Catalytic, regioselective, and green methods for rearrangement of 1,2-diaryl epoxides to carbonyl compounds employing metallic triflates, Br?nsted-acidic ionic liquids (ILs), and IL/microwave; experimental and computational substituent effect study on aryl versus hydrogen migration

Article abstract of DOI:10.1016/j.apcata.2014.08.009

The Lewis-acid catalyzed rearrangement of parent trans-stilbene oxide 1 was studied with M(OTf)₃/DCM and M(OTf)₃/[BMIM][BF₄] (M = Bi, Al, Ga, Sc, and Yb; [BMIM] = butylmethylimidazolium) and Zn(NTf₂)₂, and with Bi(OTf)₃/[BMIM][X] (X = NTf₂, OTf, PF₆, and BF₄), employing 5 mol% of catalyst. Selective formation of 2,2-dipheylacetaldehyde 2 (phenyl migration product) was observed in all cases, with Bi(OTf)₃ proving most efficient. The rearrangement of 1 was also effected in [BMIM][X] (X = NTf₂, OTf, PF₆, and BF4) without an added catalyst under microwave MW irradiation, and X = PF₆ gave the highest yield and selectivity. Efficient and selective rearrangement of 1-2 was also observed with 0.1-0.3equiv. of [BMIM(SO₃H)][OTf] in DCM and in [BMIM][X]. A substituent effect study was performed with a series of singly substituted 1,2-diphenyl oxiranes (with X = OMe, Me, F, CN, and NO₂) with 5mol% Bi(OTf)₃ in DCM and in [BMIM][NTf₂]. Notable formation of ketones was observed with the NO₂ and CN derivatives. Competing formation of ketones was also observed in [BMIM][PF₆] under MW and under Br?nsted acid catalysis with [BMIM(SO₃H)][OTf] in DCM and in [BMIM][NTf₂]. The aryl versus H migration was studied computationally by DFT and MP2 methods and by including solvation effects (IEFPCM).

Full text of DOI:10.1016/j.apcata.2014.08.009

Applied Catalysis A: General 486 (2014) 1–11
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Catalytic, regioselective, and green methods for rearrangement of
1,2-diaryl epoxides to carbonyl compounds employing metallic
triflates, Brønsted-acidic ionic liquids (ILs), and IL/microwave;
experimental and computational substituent effect study on aryl
versus hydrogen migration
Arezu Jamaliana, Benjamin Rathmana, Gabriela L. Boroskyb, Kenneth K. Laalia,∗
a Department of Chemistry, University of North Florida, 1, UNF Drive, Jacksonville, FL 32224, USA
b INFIQC, CONICET and Departamento de Matemática y Física, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria,
Córdoba 5000, Argentina
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 June 2014
Received in revised form 6 August 2014
Accepted 9 August 2014
Available online 19 August 2014
The Lewis-acid catalyzed rearrangement of parent trans-stilbene oxide 1 was studied with M(OTf)3/DCM
and M(OTf)3/[BMIM][BF4] (M = Bi, Al, Ga, Sc, and Yb; [BMIM] = butylmethylimidazolium) and Zn(NTf2)2,
and with Bi(OTf)3/[BMIM][X] (X = NTf2, OTf, PF6, and BF4), employing 5 mol% of catalyst. Selective forma-
tion of 2,2-dipheylacetaldehyde 2 (phenyl migration product) was observed in all cases, with Bi(OTf)3
proving most efficient. The rearrangement of 1 was also effected in [BMIM][X] (X = NTf2, OTf, PF6, and
BF4) without an added catalyst under microwave MW irradiation, and X = PF6 gave the highest yield
and selectivity. Efficient and selective rearrangement of 1–2 was also observed with 0.1–0.3 equiv. of
[BMIM(SO3H)][OTf] in DCM and in [BMIM][X]. A substituent effect study was performed with a series
of singly substituted 1,2-diphenyl oxiranes (with X = OMe, Me, F, CN, and NO2) with 5 mol% Bi(OTf)3 in
DCM and in [BMIM][NTf2]. Notable formation of ketones was observed with the NO2 and CN derivatives.
Competing formation of ketones was also observed in [BMIM][PF6] under MW and under Brønsted acid
catalysis with [BMIM(SO3H)][OTf] in DCM and in [BMIM][NTf2]. The aryl versus H migration was studied
computationally by DFT and MP2 methods and by including solvation effects (IEFPCM).
Keywords:
1,2-Diaryl-epoxide
Rearrangement to carbonyl compounds
Metallic triflates
Brønsted acidic ionic liquids
Substituent effect on Ar versus H migration
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
valence vanadium complexes [5], bismuth oxide perchlorate [6],
copper(II) tetrafluoroborate [7,8], iridium trichloride [9], [(␩5-
C5H5)Fe(CO)2(THF)][BF4] [10], mixed-valent iron trifluoroacetate
[11], Ce(OTf)3 and Er(OTf)3 [12], and Bi(OTf)3 [13,14]. These
reactions typically employed DCM, THF, MeCN, and Et2O as sol-
vent. A high-valent metalloporphyrin complex Cr(TPP)OTf in DCE
solvent proved efficient in regio- and stereo-selective epoxide
rearrangement to aldehydes [15,16].
The rearrangement of epoxides to carbonyl compounds, also
referred to as “Meinwald rearrangement”, is a fundamentally
important transformation with significant synthetic and indus-
trial utility, and it is therefore not surprising that a rich literature
employing a wide range of catalysts is associated with this reaction,
and interest in this transformation still continues.
Despite the significantly greater migratory aptitude of hydrogen
versus aryl, a large majority of Lewis acid-catalyzed epoxide ring
opening reactions of styrene oxides and stilbene oxides result in
the formation of aldehydes (aryl migration) (Fig. 1), but situations
where the ketone is formed, either as minor product along with the
aldehyde or as a major product, have also been reported [5].
Concerning the Brønsted acid-catalyzed rearrangement, acidic
zeolite HZSM-5 in solvents such as CH2Cl2, CHCl3 and Et2O [17],
and Nafion-H/DCM [18], proved efficient for isomerization of
styrene oxide and stilbene oxide with high selectivity toward the
Earlier studies employed stoichiometric (or excess) Lewis acids
such as InCl3, BF3·Et2O, lithium salts, and methylaluminum bis(4-
bromo-2,6-di-tert-butylphenoxide) [1–4]. With the goal to make
the process catalytic and regioselective, a number of inorganic
and organometallic catalysts have been employed, namely high
∗
Corresponding author. Tel.: +1 904 6201503; fax: +1 902 6203535.
E-mail address: Kenneth.Laali@UNF.edu (K.K. Laali).
http://dx.doi.org/10.1016/j.apcata.2014.08.009
0926-860X/© 2014 Elsevier B.V. All rights reserved.

2
A. Jamalian et al. / Applied Catalysis A: General 486 (2014) 1–11
Fig. 1. 1,2-diaryl-epoxide ring opening.
aldehyde, although minor amounts of the ketone was formed from
trans-stilbene oxide over zeolites [17].
in order to remove the unreacted benzyl alcohol and dimethyl sul-
fide. Benzyldimethylsulfonium hydrogensulfate was obtained as a
pure colorless oil in 85% yield; 1H NMR (500 MHz, d6-DMSO), ı 7.52
(s, 5H); 4.65 (s, 2H); 2.80 (s, 6H); 13C NMR (125 MHz, d6-DMSO), ı
131.2, 130.0, 129.7, 128.8, 45.9, 24.1.
