Ring opening of α,β-epoxy phenyl ketones with eerie ammonium nitrate (CAN) and potassium bromide

Article abstract of DOI:10.1139/V07-148

Ring-opening reaction of α,β-epoxy phenyl ketones was achieved cooperatively using cerium ammonium nitrate (CAN) and potassium bromide. The reaction occurred regioselectively at the β-C to afford syn-β-bromo-α-hydroxyl ketones as main outcomes.

Full text of DOI:10.1139/V07-148

142
Ring opening of ␣,␤-epoxy phenyl ketones with
ceric ammonium nitrate (CAN) and potassium
bromide
Zhou Lu, Wentao Wu, Lijun Peng, and Longmin Wu
Abstract: Ring-opening reaction of α,β-epoxy phenyl ketones was achieved cooperatively using cerium ammonium ni-
trate (CAN) and potassium bromide. The reaction occurred regioselectively at the β-C to afford syn-β-bromo-α-
hydroxyl ketones as main outcomes.
Key words: ring-opening, epoxide, ceric ammonium nitrate, potassium bromide.
Résumé : Utilisant l’effet combiné du nitrate d’ammonium cérique (NAC) et du bromure de potassium comme cataly-
seurs, on a réalisé la réaction d’ouverture de cycle de α,β-époxy phénylcétones. La réaction se fait d’une façon stéréo-
sélective au niveau du carbone β et elle conduit aux β-bromo-α-hydroxycétones syn comme produits principaux.
Mots-clés : ouverture de cycle, époxyde, nitrate d’ammonium cérique, bromure de potassium.
[Traduit par la Rédaction] Lu et al. 145
Introduction
tion of epoxides with CAN. In addition, the resulting vicinal
alcohols from the ring-opening reaction of epoxides will be
important intermediates in organic synthesis (14).
Epoxides are important starting materials and intermedi-
ates in organic synthesis (1) because of their easy prepara-
tions and ready reactivities toward nucleophiles. Among the
reports on epoxides, many were involved in ring-opening re-
actions (2). Most of the nucleophilic ring-opening reactions
proceeded via an SN2-like mechanism and afforded the cor-
responding trans-β-Nu alcohols (3). Our recent studies found
that nitric oxide (NO) caused ring opening of 2,3-epoxides
in either syn- or anti-selective fashion, which is strongly de-
pendent on the α-C substituent (4). It was found that cerium
Result and discussion
In the present work, trans chalcone epoxides were em-
ployed as substrates. We started with α,β-epoxy phenyl
ketones 1, which were easily prepared by the reaction of
chalcone with H2O2. Upon treatment of 1 equiv. of 1 with
2.2 equiv. of CAN and 5 equiv. of KBr in acetone at room
temperature (RT), ring-opening reactions occurred
regioselectively at the β-C and brominations specifically at
the β-C, giving β-bromo-α-hydroxyl ketones 2 in moderate
yields (Scheme 1 and Table 1). All products were character-
ammonium nitrate (CAN, (NH4)2Ce(NO3)6),
a single
electron oxidant in organic oxidation reactions (5–11), effi-
ciently catalyzed most ring-opening reactions of epoxides
(12). These reactions occurred in distinct regioselectivity, β-
or α-attack (12e–12f), and in anti and (or) syn manners,
strongly depending upon the molecular structure, the
stoichiometry of CAN used, and the solvent (12). CAN
brought about the conversion of epoxides into β-nitrato alco-
hols in the presence of an excess of nitrate ion (12a–12b).
Recently, it was reported that CAN mediated ring opening of
cyclopropyl alcohols and specifically gave β-functionalized
ketones in the presence of selected anions (13). The
substitutent-dependent fashion in the NO-mediated ring-
opening reaction of epoxides (4) stimulated us to explore
whether a similar effect also exists in the ring-opening reac-
1
ized by IR, MS, HRMS, H, and 13C NMR. Weber first syn-
thesized chalcone bromohydrins using SnBr4 in 1992. He
determined his products to be syn configurations mainly by
NMR parameters (15). As such, the configuration of prod-
ucts 2 was confirmed to be dominantly syn (4a, 15, 16).
