Diastereoselective 1,3-dioxolane formation by photocatalytic ring opening of a-epoxyketones

Article abstract of DOI:10.5560/ZNB.2013-3051

Photocatalytic ring opening of α-epoxyketones by 2,3-dichloro-5,6- dicyano-1,4-benzoquinone (DDQ) in acetone resulted in the diastereoselective formation of 1,3-dioxolanes through C_α-O bond cleavage. The facility of the ring opening is influenced by the nature and the location of the additional substituent on the α-epoxyketones.

Full text of DOI:10.5560/ZNB.2013-3051

Diastereoselective 1,3-Dioxolane Formation by Photocatalytic Ring
Opening of α-Epoxyketones
Hamid Reza Memarian and Sakineh Zare
Department of Chemistry, University of Isfahan, 81746-73441 Isfahan, Iran
Reprint requests to Prof. Hamid R. Memarian. Fax: +98-311-6689732.
E-mail: memarian@sci.ui.ac.ir
Z. Naturforsch. 2013, 68b, 811 – 817 / DOI: 10.5560/ZNB.2013-3051
Received February 16, 2013
Photocatalytic ring opening of α-epoxyketones by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone
(
DDQ) in acetone resulted in the diastereoselective formation of 1,3-dioxolanes through Cα –O bond
cleavage. The facility of the ring opening is influenced by the nature and the location of the additional
substituent on the α-epoxyketones.
Key words: DDQ, Electron Transfer, α-Epoxyketones, Photocatalyst, Ring Opening
Introduction
,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)
in the formation of 1,3-dioxolane, trioxolane or ether
derivatives [12, 13].
2
Previously, we have reported the light-induced ring
is a versatile reagent in organic synthesis. Owing to opening of α-epoxyketones 1 in the presence of var-
its oxidizing ability and also its relative stability under ious photocatalysts such as 2,4,6-triphenylpyrylium
various reaction conditions cause it to be one of the tetrafluoroborate (TPT) 2 [14 – 18], 7,7,8,8-tetracyano-
most used reagents to perform several organic trans- p-quinodimethane (TCNQ) 3 [19] and N-benzyl-2,4,6-
formations such as oxidation of benzhydrols [1], dehy- triphenylpyridinium tetrafluoroborate (NBTPT) 4 [20]
drogenation [2, 3], deprotection of benzyl ethers [4], in methanol, acetic acid, acetone and cyclohexanone
anodic oxidation of naphthalenes [5], thiocyanation of solutions (Scheme 1).
aromatic and heteroaromatic compounds [6, 7], and
The results obtained in these studies have shown
aromatization of 1,4-dihydropyridines [8]. DDQ is that the diastereoselectivity observed in this reaction
also a well-known electron acceptor, and its interaction depends on the type of photocatalyst and on the nu-
with a variety of electron donors via the formation of cleophilic power and the steric hindrance of the at-
charge transfer (CT) complexes has been the subject tacking species. Whereas irradiation of 1a – f in the
of several investigations [9 – 11].
presence of pyrylium salt 2 in dry acetone resulted
Epoxides, as oxygen-containing three-membered in the formation of diastereomeric cis- and trans-1,3-
heterocyclic rings, are among the most versatile build- dioxolanes 5a – f and 6a – f besides the formation of
ing blocks in organic synthesis due to their facile for- alcoholic by-products 7 and 8 [16], diastereospecific
mation and higher reactivity toward nucleophiles. Ring formation of cis-spirodioxolanes 9a – f is observed by
opening reactions of epoxides and α-epoxyketones, carrying out the irradiation in cyclohexanone solution
thermally or photochemically, have attracted consid- (Scheme 2) [15]. An interesting point is that the irradi-
erable interest from both synthetic and mechanistic ation of 1a – f in the presence of TCNQ (3) in acetone
standpoints. Single electron transfer (SET) induced resulted in the formation of cis-1,3-dioxolanes 5a – f
ring opening of these compounds in the presence of besides the formation of alcoholic by-products 7 and
a suitable catalyst or photocatalyst leads to the forma- 8 [19], while by using the photocatalyst 4, the forma-
tion of radical cation intermediates. Nucleophilic at- tion of cis-1,3-dioxolanes 5a – f accompanied by the
tack of suitable species to these intermediates results formation of a trace amount of trans-1,3-dioxolanes
©
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H. R. Memarian – S. Zare · Diastereoselective 1,3-Dioxolane Formation
NC
CN
Ph
Ph
O
H
O
H
h
ν
+
Ph
or
Ph
or
Products
Ar1
Ar2
O
+
4
Ph
N
Ph
+
−
−
BF
BF4
NC
CN
Ph
1
2
4
3
Scheme 1.