Continuing our interest in synthesis and catalysis in ionic liq-
uids (ILs) [19], we report here on catalytic and regioselective
methods for rearrangement of stilbene oxides via (a) Lewis acid-
catalysis employing a series of metallic triflates in DCM and in
[BMIM][X] (X = NTf2, OTf, PF6, and BF4), (b) Brønsted acid cataly-
sis with [BMIM(SO3H)][OTf] in DCM and in [BMIM][X] as solvents,
and (c) MW irradiation in [BMIM][X] (X = NTf2, OTf, PF6, and BF4)
without an added catalyst, and with recycling and reuse of the IL.
A substituent effect study with a series of mono-substituted 1,2-
diphenyl oxiranes (with X = OMe, Me, F, CN, and NO2) was also
undertaken in DCM and in IL solvents under Lewis acid, Brønsted
acid, and under MW without an added catalyst. To gain some
mechanistic insight, the ring opening process was also studied
computationally by density functional theory (DFT) and MP2 meth-
ods to gauge the relative energies of cationic intermediates and
substituent effect on aryl/phenyl versus hydrogen shift. The ionic
liquid version of this chemistry, with or without an added catalyst
and with recycling and reuse of the IL, offers alternative and green
methods to perform this synthetically important transformation.
2.3. General procedure for the synthesis of the singly substituted
stilbene oxides
Following the literature procedure [25] para-substituted
benzaldehyde (10.0 mmol), benzyldimethylsulfonium hydrogen-
sulfate (12.0 mmol), and 0.2 g of BTEAC were suspended in 10 mL
of CH2Cl2. The solution was stirred and cooled in an ice bath and
10.0 mL of 50% NaOH was added drop-wise. After the addition was
completed the reaction mixture was allowed to warm to room tem-
perature and stirred until completion (monitored by TLC). It was
diluted with 10 mL of water and extracted three times with 20 mL
of DCM. The combined organic extracts were dried over MgSO4
and the solvent was evaporated to yield a crude solid which was
purified by column chromatography with ethyl acetate/n-hexane
(10%).
2. Experimental
2.3.1. Preparation of 2-(4-nitrophenyl)-3-phenyl-oxirane 1e
(typical procedure)
2.1. General
4-Nitrobenzaldehyde (1.51 g, 10.0 mmol), benzyldimethylsulfo-
nium hydrogensulfate (3.0 g, 12.0 mmol) and 0.2 g of BTEAC were
suspended in 10 mL of CH2Cl2. The solution was stirred and cooled
in an ice bath and 10 mL of 50% NaOH was added drop-wise.
After the addition was completed the brownish reaction mixture
was allowed to warm to room temperature and stirred for 3 h. It
was then diluted with 10.0 mL of water and extracted three times
with 20.0 mL of DCM. The combined organic extracts were dried
over MgSO4, the solvent was evaporated, and the crude brown-
ish solid was recrystallized from CH3CN/H2O (70%). A mixture of
cis and trans isomers was obtained in 85% yield (cis: trans 2:3).
The trans isomer was separated by column chromatography with
ethyl acetate/n-hexane (10%) as the eluent. The yield of pure trans-
2-(4-nitrophenyl)-3-phenyl-oxirane 1e [26] was 1.1 g (46%): light
yellow crystals; m.p. 125–127 ◦C (lit. [27] 125–128 ◦C); IR (CH2Cl2)
3055, 2985, 1604, 1523, 1346, 1265, 1111 cm−1; 1H NMR (500 MHz,
CDCl3) ı 8.25 (d, J = 8.0 Hz, 2H) 7.52 (d, J = 8.0 Hz, 2H) 7.41–7.35
(m, 5H), 3.98 (d, J = 2.0 Hz, 1H), 3.86 (d, J = 2.0 Hz, 1H); 13C NMR
(125 MHz, CDCl3) ı 147.9, 144.4, 136.1, 128.8, 128.8, 126.3, 125.6,
123.9, 63.4, 61.7; GC–MS m/z 241 (M+), 196 (100%).
Butyl methyl imidazolium ionic liquids [BMIM][X] were
synthesized using established literature procedures [20]. 1-
Methyl-3-(4-sulfobutyl)imidazolium triflate [BMIM(SO3H)][OTf]
was synthesized following the reported methods [21,22]. Ga(OTf)3
was prepared according to the literature [23]. Other metallic tri-
flates M(OTf)3 and Zn(NTf2)2 were high purity commercial samples
and were used without further purification. Column chromatog-
raphy was performed on silica gel (200–400 mesh). NMR spectra
were recorded in CDCl3 on a Varian 500 MHz NMR instrument
(1H: 500 MHz, 19F: 470 MHz, 13C: 125 MHz). GC monitoring was
performed on an HP-5890 instrument. GC–MS analyses were per-
formed on a Varian CP-3800-Saturn 2200 instrument. Microwave
(MW) induced experiments were performed in 1-Point Support-
Biotage Initiator 2.0, and the IR spectra were recorded on a
Shimadzu FTIR-8400S spectrometer.
2.2. Synthesis of benzyldimethylsulfonium hydrogensulfate
Preparation of benzyldimethylsulfonium hydrogensulfate was
essentially carried out by the procedure reported by Forrester
et al. [24] with a slight modification in the workup. When ben-
zyldimethylsulfonium hydrogensulfate was produced according to
the Forrester’s method, the lower layer containing the sulfonium
salt was washed repeatedly with diethyl ether and dried in vacuo
Trans-2-(4-methylphenyl)-3-phenyl oxirane 1a [27], (crude yield
70%, isolated yield 48%); white solid; m.p. 55–57 ◦C (lit. [26]
59–60 ◦C); IR (CH2Cl2) 3047, 2985, 2306, 1604, 1519, 1458, 1265,
1111 cm−1
;
1H NMR (500 MHz, CDCl3) ı 7.39–7.34 (m, 5H),
7.25–7.19 (m, 4H), 3.86 (d, J = 2.0 Hz, 1H), 3.85 (d, J = 2.0 Hz, 1H),
2.38 (s, 3H); 13C NMR (125 MHz, CDCl3) ı 138.2, 137.3, 134.1, 129.3,

A. Jamalian et al. / Applied Catalysis A: General 486 (2014) 1–11
3
128.6, 128.5, 125.5, 125.5, 62.9, 62.8, 21.2; GC–MS m/z 210 (M+), 165
(100%), 181 (60%).
evaporated under vacuum and the crude product was purified by
column chromatography with ethyl acetate/n-hexane (10–20%).
Trans-2-(4-methoxyphenyl)-3-phenyl oxirane 1b [28] (crude
yield 56%, isolated yield 37%); white solid; m.p. 80–82 ◦C (lit. [26]
2.5.1. Bi(OTf)3 catalyzed isomerization in [BMIM][NTf2] – typical
procedure (Table 4, entry 1)
80–81 ◦C); IR (CH2Cl2) 2998, 2836, 1613, 1172, 1111 cm−1 1H NMR
;
(500 MHz, CDCl3) ı 7.36–7.33 (m, 5H), 7.31–7.23 (m, 2H), 6.90 (d,
Compound
1 (0.050 g, 0.25 mmol) was added to Bi(OTf)3
J = 8.5 Hz, 2H), 3.84 (d, J = 1.5 Hz, 1H), 3.80 [s, 1H and 3H(OMe)]; 13
C
(0.008 g, 5 mol%) dissolved in 1.0 mL of [BMIM][NTf2] in a schlenk
tube. The reaction was performed under sonication at ambient tem-
perature and monitored by GC. After 5 min, the reaction mixture
was extracted with 3 × 5 mL of Et2O. The combined ether extracts
was washed with water and dried over MgSO4, and the solvent was
evaporated under vacuum. The crude mixture was purified by col-
umn chromatography with ethyl acetate/n-hexane (10%) to give 2
(0.040 g; 80%).
