Photocatalytic ring opening of α-epoxyketones in cyclopentanone

Article abstract of DOI:10.1515/znb-2011-0608

Electron transfer-induced ring opening of α-epoxyketones by 2,4,6-triphenylpyrylium tetrafluoroborate (TPT) in cyclopentanone resulted in the diastereoselective formation of 2,5-dioxaspiro[4,4]- nonanes through Cα-O bond cleavage and following nucleophilic attack of cyclopentanone to radical cation intermediates. The readiness for ring opening is influenced by the nature and the location of the additional substituent on the α-epoxyketones.

Full text of DOI:10.1515/znb-2011-0608

Photocatalytic Ring Opening of α-Epoxyketones in Cyclopentanone
Hamaid R. Memarian, Gholrokh Shokuhimehr, and Mousa Soleymani
Catalysis Division, Department of Chemistry, Faculty of Science, 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. 2011, 66b, 603 – 610; received January 4, 2011
Electron transfer-induced ring opening of α-epoxyketones by 2,4,6-triphenylpyrylium tetrafluo-
roborate (TPT) in cyclopentanone resulted in the diastereoselective formation of 2,5-dioxaspiro[4,4]-
nonanes through Cα–O bond cleavage and following nucleophilic attack of cyclopentanone to radical
cation intermediates. The readiness for ring opening is influenced by the nature and the location of
the additional substituent on the α-epoxyketones.
Key words: Dioxolanes, Electron Transfer, α-Epoxyketones, Photocatalyst, Ring Opening,
Spiro Compounds
Introduction
In our recent studies, we have investigated the pho-
tocatalytic ring opening of various α-epoxyketones of
Single electron transfer- (SET) induced ring open- interest by TPT as photocatalyst in the presence of
ing of epoxides and α-epoxyketones occurs in the methanol [7], cyclohexanone [8], acetic acid [9], and
presence of suitable electron-withdrawing catalysts or acetone [10]. The aims of these studies were to elu-
photocatalysts [1 – 3]. In this case, the electron transfer cidate the effect of the additional substituent on the
process leads to the formation of radical cation inter- parent molecule and the nucleophilicity and also the
mediates, which upon attack of suitable nucleophiles steric hindrance of the solvent molecule on the rate and
accomplish the reaction. The ring opening reaction of diastereoselectivity of the reaction. Among the nucle-
α-epoxyketones has been recognized as an important ophiles studied, only the reaction in the presence of cy-
process not only in thermal but also in photochemical clohexanone resulted in the formation of a single dia-
reactions, which occur either through a C–C, Cα –O or stereomer. The reason is possibly the steric hindrance
C –O bond cleavage. Some of these reactions were re- of cyclohexanone compared to other nucleophiles in
β
ported using various catalysts or photocatalysts such the attack on the proposed reaction intermediates from
as AlCl [4], p-toluenesulfonic acid [5], dicyanoan- the less hindered side [8]. In continuation of these stud-
3
thracene (DCA) [2], tetracyanoethylene (TCNE) [1], ies, we have investigated the photocatalytic ring open-
2
1
,4,6-triphenylpyryliumtetrafluoroborate (TPT) [3, 6 – ing of certain α-epoxyketones by TPT in cyclopen-
0], 1-benzyl-2,4,6-triphenylpyridinium tetrafluoro- tanone to elucidate the effect of the nature and the
borate (NBTPT) [11, 12], 2,3-dichloro-5,6-dicyano-p- steric hindrance of the nucleophile on the diastereo-
benzoquinone (DDQ) [13, 14], and 7,7,8,8-tetracyano- selectivity of the reaction.
p-quinodimethane (TCNQ) [15].
2
,4,6-triphenylpyrylium tetrafluoroborate (TPT) is
Results and Discussion
widely used as an electron transfer photosensitizer for
various organic transformations such as decarboxyla-
tion of amino acids [16], photooxidation of N,N-di-
benzylhydroxylamine[17], photochemically promoted
Diels-Alder reactions of 1,4-diaryl-1-azabutadienes
with 2,3-dihydrofuran [18], [3+2]-cycloaddition of
electron-rich olefins to oxiranecarbonitrile [19], and
the above mentioned reactions.