It was also found that CAN and KBr acted cooperatively
to cause the ring-opening reactions. No ring-opening reac-
tion occurred in the absence of either CAN or KBr. Further-
more, the reaction proceeded very slowly when a catalytic
amount of CAN was applied. One reason for this may be
partially attributed to polar substituted epoxides having less
activity toward the ring-opening reaction (12d). Although
the reaction mechanism is far from clear, a possible pathway
for the present ring-opening reaction and bromination may
be rationalized in terms of bromine radical, which is formed
by the oxidation of bromide ion with an excess amount of
CAN (13, 17) and the subsequent addition of bromine radi-
cal to three-membered epoxide ring (10a, 18), leading to the
ring opening. On reviewing previous works on similar topics
(4, 19), it is found that the carbonyl group plays a key role
in ring-opening regioselectivity. The carbonyl group causes
Received 24 September 2007. Accepted 4 December 2007.
Published on the NRC Research Press Web site at
canjchem.nrc.ca on 17 January 2008.
Z. Lu, W.T. Wu, L.J. Peng and L.M. Wu.1 Sate Key
Laboratory of Applied Organic Chemistry, Lanzhou
University, Lanzhou 730000, China.
1Corresponding author (email: nlaoc@lzu.edu.cn).
Can. J. Chem. 86: 142–145 (2008)
doi:10.1139/V07-148
© 2008 NRC Canada

Lu et al.
143
Scheme 1.
Br
Br
O
O
O
O
CAN (2.2 equiv.), KBr (5 equiv.)
CH COCH , RT
+
3
3
3
R1
R2
R1
R2
R2
R1
2
OH
OH
1
syn-2
anti-2
dr of syn to anti up to 99:1
Table 1. Ring opening of 2,3-epoxy phenyl ketones with CAN and KBr in acetone.
Substrate
R1
R2
Time (h)
Yield (%)a
dr syn:anti (%)b
1a
1b
1c
1d
1e
1f
1g
1h
1i
Ph
Ph
Ph
Ph
10
18
18
0.1
3
16
16
14
24
20
24
77
73
70
0c
76d
80
76
85
51
71
58
> 99:1
88:12
87:13
—
90:10
> 99:1
87:13
96:4
(p)-Br-Ph
(p)-F-Ph
Ph
Ph
Ph
(p)-Br-Ph
(p)-MeO-Ph
Ph
(p)-MeO-Ph
Ph
(p)-MeO-Ph
(p)-Me-Ph
(p)-Cl-Ph
(p)-Cl-Ph
(p)-Cl-Ph
(p)-O2N-Ph
(p)-O2N-Ph
(m)-O2N-Ph
70:30
77:23
73:27
1j
1k
aYields refer to isolated products.
1
bThe ratio of syn-2 to anti-2 was evaluated using the characteristic H NMR peaks both of α- and β-H, such as in 2j, 5.56
(syn-α-H) to 5.41 ppm (anti-α-H) as well as 5.33 (syn-β-H) to 5.10 (anti-β-H).
cMaterial decomposed in 5 min, giving 91% of 4-methoxybenzaldehyde.
dAlong with 55% of 4-methylbenzaldehyde.
the ring opening uniquely at β-C, yet the stereochemistry
strongly depends on reaction conditions. The assumption of
a one-electron transfer reaction between epoxide and
Ce(IV), with a catalytic amount leading to the formation of
an expoxonium radical cation (12b–12e), will be ruled out in
the present case.
Table 2. Effect of solvents on the yield
of 2a.