O
O
Ar
2
H
O
H
H
O
Ar2
hν
CH3or
H
1a
f + 2
Ar1
Ar1
O
O
O
O
CH3
CH3 CH3
CH3 CH3
Ar1
Ar2
5
1
6
O
O
OH
a
C
6
H
5
C H
6 5
Ph
Ar2
CH OH
2
Ph
C6H5
p-CH
p-CH C H
3 6 4
b
c
OH
O
O
C
H
C H
6 5
3
6
4
7
H
O
H
O
Ar2
8
C
H
p-CH OC H
Ar1
d
e
6
5
3
6
4
p-CH
p-CH OC H
6 4
OC
H
C H
6 5
3
6
4
p-CH
OC H
6 4
f
3
3
9
Scheme 2.
6
a – f is observed [20]. In continuation of these stud- Results and Discussion
ies, we used DDQ as catalyst and also as photocata-
lyst for the ring opening reaction of α-epoxyketones
Irradiation (λ ≥ 350 nm) of α-epoxyketones 1a – i
in methanol under thermal conditions [21] and under and DDQ (10) in a molar ratio of 10:1 in dry acetone
microwave and UV irradiations [22]. The results of resulted in the opening of the epoxide ring and forma-
these studies indicate the formation of distereomeric tion of diastereomeric 1,3-dioxolanes 5a – h and 6a – g,
methoxyalcohols. The observed different behavior of and chalcones 11h and 11i (Scheme 3). The results are
the excited photocatalyst toward α-epoxyketones, es- summarized in Table 1.
pecially the diastereoselectivity of the reaction depend-
The data presented in Table 1 show that the rate
ing on the electronic nature of α-epoxyketones and of ring opening of α-epoxyketones 1a – i by DDQ
also the nucleophilicity of the solvent, led us to ex- is dependent on the nature and location of the addi-
tend our study to the photocatalytic ring opening of tional substituent on the parent molecule 1a. Since
certain α-epoxyketones using DDQ in dry acetone so- we have earlier observed catalytic ring opening
lution under UV irradiation. The aims of the present of α-epoxyketones by DDQ in methanol at room
study are to elucidate the effect of the electronic nature temperature and under reflux conditions [21], we have
of α-epoxyketones on the rate of reaction, and to com- also carried out the same reaction with 1a as a test
pare the diastereoselectivity of the reaction with that substrate, but in acetone. In contrast to the failure
observed using another photocatalysts.
of the reaction at room temperature, a fast reaction
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H. R. Memarian – S. Zare · Diastereoselective 1,3-Dioxolane Formation
Table 1. Photocatalytic ring opening reaction of 1a–i by 10 in dry acetone.
813
1
Ar1
Ar2
Irrad. time
Yield (%)b
a
(h)
Recov. 1
5
6
11
a
b
c
d
e
f
g
h
i
C6H5
C6H5
C6H5
p-CH3C6H4
C6H5
p-CH3OC6H4
C6H5
p-CH3OC6H4
C6H5
6
1.5
6
2
6
2.5
6
6
10
–
42
–
68
–
62
35
67
38 (40)
40
25 (43)
42
15 (44)
40
21 (42)
12 (20)
–
31 (32)
34
10(17)
38
10 (30)
37
9 (17)
–
–
–
–
–
–
–
–
p-CH3C6H4
C6H5
p-CH3OC6H4
p-CH3OC6H4
p-ClC6H4
C6H5
p-ClC6H4
C6H5
31 (71)
31 (91)
p-BrC6H4
6
–
a
Irradiation times are given after maximum progression of reaction (not necessarily 100% conversion);
based on used (consumed) 1a–i.
