Copper-catalyzed direct aryl quaternization of N-substituted imidazoles to form imidazolium salts

Article abstract of DOI:10.1021/jo400527r

Diaryliodonium salts are employed to directly quaternize N-substituted imidazoles by using a copper catalyst to construct aryl imidazolium salts in moderate to excellent yields. This transformation is tolerant to a broad range of functional groups and provides a straightforward, efficient, and versatile route to synthesize aryl imidazolium as well as triazolium salts, especially the unsymmetric version.

Full text of DOI:10.1021/jo400527r

Note
pubs.acs.org/joc
Copper-Catalyzed Direct Aryl Quaternization of N‑Substituted
Imidazoles to Form Imidazolium Salts
Taiyong Lv, Zhi Wang, Jingsong You,* Jingbo Lan, and Ge Gao*
Key Laboratory of Green Chemistry and Technology of Ministry of Education, College of Chemistry, Sichuan University, 29
Wangjiang Road, Chengdu 610064 P. R. China
S
* Supporting Information
ABSTRACT: Diaryliodonium salts are employed to directly
quaternize N-substituted imidazoles by using a copper catalyst to
construct aryl imidazolium salts in moderate to excellent yields.
This transformation is tolerant to a broad range of functional
groups and provides a straightforward, efficient, and versatile
route to synthesize aryl imidazolium as well as triazolium salts, especially the unsymmetric version.
n the presence of a base, primary and secondary amines are
readily arylated by aryl halides using a palladium or copper
Co(OAc)2 and Cu(acac)2 as the catalysts in the presence of
potassium carbonate (K2CO3) under mild conditions,
respectively. Herein, we wish to report that diaryliodonium
salts could further aryl-quaternize N-substituted imidazoles by
using a copper catalyst (Eq. III).
I
catalyst.1 However, N-heteroarenes with no N−H such as N-
substituted imidazoles and triazoles etc. are generally hard to be
directly arylated, i.e., quaternized to furnish imidazolium and
triazolium salts by using aryl halides, except strongly electron-
deficient ones such as 2,4-dinitrochlorobenzene (Eq. I).2 These
We started with the quaternization of N-phenylimidazole 1a
with diphenyliodonium tetrafluoroborate salt (Ph2IBF4, 2a) by
screening a range of metal salts as the catalyst in DMF at 100
°C (Table 1). To our delight, all copper salts catalyzed the aryl
quaternization of 1a efficiently, while other metal salts showed
no activity (Table 1, entries 1−8). Considering the cost of the
catalyst and the ease of handling, Cu(OAc)2·H2O was chosen
as the catalyst. Without the copper catalyst, the quaternization
did not occur (Table 1, entry 9). The reactions in DMSO,
toluene, or dioxane resulted in lower yields than in DMF
(Table 1, entries 5 and 10−12). The counteranion effect
investigation showed that the reaction did not take place when
using 2a associated with halide anions such as chloride and
bromide, whereas high yields were obtained when using 2a with
the non-nucleophilic anions (Table 1, entries 13−16). Using
1.0 equiv of 2a resulted in a diminished yield of 57% due to the
thermolysis of 2a (Table 1, entry 17). Finally, the best
conditions were to use 1.5 equiv of 2a·BF4 in the presence of 5
mol % Cu(OAc)2·H2O as the catalyst in DMF at 100 °C for 4
h, under which diphenylimidazolium salt 3a was obtained in
97% isolated yield (Table 1, entry 5).
compounds now are prevalently synthesized using multistep
ring closing methods.3 A general methodology of direct aryl
quaternization is still absent and even considered as “mission
impossible” with aryl halides.4 Nevertheless, these aryl onium
salts are important precursors of N-heterocyclic carbenes5
(NHCs) and cationic functional materials.6 Particularly
attractive is the recent spurt of interesting asymmetric catalyzes
by the chiral NHCs derived from unsymmetric arylated
imidazolium and triazolium salts.7,8 These prominent applica-
tions make us reconsider the possibility of direct aryl
quaternization strategy by using other arylating reagents.