Irradiation (λ ≥ 400 nm) of α-epoxyketones 1a –
h and the photocatalyst 2 in a molar ratio of 10 : 1
in cyclopentanone/dry acetonitrile (19 mL/1 mL) re-
sulted in the opening of the epoxide ring and formation
of the diastereomeric spiro-1,3-dioxolanes 3a – e, 4a –
e, 4g, h, of the β-diketone 5, the cis-α-epoxyketone6g,
and also of the chalcones 7e, f, h (Scheme 1). It should
0
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H. R. Memarian et al. · Photocatalytic Ring Opening of α-Epoxyketones
Scheme 1.
Table 1. Photochemical reaction of 1a – h catalyzed by 2 in in cyclohexanone [8] show that the substituted α-ep-
a
cyclopentanone solution .
oxyketones 1a – h behave totally different in the reac-
Products (yield in %)b
tion. Whereas the reaction of 1a – e in the presence of 2
in cyclohexanone resulted in the formation of solely
the cis-diastereomeric 2,5-dioxaspiro[4,5]decanes 8a –
e (Scheme 1), the formation of cis- and trans-2,5-di-
oxaspiro[4,5]nonanes 3a – e, 4a – e and 4g, h and other
products has been observed upon irradiation in cy-
clopentanone.
1
Irrad. time (h)
3
4
1
6
5
7
–
–
–
–
a
b
c
d
e
f
g
h
a
8
5
7
2
6
7
11
9
22 (33) 27 (40) 32
24 (35) 28 (40) 31
22 (32) 27 (42) 32
23 (34) 29 (41) 31
18 (34) 22 (40) 32
–
–
–
–
–
–
–
–
–
–
–
–
–
14 (20)
42 (72)
–
–
–
–
–
41
35 (50) 30 24 (35)
26 (39) 20
IR and 1H NMR data have provided useful in-
formation for the structural assignment of the prod-
ucts. Monitoring of the photoreaction (conversion of
–
32 (48) 14 (18)
Molar ratio of 1a – h : 2 was 10 : 1; b isolated yields based on used 1
(based on consumed 1).
1
a – e, 1g – h and formation of 3a – e, 4a – e, 4g – h)
be mentioned that for selective excitation of 2, the light was carried out by IR spectroscopy, which showed
was passed through a filter solution to prevent the ab- a the shift of the CO band of the aroyl group to
sorption of light by compounds 1a – h. The results are higher frequency due to the opening of the epoxide
summarized in Table 1.
The results obtained in the present study and espe- ance of the aliphatic CH stretching vibration (2850–
ring and release of the ring strain, and the appear-
−
1
cially in comparison to those obtained on irradiation 2950 cm ) because of addition of cyclopentanone.
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H. R. Memarian et al. · Photocatalytic Ring Opening of α-Epoxyketones
605
3
3
4
4
◦
3
3
4
4
◦
H –C –C –H = 145.25
H –C –C –H = 17.57
Fig. 1. The optimized structures of 3a (trans-product) and 4a (cis-product) obtained at the B3LYP/6-31++G(d,p) level of
theory.
Table 2. Comparison of the carbonyl stretching vibration in comparison to those of 3a – e (trans-products), and the
−
1
the IR spectra (ν/cm ) of compounds 1, 3, and 4.
chemical shifts of the aromatic protons are closer and
1
a
b
c
d
e
ν (C=O)
1670
1660
1665
1660
1665
1665
1670
3
a
b
c
d
e
ν (C=O)
1680
1681
1690
1690
1682
–
4
a
b
c
d
e
ν (C=O) appear at higher field for the cis-isomer, which is possi-
1688
bly due to the parallel alignment of the aromatic rings.
1697
1690
1696
1686
1695
1695
Density functional theory at the B3LYP/6-31++G**
level was applied to study structural, electronic, and
bonding characteristics of the photoproducts. The anal-
ysis showed that 4-H is located in the plane of the
phenyl ring, whereas 3-H lies parallel to the phenyl
ring of the benzoyl moiety (Fig. 1). This causes a
deshielding of 4-H and a shielding of 3-H, respectively.
g
h
–
–
g
h
–
1
3
Table 3. Characteristic H chemical shifts (δ/ppm) and J
coupling constants (J/Hz) in the 1H NMR spectra of the
3
3
4
4
trans- (3a – e) and the cis-products (4a – e and 4g, h).
The dihedral angle formed by H –C –C –H in both
isomers support the observed different coupling con-
stants. All these theoretical data confirm the assumed
assignments.