b
was observed under reflux conditions, even faster to DDQ as an electron acceptor molecule, the radi-
•+
than under UV irradiation. According to this finding, cal cation species 1a – i are formed. These species
we propose the same reaction mechanism, as was could produce three different intermediates (12 – 14),
proposed earlier [21, 22] (Scheme 4):
which are trapped by nucleophilic attack of acetone
(Scheme 5). The preferred participation of one of these
I. Single electron transfer (SET) either from 1a – i to intermediates in the reaction should depend on the
DDQ in the excited state (DDQ*) or possibly to electron-donating ability of the additional substituent
DDQ in the ground state (electron affinity of DDQ and its location. Whereas the presence of electron
•
+
∼
3 eV) [23] leads to the formation of 1a – i and donor groups such as p-methyl- or p-methoxyphenyl
•−
DDQ (path 1).
directly attached to the epoxide ring (1b, 1d, and 1f)
•+
II. Nucleophilic attack of acetone at 1a – i forms causes a facile ring opening, the p-chlorophenyl sub-
•+
1
a – i–(CH ) CO adducts (path 2).
stituent as an electron acceptor group on the same po-
3
2
•
−
to sition (1h) reduces the rate of the reaction. It should
III. Back electron transfer (BET) from DDQ
•
a – i–(CH ) CO adducts followed the cycliza- be noted that the same substituents on the phenyl
3 2
+
1
tion accomplishes the reaction (path 3).
ring of the benzoyl group (1c, 1e, 1g, and 1i) have
a less remarkable effect. This indicates the influence
Regarding the proposed mechanism, due to elec- of the substituent on the electron-donating ability of
tron transfer from 1a – i as electron donor molecules α-epoxyketones toward photoexcited DDQ.
O
O
H
O
Cl
Cl
CN
CN
O
hν > 350 nm
H
5
+ 6 +
Ar1
+
Ar1
acetone
Ar2
Ar2
O
1
a-i
10
11
Scheme 3.
_
SET
+
.
1
+ DDQ or DDQ*
.
1 + DDQ
(path 1)
(path 2)
5a h + 6a g + DDQ (path 3)
+
.
+
.
1
+ CH COCH3
1
CH COCH3
3
3
+
_
1. BET
.
.
_
_
1
CH COCH3 + DDQ
3
2
. Cyclization
Scheme 4.
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H. R. Memarian – S. Zare · Diastereoselective 1,3-Dioxolane Formation
I
O
O+. H
..
O
..
H
R1
1
2
R2
II
I, III, V
5
a
h
III
O
H
δ+.
O
+
δ
H
.
.
O
..
R1
R2
1
3
IV
II, IV, VI
6
a
g
V
O
.
O
Fig. 1 (color online). Orientation of the counterions to 1a+
•
+
H
.
.
O
H
..
obtained by electron transfer of 1a to 2, 3, 4, and 10, respec-
R1
tively, showing the steric hindrance for nucleophilic attack.
R2
1
4
VI
After electron transfer from 1a – i to the photocatalysts
Scheme 5.
2
, 3, 4 or 10, complexes between ionic species of both
molecules are formed. This is shown in Fig. 1 with the
An important result of the present study is obtained intermediate 12 as an example. Cyclic voltammetric
from a comparison of the observed diastereoselectiv- studies of both photocatalysts 2 (TPT) and 4 (NBTPT)
ity of the reaction with that obtained in the presence showed [20] that 2 with the reduction potential of
of the photocatalysts 2, 3, and 4. The light absorptiv- −0.58 V (vs. SCE) is a stronger electron acceptor
ities of the photocatalysts 2, 3, 4, and 10 are not the compared to 4 with the reduction potential of −1.4 V.
same, which definitely influences the time of reaction. These results explain that after the electron transfer
−
The observed diastereoselectivity, which is presented process to 2, BF should be a counterion of the inter-
4
in Table 2, may be explained by the steric hindrance mediate 12, while in the case of the weaker electron
of the photocatalysts during the nucleophilic attack of acceptor species 4, the whole molecule 4 with the
acetone to the proposed intermediates 12 – 14.