In 2002, Yoshida and Kunai et al. succeeded in the direct aryl
quaternization of N-alkylimidzoles in moderate yields using
arynes but N-arylimidazoles were not applicable (Eq. II).9 We
envisaged that a more electrophilic reagent instead of aryl
halides might overcome the weak nucleophilicity of N-
substituted imidazoles and eventually lead to the formation of
arylated imidazolium salts. Diaryliodonium salts, known for its
“hyperleaving group ability”10 of the aryliodanyl group (ArI),
are prominent reagents for arylations. Chen’s group11a and
Kang’s groups11b have previously reported that diaryliodonium
salts could arylate imidazole to form N-arylimidazoles by using
With the optimized conditions in hand, we tried to use 2a to
quaternize various N-substituted imidazoles to synthesize a
range of unsymmetric N,N′-diaylated imidazolium compounds
Received: March 15, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/jo400527r | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
a
groups were all intact under the reaction conditions and the
corresponding imidazolium salts were obtained in moderate to
high yields (Table 2, 3ha−3na). The bulky 1-naphthylimida-
zole was quaternized smoothly in 4 h to give the corresponding
imidazolium salt 3oa in 91% yield. The more bulky
meistylimidazole could also give rise to a good yield of 86%,
but longer reaction time was required. Further increasing the
steric hindrance of the phenylimidazole by introducing two
isopropyl groups at the C2 and C6 positions on the phenyl ring
resulted in a decreased yield of 56% (Table 2, 3pa and 3qa).
These results indicated that this reaction is sensitive to the
steric hindrance effect. Notably, N-heteroarylimidazoles were
exclusively quaternized to afford the corresponding imidazo-
lium salts. For example, N-(2-thienyl)-imidazole was success-
fully converted to the corresponding imidazolium salt 3ra in
88% yield and the C/S-arylation of the thienyl ring was not
observed.12 2a selectively quaternized the imidazole ring of N-
(2-pyridyl)-imidazole rather than the pyridine ring to afford the
corresponding imidazolium salt 3sa in 86% yield. Finally, 2a
was used to furnish a few N-sec- and -tert-alkylphenylimidazo-
lium salts, which are difficult to synthesize through quaterniza-
tion of phenylimidazole with sec- and -tert-alkyl halides.4,9
Isopropyl, t-butyl, and 1-adamantanyl substituted imidazoles all
gave the corresponding alkylphenylimidazolium salts in good
yields (Table 2, 3ta−3va). To the best of our knowledge, this is
the first direct aryl quaternization method for both N-aryl and
N-alkyl imidazoles.
Table 1. Optimization of the Reaction Conditions
b
entry
2a
catalyst
CuBr2
solvent
yield (%)
1
2
Ph2IBF4
Ph2IBF4
Ph2IBF4
Ph2IBF4
Ph2IBF4
Ph2IBF4
Ph2IBF4
Ph2IBF4
Ph2IBF4
Ph2IBF4
Ph2IBF4
Ph2IBF4
Ph2ICl
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
toluene
dioxane
DMF
DMF
DMF
DMF
DMF
86
94
96
97
97
0
CuCl2·2H2O
Cu(OTf)2
CuCl
3
4
5
Cu(OAc)2·H2O
Pd(OAc)2
Ni(OAc)2
Co(OAc)2
6
7
0
8
0
9
0
10
11
12
13
14
15
16
17
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
91
91
83
0
Ph2IBr
0
Ph2IOTs
Ph2IOTf
Ph2IBF4
92
68
57
c
a
General conditions: 1a (0.25 mmol), 2a (0.375 mmol), and
Cu(OAc)2·H2O (5 mol %) were stirred in a solvent (1 mL) at 100
b
c
°C for 4 h. Isolated yields. 2a (0.25 mmol).
By using substituted diaryliodonium salts 2, a variety of
symmetric diarylimidazolium compounds 3 were obtained, as
shown in Table 3. The di-o-, -m-, and -p-methoxyphenylimid-
zolium salts were directly synthesized by the quaternization of
o-, m-, and p-methoxyphenylimidzoles with the corresponding
diaryliodonium salts for 4−5 h in good yields (Table 3, o-3cc−
p-3cc). The quaternization of di-m- and -p-bromophenylimid-
zoles, however, needed much longer reaction time (48 h) and
3, and the results are summarized in Table 2. N-Phenyl-
imidazoles bearing common substituents on the phenyl ring
such as methyl, methoxy, and bromide at the ortho-, meta-, and
para-positions all gave very good yields (Table 2, o-3ba−p-
3da). There was no significant difference in the reactions of the
N-phenylimidazoles bearing different halide substitutents
(Table 2, p-3da−3ga). Other functional groups such as alkynyl,
acetyl, formyl, ester, cyano, N,N-dimethylamino, and hydroxyl
a b
,
Table 2. Substrate Scope of the Synthesis of Unsymmetric Diarylimidazolium Salts
a
General conditions: 1 (0.25 mmol), 2a (0.375 mmol), and Cu(OAc)2·H2O (5 mol %) were stirred in DMF (1 mL) at 100 °C for the indicated
b
c
time. Isolated yields. 2a (3.0 equiv, 0.75 mmol).