NMR (125 MHz, CDCl3) ı 159.8, 137.3, 129.1, 128.6, 128.3, 126.8,
125.5, 114.0, 62.8, 62.7, 55.4; GC–MS m/z 226 (M+), 197 (100%).
Trans-2-(4-fluorophenyl)-3-phenyl oxirane 1c [28], (crude yield
75%, isolated yield 54%); white solid; m.p.72–73 ◦C (lit. [7]
76–77 ◦C); IR (CH2Cl2) 3056, 2965, 2306, 1604, 1512, 1419, 1265,
1157 cm−1 1H NMR (500 MHz, CDCl3) ı 7.39–7.31 (m, 7H), 7.07
;
(t, J = 8.5 Hz, 2H), 3.90 (d, J = 2.0, 1H), 3.80 (d, J = 2.0, 1H); 13C NMR
(125 MHz, CDCl3) ı 162.8 (d, J = 245.0 Hz), 136.8, 132.9 (d, J = 2.8 Hz),
128.5 (d, J = 22.0 Hz), 127.2 (d, J = 8.0 Hz), 125.5, 115.6 (d, J = 22.0 Hz),
62.8, 62.3; 19F NMR (470 MHz, CDCl3) ı −113.6 (s, 1H); GC–MS m/z
214 (M+), 165 (100%).
2,2-Diphenylacetaldehyde 2 [31], clear light yellow liquid, IR
(CH2Cl2) 3060, 3030, 1724, 1657, 1599, 1495, 1278 cm−1 1H NMR
;
(500 MHz, CDCl3) ı 9.83 (d, J = 3.0 Hz, 1H), 7.28–7.26 (t, J = 16.5 Hz,
2H), 7.19 (d, J = 8.5 Hz, 2H), 7.11 (t, J = 8.5 Hz, 1H), 4.77 (d, J = 2.5 Hz,
1H); 13C NMR (125 MHz, CDCl3) ı 198.6, 136.4, 129.2, 129.1, 127.7,
64.1; GC–MS m/z 196 (M+), 167 (100%).
Trans-2-(4-cyanophenyl)-3-phenyl oxirane 1d [29] (crude yield
78%, isolated yield 47%); white solid; m.p. 67–68 ◦C; IR (CH2Cl2)
3066, 2989, 2225, 1924, 1813, 1612, 1496, 1458, 1427,1276,
1111 cm−1 1H NMR (500 MHz, CDCl3) ı 7.69 (d, J = 8.0 Hz, 2H), 7.47
;
2.6. Rearrangement in [BMIM][X] under MW irradiation
(Tables 6 and 12)
(d, J = 8.0 Hz, 2H) 7.42–7.34 (m, 5H), 3.92 (d, J = 2.0 Hz, 1H), 3.83
(d, J = 2.0 Hz, 1H); 13C NMR (125 MHz, CDCl3) ı 142.8, 136.5, 132.7,
129.1, 129.0, 126.5, 125.8, 119.1, 112.3, 63.6, 62.2; GC–MS m/z 221
(M+), 165 (100%).
The diaryl-epoxide (0.25 mmol) was added to a MW vial con-
taining [BMIM][X] (1 mL) and the reaction mixture was subjected
to MW irradiation in sealed vials at 100 W until the vial tempera-
ture reached 200 ◦C (45–140 s depending on the sample), at which
point the reaction was stopped, the reaction mixture was cooled to
r.t. and extracted repeatedly with 5 mL portions of Et2O. The com-
bined ether extracts was concentrated under vacuum to give the
crude product mixtures which were purified by chromatography
with ethyl acetate/n-hexane (10%). Chromatographic separation of
2b/4b mixture was only partially successful.
2.4. Bi(OTf)3 catalyzed isomerizations in DCM – general
procedure (Table 8)
The diaryl-epoxide was added to 5 mol% of Bi(OTf)3 dissolved
in dry DCM (2 mL) in a 5 mL round bottom flask and the reaction
mixture was stirred at r.t. and monitored by GC until completion. It
was then diluted with DCM (5 mL) and washed with water (5 mL).
The organic layer was dried (MgSO4) and the solvent was removed
under vacuum. The corresponding product was purified by column
chromatography with ethyl acetate/n-hexane (10%).
2-(4-Methoxyphenyl)-2-(phenyl)acetaldehyde 2b [8] 1H NMR
(500 MHz, CDCl3) (in a mixture with 4b): ı 9.92 (d, J = 2.5, 1H), 7.37
(d, J = 7.5, 2H), 7.31 (d, J = 7.5, 1H), 7.21 (d, J = 9.5 Hz, 2H), 7.14 (d,
J = 9.5 Hz, 2H), 6.92 (d, J = 9.5), 4.84 (d, J = 2.5, 1H), 3.80 (s, 3H).
2-(4-Methoxyphenyl)-phenyl-ethanone 4b [32] (present as minor
2.4.1. Bi(OTf)3 catalyzed isomerization of 1a in DCM solvent –
typical procedure (Table 8, entry 1)
component together with 2b) 1H NMR (500 MHz, CDCl3)
ı
8.01–8.02 (m, 2H), 7.55 (m, 1H), 7.47–7.43 (m, 2H), 7.17 (d, J = 9.0 Hz,
2H), 6.87 (d, J = 9.0 Hz, 2H), 4.23 (s, 2H), 3.78 (s, 3H).
Compound 1a (0.053 g) was added to 5 mol% of Bi(OTf)3 (0.008 g)
dissolved in 2 mL of dry DCM in a 5-mL round bottom flask. The
reaction mixture was stirred at r.t. for 5 min, diluted with dry DCM
(5 mL) and washed with water (5 mL). The organic layer was dried
with MgSO4 and the solvent was removed under vacuum. The crude
2-(phenyl)-2-(4-methylphenyl)-acetaldehyde 2a was purified by
column chromatography using ethyl acetate/n-hexane (10%), and
pure 2-(4-methylphenyl)-2-(phenyl)acetaldehyde 2a was obtained
in 90% yield (0.048 g).
1-(4-Nitrophenyl)-2-phenyl ethanone 3e [33], yellow solid, m.p.
156–157 ◦C; IR(CH2Cl2) 1693, 1527, 1350 cm−1 1H NMR (500 MHz,
;
CDCl3) ı 8.30 (d, J = 8.0 Hz, 2H), 8.14 (d, J = 8.0 Hz, 2H), 7.36–7.24 (m,
5H), 4.33 (s, 2H) 13C NMR (125 MHz, CDCl3) ı 196.4, 152.2, 141.3,
130.0, 129.7, 129.3, 127.7, 124.24, 121.9, 46.4.
2-(4-Nitrophenyl)-2-phenylacetaldehyde 2e, IR (CH2Cl2) 2306,
1732 cm−1 1H NMR (500 MHz, CDCl3) (from crude product mix-
,
ture) ı 9.96 (d, J = 2.5 Hz, 1H), 8.33 (d, J = 8.5, 2H), 7.94 (d, J = 8.5,
2H), 7.81–7.79 (m, 2H), 7.64 (d, J = 8.5, 2H), 7.53 (t, 2H), 7.33 (t, 2H),
5.05 (s, 1H).