partial positive charge on its nitrogen atom orientated
Density functional theory at the B3LYP/6- towards the oxygen of the epoxide ring (as a charge
3
1++G(d,p) level was applied to explain the observed transfer complex formed in the excited state, exciplex)
diastereoselectivity of the nucleophilic attack of should be the counterion of this intermediate. This
acetone in the presence of various photocatalysts. explains the possibility of a nucleophilic attack of
acetone from both sides in the former case, whereas
in the latter case the presence of the voluminous 4
Table 2. The diastereoselectivity in the photocatalytic ring
adjacent to the epoxide ring causes a steric hindrance
opening reaction of 1a–f by 2, 3 and 4 in dry acetone.
on the upper side. This proposal is supported by the
highly stereoselective formation of 1,3-dioxolanes 6
using the photocatalyst 4 [20], whereas in the case of
1
2
3
4
5
(%)
6 (%)
5 (%)
6 (%)
5 (%)
6 (%)
a
b
c
d
e
f
23
28
24
29
27
23
14
10
11
11
8
41
60
35
54
38
42
–
–
–
–
–
–
68
70
69
72
68
67
trace
trace
trace
trace
trace
trace
2
the formation of both diastereomers, types 5 and 6
has been observed [16]. Irradiation of α-epoxyketones
1a – f in the presence of TCNQ (3) in acetone re-
sulted also in the highly stereoselective formation of
–
1,3-dioxolanes 6. This explains the alignment of the
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815
−
large TCNQ species at the epoxy oxygen atom of on used 1a) of 6a, recrystallized from n-hexane-ethyl acetate,
◦
◦
1
2, which hinders the nucleophilic attack of acetone m. p.: 85 C, lit. [16] 87 – 89 C. Zone 2: Rf = 0.56, recovered
from the upper side [19]. In the present study, using
the photocatalyst DDQ (10), the DDQ radical anion
is formed after electron transfer. Due to the favorable
1
a (19 mg, 10% based on used 1a); zone 3 (R = 0.5), 42 mg
f
−
(40% based on consumed 1a and 38% based on used 1a) of
5
◦
a, recrystallized from n-hexane-ethyl acetate; m. p.: 120 C,
◦
lit. [16] 116 – 118 C.
formation of the aromatic ring in this species, the
negative charge is more localized on the oxygen atom. cis-4-Benzoyl-2,2-dimethyl-5-phenyl-1,3-dioxolane (5a)
The ring is far enough from the heterocycle, which
again explains the possibility for a nucleophilic attack
of acetone from both sides. This argument supports
the formation of both diastereomers, types 5 and 6, in
the present study.
1
H NMR (400 MHz, CDCl ): δ = 1.61 (s, 3H, CH ),
3
3
1
.88 (s, 3H, CH ), AB system (δ = 5.56, δB = 5.84,
JAB = 8.0 Hz, 2H, 4-H, 5-H), 7.05 – 7.12 (m, 5H, phenyl),
.22 – 7.28 (m, 2H, m-H of PhCO), 7.38 – 7.42 (m, 1H, p-H
of PhCO), 7.47 (d, J = 8.0 Hz, 2H, o-H of PhCO) ppm.
3 A
3
7
Another result of this study is the deoxygenation of
some α-epoxyketones 1h and 1i to the corresponding
chalcones11hand11i. Thesamereactionalsooccursby
irradiation of these compounds in the presence of 4 [20].
trans-4-Benzoyl-2,2-dimethyl-5-phenyl-1,3-dioxolane (6a)
1
H NMR (400 MHz, CDCl ): δ = 1.53 (s, 3H, CH ), 1.70
3
3
3
(
s, 3H, CH ), AB system (δ = 5.02, δB = 5.49, J
.6 Hz, 2H, 4-H, 5-H), 7.28 – 7.47 (m, 7H, phenyl H and m-
=
3
A
AB
7
H of PhCO), 7.54 – 7.58 (m, 1H, p-H of PhCO), 7.90 (d,
J = 8.0 Hz, 2H, o-H of PhCO) ppm.