B
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Note
a b
,
The generality of the present methodology was further
investigated by the quaternization of N-heteroarenes other than
imidazoles (Table 4). N-Phenylbenzimidazole was smoothly
Table 3. Synthesis of Symmetric Diarylimidazolium Salts
a b
,
Table 4. Quaternization of Other N-Heteroarenes
a
General conditions: heteroarene (0.25 mmol), 2 (0.375 mmol), and
Cu(OAc)2·H2O (5 mol %) were stirred in DMF (1 mL) at 100 °C for
b
c
d
the indicated time. Isolated yields. 2p (3.0 equiv, 0.75 mmol). 2a
a
(2.0 equiv, 0.50 mmol).
General conditions: 1 (0.25 mmol), 2 (0.375 mmol), and
Cu(OAc)2·H2O (5 mol %) were stirred in DMF (1 mL) at 100 °C
b
c
for the indicated time. Isolated yields. 2 (3.0 equiv, 0.75 mmol).
quaternized by 2a to afford diphenylbenzimidazolium salt 4 in
91% yield. Imidazo[1,5-a]pyridine was converted to the desired
onium salt 5 in 89% yield. The partially hydrogenated
imidazole, imidazoline compound could also be directly
quaternized. We obtained dimeistylimidazolinium salt 613 in
74% yield by using [mesityl]2IBF4 to quaternize N-
mesitylimidazoline. N-Phenyl 1,2,3- and 1,2,4-triazoles were
directly quaternized at the 3 and 4 positions to afford the
corresponding triazolium salts 7 and 8 in excellent yields,
respectively.
Although Canty et al. suggested that the reaction of
diaryliodonium salts with neutral nucleophiles may proceed
through a radical pathway,15 the preliminary mechanism study
ruled out the possibility. When 2,2,6,6-tetramethyl-1-piperidi-
nyloxy (TEMPO) or 2,6-di-tert-butyl-4-methylphenol (BHT)
was added as the radical scavenger into the reaction of 1a and
2a, both the reactions gave the desired imidazolium salt 3a after
4 h in 94% and 91% yields, respectively. The process possibly
involved a typical mechanism for Cu-catalyzed C−H arylation
by diaryliodonium salts through CuIII species (Supporting
Information, Section IV).16 Because of the weak nucleophilicity
of N-substituted imidazoles, only the counteranions with even
weaker nucleophilicity could be displaced at the CuIII center.
This explained the counteranion effect we observed in this
reaction.
yet afforded lowered yields (Table 3, m-3dd and p-3dd). These
results suggested that electron-rich diaryliodonium salts are
more reactive to quaternize imidazoles than electron-deficient
diaryliodonium salts. Bulky diarylimidazolium salts were also
accessible directly. For example, di-1-naphthylimidazolium salt
3oo was obtained in 88% yield after 6 h; a 83% yield was
achieved for the classic dimeistylimidazolium salt 3pp13 after 6
h, but 3 equiv of [mesityl]2IBF4 was needed to consume all the
imidazole 1p. It was delightful that diheteroarylimidazolium
salts could be prepared under our standard conditions. We
obtained di(2-thienyl)imidazolium OTs salt 3rr in 86% yield by
the quaternization of N-(2-thienyl)-imidazole with [2-thieny-
l]2IOTs in 5 h.
Obviously, unsymmetric diarylimidazolium salts bearing an
electron-deficient aryl and an electron-rich aryl could be
synthesized in two directions. Namely, an electron-deficient
arylimidazole reacts with an electron-rich diaryliodonium salt or
vice versa. In view of the higher reactivity of the electron-rich
diaryliodonium salts, the former strategy should be the prime
consideration. For instance, N-(4-bromophenyl)-N′-(4-me-
thoxyphenyl)-imidazolium salt (p-3cd or p-3dc) was obtained
in 93% yield by using [p-MeOPh]2IBF4 p-2cc to quaternize p-
1d for 5 h, whereas only 76% yield was given by using [p-
BrPh]2IBF4 p-2dd to quaternize p-1c even for 48 h (Supporting
Information, Section II).