Solvent
Yield of 2a (%)
CH3COCH3
CH3CN
77
60
The effect of solvents on this reaction was examined using
1a as a substrate (Table 2). From Table 2 we can find that
some aprotic solvents such as acetone and THF were the
most favorable solvents, whereas CH2Cl2 disfavored the
ring-opening reaction. In general, CAN is insoluble in or-
ganic solvents. If a small amount of water is contained in
solvents, then the solvent polarity somewhat affects the solu-
bility of CAN in reaction media. Otherwise, protic solvents
would join the reaction (12c, 19a), as in the case of metha-
nol (Table 2).
THF
Et2O
66
64
CH3COOEt
CH2Cl2
33
0
19a
CH3OH
Note: The ratio of syn to anti in all sol-
vents was ca. 99:1.
aAlong with 75% of 2-hydroxy-3-methoxy-
1,3-diphenylpropan-1-one (19a).
In summary, we have developed an efficient method for
the regioselective and syn-selective conversion of trans
chalcone epoxides to syn chalcone bromohydrins by CAN
and potassium bromide.
Mercury Plus 300 MHz NMR spectrometer. Chemical shifts
1
(δ) for H and 13C NMR spectra are reported in parts per
million (ppm) from solvent CDCl3 (7.26 ppm) and
(77.0 ppm), respectively, as internal standards relative to
tetramethylsilane. MS data were obtained with EI (70 eV)
on an HP-5988 spectrometer by direct inlet at 70 eV. HRMS
data was obtained on a Bruker Daltonics APEX FT-ICR
spectrometer. Chemicals were of highest grade commer-
cially available and used as received, unless otherwise
stated. All reagents were weighed and handled in air at RT.
Experimental
General
Flash chromatography was carried out using silica gel 60
(200–300 mesh, particle size 0.040–0.062 mm) supplied by
Qingdao Ocean Chemical Plant. Melting points were mea-
sured with a digital Koffer apparatus and were uncorrected.
IR (KBr) analysis of solid compounds was performed on a
Nicolet NEXUS 670 FT-IR spectrophotometer and reported
in cm–1. 1H and 13C NMR spectra were recorded on a Varian
Typical procedure for the preparation of 1a
To a solution of 1.040 g of chalcone (5 mmol) in 25 mL
of methanol were added 1.035 g of K2CO3 (7 mmol) and
© 2008 NRC Canada

144
Can. J. Chem. Vol. 86, 2008
2 mL of H2O2 (30%). The mixture was stirred at ambient
temperature until a white precipitate appeared, then isolated
by filtration with the aid of Celite, and washed with water,
affording 1a. Other substrates were prepared by similar pro-
cedures.
J = 8.1 Hz, 0.12H), 7.61 (d, J = 8.1 Hz, 1H), 7.53 (d, J =
8.1 Hz, 0.2H), 7.50 (d, J = 8.1 Hz, 2H), 7.28 (d, J = 8.1 Hz,
2H), 7.20 (d, J = 8.1 Hz, 0.2), 7.13 (d, J = 8.1 Hz, 2H), 7.07
(d, J = 8.1 Hz, 0.2H), 6.08 (d, J = 4.2 Hz, 1H), 5.81 (d, J =
8.1 Hz, 0.11H), 5.54 (d, J = 8.1 Hz, 0.11H), 5.37 (d, J =
4.2 Hz, 1H), 4.11 (s, 1H), 2.35 (s, 3H). 13C NMR (75 MHz,
CDCl3, ppm) δ: 197.5, 139.3, 133.7, 130.8, 129.2, 128.6,
128.3, 127.8, 127.0, 84.3, 74.2, 21.1. MS-EI m/z: 318 [M+],
320 [M + 2], 239 [M – Br], 238 [M – HBr].