2-(4-Methylphenyl)-2-(phenyl)acetaldehyde 2a [30], yellow oil,
IR (CH2Cl2) 3028, 2920, 2816, 1716, 1600, 1512, 1454, 1114 cm−1
;
1H NMR (500 MHz, CDCl3) ı 10.00 (d, J = 2.0 Hz, 1 H), 7.46–7.20 (m,
9H), 4.93 (d, J = 2.0 Hz, 1H), 2.42 (s, 3H); 13C NMR (125 MHz, CDCl3)
ı 198.9, 137.6, 136.8, 133.5, 130.0, 129.4, 129.3, 129.2, 127.8, 64.0,
21.3; GC–MS m/z 210 (M+), 181 (100%).
2.7. [BMIM(SO3H)][OTf] catalyzed isomerization in [BMIM][NTf2]
– general procedure (Table 11)
The diaryl-epoxide (0.25 mmol) was added to a pre-sonicated
homogeneous mixture of [BMIMSO3H][OTf] (10 mol%) and
[BMIM][NTf2] (1 mL). The reaction was performed under son-
ication at ambient temperature and monitored by GC. After
completion, the reaction mixture was repeatedly extracted with
Et2O and the combined ether extracts was washed with water and
dried over MgSO4. The solvent was evaporated under vacuum and
the residue was purified by column chromatography with ethyl
acetate/n-hexane (10–20%).
2.5. Bi(OTf)3 catalyzed isomerization reactions in [BMIM][NTf2] –
general procedure (Table 9)
The diaryl-epoxide (0.25 mmol) was added to Bi(OTf)3 dissolved
in 1 mL of [BMIM][NTf2] in a small schlenk tube. The reaction was
performed under sonication at ambient temperature and moni-
tored by GC. After completion, the reaction mixture was extracted
repeatedly with diethyl ether. The combined organic extract
was washed with water, dried over MgSO4, and the solvent was

4
A. Jamalian et al. / Applied Catalysis A: General 486 (2014) 1–11
2.7.1. Rearrangement of trans-2-4-(cyanophenyl)-3-phenyl
oxirane 2d catalyzed by [BMIM(SO3H)][OTf] in [BMIM][NTf2] –
typical procedure (Table 11 entry 4)
set were performed at the B3LYP/6-31G(d,p) optimized geome-
tries. Solvation effects were included by performing SCRF-polarized
continuum model (IEFPCM) [38] energy minimizations in CH2Cl2
(dielectric constant ε = 8.93).
To
a
pre-sonicated
homogeneous
mixture
of
[BMIM(SO3H)][OTf] (10 mol%) and [BMIM][NTf2] (1 mL) was
added 0.25 mmol (0.055 g) of 2-(4-cyanophenyl)-3-phenyl oxirane
1d. The reaction was performed under sonication at ambient
temperature and monitored by GC. After completion, the reaction
mixture was extracted repeatedly with diethyl ether and the com-
bined ether extracts was washed with water, dried over MgSO4,
and the solvent was evaporated under vacuum. The crude product
mixture consisting of 2d (major) and 3d (minor) was purified by
column chromatography with ethyl acetate/n-hexane (20%).
4’-Cyano-2-phenylacetophenone 3d [8], white solid, m.p.
97–99 ◦C, IR (CH2Cl2) 2225, 1693; 1H NMR (500 MHz, CDCl3) ı
8.00 (d, J = 8.0 Hz, 2H), 7.68 (d, J = 8.0 Hz, 2H), 7.26 (t, J = 7.0 Hz, 2H),
7.21–7.15 (m, 3H), 4.22 (s, 2H); 13C NMR (125 MHz, CDCl3) ı 196.6,
139.8, 133.8, 132.9, 129.7, 129.4, 129.3, 127.7, 118.2, 116.8, 46.2.
2-(4-Cyanophenyl)-2-phenyl acetaldehyde 2d, [931426–36–7],
1H NMR (500 MHz, acetone-d6) ı 10.0 (d, J = 1 Hz, 1H), 7.82 (d, J = 8.5,
2H), 7.56 (d, J = 8.5 Hz, 2H), 7.36–7.35 (m, 5H), 5.3 (s, 1H).
4. Results and discussion
4.1. Catalysis by Lewis acids in DCM and in ionic liquids
At the onset a series of control experiments were performed
with trans-stilbene oxide 1 by using 5% and 10% Bi(OTf)3 in DCM as
solvent and the reactions were monitored by GC (Fig. 2, Table 1).
These studies showed that in line with earlier reported studies
[13,14], 5% Bi(OTf)3 was sufficient for near quantitative conversion
to diphenylacetaldehyde 2 after just 5 min at r.t.
In the next step, Al(OTf)3, Ga(OTf)3, Sc(OTf)3, and Yb(OTf)3 were
tested along with Zn(NTf2)2 for their relative efficiency by using
5 mol% of catalyst, and the reactions were allowed to continue for
30 min. The data (Table 2) shows that conversion to 2 with Al, Ga,
and Sc triflates were in the 81–86% range with up to 19% side prod-
ucts (heavy, aldol condensation derived products), with Yb(OTf)3
and Zn(NTf2)2 exhibiting significantly lower activity. It is note-
worthy that all systems proved to be highly regio-selective (no
deoxybenzoin 3 was observed).
2.8. [BMIM(SO3H)][OTf] catalyzed isomerization reactions in
DCM as solvent – general procedure (Table 10)
With the goal to substitute volatile organic solvents with ionic
liquid solvents (ILs), and with the added prospect for recycling
and reuse, the Lewis acid assay was repeated in [BMIM][BF4] using
5 mol% catalyst and the results are summarized in Table 3. In a blank
experiment no rearrangement was observed in [BMIM][BF4] alone
after 30 min r.t., and subsequently 5 mol% catalyst was employed.
GC monitoring of the progress of the reaction indicated slower con-
version in ILs compared to DCM, and this is attributed to solubility
and mixing issues in a more viscous environment (in comparison
to DCM) and in the presence of a very small quantity of catalyst.
For short reaction times (up to 30 min), Bi(OTf)3 produced the best
results in terms of efficiency and chemo-selectivity. It is notewor-
thy that despite a sluggish start, Al(OTf)3 proved worthy under
longer reaction times, reaching high conversion (89%) with no side
reactions.
The diaryl-epoxide (0.25 mmol) was added to a solution of 10
mol% [BMIM(SO3H)][OTf] in 2 mL of dry DCM. The reaction mix-
ture was stirred at room temperature and monitored by GC. After
completion, the reaction was quenched by adding 5 mL of water.
The two layers were separated and the aqueous layer was washed
with 2 × 5 mL of CH2Cl2. The combined organic layers were dried
over MgSO4 and the solvent was evaporated under vacuum and
the residue was purified by column chromatography with ethyl
acetate/n-hexane (10–20%).
2.8.1. [BMIM(SO3H)][OTf] catalyzed isomerization reactions of
trans-2-(4-fluorophenyl)-3-phenyl oxirane 1c in DCM as solvent
– typical procedure (Table 10 entery 3)
Trans-2-(4-fluorophenyl)-3-phenyl oxirane 1c (0.25 mmol,
0.054 g) was added to a solution of [BMIM(SO3H)][OTf] (10 mol%)
in 2 mL of dry DCM and the reaction mixture was stirred at room
temperature and monitored by GC. After completion (5 min), the
reaction was quenched by adding 5 mL of water, the aqueous layer
was washed with 2 × 5 mL of CH2Cl2, and the combined organic
extracts were dried over MgSO4. The solvent was evaporated under
vacuum to give the crude products. Column chromatography with
ethyl acetate/n-hexane (10%) furnished the pure fluorinated
aldehyde 2c in 92% yield.
In an effort to select an optimal [BMIM][X] for this transfor-
mation, rearrangement of 1 was studied in three other ILs with
X = NTf2, OTf, and PF6 for comparison with X = BF4, by using 5 mol%
Bi(OTf)3 at room temperature, and the reactions were monitored
Table 1
Rearrangement of trans-stilbene oxide in the presence of different amounts of
Bi(OTf)3 in dry DCM at r.t.