In conclusion, we disclose herein to use diaryliodonium salts
for the direct aryl quaternization of N-substituted imidazoles in
the presence of a copper catalyst. This methodology solves a
long-standing problem in imidazolium salt synthesis and has
the following advantages: (1) it is straightforward, efficient and
versatile to quaternize a variety of imidazoles, as well as
imidazoline, triazoles, and imidazo[1,5-a]pyridine, etc.; (2) it is
particularly convenient to synthesize unsymmetric imidazolium
salts; (3) it is tolerant to sensitive functional groups such as
acetyl, formyl, ester, and hydroxyl groups, etc.; (4) the reaction
conditions are mild with no need for a strong base or acid and
inert atmosphere; and (5) the procedure is simple and easy to
scale up for mass production. It would provide a new possibility
to construct complicated and diverse azolium salts, especially
unsymmetric ones, for novel N-heterocyclic carbenes and
functional materials.
The selectivity of this reaction toward unsymmetric diary-
liodonium salts was also investigated. [p-MeOPh-I-(p-BrPh)]-
OTf 2cd reacted with N-phenylimidazole 1a for 4 h to afford
3ac and 3ad in a 1:1 ratio, which exhibited no chemoselectivity
of the electron-rich phenyl ring over the electron-deficient
phenyl ring (Supporting Information, Section III, eq 1).
However, when [Ph-I-thienyl]OTf 2ar was used instead, the
more electron-rich thienyl ring was preferentially transferred to
afford a 3.8:1 mixture of 3ar in 74% yield and 3aa in 17% yield
(Supporting Information, Section III, eq 2). In addition, [Ph-I-
mesityl]OTf 2ap quaternized 1a to exclusively afford 3aa in
94% yield (Supporting Information, Section III, eq 3),
suggesting that the bulky mesityl group could serve as a
“dummy ligand” in circumstances that starting materials are
expensive or symmetric iodonium salts are difficult to
make.10c,14
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The Journal of Organic Chemistry
Note
130.0, 127.3, 126.7, 124.6, 122.1, 121.4, 17.1. HRMS (ESI) [M
EXPERIMENTAL SECTION
■
− +
− BF4 ] calcd for C16H15N2, 235.1230; found, 235.1228.
Synthesis of 1-(2-Bromophenyl)-1H-imidazole (o-1d).
1,2-Dibromobenzene (1.18 g, 5.0 mmol), imidazole (0.48 g, 7.0
mmol), CuI (0.19 g, 1 mmol), Cs2CO3 (3.26 g, 10.0 mmol),
and freshly distilled DMF (10 mL) were added to a flame-dried
Schlenk tube with a magnetic stir bar under N2. The reaction
was stirred at 120 °C for 40 h. After cooled down to room
temperature, the reaction mixture was diluted with 10−15 mL
of ethyl acetate, filtered, and the solid was washed with 50−100
mL of ethyl acetate. The combined extracts were then
concentrated under reduced pressure and the residue was
passed through a silica gel column (petroleum/ethyl acetate =
1:1 v/v) to afford the desired product (0.51 g, 46% yield); mp
52−54 °C. 1H NMR (400 MHz, CDCl3): δ 7.73 (d, J = 8.0 Hz,
1H), 7.67 (s, 1H), 7.45−7.41 (m, 1H), 7.34−7.30 (m, 2H),
7.21 (s, 1H), 7.13 (s, 1H). 13C NMR (100 MHz, CDCl3): δ
137.6, 136.7, 134.0, 130.2, 129.3, 128.5, 128.2, 120.6, 120.0.
HRMS (ESI) [M + Na]+ calcd for C9H7BrN2Na, 244.9690;
found, 244.9689.
