproducts. The IR spectra of the new 1,3-dioxolanes (3f-3h) compared with the IR spectra of α-
epoxyketones (1f-1h) showed an increase of aliphatic CH-stretching due to addition of acetone. Owing to
the ring opening and the loss of the epoxide ring strain, a shift of CO-stretching to higher frequency has
been observed. A comparison of the CO-stretching in the IR spectra of (1a-1h) and (3a-3h) is shown in
Table 2.
Table 2. Comparison of the CO-stretching in the IR-spectra of 1a-1h with those of 3a-3h
1
a
b
c
CO / cm-1
1670
3
a
b
c
CO / cm-1
1695
ref.
22
22
1660
1665
1685
1685
22
d
e
1660
1665
d
e
1688
1685
22
22
f
g
h
1661
1677
1674
f
g
h
1693
1695
1686
this work
this work
this work
The 1H NMR spectra of 3a-3h showed two singlets for the methyl groups and also an AB-system for the
4-H and 5-H of the dioxolane ring. Cis-orientation of the hydrogens of the dioxolane ring was confirmed
by comparison of their chemical shifts, coupling constants and upfield shift of one methyl group

HETEROCYCLES, Vol. 68, No. 9, 2006
1865
compared to the other one due to anisotropy effect of both aryl and aroyl groups. A comparison of these
data with those of the known dioxolanes22 supports this suggestion (Table 3).
Regarding the results obtained from the control experiment and the results presented in Table 1 we found
that:
1. 1. The presence of photocatalyst NBTPT is necessary for the reaction, because irradiation of 1a-1l
without NBTPT resulted only in the conversion of smaller amounts of some of these compounds to
their corresponding precursors chalcones and we did not observe the formation of any 1,3-dioxolanes
(3) and (4), and also the cis-isomer (14).
2. Stepwise addition of 11 to the solution of α-epoxyketones resulted in the complete conversion of
them, shortening of the irradiation time and also increasing the yield of all products (Table 4).
3. Whereas irradiation of 11 alone in acetone solution resulted in the formation of only 10 % of 12,
complete consumption of 11 has been observed on its irradiation in the presence of 1a-1l.
4. Two types of reactions, photo-degradation of 11 to 12 and photoelectron transfer from α-
epoxyketones to excited 11, were occurred simultaneously.
Table 3. Structurally relevant 1HNMR chemical shift (δ/ppm) and 1H-1H couplings (J/Hz) of 3a-3h.
3
JAB
CH3
ref.
δA
δB
4-H
5.48
5.45
5.48
5.47
5.49
5.52
5.59
5.53
5-H
5.75
5.80
5.74
5.73
5.72
5.84
5.80
5.83
a
b
c
d
e
f
g
h
8.2
7.6
7.6
7.6
7.4
8.0
8.0
7.9
1.57
1.49
1.52
1.52
1.53
1.60
1.62
1.61
1.81
1.79
1.80
1.79
1.82
1.86
1.90
1.86
22
22
22
22
22
this work
this work
this work
Table 4. Photochemical reactions of 1a-1l in acetone catalyzed by stepwise addition of 11a
Product (%)b
1
Irradiation time (h)a 12 (mg) Dioxolanes
Chalcones
Cis
3
4
a
b
c
d
e
f
g
h
i
7
5
6.5
5
6
7
7
7
7
7.5
7
23
22
22
21
22
22
23
23
21
22
23
22
a (82)
b (84)
c (81)
d (83)
e (80)
f (79)
g (80)
h (78)
-
a (trace)
b (trace)
c (trace)
d (trace)
e (trace)
f (trace)
g (trace)
h (trace)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
13a (81)
-
13b (79)
13c (74)
-
j
k
l
-
-
-
-
-
-
14 (90)
-
-
7
a 0.0039g of photocatalyst [11] = 0.004 M was added in three times. [1a-l] = 0.04 M, b Isolated yield.

1866
HETEROCYCLES, Vol. 68, No. 9, 2006
On the basis of the foregoing results, the following mechanism is proposed for the reactions (Scheme 4).