3
δA
δB
JAB
4
δA
δB
JAB
a
b
c
d
e
5.00
4.97
4.98
4.99
4.96
5.42
5.34
5.41
5.31
5.41
7.2
7.2
7.2
7.2
7.2
a
b
c
d
e
g
h
5.57
5.54
5.56
5.43
5.45
5.67
5.46
5.84
5.80
5.81
5.67
5.65
6.08
5.61
8.0
8.0
8.0
7.6
8.0
8.0
8.0
Due to the failure of the ring opening reaction of α-
epoxyketones in the absence of light and photocatalyst,
we have proposed a mechanism involving an electron
transfer-induced ring opening in the presence of var-
ious photocatalysts [7]. The proposed electron trans-
A comparison of the CO frequencies is shown in fer from α-epoxyketones to the electronically excited
Table 2.
photocatayst leads to the formation of three different
1H NMR spectra were helpful for the stereochem- radical cation intermediates 9 – 11 (Scheme 2). Their
ical assignment of the isomeric dioxolanes (Table 3). stability and their involvement in the reaction depend
An AB system for protons 3-H and 4-H of the diox- on the location of the additional substituent in the par-
olane ring was observed at δ = 4.96– 6.08 ppm. Ac- ent molecule 1a. The attack of a suitable nucleophilic
cording to the Karplus-Conroy equation, and using the solvent to the proposed intermediates either from the
Karplus diagram [20], a larger coupling constant is upper side or the lower side accomplishes the reaction.
expected for 3-H and 4-H in the cis-products (4a – e This indicates also that the size and the nucleophilic
and 4g, h). The chemical shifts for 3-H and 4-H of strength of the solvent molecule can explain the ob-
4
a – e, 4g, h (cis-products) are closer to each other in served diastereoselectivity and the rate of reaction.
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H. R. Memarian et al. · Photocatalytic Ring Opening of α-Epoxyketones
Scheme 2.
The interesting results in the present study, espe-
Another result of this study is the deoxygenation of
cially compared with the reaction in cyclohexanone some α-epoxyketones to the corresponding chalcones.
solution, indicate that due to the smaller size of cy- The same reaction also occurs by irradiation of these
clopentanone, a nucleophilic attack at both sides to the compounds in the presence of 1-benzyl-2,4,6-triphen-
reaction intermediates leads to the formation of both ylpyridinium tetrafluoroborate (NBTPT) as photocata-
diastereomers 3 and 4. The results show also that the lyst [11]. We have observed again the same reaction in
preferred attack of cyclopentanone at the reaction in- the presence of the photocatalyst 2 for the formation of
termediates occurs from the less-hindered side to from the chalcones 7e, f, h.
the cis-isomers 4a – e and 4g, h, and that the electronic
Another interesting result in the present study is the
nature of the α-epoxyketone depending on the location conversion of 1h to 5. Photorearrangement of com-
of the additional substituent in the parent molecule 1a pound 1h to the β-diketone 5 has already been reported
explains its effect on the required time of irradiation.
upon irradiation (Scheme 3a) [22]. Since the light has
The photoisomerization of trans-α-epoxyketones to been passed through the filter solution to avoid direct
the corresponding cis-compounds has been explained excitation of α-epoxyketones, we can propose a mech-
with heterolytic Cα –O bond cleavage [21]. Recently, anism, in which the photocatalyst is involved in the
we have reported the same photoisomerization, but conversion (Scheme 3b).
in the presence of 1-benzyl-2,4,6-triphenylpyridinium
According to the proposed mechanism, Cα –O
tetrafluoroborate (NBTPT) as photocatalyst [11]. The cleavage of the complex leads to the formation of a rad-
same mechanism is proposed for the photoisomeriza- ical cation intermediate. Back electron transfer (BET)
tion of 1g in the presence of the photocatalyst 2 to the to this intermediate gives the 1,3-carbo-oxy diradical,
corresponding cis-α-epoxyketone 6 in this study.
the same diradical intermediate proposed to be pro-
Scheme 3. TPT: 2,4,6-triphenylpyrylium tetrafluoroborate; BET: back electron transfer.
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H. R. Memarian et al. · Photocatalytic Ring Opening of α-Epoxyketones
607
duced by direct irradiation of 1h. Hydrogen shift in this 5.42, 3JAB = 7.2 Hz, 2H, 3-H, 4-H), 7.40 (mc, 7H, phenyl
intermediate accomplishes the reaction under forma- H and 2 m-H of PhCO), 7.56 (mc, 1H,p-H of PhCO),
7
7
2
.92 (d, J = 8.4 Hz, 2H, 2 o-H of PhCO). – MS (EI,
tion of the β-diketone 5.