Synthesis of Bis(3-methoxyphenyl)iodonium Tetra-
fluoroborate (m-2cc). This compound was synthesized by a
modified procedure of similar compounds previously re-
ported:17 BF3·Et2O was added to a dichloromethane (25 mL)
solution of 3-methoxyphenylboronic acid (0.76 g, 5.0 mmol) at
room temperature. After stirring at room temperature for 15
min, a solution of 3-methoxyphenyliodine diacetate (1.94 g, 5.5
mmol) in dichloromethane (25 mL) was added. The reaction
was stirred at reflux for 60 min and quenched by adding a
saturated aqueous solution of sodium tetrafluoroborate (30
mL). The organic phase was separated and the aqueous phase
was extracted with dichloromethane twice. The combined
organic phases were dried over Na2SO4. After removal of the
volatile solvents, the residue was purified by column
chromatography (dichloromethane/methanol = 30:1 v/v) to
afford the desired product (0.64 g, 30% yield); mp 170−172
°C. 1H NMR (400 MHz, DMSO-d6): δ 7.93 (s, 2H), 7.80 (d, J
= 7.6 Hz, 2H), 7.47−7.43 (m, 2H), 7.22 (d, J = 8.4 Hz, 2H),
3.80 (s, 6H). 13C NMR (100 MHz, DMSO-d6): δ 160.4, 132.5,
3-Phenyl-1-m-tolyl-1H-imidazol-3-ium Tetrafluorobo-
rate (m-3ba). Reacted for 4 h. A gray solid (77 mg, 95%
1
yield); mp 128−130 °C. H NMR (400 MHz, DMSO-d6): δ
10.33 (s, 1H), 8.58 (s, 2H), 7.92 (d, J = 7.6 Hz, 2H), 7.78 (s,
1H), 7.72−7.70 (m, 3H), 7.65−7.58 (m, 2H), 7.45 (d, J = 7.6
Hz, 1H), 2.46 (s, 3H). 13C NMR (100 MHz, DMSO-d6): δ
140.1, 134.73, 134.66, 134.4, 130.6, 130.2, 130.1, 130.0, 122.4,
− +
122.1, 122.0, 121.9, 119.1, 20.9. HRMS (ESI) [M − BF4 ]
calcd for C16H15N2, 235.1230; found, 235.1230.
3-Phenyl-1-p-tolyl-1H-imidazol-3-ium Tetrafluorobo-
rate (p-3ba).19 Reacted for 6 h. A gray solid (74 mg, 92%
yield); mp 146−148 °C (literature,19 135 °C). H NMR (400
1
MHz, DMSO-d6): δ 10.30 (s, 1H), 8.56 (s, 1H), 8.55 (s, 1H),
7.92 (d, J = 8.4 Hz, 2H), 7.81 (d, J = 8.0 Hz, 2H), 7.73−7.70
(m, 2H), 7.63 (t, J = 7.2 Hz, 1H), 7.52 (d, J = 8.0 Hz, 2H), 2.43
(s, 3H).
1-(2-Methoxyphenyl)-3-phenyl-1H-imidazol-3-ium
Tetrafluoroborate (o-3ca). Reacted for 12 h. A gray solid (82
mg, 96% yield); mp 113−115 °C. 1H NMR (400 MHz,
DMSO-d6): δ 10.15 (s, 1H), 8.53 (s, 1H), 8.33 (s, 1H), 7.90 (d,
J = 8.0 Hz, 2H), 7.76−7.62 (m, 5H), 7.42 (d, J = 8.4 Hz, 1H),
7.24 (t, J = 7.6 Hz, 1H), 3.92 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ 152.3, 136.2, 134.6, 132.1, 130.2, 130.1, 126.5,
124.8, 123.3, 122.2, 121.1, 113.3, 56.4. HRMS (ESI) [M −
− +
BF4 ] calcd for C16H15N2O, 251.1179; found, 251.1178.
1-(3-Methoxyphenyl)-3-phenyl-1H-imidazol-3-ium
Tetrafluoroborate (m-3ca). Reacted for 6 h. A gray solid (81
mg, 95% yield); mp 144−146 °C. 1H NMR (400 MHz,
DMSO-d6): δ 10.34 (s, 1H), 8.60 (s, 1H), 8.58 (s, 1H), 7.92 (d,
J = 7.6 Hz, 2H), 7.72 (t, J = 7.6 Hz, 2H), 7.66−7.60 (m, 2H),
7.54 (s, 1H), 7.49 (d, J = 8.0 Hz, 1H), 7.20 (d, J = 8.4 Hz, 1H),
3.89 (s, 3H). 13C NMR (100 MHz, DMSO-d6): δ 160.4, 135.7,
134.7, 134.6, 131.2, 130.2, 130.1, 122.1, 121.9, 115.6, 113.8,
− +
108.0, 55.9. HRMS (ESI) [M − BF4 ] calcd for C16H15N2O,
251.1179; found, 251.1182.