Typical procedure for the ring-opening reaction of 1a
with CAN and KBr
To a solution of 0.112 g (0.5 mmol) of 1a in 15 mL of ac-
etone were added 0.300 g of KBr (2.5 mmol) and 0.600 g of
CAN (1.1 mmol). The mixture was stirred at ambient tem-
perature until the reaction completed, water then added to
dissolve the salts, and extracted with 3 × 10 mL Et2O. The
organic layer was dried over anhyd. Na2SO4, filtered, con-
centrated under vacuum, and purified by flash column chro-
matography on silica gel (petroleum ether/acetic ether 10:1),
giving pure 2a. All compounds were recrystalized from pe-
troleum ether (60–80 °C)-acetic ether. Other ring-opening
reactions were performed accordingly.
Syn-2f (15)
Yellow solid, yield 80%, mp 93–95. IR (KBr, cm–1) ν:
3512, 1692, 1280, 836. 1H NMR (300 MHz, CDCl3, ppm) δ:
7.84 (d, J = 7.5 Hz, 2H), 7.64 (t, J = 7.5 Hz, 1H), 7.45 (d,
J = 7.5 Hz, 2H), 7.17 (m, 4H), 5.57 (d, J = 3.0 Hz, 1H), 5.30
(d, J = 3.0 Hz, 1H), 3.84 (s, 1H). 13C NMR (75 MHz,
CDCl3, ppm) δ: 196.9, 134.7, 134.5, 134.4, 133.8, 129.9,
129.2, 128. 6, 128.4, 76.8, 52.1. MS-EI m/z: 338 [M+], 340
[M + 2], 259 [M – Br], 258 [M – HBr], 261, 260.
Characterization data for products
2g (New compound obtained as a mixture 6.7:1 of
syn/anti isomers)
Syn-2a (15)
Yellow solid, yield 76%, mp 140–142. IR (KBr, cm–1) ν:
3510, 1688, 1276, 830. 1H NMR (300 MHz, CDCl3, ppm) δ:
7.86 (d, J = 8.4 Hz, 0.6 H), 7.70 (dd, J = 8.4 Hz, J = 8.4 Hz,
4H), 7.37 (d, J = 8.4 Hz, 0.6H), 7.21 (dd, J = 8.4 Hz, J =
8.4 Hz, 4H), 5.49 (d, J = 3.9 Hz, 1H), 5.30 (d, J = 9.0 Hz,
0.16H), 5.22 (d, J = 3.9 Hz, 1H), 5.06 (d, J = 8.7 Hz,
0.15H), 3.70 (s, 1H). 13C NMR (75 MHz, CDCl3, ppm) δ:
196.3, 134.9, 134.4, 132.7, 132.5, 132.2, 130.4, 130.1,
128.5, 76.7, 51.9. MS-EI m/z: 337 [M – Br], 336 [M – HBr],
338, 339. HRMS m/z calcd. for C15H11O2ClBr2 [M + Na]+:
440.8398; found: 440.8392.
Yellow solid, yield 77%, mp 90–92. IR (KBr, cm–1) ν:
3472, 1673, 1271, 977. 1H NMR (300 MHz, CDCl3, ppm) δ:
7.85 (d, J = 7.2 Hz, 2H), 7.64 (t, J = 7.5 Hz, J = 7.8 Hz,
1H), 7.50 (m, J = 7.5 Hz, J = 7.8 Hz, 2H), 7.18–7.23 (m,
5H), 5.59 (dd, J = 3.9 Hz, J = 7.2 Hz, 1H), 5.34 (d, J =
3.9 Hz, 1H), 3.73 (d, J = 7.5 Hz, 1H). 13C NMR (75 MHz,
CDCl3, ppm) δ: 197.2, 135.8, 134.4, 134.2, 129.0, 128.9,
128.7, 128.6, 128.2, 76.9, 53.4. EI-MS m/z: 306 [M + 2],
304 [M+], 224, 135. HRMS m/z calcd. for C15H13O2Br [M +
Na]+: 326.9991; found: 326.9995.