According to the proposed mechanism, irradiation of a mixture of 11 and α-epoxyketone leads to
excitation of 11. The excited 11 then interacts with the present α-epoxyketone to form a charge transfer
-
complex (15). The nucleophilic attack of acetone to this complex leads to the intermediates [3+4]+. BF4
and the radical (16) (path b). Back electron transfer (BET) gives the product (3) and (4), and recovery of
11 (path d). Triphenylpyridine (12) can be formed either by photo-degradation of 11 according to a
heterolytic cleavage of excited NBTPT (path e) or the homolytic cleavage of the intermediate (16) (path
f). This argument can be supported according to the obtained results mentioned in point 3. It should be
noted that we did not obtain any product derived from benzyl cation or radical intermediates.
*
Ph
+
Ph
N
Ph
BF4
-
a
hv
Ph
1a-1l
e
+
-
BF4
PhCH2
Ph
Ph
*
[
NBTPT..........
1a-1l
]
+
15
Ph
N
Ph
BF4
Ph
N
Ph
-
12
.
Ph
PhCH2
11
f
O
b
c
H3C CH3
Ph
other products
BET
13, 14
3 + 4
.
+
-
+
[ 3 + 4 ]
BF4
d
.
Ph
N
Ph
Ph
16
Scheme 4
The photoisomerization of α-epoxyketones through heterolytic Cα-O bond cleavage has been reported.37
Since the presence of the photocatalyst (NBTPT) is involved in the isomerization of 1j, according to the
reported mechanism,37 we will present the same mechanism but with the involvement of NBTPT as a first
example of photoinduced electron transfer isomerization of an α-epoxyketone as follows (Scheme 5).
The interesting point in our reaction is also deoxygenation of some α-epoxyketones. Our results indicated
that the presence of NBTPT increased especially the yield of chalcones (13a-13c) during the
deoxygenation of α-epoxyketones (1i), (ik), and (1l), respectively. Therefore, the following mechanism
can be presented for this conversion (Scheme 6).

HETEROCYCLES, Vol. 68, No. 9, 2006
1867
According to the proposed mechanism, Cβ-O cleavage of the complex leads to formation of the
intermediate (17). Back electron transfer (BET) to 17 gives the 1,3-carbo-oxy diradical (18). Coupling of
the diradical (18) leads to the formation of peroxy diradical intermediate (19). This intermediate
accomplished the reaction by formation of the chalcones (13a-13c) by elimination of molecular oxygen.
*
NBTPT
H
O
O
H
O
H
O
*
(NBTPT)
Cβ-O Cleavage
Cl
Cl
H
1j
-
-
BF4
BF4
+
+
O
O
.
Cl
O
Cl
.
rotation
180 o
.
H
NBTPT
+
NBTPT
+
H
.
H
H
O
.
O
H
NBTPT
BET
O
Cl
Cl
H
H
O
H
O
.
+
-
BF4
14
Scheme 5
*
NBTPT
H
O
H
O
O
O
hv
H
+
NBTPT
H
R1
R1
1
2
R2
1i: R = Br, R = CH
3
R2
1
2
1k: R = H, R = Cl
1
2
1l: R = Br, R = Cl
O
O
-
.
.
BF4
+
O
O
.
H
H
BET
cleavage
Cβ-O
.
NBTPT
+
+
NBTPT
H
H
R1
R1
R2
18
17
R2
O
R1
.
H
.
H
.
R2
coupling
O
- O2
13a-13c
O
O
H
.
H
R2
R1
19
Scheme 6

1868
HETEROCYCLES, Vol. 68, No. 9, 2006
Cyclic voltammetric studies of the photocatalysts
One-electron reduced species of an acceptor molecule plays an important role especially in reactions in
which the electron transfer step is the key step to the reaction. Since the observed ring opening of α-
epoxyketones does not occur either in the absence of light and NBTPT or TPT as photocatalysts, we were
interested to compare the cyclic voltammograms of NBTPT and TPT in the absence and in the presence
of light in order to elucidate their reactivity towards incoming electron in both ground and excited states.
The cyclic voltammograms (CVs) of NBTPT and TPT in Ar-saturated dichloromethane solutions
containing 0.05 M tetrabutylammonium perchlorate are shown in Figure1.