1-(4-Methoxyphenyl)-3-phenyl-1H-imidazol-3-ium
Tetrafluoroborate (p-3ca). Reacted for 4 h. A gray solid (76
mg, 89% yield); mp 151−153 °C. 1H NMR (400 MHz,
DMSO-d6): δ 10.24 (s, 1H), 8.54 (s, 1H), 8.49 (s, 1H), 7.91 (d,
J = 8.0 Hz, 2H), 7.84 (d, J = 8.8 Hz, 2H), 7.73−7.70 (m, 2H),
7.63 (t, J = 7.6 Hz, 1H), 7.25 (d, J = 8.8 Hz, 2H), 3.87 (s, 3H).
13C NMR (100 MHz, DMSO-d6): δ 160.3, 134.8, 134.2, 130.2,
130.0, 127.8, 123.7, 122.2, 122.0, 121.7, 115.2, 55.8. HRMS
− +
127.1, 120.7, 117.8, 116.5, 55.9. HRMS (ESI) [M − BF4 ]
calcd for C14H14IO2, 341.0038; found, 341.0033.
General Procedure for Quaternization of N-Hetero-
arenes by Diaryliodonium Salts. A N-heteroarene (0.25
mmol), a diaryiodonium salt (0.375 mmol), Cu(OAc)2·H2O
(2.5 mg, 5 mol %), and DMF (1 mL) were added to an
schlenck tube with a magnetic stir bar. The reaction was stirred
at 100 °C for an indicated time in an oil bath. After cooled
down to room temperature, the solvent was removed under
reduced pressure, and the residue was passed through a silica
gel column (dichloromethane/acetone = 5:1−2:1 v/v) to afford
the desired onium salt.
1,3-Diphenyl-1H-imidazol-3-ium Tetrafluoroborate
(3aa).18 Reacted for 4 h. A gray solid (75 mg, 97% yield);
mp 143−145 °C. 1H NMR (400 MHz, (CD3)2CO): δ 10.10 (s,
1H), 8.43 (s, 2H), 7.96 (d, J = 8.0 Hz, 4H), 7.73−7.64 (m,
6H).
− +
(ESI) [M − BF4 ] calcd for C16H15N2O, 251.1179; found,
251.1173.
1-(2-Bromophenyl)-3-phenyl-1H-imidazol-3-ium Tet-
rafluoroborate (o-3da). Reacted for 6 h. A gray solid (92
mg, 95% yield); mp 118−120 °C. 1H NMR (400 MHz,
DMSO-d6): δ 10.29 (s, 1H), 8.64 (s, 1H), 8.42 (s, 1H), 8.03 (d,
J = 7.6 Hz, 1H), 7.92−7.90 (m, 3H), 7.76−7.63 (m, 5H). 13C
NMR (100 MHz, DMSO-d6): δ 136.7, 134.5, 133.9, 133.0,
130.4, 130.3, 129.4, 129.0, 125.2, 122.1, 121.4, 119.1. HRMS
− +
(ESI) [M − BF4 ] calcd for C15H12BrN2, 299.0178; found,
299.0184.
1-(3-Bromophenyl)-3-phenyl-1H-imidazol-3-ium Tet-
rafluoroborate (m-3da). Reacted for 4 h. A gray solid (80
mg, 83% yield); mp 110−113 °C. 1H NMR (400 MHz,
DMSO-d6): δ 10.40 (s, 1H), 8.61 (s, 1H), 8.60 (s, 1H), 8.27 (s,
1H), 7.97−7.91 (m, 3H), 7.85 (d, J = 8.0 Hz, 1H), 7.75−7.63
(m, 4H). 13C NMR (100 MHz, DMSO-d6): δ 135.9, 134.9,
134.6, 132.8, 132.0, 130.23, 130.15, 125.0, 122.6, 122.1, 122.0,
3-Phenyl-1-o-tolyl-1H-imidazol-3-ium Tetrafluorobo-
rate (o-3ba). Reacted for 6 h. A gray solid (73 mg, 91%
1
yield); mp 133−135 °C. H NMR (400 MHz, DMSO-d6): δ
10.12 (s, 1H), 8.59 (s, 1H), 8.35 (s, 1H), 7.91 (d, J = 8.0 Hz,
2H), 7.74−7.50 (m, 7H), 2.34 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ 136.2, 134.7, 134.2, 133.5, 131.7, 130.8, 130.1,
D
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The Journal of Organic Chemistry
Note
− +
121.9, 121.2. HRMS (ESI) [M − BF4 ] calcd for C15H12BrN2,
299.0178; found, 299.0178.