Conclusion
In the present study, photocatalytic ring opening of Irradiation of trans-3-(p-methylphenyl)-1-phenyl-2,3-
epoxy-1-propanone (1b)
α-epoxyketones by DDQ in acetone resulted in the for-
mation of diastereomeric 1,3-dioxolanes. These results
PLC, n-hexane-ethyl acetate = 5 : 1; zone 1 (R = 0.6),
f
and those of our previous investigations explain that be- 40 mg(34%basedonconsumed1b)of6b, recrystallizedfrom
◦
◦
sides steric hindrance for the nucleophile, the type of the n-hexane-ethyl acetate; m. p.: 50 C, lit. [16] 45 – 48 C.
photocatalyst determines the diastereoselectivity of the
reaction.
cis-4-Benzoyl-2,2-dimethyl-5-(p-methylphenyl)-1,3-
dioxolane (5b)
1
H NMR (400 MHz, CDCl ): δ = 1.59 (s, 3H, CH ), 1.87
3
3
Experimental Section
(
5
s, 3H, CH ), 2.17 (s, 3H, CH ), AB system (δ = 5.54, δ =
.81, J = 8.0 Hz, 2H, 4-H, 5-H), 6.83 (d, J = 8.0 Hz, 2H,
3 3 A B
3
AB
Melting points were determined with a Stuart Scien-
tific SMP2 apparatus and are uncorrected. IR spectra were
recorded using KBr pellets on a Jasco FT/IR-6300 spectrom-
m-H of aryl), 6.99 (d, J = 8.0 Hz, 2H, o-H of aryl), 7.23 – 7.28
m, 2H, m-H of PhCO), 7.39 – 7.42 (m, 1H, p-H of PhCO),
.48 (d, J = 7.6 Hz, 2H, o-H of PhCO) ppm.
(
7
1
eter. H NMR spectra were recorded on a Bruker 400 MHz
spectrometer in CDCl . Mass spectra were measured by elec- trans-4-Benzoyl-2,2-dimethyl-5-(p-methylphenyl)-1,3-
3
tron impact at 70 eV on a Micromass Platform II instrument. dioxolane (6b)
Preparative thin layer chromatography (PTLC) was carried
1
H NMR (400 MHz, CDCl ): δ = 1.52 (s, 3H, CH ), 1.69
3
3
2
out on 20×20 cm plates, coated with a 1 mm layer of Merck
(
s, 3H, CH ), 2.35 (s, 3H, CH ), AB system (δ = 5.01, δ =
5.44, J = 7.6 Hz, 2H, 4-H, 5-H), 7.17 (d, J = 7.6 Hz, 2H,
m-H of aryl), 7.29 – 7.35 (m, 4H, m-H and o-H of PhCO),
.61 – 7.66 (m, 1H, p-H of PhCO), 7.91 (d, J = 7.6 Hz, o-H
ofaryl)ppm;zone2:R = 0.33,5b(45 mg,40%basedonused
b), washed with n-hexane-ethyl acetate; m. p.: 150 – 152 C,
lit. [16] 147 – 149 C.
3 3 A B
silica gel PF , prepared by applying the silica as slurry and
3
2
54
AB
drying in air. All irradiations were carried out in a 20 mL Du-
ran cell with a 5 × 25 Watt lamp (λ = 350 nm) in a Rayo-
net reactor, Model PRP-100. A solution of 0.8 mmol of 1a – i
in 20 mL of acetone (c = 0.04 M) and 0.08 mmol of DDQ
7
f
◦
1
(
c = 0.004 M) was irradiated for the time given in Table 1.
◦
Some of the photoproducts are known, and their spectroscopic
data have already been reported [16].
Irradiation of trans-1-(p-methylphenyl)-3-phenyl-2,3-
epoxy-1-propanone (1c)
Irradiation of trans-1,3-diphenyl-2,3-epoxy-1-propanone
PLC, n-hexane-ethyl acetate = 5 : 1; zone 1 (R = 0.83),
2 mg (17% based on consumed 1c and 10% based on used
PTLC, n-hexane-ethyl acetate = 5 : 1, two times; zone 1 1c) of 6c, washed with n-hexane-ethyl acetate; m. p.: 81 C,
Rf = 0.7),35 mg(32%basedonconsumed1aand31%based lit. [16] 82 – 83 C.