-80
-60
-40
-20
0
-40
-20
0
20
20
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
0.0
-0.2
-0.4
-0.6
-0.8
(A) E / V vs. SCE
(B) E / V vs. SCE
Figure 1. Cyclic voltammograms of (A) NBTPT (1 × 10-3 M) (B) TPT (1 × 10-3 M) in the absence of
light (—) and in the presence of light (----) in argon saturated dichloromethane solutions containing
tetrabutylammonium perchlorate (0.05 M) as the supporting electrolyte at a scan rate of 200 mV s-1.
(SCE = standard calomel electrode)
As can be seen, TPT is more readily reduced compared to NBTPT, both in presence and absence of light;
the reduction peak potential for TPT occurs at - 0.58 V ( vs. SCE ) in comparison to - 1.4 V for NBTPT.
Although reduction of NBTPT is more sensitive to light, i.e., it shows an approximately 440 mV positive
shift in the reduction peak potential in the presence of light, but even in the presence of light TPT is still a
better electron acceptor.
The results of cyclic voltammetric studies of photocatalyst TPT and NBTPT explain the observed highly
stereoselective ring opening of 1a-1h in the presence of NBTPT compared with TPT in acetone solution.
Owing to efficient electron transfer from α-epoxyketones to TPT, as stronger electron acceptor compared
-
with NBTPT, one of the proposed intermediates (8-10) should be formed, in which BF4 is the counter ion
of these intermediates. The presence of electron donor groups on the phenyl ring attached to the epoxide
ring (R2 in Scheme 2), facilitates the electron transfer to the excited TPT and decreasing stereoselectivity
of the reaction. Cyclic voltammetric studies support our suggestion that NBTPT is a weaker electron
acceptor compared with TPT. Therefore, we should not expect complete electron transfer from donor
molecule (α-epoxyketone) to NBTPT and formation of one of the intermediates (8-10). Indeed, we need
to propose a complex between excited NBTPT and α-epoxyketones. This complex leads to the preferred

HETEROCYCLES, Vol. 68, No. 9, 2006
1869
attack of acetone as a nucleophilic reagent to the carbon atom in the rear of the bond comprising the
oxygen leaving group due to the steric hindrance of NBTPT. This suggestion also supports the
observation that the effect of the additional substituents on the parent molecules (1a-1h) does not affect
the extent of stereoselectivity of the reactions (Scheme 7).
Ph
Ph
BF4
-
+
N
Ph
Ph
O
I
O
H
I
4a-4h
3a-3h
R1
H
II
R2
O
II
Scheme 7
It is interesting to compare the results obtained on reaction of 1a-1h compared with those obtained with
1i-1l. We measured the oxidation potential of these α-epoxyketones by means of cyclic voltammetry to
calculate the free energy. The ∆G values for the reaction (in kJ/mol) can be calculated from the simplified
Rehm-Weller Equation.38
∆G = 96.5 (Eox - Ered) - Es
Where Es is the singlet energy of NBTPT obtained from intersection of the normalized absorption and
emission spectra (λ0.0 = 375 nm), 319 kJ/mol. Ered the redox potential of NBTPT -1.4 V versus SCE and
Eox the oxidation potential of 1a-1l. Thus, the ∆G were obtained (Table 5). These data show that the
electron-transfer process is exothermic for 1a-1h but not for 1i-1l. Therefore, better formation of charge
transfer complex (15) (Scheme 4) for 1a-1h should be expected. On the other hand, formation of a very
weaker complex shown in Scheme 5 and 6 should be involved by reaction with 1i-1l.
Table 5. Free energy change for electron transfer from 1a-1l to singlet NBTPT
1a
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
2.064
+15.28
compound
Eox (V)
1.110
-76.79
1.107
-77.07
1.108
-76.98
1.322
-56.33
1.180
-70.03
1.203
-67.81
1.172
-70.80
1.214
-66.75
2.229
+31.20
2.072
+16.05
2.110
+19.72
∆G (kJ/mol)

1870
HETEROCYCLES, Vol. 68, No. 9, 2006
EXPERIMENTAL
Melting points were determined with a Stuart Scientific SMP2-apparatus and are uncorrected. NBTPT
has been prepared according to the reported procedure.39 IR spectra were recorded on a Philips PU-9716.