2b (15) (Obtained as a mixture 7:1 syn/anti isomers)
Yellow solid, yield 73%, mp 128–130. IR (KBr, cm–1) ν:
3489, 1677, 1300, 860. 1H NMR (300 MHz, CDCl3, ppm) δ:
7.87 (d, J = 9.0 Hz, 0.4H), 7.72 (d, J = 9.0 Hz, 2H), 7.63 (d,
J = 9.0 Hz, 2H), 7.46 (d, J = 9.0 Hz, 0.4H), 7.38 (d, J =
9.0 Hz, 0.4H), 7.33 (m, 2H), 7.23 (m, 3H), 5.72 (d, J =
8.1 Hz, 0.16H), 5.53 (d, J = 3.6 Hz, 1.1H), 5.31 (d, J =
3.6 Hz, 0.98H), 5.15 (d, J = 8.1 Hz, 0.14H), 3.73 (s, 1H).
13C NMR (75 MHz, CDCl3, ppm) δ: 196.5, 135.8, 133.0,
132.2, 131.3, 130.1, 129.3, 128.4, 127.2, 77.6, 53.2. MS-EI
m/z: 304 [M – HBr], 303 [M – Br], 305, 302, 215, 213.
2h (New compound obtained as a mixture 25:1 of
syn/anti isomers)
Yellow solid, yield 85%, mp 88–90. IR (KBr, cm–1) ν:
3515, 1684, 1286, 836. 1H NMR (300 MHz, CDCl3, ppm) δ:
7.83 (d, J = 8.7 Hz, 2H), 7.17 (m, 3H), 6.98 (t, J = 8.7 Hz,
3H), 5.73 (d, J = 8.1 Hz, 0.06H), 5.50 (d, J = 3.6 Hz, 1H),
5.27 (d, J = 3.6 Hz, 1H), 5.11 (d, J = 8.1 Hz, 0.04H), 3.91
(s, 3H), 3.82 (s, 1H). 13C NMR (75 MHz, CDCl3, ppm) δ:
194.9, 164.6, 134.5, 131.0, 129.9, 128.8, 128.2, 126.5,
114.3, 76.2, 55.5, 52.5. MS-EI m/z: 289 [M – Br], 288 [M –
HBr], 291, 290, 135. HRMS m/z calcd. for C16H15O3ClBr
[M + Na]+: 392.9868; found: 392.9862
2c (15) (Obtained as a mixture 6.7:1 syn/anti isomers)
Yellow solid, yield 70%, mp 98–101. IR (KBr, cm–1) ν:
3510, 1680, 1270, 863. 1H NMR (300 MHz, CDCl3, ppm) δ:
8.05 (t, J = 8.1 Hz, 0.17H), 7.89 (t, J = 8.1 Hz, 1.4H), 7.48
(t, J = 8.1 Hz, 0.6H), 7.46–7.15 (m, 7.7H), 6.87 (t, J =
8.1 Hz, 0.35H), 5.75 (d, J = 8.1 Hz, 0.15H), 5.53 (d, J =
4.2 Hz, 1H), 5.29 (d, J = 4.2 Hz, 1H), 5.20 (d, J = 8.1 Hz,
0.16H), 3.91 (s, 1H). 13C NMR (75 MHz, CDCl3, ppm) δ:
195.8, 167.9, 135.9, 131.4, 130.5, 128.7, 128.4, 127.2,
116.3, 76.3, 53.3. MS-EI m/z: 322 [M+], 324 [M + 2], 306,
304, 169, 171, 153.
2i (New compound obtained as a mixture 2.3:1 of
syn/anti isomers)
Yellow solid, yield 51%, mp 112–115. IR (KBr, cm–1) ν:
3530, 1705, 1355, 844. 1H NMR (300 MHz, CDCl3, ppm) δ:
8.22 (d, J = 8.1 Hz, 1H), 8.04 (m, 2H), 7.86 (d, J = 7.8 Hz,
1H), 7.49 (m, 3H), 7.36 (d, J = 8.1 Hz, 1H), 5.61 (d, J =
4.2 Hz, 0.7H), 5.41 (d, J = 8.4 Hz, 0.3H), 5.26 (d, J =
4.2 Hz, 0.7H), 5.14 (d, J = 8.4 Hz, 0.3H), 3.89 (s, 1.38H).
13C NMR (75 MHz, CDCl3, ppm) δ: 197.2, 193.5, 148.2,
146.3, 144.7, 142.3, 134.5, 133.3, 133.1, 132.7, 128.4,
128.1, 127.5, 127.1, 119.4, 119.1, 76.3, 74.5, 55.2, 52.8.