131.2, 130.2, 122.6, 122.2, 122.1, 121.7. HRMS (ESI) [M −
− +
BF4 ] calcd for C16H13N2O, 249.1022; found, 249.1021.
1-(4-Bromophenyl)-3-phenyl-1H-imidazol-3-ium Tet-
rafluoroborate (p-3da). Reacted for 6 h. A gray solid (79
mg, 82% yield); mp 246−248 °C. 1H NMR (400 MHz,
DMSO-d6): δ 10.37 (s, 1H), 8.58 (s, 2H), 7.97 (d, J = 8.4 Hz,
2H), 7.92−7.88 (m, 4H), 7.74−7.70 (m, 2H), 7.64 (t, J = 7.2
Hz, 1H). 13C NMR (100 MHz, DMSO-d6): δ 134.8, 134.7,
134.0, 133.1, 130.23, 130.15, 124.2, 123.1, 122.1, 122.0, 121.9.
1-(4-(Methoxycarbonyl)phenyl)-3-phenyl-1H-imida-
zol-3-ium Tetrafluoroborate (3ka). Reacted for 5 h. A gray
1
solid (61 mg, 66% yield); mp 196−198 °C. H NMR (400
MHz, DMSO-d6): δ 10.47 (s, 1H), 8.68 (s, 1H), 8.62 (s, 1H),
8.27 (d, J = 8.4 Hz, 2H), 8.10 (d, J = 8.4 Hz, 2H), 7.93 (d, J =
7.6 Hz, 2H), 7.73 (m, 2H), 7.65 (t, J = 7.2 Hz, 1H), 3.92 (s,
3H). 13C NMR (100 MHz, DMSO-d6): δ 165.2, 138.1, 135.1,
134.6, 131.1, 130.8, 130.2, 122.3, 122.2, 122.1, 121.8, 52.6.
− +
HRMS (ESI) [M − BF4 ] calcd for C15H12BrN2, 299.0178;
found, 299.0187.
− +
HRMS (ESI) [M − BF4 ] calcd for C17H15N2O2, 279.1128;
1-(4-Fluorophenyl)-3-phenyl-1H-imidazol-3-ium Tet-
rafluoroborate (3ea). Reacted for 5 h. A gray solid (68 mg,
89% yield); mp 202−204 °C. 1H NMR (400 MHz, DMSO-d6):
δ 10.32 (s, 1H), 8.58 (s, 1H), 8.55 (s, 1H), 8.00−7.96 (m, 2H),
7.91 (d, J = 7.6 Hz, 2H), 7.72 (t, J = 7.6 Hz, 2H), 7.66−7.59
(m, 3H). 13C NMR (100 MHz, DMSO-d6): δ 162.5 (d, J = 246
Hz), 134.8, 134.7, 131.2 (d, J = 3 Hz), 130.2, 130.1, 124.8 (d, J
= 9 Hz), 122.3, 122.1, 121.9, 117.1 (d, J = 23 Hz). HRMS
found, 279.1125.
1-(4-Cyanophenyl)-3-phenyl-1H-imidazol-3-ium Tet-
rafluoroborate (3la). Reacted for 5 h. A gray solid (55 mg,
67% yield); mp 222−224 °C. 1H NMR (400 MHz, DMSO-d6):
δ 10.48 (s, 1H), 8.67 (s, 1H), 8.62 (s, 1H), 8.27 (d, J = 8.4 Hz,
2H), 8.16 (d, J = 8.4 Hz, 2H), 7.92 (d, J = 8.0 Hz, 2H), 7.73
(m, 2H), 7.65 (t, J = 7.6 Hz, 1H). 13C NMR (100 MHz,
DMSO-d6): δ 138.0, 135.3, 134.6, 134.5, 130.3, 122.9, 122.3,
− +
− +
(ESI) [M − BF4 ] calcd for C15H12FN2, 239.0979; found,
122.1, 121.7, 117.8, 112.6. HRMS (ESI) [M − BF4 ] calcd for
239.0975.