+
+
0 eV): m/z (%) = 308 (3) [M] , 224 (93) [M–C H O] ,
5
8
+
+
03 (100) [M–C H CO] , 202 (66) [M–C H CHO] , 119
Conclusion
6
5
6
5
+
+
(
98) [C H COCH ] , 105 (100) [C H CO] , 91 (89)
6 5 6 5
2
+
+
In conclusion, we have found that due to the smaller
[
C H CH ] , 77 (90) [C H ] ; zone 2: R = 0.52, recov-
6
5
2
6
5
f
size of cyclopentanone compared with cyclohexanone, ered 1a (56 mg, 32 % based on used 1a); zone 3 (R = 0.49),
f
nucleophilic attack of the former at the proposed re- 48 mg (40 % based on consumed and 27 % based on used 1a)
action intermediates results in the formation of dia- of 4a, recrystallized from n-hexane/ethyl acetate; m. p.: 122 –
◦
stereomeric spiro-1,3-dioxolanes. The formation of 125 C.
cis-α-epoxyketones, chalcones and β-diketones has
also been observed in the present study.
cis-3-Benzoyl-4-phenyl-2,5-dioxaspiro[4,4]nonane (4a)
IR:
ν
=
3070, 2982 – 2940, 1688, 1597, 1269,
−
1
1
Experimental Section
1208 cm . – H NMR (400 MHz, CDCl ): δ = 1.58
mc, 4H, cyclopentane H), 1.88 (brd s, 4H, cyclopentane H),
AB system (δA = 5.57, δB = 5.84, J = 8.0 Hz, 2H, 3-H,
-H), 7.10 (mc, 4H, aromatic H), 7.25 (mc, 3H, aromatic
3
(
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-
3
AB
4
H), 7.39 (mc, 1H, p-H of PhCO), 7.47 (d, J = 6.8 Hz, 2
1
eter. H NMR spectra were recorded on a Bruker 400 MHz
+
o-H of PhCO). – MS (EI, 70 eV): m/z(%) = 308 (4) [M] ,
spectrometer in CDCl and [D ]DMSO with TMS as inter-
3
6
+
+
2
24 (97) [M–C H O] , 203 (97) [M–C H O] , 202 (74)
5
8 7
5
nal standard. Mass spectra were measured by electron impact
at 70 eV on a Micromass Platform II instrument. Prepara-
+
+
[
[
(
M–C H CHO] , 119 (94) [C H COCH ] , 105 (100)
6 5 6 5
2
+
+
+
C H CO] , 91 (88) [C H CH ] , 89 (80) [C H ] , 77
6
5
6
5
2
7
5
tive thin layer chromatography (PTLC) was carried out on
+
92) [C H ] .
2
6 5
2
0 × 20 cm plates, coated with a 1 mm layer of Merck
silica gel PF254, prepared by applying the silica as slurry
and drying in air. All irradiations were carried out using a
Irradiation of trans-3-p-methylphenyl-1-phenyl-2,3-epoxy-
1-propanone (1b)
400 W high-pressure Hg lamp from NARVA in Duran glass
PLC, petroleum ether:ethyl acetate = 15 : 2, two times;
equipment. The light was passed through a filter solution
−1
−1
zone 1 (R = 0.74), 46 mg (35 % based on consumed 1b
(
75 g L
of NaNO2 and 4.4 g L of CuSO4 in 2.7 M
f
and 24 % based on used 1b) of 3b, washed with n-hexane;
NH OH) [23] to obtain λ ≥ 400 nm for the selective excita-
4
◦
m. p.: 111 – 115 C.
tion of the photocatalyst 2 and also to prevent the absorption
of the light by 1a – h.
trans-3-Benzoyl-4-(p-methylphenyl)-2,5-dioxaspiro-
To a solution of 0.08 mmol of 2 in dry acetonitrile (1 mL)
and cyclopentanone (19 mL) (c = 0.004 M) was added
[4,4]nonane (3b)
0
.8 mmol of an α-epoxyketone 1a – h (c = 0.04 M), and the
−1
IR: ν = 2962, 2862, 1681, 1595, 1218, 1110 cm . –
mixtures were irradiated until maximum progression of the
reaction was observed. The irradiation times are given in Ta-
ble 1. The excess of cyclopentanone was evaporated under
reduced pressure, and the residue was purified by preparative
TLC (PTLC).