2-(4-Fluorophenyl)-2-phenylacetaldehyde 2c, [496880–72–9],
pale yellow liquid, IR (CH2Cl2) 1659, 1270 cm−1; 1H NMR (500 MHz,
CDCl3) ı 9.94 (d, J = 2.0 Hz, 1H), 7.40 (t, J = 7.0 Hz, 2H), 7.23–7,17
(m, 5H), 7.07 (t, J = 9.0 Hz, 2H), 4.91 (d, J = 2.0 Hz, 1H); 13C NMR
(125 MHz, CDCl3) ı 198.6, 162.5 (J = 245.2 Hz), 136.0, 132.6 (J = 19.4),
132.0 (J = 2.9), 130.7 (J = 8.2 Hz), 129.1 (J = 4.6 Hz), 127.8, 116.2
(J = 21.2 Hz), 63.6; GC–MS m/z 214 (M+), m/z 165 (100%).
Entry Molar ratio of t-stilbene
GC yield (%) [1: 2: 3: SP]a
oxide to Bi(OTf)3
5 min
10 min
30 min
1
2
1–0.05
1–0.1
[0: 96: 0: 4] [0: 96: 0: 4] [0: 93: 0: 7]
[0: 94: 0: 6] [0: 93: 0: 7] [0: 93: 0: 7]
aSP, side products.
Table 2
3. Computational methods
Rearrangement of t-stilbene oxide in the presence of 5 mol% catalyst in DCM at r. t.
after 30 min.
Calculations were carried out with the Gaussian 09 package
[34]. Structures were fully optimized by the DFT-B3LYP [35] func-
tional, and at the MP2 [36] level, using the 6-31G(d,p) basis set
at both levels. Stationary points were characterized as minima (no
imaginary frequencies) or transition states (only one imaginary fre-
quency) by harmonic vibrational frequency calculations. In order to
get accurate activation and reaction energies, single-point calcula-
tions with the MPWB1K [37] functional and the 6-311+G(d,p) basis
Entry
Lewis acid
GC yield (%) [1: 2: 3: SP]a
1
2
3
4
5
Al(OTf)3
Ga(OTf)3
Sc(OTf)3
Yb(OTf)3
Zn(NTf2)2
[0: 81: 0: 19]
[0: 86: 0: 14]
[0: 84: 0: 16]
[42: 54: 0: 4]
[65: 32: 0: 3]
a
SP: side products

A. Jamalian et al. / Applied Catalysis A: General 486 (2014) 1–11
5
Fig. 2. Rearrangement of trans-stilbene oxide.
Table 3
Rearrangement of t-stilbene oxide in the presence of 5 mol% of different Lewis acids in [BMIM][BF4] at r.t.
Entry
Lewis acid
GC yield (%) [1: 2: 3: SP]a
5 min
10 min
30 min
60 min
90 min
1
2
3
4
5
6
Al(OTf)3
Ga(OTf)3
Sc(OTf)3
Yb(OTf)3
Bi(OTf)3
Zn(NTf2)2
[85: 15: 0: 0]
[65: 32: 0: 0]
[91: 9: 0: 0]
[84: 7: 0: 9]
[45: 55: 0: 0]
[86: 14: 0: 0]
[74: 26: 0: 0]
[55: 45: 0: 0]
[86:14: 0: 0]
[85: 7: 0: 8]
[43: 57: 0: 0]
[83: 17: 0: 0]
[70: 30: 0: 0]
[50: 50: 0: 0]
[70: 21: 0: 0]
[84: 8: 0: 8]
[34: 65: 0: 0]
[76: 24: 0: 0]
[35: 65: 0: 0]
[47: 53: 0: 0]
[57: 43: 0: 0]
[80: 10: 0: 10]
–
[11: 89: 0: 0]
[44: 56: 0: 0]
[56: 44: 0: 0]
[81: 9: 0: 10]
–
[58: 42: 0: 0]
–
a
SP: side products.
Table 4
Table 6
Rearrangement of t-stilbene oxide in [BMIM][X] the presence of 5 mol% of Bi(OTf)3
Rearrangement of t-stilbene oxide in [BMIM][X] under MW condition with no added
at r.t.
catalyst.
Entry
Solvent
GC yield (%) [1: 2: 3: SP]a
Entry
Ionic liquida
GC yield (%) [1: 2: 3]
1
2
3
4
[BMIM][PF6]
[BMIM][NTf2]
[BMIM][BF4]
[BMIM][OTf]
[10: 90: 0]
[13: 75: 12]
[23: 65: 12]
[46: 47: 7]
5 min
10 min
30 min
1
2
3
4
[BMIM][NTf2]
[BMIM][OTf]
[BMIM][PF6]
[BMIM][BF4]
[0: 85: 0:15]
[0:91: 0: 9]
[0: 95: 0: 0]
[45: 55: 0: 0]
[0: 83: 0:17]
[0: 91: 0: 9]
[0: 73: 0: 36]
[43: 57: 0: 0]
[0: 82: 0: 18]
[0: 80: 0: 20]
[0: 65: 0: 35]
[34: 65: 0: 0]
a
45 s reaction time.
a
SP: side products.
4.3. Reactions in IL solvents under microwave MW with no added
catalyst
by GC at intervals. The data summarized in Table 4 shows that
initially [BMIM][OTf] and [BMIM][PF6] exhibited high conver-
sion and good selectivity but overtime they produced more side
products and on balance [BMIM][NTf2] performed better. The reac-
tions were noticeably slower in [BMIM][BF4] but selectivity was
excellent.
Our attention was next turned to IL/MW reactions without
an added catalyst. We reasoned that the Lewis-acidity of the IL’s
cationic core may be adequate in conjunction with MW irradiation
and very short reaction times to bring about this rearrangement
with high selectivity, thus eliminating the need for an added cat-
alyst altogether. Rearrangement of 1 was studied in four different
[BMIM][X] with X = PF6, NTf2, BF4, and OTf, and the results are sum-
marized in Table 6. Among the ILs examined [BMIM][PF6] with
90% conversion and no side-reactions (GC analysis) proved most
promising. It is noteworthy that with the other ILs minor amounts
of deoxybenzoin 3 (hydrogen shift derived product) was produced.
The prospects for recycling and reuse of the IL was examined
next by using [BMIM][PF6] (Table 7), and the reaction was repeated
five time with no significant decrease in the conversions (GC).
4.2. Catalysis by Brønsted acidic IL
Compared to significant literature on the Lewis-catalyzed
epoxide rearrangements fewer studies have dealt with catalytic
Brønsted acid-catalyzed version of this transformation [17,18]. We
previously employed [BMIM(SO3H)][OTf]/IL systems in a number
of transformations such as the Schmidt reaction of aldehydes [19f]
and Rupe rearrangement [19a].
As summarized in Table 5 the [BMIM(SO3H)][OTf]/IL systems
also proved useful in the present study, employing catalytic
amounts of Brønsted acidic IL, and with little side products being
formed and with no ketone detected.
4.4. Substituent effect study – the aryl versus hydrogen shift
Having identified the most efficient and selective Lewis and
Brønsted acidic systems and solvents for isomerization of parent
Table 5
Rearrangement of trans-stilbene oxide catalyzed by [BMIM(SO3H)][OTf] in [BMIM][X] and in DCM at r.t.
Entry
BMIM(SO3H)[OTf] (equiv.)