MS-EI m/z: 270 [M – Br], 269 [M – HBr], 165, 105. HRMS
m/z calcd. for C15H12O4NBr [M + H]+: 351.0111; found:
351.0115.
2e (15) (Obtained as a mixture 9.5:1 of syn/anti isomers)
Yellow solid, yield 76%, mp 88–91. IR (KBr, cm–1) ν:
3480, 1658, 1266, 810. 1H NMR (300 MHz, CDCl3, ppm) δ:
7.92 (d, J = 8.1 Hz, 0.2H), 7.87 (d, J = 8.1 Hz, 2H), 7.70 (d,
© 2008 NRC Canada

Lu et al.
145
X.J. Shang, Z.Q. Liu, and L.M. Wu. Synth. Commun. 36,
3149 (2006).
2j (New compound obtained as a mixture 3.3:1 of
syn/anti isomers)
Yellow solid, yield 71%, mp 103–105. IR (KBr, cm–1) ν:
3518, 1695, 1338, 835. 1H NMR (300 MHz, CDCl3, ppm) δ:
8.22 (d, J = 8.7 Hz, 0.6H), 8.06 (d, J = 8.7 Hz, 2H), 7.97 (d,
J = 8.7 Hz, 0.7H), 7.86 (d, J = 8.7 Hz, 2H), 7.66 (d, J =
8.7 Hz, 0.6H), 7.37 (d, J = 8.7 Hz, 2H), 7.00 (d, J = 8.7 Hz,
2H), 6.94 (d, J = 8.7 Hz, 0.6H), 5.56 (d, J = 3.6 Hz, 1H),
5.41 (d, J = 8.1 Hz, 0.3H), 5.33 (d, J = 3.3 Hz, 1H), 5.10 (d,
J = 8.1 Hz, 0.3H), 3.91 (s, 4H), 3.87 (s, 1.2H). 13C NMR
(75 MHz, CDCl3, ppm) δ: 194.7, 191.1, 164.9, 147.8, 142.9,
131.5, 131.2, 129.7, 128.4, 126.2, 123.5, 123.2, 114.6,
114.2, 109.7, 76.1, 55.7, 51.4. MS-EI m/z: 301 [M – Br],
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2k (New compound obtained as a mixture 2.8:1 of
syn/anti isomers)
Yellow solid, yield 58%, mp 86–88. IR (KBr, cm–1) ν:
3528, 1712, 1357, 720. 1H NMR (300 MHz, CDCl3, ppm) δ:
8.12 (m, 4H), 7.88 (m, 2H), 7.68 (m, 1H), 7.53 (m, 6H),
5.61 (d, J = 4.2 Hz, 1H), 5.42 (d, J = 8.4 Hz, 0.38H), 5.38
(d, J = 4.2 Hz, 1H), 5.19 (d, J = 8.4 Hz, 0.36H), 3.97 (s,
1.4H). 13C NMR (75 MHz, CDCl3, ppm) δ: 197.0, 193.8,
148.0, 147.8, 138.0, 134.5, 134.3, 134.0, 129.8, 129.6,
128.4, 128.1, 127.8, 123.7, 123.4, 122.0, 76.4, 73.8, 51.0,
47.5. MS-EI m/z: 270 [M – Br], 269 [M – HBr], 165, 105.
HRMS m/z calcd. for C15H12O4NBr [M + H]+: 351.0111;
found: 351.0108.
Acknowledgement
Project 20572040 was supported by National Natural Sci-
ence Foundation of China.
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