1
H NMR (400 MHz, CDCl ): δ = 1.93 (mc, 8H, cy-
clopentane H), 2.34 (s, 3H, CH ), AB system (δ = 4.97,
δB = 5.34, JAB = 7.2 Hz, 2H, 3-H, 4-H), 7.24 (mc, 5H,
p-H of PhCO and phenyl H), 7.41 (mc, 2H, 2 m-H of
PhCO), 7.91 (mc, 2H, 2 o-H of PhCO). – MS (EI, 70 eV):
3
3
A
3
+
m/z (%) = 238 (7) [M–cyclopentanone] , 147 (3) [M–
Irradiation of trans-1,3-diphenyl-2,3-epoxy-1-propanone
+
+
cyclopentanone–CH C H ] , 134 (10) [PhCOCHO] , 105
3
6
4
(
1a)
+
+
+
(
100) [C H CO] , 91 (23) [CH C H ] , 77 (85) [C H ] ;
6 5 6 6 5
3 4
zone 2: R = 0.54, recovered 1b (59 mg, 31 % based on
f
PLC, petroleum ether:ethyl acetate = 15 : 2, two times;
used 1b); zone 3 (R = 0.46), 53 mg (40 % based on con-
f
zone 1 (R = 0.71), 39 mg (33 % based on consumed 1a
f
sumed 1b and 28 % based on used 1b) of 4b, recrystallized
and 22 % based on used 1a) of 3a, washed with n-hexane;
◦
◦
from n-hexane/ethyl acetate; m. p.: 145 – 148 C.
m. p.: 103 – 105 C.
trans-3-Benzoyl-4-phenyl-2,5-dioxaspiro[4,4]nonane (3a)
cis-3-Benzoyl-4-(p-methylphenyl)-2,5-dioxaspiro-
[
4,4]nonane (4b)
IR: ν = 2922, 1697, 1216, 1037 cm . – 1H NMR
(400 MHz, CDCl ): δ = 1.59 – 1.86 (mc, 8H, cyclopen-
IR: ν
= 3068, 2963 – 2869, 1680, 1595, 1218,
1
2
110 cm 1. – H NMR (400 MHz, CDCl ): δ = 1.74 –
−
1
−1
3
.16 (m, 8H, cyclopentane H), AB system (δA = 5.00, δB
=
3
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H. R. Memarian et al. · Photocatalytic Ring Opening of α-Epoxyketones
tane H), 2.16 (s, 3H, CH ), AB system (δ = 5.53, δB trans-3-Benzoyl-4-(p-methoxyphenyl)-2,5-dioxaspiro-
=
3
A
3
5
2
7
6
2
1
.79, JAB = 8.0 Hz, 2H, 3-H, 4-H), 6.84 (d, J = 8.4 Hz, [4,4]nonane (3d)
H, 2 o-H of phenyl), 6.98 (mc, 2H, 2 m-H of phenyl),
IR:
ν
= 3031, 2992 – 2935, 1690, 1607, 1208,
.26 (mc, 3H, 2 m-H and p-H of PhCO), 7.48 (d, J =
.8 Hz, 2H, 2 o-H of PhCO). – MS (EI, 70 eV): m/z (%) =
−
1
1
1
039 cm . – H NMR (400 MHz, CDCl ): δ = 1.74 – 2.14
(3m, 8H, cyclopentane H), 3.81 (s, 3H, OCH3), AB system
(δA = 4.99, δB = 5.31, JAB = 7.2 Hz, 2H, 3-H, 4-H),
.89 (d, J = 8.0 Hz, 2H, 2 o-H of phenyl), 7.38 (mc, 4H,
m-H of PhCO and 2 m-H of phenyl), 7.55 (mc, 1H, p-H
3
+
+
38 (9) [M–cyclopentanone] , 134 (8) [C H COCHO] ,
6
5
3
+
+
33 (21) [C H COCO] , 105 (100) [C H CO] , 91 (22)
6
5
6 5
6
2
+
+
[
CH C H ] , 77 (86) [C H ] .