1H NMR spectra were measured in CDCl3 solutions containing tetramethylsilane (TMS) as internal
standard on a Bruker drx-500 (500 MHz). MS were obtained on a Plattform II from Micromass. The
cyclic voltammetric experiments were performed on AUTOLAB 30, Potentiostat Galvanostat. The
electrochemical studies were conducted by using dichloromethane solution containing
tetrabutylammonium perchlorate under argon. A three electrode with a saturated calomel electrode (SCE)
as the reference, a platinium foil as the counter electrode and a platinium disk as the working electrode
was used. Preparative layer chromatography (PLC) was carried out on 20 × 20 cm2 plates coated with 1
mm layer of Merck silica gel PF254 prepared by applying the silica as a slurry and drying in air. All
irradiations were carried out using a 400 W high-pressure Hg vapor lamp from Narva. The samples were
placed in Duran glass, which were cooled by running cold water.
A solution of 0.8 mmol of 1a-1l in 20 mL of acetone (c = 0.04 M) and 0.08 mmol of 11 (c = 0.004 M)
was irradiated for the time given in Table 1.
Irradiation of 1,3-diphenyl-2,3-epoxy-1-propanone (1a)
PLC, petroleum ether:AcOEt = 12:1, two times; zone 1, 23 mg of 12, recrystallized from EtOH, mp: 134-
o
o
135 C (lit.,40: 135 C); zone 2, 18 mg of 1a; zone 3, trace of 4a; zone 4, 138 mg (68 %) of 3a,
recrystallized from n-hexane, mp 116-118 ºC (lit.,22: 116-118 ºC).
cis-4-Benzoyl-2,2-dimethyl-5-phenyl-1,3-dioxolane (3a)
IR (KBr): 3050, 2920-2990, 1695, 1600 cm-1.
Irradiation of 3-(p-methylphenyl)-2,3-epoxy-1-propanone (1b)
PLC, petroleum ether:AcOEt = 12:1, two times; zone 1, 22 mg of 12; zone 2, trace of 4b; zone 3, 15 mg of
1b; zone 4, 153 mg (70 %) of 3b, recrystallized from n-pentane, mp 148-150 ºC (lit.,22: 147-149 ºC).
cis-4-Benzoyl-2,2-dimethyl-5-(p-methylphenyl)-1,3-dioxolane (3b)
IR (KBr): 3030, 2870-2995, 1685, 1595 cm-1.
Irradiation of 1-(p-methylphenyl)-3-phenyl-2,3-epoxy-1-propanone (1c)
PLC, petroleum ether:AcOEt = 12:1, two times; zone 1, 23 mg of 12; zone 2, trace of 4c; zone 3, 23 mg
of 1c; zone 4, 144 mg (69 %) of 3c, washed with n-pentane:Et2O, mp 131-132 ºC (lit.,22: 132-133 ºC).
cis-2,2-Dimethyl-4-(p-methylbenzoyl)-5-phenyl-1,3-dioxolane (3c)
IR (KBr): 3045, 2900-2995, 1685, 1610 cm-1.
Irradiation of 3-(p-methoxyphenyl)-1-phenyl-2,3-epoxy-1-propanone (1d)
PLC, petroleum ether:AcOEt = 10:1, two times; zone 1, 23 mg of 12; zone 2, trace of 4d; zone 3, 30
mg of 1d; zone 4, 153 mg (72 %) of 3d, recrystallized from n-hexane, mp 128-129 ºC ((lit.,22: 127-129
ºC).

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1871
cis-4-Benzoyl-5-(p-methoxyphenyl)-2,2-dimethyl-1,3-dioxolane (3d)
IR (KBr): 3010, 2860-2950, 1688, 1620 cm-1.
Irradiation of 1-(p-methylphenyl)-3-phenyl-2,3-epoxy-1-propanone (1e)
PLC, petroleum ether:AcOEt = 10:1, two times; zone 1, 23 mg of 12; zone 2, trace of 4e; zone 3, 22 mg
of 1e; zone 4, 151 mg (68 %) of 3e, recrystallized from n-hexane, mp 120-122 ºC ((lit.,22: 121-123 ºC).
cis-4-(p-Methoxybenzoyl)-2,2-dimethyl-5-phenyl-1,3-dioxolane (3e)
IR (KBr): 3050, 2820-2980, 1685, 1600 cm-1.