Solvent
GC yield (%) [1: 2: 3: SP]a
5 min
10 min
30 min
1
2
3
4
5
0.1
0.2
0.3
0.1
0.1
[BMIM][NTf2]
[BMIM][NTf2]
[BMIM][NTf2]
[BMIM][PF6]
DCM
[20: 73: 0: 7]
[14: 72: 0: 14]
[15: 74: 0: 11]
[15: 73: 0: 12]
[1: 92: 0: 7]
[18: 75: 0: 7]
[14: 72: 0: 14]
[13: 74: 0: 13]
[12: 78: 0: 20]
[0: 93: 0: 7]
[17: 75: 0: 8]
[11: 75: 0: 14]
[13: 75: 0: 12]
[4: 65: 0: 31]
[0: 90: 0: 10]
a
SP: side products.

6
A. Jamalian et al. / Applied Catalysis A: General 486 (2014) 1–11
Fig. 3. Catalytic stilbene oxide ring opening with singly substituted derivatives.
Table 7
Table 9
Recycling and reuse of [BMIM][PF6] in catalyst-free reaction under MW.
Rearrangement of singly substituted stilbene oxides 1a–1e in the presence of 5 mol%
of Bi(OTf)3 in [BMIM][NTf2] at r.t.
Number of runs
GC Yield (%) [1: 2]
Entry
X
GC yield (%) [1: 2: 3: 4: SP]a
1
2
3
4
5
[10: 90]
[10: 90]
[10: 90]
[12: 88]
[10: 90]
5 min
10 min
30 min
1
2
3
4
5
Me (a)
OMe (b)
F (c)
CN (d)
NO2 (e)
[10: 66: 0: 0: 24]
[36: 52: 0: 0: 12]
[13: 65: 7: 0: 15]
[14: 56: 12: 0: 18]
[10: 27: 66: 0: 0]
[0: 62: 0: 0: 38]
[25: 58: 0: 0:17]
[0: 70: 10: 0: 20]
[9: 60: 13: 0: 18]
[4: 26: 70: 0: 0]
[0: 62: 0: 0: 38]
[24: 51: 0: 0: 25]
[0: 70: 10: 0: 20]
[0: 67: 15: 0: 18]
[0: 22: 70: 0: 8]
trans-stilbene oxide, and since the hydrogen migration product 3
was not observed under these conditions, except as a minor product
in the MW assisted reactions, we sought to explore the effect of acti-
vating and deactivating substituents on product distribution and
the possibility to form more ketones, and to that end the singly sub-
stituted stilbene oxides 1a–1e were synthesized for this purpose
(Fig. 3).
a
SP: unidentified side-products.
Cu(BF4)2·nH2O [7] was reported to give the corresponding alde-
hyde in 93% yield after 24 h, whereas isomerization of the p-NO2
derivative with this catalyst gave only a 10% yield of the aldehyde
after 6 h reflux in DCM.
4.4.1. Bi(OTf)3-catalyzed isomerization of the singly substituted
derivatives 1a–1e in DCM and in [BMIM][NTf2]
4.4.2. [BMIM(SO3H)][OTf] catalyzed isomerization of the singly
substituted derivatives 1a–1e in DCM and in [BMIM][NTf2]
Epoxides 1a–1e were allowed to react with 5 mol% Bi(OTf)3 in
DCM at r.t. and the reactions were monitored by GC (Table 8). The
p-Me and p-F derivatives reacted cleanly and selectively to produce
2 with minimal side products and no ketones were observed. With
the p-OMe derivatives the yield of 2 was lower and a number of
unidentified side products were observed by GC. With the p-CN
and p-NO2 derivatives significant amounts of the ketones 3 were
formed, with 3 becoming the major product in the case of p-NO2.
Absence of ketone 4 implies that the direction of hydrogen shift is
rather specific and occurs from the benzylic position that bears the
electron withdrawing substituent.
The isomerization reactions were repeated by using 5 mol%
Bi(OTf)3 in [BMIM][NTf2] as solvent and the reactions were moni-
tored by GC as before (Table 9). As was observed with parent 1, the
reactions were slower in the IL, and in some cases led to increased
side product formation. The p-Me and p-OMe derivatives gave no
ketones. Small quantities of the ketone 3 were formed in the case
of p-F derivative, whereas none was detected in DCM. The % ketone
formed in the case of the p-CN derivative was lower than that in
DCM. Compound 3 was formed as a major product with the p-
NO2 derivative. For comparison, isomerization of the p-OMe with
Epoxides 1a–1e were allowed to react with 10%
[BMIM(SO3H)][OTf] in DCM at r.t. and the reactions were mon-
itored by GC (Table 10). The p-Me and p-F derivatives reacted
cleanly and selectively to produce 2 with minimal formation of
side products, and no ketones were observed. The reaction did not
work well with the p-OMe derivatives and side-product formation
was extensive. The p-CN and p-NO2 derivatives were rather cleanly
converted to give a mixture of 2 and 3 (ketone 4 was not detected),
and with the p-NO2 derivative near equivalent amounts of 2e and
3e were formed.
As in earlier described cases, isomerization reactions progressed
slower in the IL solvent as compared to DCE (Table 11), but the selec-
tivity trends were somewhat similar with 1a reacting most cleanly,
and 1b producing extensive side products. Isomerization of the p-F
derivative 1c was less selective in the IL than in DCM (side-products
were formed in IL). Formation of ketone 3 was observed with the
p-CN and p-NO2 derivatives but the conversions were lower.
Table 10
Rearrangement of singly substituted stilbene oxides with 10 mol%
[BMIM(SO3H)][OTf] in DCM at r.t.
Table 8
Rearrangement of singly substituted stilbene oxides 1a–1e in the presence of 5 mol%
of Bi(OTf)3 in DCM at r.t.
Entry
X
GC yield (%) [1: 2: 3: 4: SP]a
5 min
10 min
30 min
Entry
X
GC yield (%) [1: 2: 3: 4: SP]a
1
2
3
4
5
Me (a)
[9: 83: 0: 0: 8]
[4: 85: 0: 0: 11]
[12: 37: 0: 0: 51] [10: 37: 0: 0: 53]
[0: 100: 0: 0: 0]
[0: 74: 23: 0: 3]
[4: 84: 0: 0: 12]
5 min
10 min
30 min
OMeb (b) [13: 38: 0: 0: 49]
1
2
3
4
5
Me (a)
OMe (b)
F (c)
CN (d)
NO2 (e)
[0: 96: 0: 0: 4]
[17: 53: 0: 0: 30]
[0: 97: 0: 0: 3]
[10: 60: 30: 0: 0]
[17: 19: 57: 0: 7]
[0: 86: 0: 0:14]
[16: 52: 0: 0: 32]
[0: 96: 0: 0: 4]
[3: 65: 32: 0: 0]
[2: 26: 63: 0: 9]
[0: 84: 0: 0: 16]
[16: 52: 0: 0: 32]
[0: 95: 0: 0: 5]
[0: 55: 35: 0: 10]
[2: 20: 59: 0: 19]
F (c)
CN (d)
NO2 (e)
[0: 100: 0: 0: 0]
[10: 68: 19: 0: 3]
[17: 29: 37: 0: 17] [0: 41: 42: 0: 17] [0: 40: 42: 0: 18]
[0: 92: 0: 0: 8]
[0: 70: 23: 0: 7]
a
SP: side-products.
b
In the case of 2-(4-MeO-phenyl)-3-phenyl oxirane 1b in addition to the corre-
sponding aldehyde several unidentified products were produced.
a
SP: unidentified side products.

A. Jamalian et al. / Applied Catalysis A: General 486 (2014) 1–11
7
Scheme 1. Ring opening of parent 1.