f
(
1a)
1
◦
◦
(
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H. R. Memarian – S. Zare · Diastereoselective 1,3-Dioxolane Formation
cis-4-(p-Methylbenzoyl)-2,2-dimethyl-5-phenyl-1,3-
1c) of 6e as a viscous oil; zone 2: R = 0.4, recovered 1e
f
dioxolane (5c)
(69 mg, 68% based on used 1e); zone 3 (R = 0.24), 18 mg
f
(
5
44% based on consumed 1e and 15% based on used 1e) of
1
H NMR (400 MHz, CDCl ): δ = 1.60 (s, 3H, CH ), 1.88
◦
3
3
e, recrystallized from n-hexane-ethyl acetate; m. p.: 120 C,
(
5
s, 3H, CH ), 2.32 (s, 3H, CH ), AB system (δ = 5.56, δ =
.81, J = 8 Hz, 2H, 4-H, 5-H), 7.03 – 7.11 (m, 7H, phenyl
◦
3
3
A
B
lit. [16] 121 – 123 C.
3
AB
and m-H of ArCO), 7.40 (d, J = 8.0 Hz, 2H, o-H of ArCO) Irradiation of trans-1,3-di(p-methoxyphenyl)-2,3-
ppm.
epoxy-1-propanone (1f)
trans-4-(p-Methylbenzoyl)-2,2-dimethyl-5-phenyl-1,3-
dioxolane (6c)
PLC, n-hexane-ethyl acetate = 5 : 1; zone 1 (Rf = 0.57),
50 mg (37% based on used 1e) of 6f as a viscous oil.
1
H NMR (400 MHz, CDCl ): δ = 1.50 (s, 3H, CH ), 1.68 trans-4-(p-Methoxybenzoyl)-5-methoxyphenyl-2,2-dimethyl-
3
3
(
s, 3H, CH ), 2.40 (s, 3H, CH ), AB system (δ = 5.00, 1,3-dioxolane (6f)
δ = 5.47, J = 7.6 Hz, 2H, 4-H, 5-H), 7.20 (d, J = 8.0 Hz,
H, o-H of phenyl), 7.28 – 7.37 (m, 3H, m-H and o-H of
phenyl), 7.44 (d, J = 7.6 Hz, 2H, m-H of ArCO), 7.80 (d,
J = 8.0 Hz, 2H, o-H of ArCO) ppm; zone 2: R = 0.61, re-
covered 1c (40 mg, 42% based on used 1c); zone 3 (R = 0.5),
0 mg (43% based on consumed 1c and 25% based on used
3 3 A
3
B
AB
IR: ν = 2987 (aromatic CH), 2838 – 2935 (aliphatic
2
−1
1
CH), 1678 (C=O), 1599 (C=C) cm . – H NMR
400 MHz, CDCl ): δ = 1.53 (s, 3H, CH ), 1.68 (s, 3H,
(
3
3
f
CH ), 3.81 (s, 3H, CH ), 3.85 (s, 3H, CH ), AB system
3
3
3
f
3
(
6
δA = 4.97, δB = 5.39, JAB = 8.0 Hz, 2H, 4-H, 5-H),
.86 – 6.90 (m, 4H, m-H of aryl and ArCO), 7.38 (d,
3
1
◦
c) of 5c, washed with n-hexane-ethyl acetate; m. p.: 131 C,
lit. [16] 132 – 133 C.
J = 7.6 Hz, 2H, o-H of aryl), 7.89 (d, J = 8.4 Hz, 2H, o-H
◦
◦
of ArCO) ppm. – MS (EI, 70 eV, 50 C): m/z (%) = 284
+
+
[
(
M−CH COCH ] (100), 269 [M−CH COCH −CH ]
Irradiation of trans-3-(p-methoxyphenyl)-1-phenyl-2,3-
epoxy-1-propanone (1d)
3
3
3
3
3
+
22), 177 [M−CH COCH −CH OC H ] (84), 149 [M−
3
3
3
6
4
+
CH COCH −CH OC H CO] (95), 135 [CH OC H
3
+
3
3
6
4
3
6
4
PLC, n-hexane-ethyl acetate = 5 : 1; zone 1 (R = 0.42),
5 mg (38% based on used 1d) of 6d, washed with n-hexane-
ethyl acetate; m. p.: 45 – 48 C, lit. [16] 43 – 47 C.