3 4
6 6 5
of PhCO), 7.89 (d, J = 8.0 Hz, 2H, 2 o-H of PhCO). –
Irradiation of trans-1-p-methylphenyl-3-phenyl-2,3-epoxy-
+
MS (EI, 70 eV): m/z (%) = 338 (2) [M] , 231 (2) [M–
1-propanone (1c)
+
+
CH OC H ] , 149 (11) [M–cyclopentanone–C H CO] ,
3
6
4
6
5
+
1
35 (6) [CH OC H CO] , 119 (12) [M–CH OC H CO–
3 4 3 4
6
6
PLC, petroleum ether:ethyl acetate = 15 : 2, two times;
+
+
+
cyclopentanone] , 105 (13) [C H CO] , 77 (43) [C H ] ;
6
5
6 5
zone 1 (R = 0.72), 42 mg (32 % based on consumed 1c and
f
zone 2: R = 0.52, recovered 1d (64 mg, 31 % based on
f
22 % based on used 1c) of 3c as a viscous oil.
used 1d); zone 3 (R = 0.46), 59 mg (41 % based on con-
f
sumed 1d and 29 % based on used 1d) of 4d, recrystallized
trans-3-(p-Methylbenzoyl)-4-phenyl-2,5-dioxaspiro-
◦
from n-hexane/ethyl acetate; m. p.: 108 – 111 C.
[4,4]nonane (3c)
IR:
ν
=
3032, 2992 – 2936, 1690, 1607, 1208, cis-3-Benzoyl-4-(p-methoxyphenyl)-2,5-dioxaspiro-
−
100 cm . – H NMR (400 MHz, CDCl ): δ = 1.75 – 1.90 [4,4]nonane (4d)
3
1
1
1
(
(
(
2m, 8H, cyclopentane H), 2.41 (s, 3H, CH ), AB system
3
−1
IR: ν = 2985 – 2921, 1696, 1514, 1210, 1037 cm . –
3
δA = 4.98, δB = 5.41, J = 7.2 Hz, 2H, 3-H, 4-H), 7.21
AB
1
H NMR (400 MHz, CDCl ): δ = 1.8 – 1.98 (2m, 8H,
3
d, J = 8 Hz, 2H, 2 o-H of phenyl), 7.37 (mc, 4H, m-H
cyclopentane H), 3.68 (s, 3H, OCH ), AB system (δ
=
3
A
of phenyl and ArCO), 7.45 (d, J = 6.8 Hz, 1H, p-H of
3
5
(
2
.43, δB = 5.67, JAB = 7.6 Hz, 2H, 3-H, 4-H), 6.59
d, J = 8.0 Hz, 2H, 2 o-H of phenyl), 7.01 (m, 2 H,
m-H of phenyl), 7.28 (m, 3H, 2 m-H and p-H of
PhCO), 7.55 (d, J = 7.2 Hz, 2H, 2 o-H of PhCO). – MS
phenyl), 7.82 (d, J = 7.6 Hz, 2H, 2 o-H of ArCO). – MS
+
(
(
(
EI, 70 eV): m/z (%) = 238 (36) [M–cyclopentanone] , 203
+
+
11) [M–CH C H CO] , 119 (100) [CH C H CO] , 105
3
6
4
6
3 4
+
+
+
6) [C H CHO] , 91 (58) [CH C H ] , 77 (10) [C H ] ;
6
4
3
6
4
6
5
+
(
2
EI, 70 eV): m/z (%) = 254 (20) [M–cyclopentanone] ,
zone 2: R = 0.54, recovered 1c (61 mg, 32 % based on
f
+
03 (4) [M–CH OC H CO] , 202 (19) [M–C H CO–
3 4
6 6 5
used 1c); zone 3 (R = 0.48), 54 mg (42 % based on con-
f
+
+
OCH ] , 149 (18) [M–cyclopentanone–C H CO] , 135
3
6
5
sumed 1c and 27 % based on used 1c) of 4c, recrystallized
+
+
(
[
7) [CH OC H CO] , 107 (4) [CH OC H ] , 105 (100)
◦
3 4 3 4
6
6
from n-hexane/ethyl acetate; m. p.: 134 – 136 C.
+
+
C H CO] , 77 (65) [C H ] .
6
5
6 5
cis-3-(p-Methylbenzoyl)-4-phenyl-2,5-dioxaspiro-
Irradiation of trans-1-p-methoxyphenyl-3-phenyl-2,3-epoxy-
[4,4]nonane (4c)
1-propanone (1e)
IR:
ν
=
3031, 2992 – 2936, 1690, 1608, 1210,
PLC, petroleum ether:ethyl acetate = 5 : 2, two times;
−
1
1
1
(
(
8
039 cm . – H NMR (400 MHz, CDCl ): δ = 1.60
s, 5H, cyclopentane H), 1.86 (s, 3H, cyclopentane H), 2.32
s, 3H, CH ), AB system (δA = 5.56, δB = 5.81, JAB
.0 Hz, 2H, 3-H, 4-H), 7.07 (mc, 7H, phenyl H and 2 m-H
of ArCO), 7.41 (d, J = 7.6 Hz, 2H, 2 o-H of ArCO). – MS
EI, 70 eV): m/z (%) = 238 (6) [M–cyclopentanone] , 119
96) [CH C H CO] , 105 (13) [C H CHO] , 91 (100)
3
zone 1 (R = 0.78), 38 mg (34 % based on consumed 1e and
f
1
8 % based on used 1e) of 3e as a viscous oil.