Table 11
must prevent side-product formation since the usual side-products
were not detected by GC. Stilbene oxides 1a and 1c gave their cor-
responding aldehydes 2a and 2c in high yields and no ketones were
observed. Competitive formation of ketones was observed with 1d
and 1e and to a less extent with 1b. The observed high chemo-
selectivity in IL solvent without using an added catalyst, and taking
into account the possibility of recycling and reuse of the IL makes
the IL/MW method promising as a synthetic method for epoxide
isomerization to carbonyl compounds.
Rearrangement of singly substituted stilbene oxides 1a–1e with 10 mol% of
[BMIM(SO3H)][OTf] in [BMIM][NTf2] at r.t.
Entry
X
GC yield (%) [1: 2: 3: 4: SP]a
5 min
10 min
30 min
1
2
3
4
5
Me (a)
[56: 40: 0: 0: 4]
[44: 51: 0: 0: 5]
[15: 49: 0: 0: 36]
[20: 56: 0: 0: 24]
[44: 49: 0: 0: 7]
[14: 48: 0: 0: 38]
[12: 62: 0: 0: 26]
OMe (b) [21: 45: 0: 0: 34]
F (c)
CN (d)
NO2 (e)
[22: 55: 0: 0: 23]
[16: 57: 15: 0: 12] [10: 60: 16: 0:14] [6: 56: 18: 0: 20]
[68: 24: 8: 0: 0] [65: 26: 9: 0: 0] [44: 40: 16: 0: 0]
a
SP: unidentified side-products.
4.5. Computational study of aryl versus hydrogen shift
4.4.3. Rearrangement of singly substituted stilbene oxides in
[BMIM][PF6]/MW with no added catalyst
Epoxides 1a–1e were cleanly isomerized in [BMIM][PF6] under
MW irradiation without an added catalyst (Table 12). In this mode,
despite reaching rather high temperatures, short contact times
It has been shown [28] that regio-selectivity of nucleophilic cap-
ture by bromide ion in ring opening of singly substituted 2,3-diaryl
oxiranes with LiBr/Amberlyst 15 (leading to bromohydrins) corre-
lates with relative benzylic carbocation stabilities. Thus with p-NO2
or p-CF3 derivatives nucleophilic attack occurred on the beta-
carbon and with p-OMe bromide ion captured the alpha-carbon.
The computed relative energies for the two possible benzylic carbo-
cations (with p-NO2 and p-OMe) were in concert with the observed
experimental regio-selectivity. In the context of the present study,
with the goal to address aryl versus hydrogen migration, ring open-
ing of parent trans-stilbene oxide 1, the p-OMe 1b and p-NO2 1e
were studied computationally by DFT at various basis sets and with
MP2 level of theory, and by including solvation effect (IEFPCM).
Protonation of 1 is highly exothermic. With B3LYP, proto-
nation and ring opening of the protonated epoxide take place
in a single barrierless step with ꢀE = −227 kcal/mol (Scheme 1).
Table 12
Rearrangement of singly substituted stilbene oxides 1a–1e in [BMIM][PF6]/MW with
no added catalyst.
Entry
X
Max. temperature
(◦C)
Reaction
time (s)
GC yield (%) [1:
2: 3: 4]
1
2
3
4
5
Me (a)
OMe (b)
F (c)
CN (d)
NO2 (e)
216
217
203
216
213
120
67
120
140
118
[7: 93: 0: 0]
[0: 72: 0: 28]
[4: 96: 0: 0]
[0: 41: 59: 0]
[0: 59: 41: 0]

8
A. Jamalian et al. / Applied Catalysis A: General 486 (2014) 1–11
Scheme 2. Ring opening of 1e and 1b by B3LYP.

A. Jamalian et al. / Applied Catalysis A: General 486 (2014) 1–11
9
Scheme 3. Ring opening of 1e and 1b by MP2.

10
A. Jamalian et al. / Applied Catalysis A: General 486 (2014) 1–11
Table 13
Computed energies and free energies of reaction, and activation barriers for the migration processes by different methods.
Method
H shift (kcal/mol)
Ph shift (kcal/mol)
ꢀE =/ (ꢀG =/
ꢀE =/ (ꢀG =/
)
ꢀEr (ꢀGr)
)
ꢀEr (ꢀGr)
B3LYP/6-31G(d,p)
10.86 (9.35)
9.82 (8.25)
8.70
7.70
12.88 (11.19)
11.72 (9.81)
−16.27 (−17.41)
−20.41 (−19.35)
−17.44
10.70 (11.28)
4.56 (5.34)
7.26
0.98
5.16 (6.00)
3.68 (4.53)
1.78 (2.22)
−2.86 (−2.01)
−1.50
B3LYP/6-31G(d,p)-PCM(CH2Cl2)
MPWB1K/6-311+G(d,p)a
MPWB1K/6-311+G(d,p)-PCM(CH2Cl2)a
MP2/6-31G(d,p)
−21.54
−6.08
−16.74 (−17.40)
−21.05 (−21.00)
−3.74 (−3.22)
−8.50 (−8.21)
MP2/6-31G(d,p)-PCM(CH2Cl2)
a
Single points at B3LYP/6-31G(d,p) optimized geometries.
By contrast, with MP2 the oxonium ion is a minimum with
a formation ꢀE = −211 kcal/mol. Subsequent ring opening step
presents ꢀE = −10 kcal/mol, which gives a total exothermicity of
−221 kcal/mol for the whole process. Solvation effect (PCM) further
facilitates oxonium ion formation (ꢀE = −247 kcal/mol; Scheme 1).
The benzylic carbocation via hydrogen migration has a lower
energy as compared to the carboxonium ion via phenyl migration.
This is consistently the case at various levels of theory and basis
sets and by including solvation effects (see Table 13). However, the
phenyl migration process presents lower activation energy, thus
pointing to the aldehyde as the kinetically favored product.
For the substituted derivatives (Schemes 2 and 3), the electronic
nature of the p-substituent determines the relative stability of the
carbocations that originate from epoxide ring opening. With the
p-NO2 and p-OMe the benzylic carbocations leading to PhCH2COAr
(3e) and ArCH2COPh (4b) respectively are more stable than the
corresponding phenyl shift carbocations leading to the aldehydes.
According to the computed activation barriers, hydrogen migration
and phenyl/Aryl migration were identified as feasible reactions,
although a preference for migration of the aromatic groups was
indicated by the MP2 results.
[3] B. Rickborn, in: B.M. Trost (Ed.), Comprehensive Organic Synthesis, vol. 3, Per-
gamon, Oxford, 1991, pp. 733–775 (Chapter 3.3);
B. Rickborn, R.M. Gerkin, J. Am. Chem. Soc. 93 (1971) 1693–1700;
(b) R. Sudha, K.M. Narasimhan, V.G. Saraswathy, S. Sankararaman, J. Org. Chem.
61 (1996) 1877–1879.
[4] K. Maruoka, T. Ooi, H. Yamamoto, Tetrahedron 48 (1992) 3303–3312.
[5] F. Martinez, C. del Campo, E.F. Llama, J. Chem. Soc., Perkin Trans. 1 (2000)
1749–1751.
[6] A.M. Anderson, J.M. Blazek, P. Garg, B.J. Payne, R.S. Mohan, Tetrahedron Lett. 41
(2000) 1527–1530.
[7] M.W.C. Robinson, K.S. Pillinger, A.E. Graham, Tetrahedron Lett. 47 (2006)
5919–5921.
[8] M.W.C. Robinson, K.S. Pillinger, I. Mabbett, D.A. Timms, A.E. Graham, Tetrahe-
dron 66 (2010) 8377–8382.