+
f
CO] (100), 121 [CH OC H CH ] (100), 107 [CH3
6
3 4 2
4
+
+
OC H ] (94), 92 [C H O] (93); zone 2: R = 0.31,
6
4
6
4
f
◦
◦
(
54 mg, 40% based on used 1f).
cis-4-(p-Benzoyl)-5-methoxyphenyl-2,2-dimethyl-1,3-
dioxolane (5d)
Irradiation of trans-1-(p-chlorophenyl)-3-phenyl-2,3-
epoxy-1-propanone (1g)
1
H NMR (400 MHz, CDCl ): δ = 1.59 (s, 3H, CH ), 1.87
3
3
PLC, n-hexane-ethyl acetate = 5 : 1; zone 1 (R = 0.61),
22 mg (17% based on consumed 1g and 9% based on used
1g) of 6g as a viscous oil.
f
(
5
s, 3H, CH ), 3.68 (s, 3H, CH ), AB system (δ = 5.53, δ =
.80, J = 7.6 Hz, 2H, 4-H, 5-H), 6.58 (d, J = 8.0 Hz, 2H,
3 3 A B
3
AB
o-H of aryl), 7.02 (m, 2H, m-H of aryl), 7.24 – 7.28 (m, 2H,
m-H of PhCO), 7.39 – 7.43 (m, 1H, p-H of PhCO), 7.50 (d,
J = 7.2 Hz, 2H, o-H of PhCO) ppm.
cis-4-(p-Chlorobenzoyl)-2,2-dimethyl-5-phenyl-1,3-
dioxolane (5g)
IR:ν = 3372(aromaticCH), 2933 – −2983(aliphaticCH),
trans-4-(p-Benzoyl)-5-methoxyphenyl-2,2-dimethyl-1,3-
dioxolane (6d)
−1
1
1
695 (C=O), 1588 (C=C) cm . – H NMR (400 MHz,
CDCl ): δ = 1.60 (s, 3H, CH ), 1.87 (s, 3H, CH ), AB sys-
3
3
3
1
3
H NMR (400 MHz, CDCl ): δ = 1.52 (s, 3H, CH ), 1.68 tem (δA = 5.56, δB = 5.74, J = 7.6 Hz, 2H, 4-H, 5-H),
3
3
AB
(
s, 3H, CH ), 3.82 (s, 3H, CH ), AB system (δ = 5.00, 7.08–7.11 (m, 4H, o-H and m-H of phenyl), 7.20 (m, 2H, m-H
3 3 A
3
δ = 5.39, J = 7.6 Hz, 2H, 4-H, 5-H), 6.89 (d, J = 8.0 Hz, of ArCO), 7.27(brds, 1H, p-Hofphenyl), 7.42(d, J = 7.2 Hz,
B
AB
2
7
H, o-H of aryl), 7.28 – 7.43 (m, 4H, m-H of aryl and PhCO), 2H, o-H of ArCO) ppm.
.54 – 7.55 (m, 1H, p-H of PhCO), 7.89 (d, J = 6.8 Hz, 2H,
trans-4-(p-Chlorobenzoyl)-2,2-dimethyl-5-phenyl-1,3-
o-H of PhCO) ppm; zone 2 (R = 0.17), 50 mg (42% based
f
dioxolane (6g)
on used 1d) of 5d, washed with n-hexane-ethyl acetate; m. p.:
◦ ◦
30 – 133 C, lit. [16] 127 – 129 C.