3
=
3
trans-3-(p-Methoxybenzoyl)-4-phenyl-2,5-dioxaspiro-
4,4]nonane (3e)
[
+
(
(
[
+
+
IR:
ν
= 3067, 2985 – 2918, 1683, 1560, 1237,
3
6
4
6
4
+
+
+
−1
1
CH C H ] , 77 (29) [C H ] , 65 (54) [C H ] .
1061 cm . – H NMR (400 MHz, CDCl3): δ = 1.89 – 2.14
3m, 8H, cyclopentane H), 3.87 (s, 3H, OCH , AB system
δA = 4.96, δB = 5.41, J = 7.2 Hz, 2H, 3-H, 4-H), 6.88
d, J = 8.0 Hz, 2H, 2 m-H of PhCO), 7.56 (mc, 7H, 2 o-H
3
6
4
6
5
5 5
(
(
(
3
3
AB
Irradiation of trans-3-p-methoxyphenyl-1-phenyl-2,3-epoxy-
-propanone (1d)
1
of PhCO and phenyl H). – MS (EI, 70 eV): m/z (%) = 254
+
+
PLC, petroleum ether:ethyl acetate = 5 : 2, two times; (7) [M–cyclopentanone] , 135 (71) [CH OC H CO] ,
3
6
4
+
zone 1 (R = 0.69), 48 mg (34 % based on consumed 1d 119 (17) [M–CH OC H CO–cyclopentanone] , 105 (4)
f
3
6
4
+
+
and 23 % based on used 1d) of 3d, washed with n-hexane; [C H CHO] , 77 (53) [C H ] ; zone 2: R = 0.59, 28 mg
6
4
6
5
f
◦
m. p.: 93 – 95 C.
(20 % based on consumed 1e and 14 % based on used 1e) 7e;
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H. R. Memarian et al. · Photocatalytic Ring Opening of α-Epoxyketones
609
zone 3 (R = 0.55) recovered 1e (66 mg, 32 % based on cis-3-Benzoyl-4-(p-chlorophenyl)-2,5-dioxaspiro-
f
used 1e); zone 4 (R = 0.45), 45 mg (40 % based on con- [4,4]nonane (4g)
f
sumed 1e and 22 % based on used 1e) of 4e, recrystallized
IR:
ν
= 3049, 2986 – 2936, 1695, 1577, 1213,
◦
from n-hexane/ethyl acetate; m. p.: 110 – 113 C.
−
1
1
1
1
039 cm . – H NMR (400 MHz, [D ]DMSO): δ =
.52 (s, 4H, cyclopentane H), 1.70 (s, 4H, cyclopentane
H), AB system (δA = 5.67, δB = 6.08, J = 8.0 Hz, 2H,
-H, 4-H), 7.03 (2m, 5H, aromatic H), 7.06 (mc, 4H, phenyl
6
cis-3-(p-Methoxybenzoyl)-4-phenyl-2,5-dioxaspiro-
3
AB
[4,4]nonane (4e)
3
IR: ν = 2954, 1686, 1576, 1250, 1183, 1028 cm 1. – H0), 7.32 (m , 2H, 2 m-H of PhCO), 7.49 (m , 1H, p-H of
−
c
c
1
H NMR (400 MHz, CDCl ): δ = 1.82 – 2.32 (m, 8H, cy- PhCO), 7.57 (d, J = 7.6 Hz, 2H, 2 o-H of PhCO). – MS (EI,
3
+
+
clopentane H), 3.82 (s, 3H, OCH ), AB system (δ = 5.45, 70 eV): m/z (%) = 342 (11) [M] , 314 (10) [M–C H ] ,
3
A
2
4
3
+
+
δ = 5.65, J = 8.0 Hz, 2H, 3-H, 4-H), 6.75 (d, J = 8.4 Hz, 139 (10) [ClC H CO] , 111 (5) [C H Cl] .