[9] I. Karamé, M.L. Tommasino, M. Lemaire, Tetrahedron Lett. 44 (2003)
7687–7689.
[10] J. Picione, S.J. Mahmood, A. Gill, M. Hilliard, M.M. Hossain, Tetrahedron Lett. 39
(1998) 2681–2684.
[11] E. Ertürk, M. Göllü, A.S. Demir, Tetrahedron 66 (2010) 2373–2377.
[12] A. Procopio, R. Dalpozzo, A. De Nino, M. Nardi, G. Sindona, A. Tagarelli, Synlett
(2004) 2633–2635.
[13] K.A. Bhatia, K.J. Eash, N.M. Leonard, M.C. Oswald, R.S. Mohan, Tetrahedron Lett.
42 (2001) 8129–8132.
[14] J.E. Christensen, M.G. Huddle, J.L. Rogers, H. Yung, R.S. Mohan, J. Chem. Educ.
85 (2008) 1274–1275.
[15] K. Suda, T. Kikkawa, Sh.-I. Nakajima, T. Takanami, J. Am. Chem. Soc. 126 (2004)
9554–9555.
[16] K. Suda, Sh.-I. Nakajima, Y. Satoh, T. Takanami, Chem. Commun. (2009)
1255–1257.
5. Conclusion
[17] K. Smith, G.A. El-Hiti, M. Al-Shamali, Catal. Lett. 109 (2006) 77–82.
[18] G.K.S. Prakash, T. Mathew, S. Krishnaraj, E.R. Marinez, G.A. Olah, Appl. Catal. A:
Gen. 181 (1999) 283–288.
The present study has identified new methods and reagents
for catalytic and regioselective conversion of 1,2-diaryl-epoxides
to carbonyl compounds. Whereas the M(OTf)3/[BMIM][X] and
[BMIM(SO3H)][OTf]/[BMIM][X] systems are highly efficient meth-
ods for Lewis acid and Brønsted acid catalyzed epoxide ring
openings, the [BMIM][X]/MW requires no added catalyst. The
recycling and reuse of the IL provides an added advantage for the
described methods. In a substituent effect study with singly substi-
tuted 1,2-diarylepoxides significant ketone formation (hydrogen
migration product) was only observed with the p-NO2 and p-CN
derivatives, except in the MW-induced reaction where ketone for-
mation was also observed with p-OMe. Computational study of
acid-induced ring opening of parent trans-stibene oxide pointed
to the aldehydes as the kinetically favored product. Formation of
3e and 4b as hydrogen shift-derived ketones agrees with the com-
putational results.
[19] (a) For represented examples see: G.C. Nandi, B. Rathman, K.K. Laali, Tetrahe-
dron Lett. 54 (2013) 6258–6263;
(b) R.G. Kalkhambkar, K.K. Laali, Tetrahedron Lett. 53 (2012) 4212–4215;
(c) G.G.K.S. Narayanan Kumar, K.K. Laali, Org. Biomol. Chem. 10 (2012)
7347–7355;
(d) D. Vrazic, M. Jereb, K.K. Laali, S. Stavber, Molecules 18 (2013) 74–96;
(e) G.G.K.S. Narayanan Kumar, K.K. Laali, Tetrahedron Lett. 54 (2013) 965–969;
(f) G.C. Nandi, K.K. Laali, Tetrahedron Lett. 54 (2013) 2177–2179;
(g) R. Prebil, K.K. Laali, S. Stavber, Org. Lett. 15 (2013) 2108–2111.
[20] M. Shukla, N. Srivastava, S. Saha, in: S.T. Handy (Ed.), Ionic Liquids-Classes and
Properties, In Tech, 2011, pp. 153–170 (Chapter 7).
[21] A.C. Cole, J.L. Jensen, I. Ntai, K.L.T. Tran, K.J. Weaver, D.C. Forbes, J.H. Davis Jr., J.
Am. Chem. Soc. 124 (2002) 5962–5963.
[22] Z. Du, Z. Li, Y. Deng, Synth. Commun. 35 (2005) 1343–1349.
[23] G.K.S. Prakash, T. Mathew, G.A. Olah, Acc. Chem. Res. 45 (2012) 565–577.
[24] J. Forrester, R.V.H. Jones, L. Newton, P.N. Preston, Tetrahedron 57 (2001)
2871–2884.
[25] E. Akgün, M.B. Glinski, K.L. Dhawan, T. Durst, J. Org. Chem. 46 (1981)
2730–2734.
[26] M. Imuta, H. Ziffer, J. Org. Chem. 44 (1979) 2505–2509.
[27] V.K. Aggarwal, E. Alonso, I. Bae, G. Hynd, K.M. Lydon, M.J. Palmer, M. Petal, M.
Porcelloni, J. Richardson, R.A. Stenson, J.R. Studley, J.-L. Vasse, C.L. Winn, J. Am.
Chem. Soc. 125 (2003) 10926–10940.
Acknowledgement
[28] A. Solladié-Cavallo, P. Lupattelli, C. Bonini, J. Org. Chem. 70 (2005) 1605–1611.
[29] H. Kinoshita, A. Ihoriya, M. Ju-ichi, T. Kimachi, Synlett (2010) 2330–2334.
[30] P. Nilsson, M. Larhed, A. Hallberg, J. Am. Chem. Soc. 123 (2001) 8217–8225.
[31] M.W.C. Robinson, A.M. Davies, R. Buckle, I. Mabbett, S.H. Taylor, A.E. Graham,
Org. Biomol. Chem. 7 (2009) 2559–2564.
[32] V.C. Purohit, S.P. Allwein, R.P. Bakale, Org. Lett. 15 (2013) 1650–1653.
[33] A.J. Wommack, D.C. Moebius, A.L. Travis, Org. Lett. 11 (2009) 3202–3205.
[34] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M.
Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro,
M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi,
We thank University of Florida for access to UF Research Com-
puting and University of North Florida for the award of Presidential
Professorship to K.K.L.
References
[1] B.C. Ranu, U. Jana, J. Org. Chem. 63 (1998) 8212–8216.
[2] (a) H.O. House, J. Am. Chem. Soc. 77 (1955) 3070–3075;
(b) Y. Kita, S. Kitagaki, Y. Yoshida, S. Mihara, D.F. Fang, M. Kondo, S. Okamoto,
R. Imai, S. Akai, H. Fujioka, J. Org. Chem. 62 (1997) 4991–4997.

A. Jamalian et al. / Applied Catalysis A: General 486 (2014) 1–11
11
J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M.
Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C.
Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth,
P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, Ö. Farkas, J.B. Fores-
man, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, Revision A.01, Gaussian,
Inc., Wallingford, CT, 2009.
(c) B. Miehlich, A. Savin, H. Stoll, H. Preuss, Chem. Phys. Lett. 157 (1989)
200–206.
[36] C. Møller, M.S. Plesset, Phys. Rev. 46 (1934) 618–622.
[37] Y. Zhao, D.G. Truhlar, J. Phys. Chem. A 108 (2004) 6908–6918.
[38] (a) M.T. Cancès, V. Mennucci, J. Tomasi, J. Chem. Phys. 107 (1997) 3032–3041;
(b) B. Mennucci, J. Tomasi, J. Chem. Phys. 106 (1997) 5151–5158;
(c) B. Mennucci, E. Cancès, J. Tomasi, J. Phys. Chem. B 101 (1997) 10506–10517;
(d) J. Tomasi, B. Mennucci, E. Cancès, J. Mol. Struct. (Theochem) 464 (1999)
211–226.
[35] (a) A.D. Becke, J. Chem. Phys. 98 (1993) 5648–5652;
(b) C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785–789;