1
IR: ν = 3432 (aromatic CH), 2849 – 2918 (aliphatic CH),
−1
1
1
687 (C=O), 1590 (C=C) cm . – H NMR (400 MHz,
Irradiation of trans-1-(p-methoxyphenyl)-3-phenyl-2,3-
epoxy-1-propanone (1e)
CDCl ): δ = 1.50 (s, 3H, CH ), 1.69 (s, 3H, CH ), AB
3
3
3
3
system (δA = 4.94, δB = 5.48, J = 7.20 Hz, 2H, 4-H,
AB
PLC, n-hexane-ethyl acetate = 5 : 1; zone 1 (R = 0.46), 5-H), 7.33 – 7.40 (m, 5H, phenyl H), 7.46 (d, J = 6.4 Hz,
f
1
2 mg (30% based on consumed 1e and 10% based on used 2H, m-H of ArCO), 7.87 (d, J = 7.6 Hz, 2H, o-H of ArCO)
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H. R. Memarian – S. Zare · Diastereoselective 1,3-Dioxolane Formation
817
◦
37
+
ppm. – MS (EI, 70 eV, 60 C): m/z (%) = 319 [M Cl] (2), (400 MHz, CDCl ): δ = 1.60 (s, 3H, CH ), 1.86 (s, 3H,
3
3
3
5
+
37
+
3
3
17 [M Cl] (6), 261 [M Cl−CH COCH ] (24), 259 CH ), AB system (δ = 5.53, δB = 5.82, JAB = 8 Hz,
3
3
3
A
35 + +
[
1
M Cl−CH COCH ] (83), 177 [M−ClC H CO] (86), 2H, 4-H, 5-H), 7.02 – 7.03 (m, 4H, m-H of aryl and
3
3
6 5
+
19 [M−CH COCH −ClC H CO] (93); zone 2: R = PhCO), 7.27 – 7.28 (m, 3H, p-H of PhCO and o-H of
3
3
6
4
f
0
(
.53, recovered 1f (65 mg, 62% based on used 1f); zone 3 aryl), 7.44 – 7.49 (m, 2H, o-H of PhCO) ppm. – MS (EI,
◦
37
+
Rf = 0.31), 20 mg (42% based on consumed 1g and 21% 70 eV, 60 C): m/z (%) = 261 [M Cl−CH COCH ]
3
3
35 + 35
based on used 1g) of 5g, washed with n-hexane-ethyl acetate; (10), 259 [M Cl−CH COCH ] (32), 212 [M Cl−
3
3
◦
+
37
+
m. p.: 115 C.
C H CO] (16), 214 [M Cl−C H CO] (5), 154 [M−
6
5
6 5
+
37
+
CH COCH −C H CO] (50), 113 [ ClC H ] (3), 111
3
3
6
5
6
4
Irradiation of trans-3-(p-chlorophenyl)-1-phenyl-2,3-
35
+
+
[
ClC H ] (9), 105 [C H CO] (100).
6
4
6 5
epoxy-1-propanone (1h)
Irradiation of trans-3-(p-bromophenyl)-1-phenyl-2,3-
epoxy-1-propanone (1i)
PLC, n-hexane-ethyl acetate = 5 : 1, two times; zone 1
Rf = 0.65), 40 mg (71% based on consumed 1h and 31%
(
based on used 1h) of 11h, recrystallized from n-hexane-ethyl
acetate; m. p.: 108 – 110 C, lit. [24] 111 – 113 C; zone 2:
Rf = 0.52, recovered 1h (47 mg, 35% based on used 1h); zone
PLC, n-hexane-ethyl acetate = 5 : 1, two times; zone 1
Rf = 0.63), 45 mg (91% based on consumed 1i and 32%
◦
◦
(
based on used 1i) of 11i, recrystallized from n-hexane-ethyl
3
(R = 0.3), 15 mg (20% based on consumed 1h and 12%
f
◦
◦
acetate; m. p.: 121 C, lit. [24] 127 – 128 C; zone 2: R =
f
based on used 1h) of 5h, washed with n-hexane-ethyl acetate,
0
.53, recovered 1i (95 mg, 67% based on used 1i).
◦
m. p.: 130 C.
Acknowledgement
cis-4-Benzoyl-5-(p-chlorophenyl)-2,2-dimethyl-1,3-
dioxolane (5h)
We are thankful to the Research Council of the University
IR: ν = 3372 (aromatic CH), 2853 – 2924 (aliphatic ofIsfahanandtheOfficeofGraduateStudiesfortheirfinancial
−
1
1
CH), 1695 (C=O), 1597 (C=C) cm . – H NMR support.
[
[
[
[
[
[
[
[
[
1] G. P. Kalena, S. M. Jadhav, A. Banerji, Molecules 2000, [13] E. Hasegawa, M. Kamata in CRC Handbook of Organic
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1
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