Irradiation of 3-(p-bromophenyl)-1-phenyl-2,3-epoxy-1-propanone (1f)
PLC, petroleum ether:AcOEt = 11:1, two times; zone 1, 21 mg of 12; zone 2, trace of 4f; zone 3, 51 mg of
1f; zone 4, 153 mg (67 %) of 3f, recrystallized from n-hexane:AcOEt, mp 164-165 ºC.
cis-4-Benzoyl-5-(p-bromophenyl)-2,2-dimethyl-1,3-dioxolane (3f)
IR (KBr): 3020, 2910-2990, 1693, 1595, 1397, 1250, 1100 cm-1; H NMR (500 MHz, CDCl3): 1.60 (s,
1
3H, CH3), 1.86 (s, 3H, CH3), AB-system (δA = 5.52, δB = 5.84, 3JAB = 8.0 Hz, 2H, 4-H, 5-H), AB-system
(δA = 6.69, δB = 7.17, 3JAB = 8.1 Hz, 4H, aromatic H), 7.28-7.50 (m, 5H, aromatic H) ppm; EI-MS (70 eV,
50 ºC): m/z (%) = 361 [M+] (2), 304 [M+ 81Br - CH3COCH3] (3), 303 [M+ 81Br - C3H7O] (3), 302 [M+ 79Br
- CH3COCH3] (3), 301 [M+ 79Br - C3H7O] (3), 186 [81BrC6H4CHO+] (3), 185 [81BrC6H4CO+] (7), 184
+
+
[79BrC6H4CHO+] (3), 183 [79BrC6H4CO+] (7), 157 [81BrC6H4 ] (4), 155 [79BrC6H4 ] (4), 105 [C6H5CO+]
(47), 77 [C6H5 ] (98), 69 [C3H5CO+] (100).
+
Irradiation of 1-(p-bromophenyl)-3-phenyl-2,3-epoxy-1-propanone (1g)
PLC, petroleum ether:AcOEt = 10:1, two times; zone 1, 23 mg of 12; zone 2, trace of 4g; zone 3, 46 mg
of 1g; zone 4, 154 mg (66 %) of 3g, recrystallized from n-hexane:AcOEt, mp 125-126 ºC.
cis-4-(p-Bromobenzoyl)-2,2-dimethyl-5-phenyl-1,3-dioxolane (3g)
IR (KBr): 3050, 2940-2980, 1695, 1585, 1476, 1210, 1090 cm-1; H NMR (500 MHz, CDCl3): 1.62 (s,
1
3H, CH3), 1.90 (s, 3H, CH3), AB-system (δA=5.59, δB=5.80, 3JAB = 8.0 Hz, 2H, 4-H, 5-H), 7.10-7.15 (m,
3
5H, aromatic H), AB-system (δA = 7.36, δB = 7.40, JAB = 8.5 Hz, 4H, aromatic H) ppm; EI-MS (70 eV,
50 ºC): m/z (%) 361 [M+] (3), 304 [M+ 81Br - CH3COCH3] (9), 302 [M+ 79Br - CH3COCH3] (9), 185
+
+
[81BrC6H4CO+] (67), 183 [79BrC6H4CO+] (67), 157 [81BrC6H4 ] (28), 155 [79BrC6H4 ] (28), 105
[C6H5CO+] (77), 91 [C7H7 ] (100), 77 [C6H5 ] (82).
+
+
Irradiation of 3-(p-bromophenyl)-1-(p-methylphenyl)-2,3-epoxy-1-propanone (1h)
PLC, petroleum ether:AcOEt = 11:1, two times; zone 1, 23 mg of 12; zone 2, trace of 4h; zone 3, 11 mg of
1h; zone 4, 163 mg (68 %) of 3h, recrystallized from n-hexane:AcOEt, mp 140-141 ºC.