B
AB
4
6
4
6
2
2
H, 2 m-H of ArCO), 7.33 (mc, 5H, phenyl H), 7.84 (mc, 2H,
o-H of ArCO). – MS (EI, 70 eV): m/z (%) = 254 (6) [M–
Irradiation of trans-1-p-chlorophenyl-3-phenyl-2,3-epoxy-1-
propanone (1h)
+
+
cyclopentanone] , 135 (100) [CH OC H CO] , 119 (19)
M–CH OC H CO] , 107 (15) [CH OC H ] , 77 (51)
3
6
4
+
+
[
[
3 4 3 4
6 6
+
PLC, petroleum ether:ethyl acetate = 15 : 2, two times;
C H ] .
6
5
zone 1 (R = 0.84), 68 mg (48 % based on consumed 1h
f
and 32 % based on used 1h) of 5, washed with n-hexane;
Irradiation of trans-1,3-di(p-methoxyphenyl)-2,3-epoxy-1-
propanone (1f)
◦
m. p.: 85 – 88 C; zone 2: R = 0.61, 30 mg (18 % based on
f
consumed 1h and 14 % based on used 1h) of 7h; zone 3
PLC, petroleum ether:ethyl acetate = 5 : 1, two times;
(
Rf = 0.49) recovered 1h (43 mg, 20 % based on used 1h);
zone 1 (R = 0.72), 95 mg (72 % based on consumed 1f and
f
zone 4 (R = 0.38), 56 mg (39 % based on consumed 1h
f
4
2 % based on used 1f) of 7f; zone 2 (R = 0.56) recovered 1f
f
and 26 % based on used 1h) of 4h, recrystallized from n-
(
96 mg, 42 % based on used 1f).
◦
hexane/ethyl acetate; m. p.: 113 – 116 C.
Irradiation of trans-3-p-chlorophenyl-1-phenyl-2,3-epoxy-1-
propanone (1g)
cis-3-(p-Chlorobenzoyl)-4-phenyl-2,5-dioxaspiro-
[4,4]nonane (4h)
PLC, petroleum ether:ethyl acetate = 5 : 2, two times;
IR:
ν
= 3067, 2983 – 2933, 1695, 1588, 1217,
zone 1 (R = 0.70) recovered 1g (64 mg, 30 % based on
−1
1
f
1
(
1
5
050 cm . – H NMR (400 MHz, CDCl ): δ = 1.59 – 1.88
3
used 1g), zone 2: R = 0.50, 51 mg (35 % based on con-
f
m, 8H, cyclopentane H), δ = 1.60 (s, 5H, cyclopentane H),
sumed 1g and 24 % based on used 1g) 6.
.88 (s, 3H, cyclopentane H), AB system (δ = 5.45, δB
=
A
3
.61, J = 8.0 Hz, 2H, 3-H, 4-H), 7.1 (s, 4H, o-H and m-H
AB
cis-3-p-Chlorophenyl-1-phenyl-2,3-epoxy-1-propanone (6)
of phenyl), 7.25 (mc, 2H, 2 m-H of PhCO), 7.28 (s, 1H, p-H
IR: ν = 3087, 1658, 1576, 1093 cm 1. – 1H NMR of phenyl), 7.47 (d, J = 8.4 Hz, 2H, 2 o-H of PhCO). – MS
−
+
(
(
400 MHz, [D ]DMSO): δ = 5.28 (s, 2H, 3-H, 4-H), 7.41 (EI, 70 eV): m/z (%) = 139 (20) [ClC6H4CO] , 111 (25)
6
+
+
mc, 4H, phenyl), 7.48 (mc, 2H, m-H of PhCO), 7.64 (mc, [C6H4Cl] , 77 (45) [C6H5] .
1
H, p-H of PhCO), 7.88 (d, J = 7.6 Hz, o-H of PhCO). – MS
35
+
(
EI, 70 eV): m/z (%) = 258 (4) [M, Cl] , 153 (13) [M–
Acknowledgement
+
+
+
PhCO] , 111 (5) [ClC H ] , 105 (73) [PhCO] , 77 (100)
6
4
+
[
C H ] ; zone 3 (R = 0.44), 75 mg (51 % based on con-
We are thankful to the Center of Excellence (Chemistry)
6
5
f
sumed 1g and 35 % based on used 1g) of 4g, recrystallized and Research Council of the University of Isfahan and the
◦
from n-hexane/ethyl acetate; m. p.: 126 – 129 C.
Office of Graduate Studies for their financial support.
[
[
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610
H. R. Memarian et al. · Photocatalytic Ring Opening of α-Epoxyketones
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