cis-5-(p-Bromophenyl)-2,2-dimethyl-4-(p-methylbenzoyl)-1,3-dioxolane (3h)
1
IR (KBr): 3020, 2920-2980, 1686, 1610, 1397, 1205, 1096 cm-1; H NMR (500 MHz, CDCl3): 1.61 (s,
3H, CH3), 1.87 (s, 3H, CH3), 2.38 (s, 3H, CH3), AB-system (δA = 5.53, δB = 5.83, 3JAB = 7.9 Hz, 2H, 4-H,

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HETEROCYCLES, Vol. 68, No. 9, 2006
5-H), AB-system (δA = 7.00, δB = 7.21, 3JAB = 8.3 Hz, 4H, aromatic H), AB-system (δA = 7.11, δB = 7.44,
3JAB = 8.1 Hz, 4H, aromatic H), ppm; EI-MS (70 eV, 50 ºC): m/z (%) 375 [M+] (3), 318 [M+ 81Br-
CH3COCH3] (9), 316 [M+ 79Br- CH3COCH3] (10), 285 [M+ 81Br - C7H7] (2), 256 [M+-C7H7CO] (4), 186
[81BrC6H4CHO+] (6), 185 [81BrC6H4CO+] (14), 184 [79BrC6H4CHO+] (7), 183 [79BrC6H4CO+] (13), 157
+
+
+
[81BrC6H4 ] (9), 155 [79BrC6H4 ] (9), 149 [C7H7COCO+] (6), 119 [C7H7CO+] (21), 91 [C7H7 ] (22), 69
[C3H5CO+] (100).
Irradiation of 1-(p-bromophenyl)-3-(p-methylphenyl)-2,3-epoxy-1-propanone (1i)
PLC, petroleum ether:AcOEt = 10:1, two times; zone 1, 22 mg of 12; zone 2, 149 mg (76%) of 13a, mp 162-
164 ºC ((lit.,41: 163-164 ºC); zone 3, 46 mg of 1i.
Irradiation of 1-(p-chlorophenyl)-3-phenyl-2,3-epoxy-1-propanone (1j)
PLC, petroleum ether:AcOEt = 10:3, two times; zone 1, 23 mg of 12; zone 2, 23 mg of 1j; zone 3, 149 mg
(81 %) of 14, recrystallized from MeOH, mp 116-117 ºC.
cis-1-(p-Chlorophenyl)-3-phenyl-2,3-epoxy-1-propanone (14)
IR (KBr): 3040, 2900-2950, 1696, 1584, 1414, 1226, 1087 cm-1; H NMR (500 MHz, CDCl3): AB-
1
system (δA = 4.12, δB = 4.29, 3JAB = 1.3 Hz, 2H, 2-H, 3-H), 7.40-7.46 (m, 5H, aromatic H), AB-system (δA
= 7.51, δB = 8.01, 3JAB = 8.4 Hz, 4H, aromatic H), ppm; EI-MS (70 eV, 50 ºC): m/z (%) 258 [M+ 35Cl] (3),
+
166 [37ClC6H4COCHO+] (6), 141 [37ClC6H4CO+] (27), 139 [35ClC6H4CO+] (88), 113 [37ClC6H4 ] (14),
+
+
+
+
+
111 [35ClC6H4 ] (42), 91 [C7H7 ] (38), 87 [37ClC4H2 ] (31), 85 [35ClC4H2 ] (100), 77 [C6H5 ] (22), 75
+
+
+
[C6H3 ] (43), 65 [C5H5 ] (24), 63 [C5H3 ] (25), 51 (95).
Irradiation of 3-(p-chlorophenyl)-1-phenyl-2,3-epoxy-1-propanone (1k)
PLC, petroleum ether:AcOEt = 10:1, two times; zone 1, 23 mg of 12; zone 2, 114 mg (71 %) of 13b, mp 112-
114 ºC ((lit.,41: 111-113 ºC); zone 3, 35 mg of 1k.
Irradiation of 1-(p-bromophenyl)-3-(p-chlorophenyl)-2,3-epoxy-1-propanone (1l)
PLC, petroleum ether:AcOEt = 10:1, two times; zone 1, 23 mg of 12; zone 2, 139 mg (67 %) of 13c, mp 165-
166 ºC ((lit.,41: 166-167 ºC); zone 3, 51 mg of 1l.
ACKNOWLEDGEMENTS
We are thankful to the Office of Graduate Studies of the University of Isfahan for their financial support.
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