C16H12N3, 246.1026; found, 246.1022.
1-(4-Chlorophenyl)-3-phenyl-1H-imidazol-3-ium Tet-
rafluoroborate (3fa). Reacted for 4 h. A gray solid (73 mg,
85% yield); mp 230−232 °C. 1H NMR (400 MHz, DMSO-d6):
δ 10.36 (s, 1H), 8.58 (s, 2H), 7.96 (d, J = 8.8 Hz, 2H), 7.91 (d,
J = 7.6 Hz, 2H), 7.83 (d, J = 8.8 Hz, 2H), 7.74−7.70 (m, 2H),
7.64 (t, J = 7.2 Hz, 1H). 13C NMR (100 MHz, DMSO-d6): δ
134.8, 134.7, 134.6, 133.6, 130.2, 130.2, 124.0, 122.1, 122.0.
1-[4-(Dimethylamino)phenyl]-3-phenyl-1H-imidazol-
3-ium Tetrafluoroborate (3ma). Reacted for 5 h. A gray
1
solid (50 mg, 57% yield); mp 162−164 °C. H NMR (400
MHz, DMSO-d6): δ 10.17 (s, 1H), 8.52 (s, 1H), 8.45 (s, 1H),
7.90 (d, J = 8.0 Hz, 2H), 7.72−7.67 (m, 4H), 7.62 (t, J = 7.2
Hz, 1H), 6.92 (d, J = 8.8 Hz, 2H), 3.00 (s, 6H). 13C NMR (100
MHz, DMSO-d6): δ 151.0, 134.8, 133.4, 130.2, 129.9, 123.4,
122.8, 122.02, 121.99, 121.6, 112.3, 40.0. HRMS (ESI) [M −
− +
HRMS (ESI) [M − BF4 ] calcd for C15H12ClN2, 255.0684;
found, 255.0683.
− +
BF4 ] calcd for C17H18N3, 264.1495; found, 264.1498.
1-(4-Iodophenyl)-3-phenyl-1H-imidazol-3-ium Tetra-
fluoroborate (3ga). Reacted for 4 h. A gray solid (102 mg,
94% yield); mp 248−250 °C. 1H NMR (400 MHz, DMSO-d6):
δ 10.36 (s, 1H), 8.58 (s, 2H), 8.11 (d, J = 8.8 Hz, 2H), 7.91 (d,
J = 8.0 Hz, 2H), 7.74−7.70 (m, 4H), 7.64 (t, J = 7.2 Hz, 1H).
13C NMR (100 MHz, DMSO-d6): δ 138.9, 134.6, 134.5, 130.2,
130.1, 124.0, 122.1, 122.0, 121.8, 96.3. HRMS (ESI) [M −
1-(4-Hydroxylphenyl)-3-phenyl-1H-imidazol-3-ium
Tetrafluoroborate (3na). Reacted for 4 h. A gray solid (52
mg, 64% yield); mp 188−190 °C. 1H NMR (400 MHz,
DMSO-d6): δ 10.20 (s, 1H), 10.18 (s, 1H), 8.52 (s, 1H), 8.43
(s, 1H), 7.90 (d, J = 8.0 Hz, 2H), 7.72−7.69 (m, 4H), 7.62 (t, J
= 7.2 Hz, 1H), 7.02 (d, J = 8.8 Hz, 2H). 13C NMR (100 MHz,
DMSO-d6): δ 158.8, 134.8, 134.1, 130.2, 130.0, 126.4, 123.8,
− +
− +
122.3, 122.0, 121.7, 116.3. HRMS (ESI) [M − BF4 ] calcd for
C15H13N2O, 237.1022; found, 237.1025.
BF4 ] calcd for C15H12IN2, 347.0040; found, 347.0038.
1-(4-Ethynylphenyl)-3-phenyl-1H-imidazol-3-ium Tet-
rafluoroborate (3ha). Reacted for 4 h. A gray solid (66 mg,
80% yield); mp 206−208 °C. 1H NMR (400 MHz, DMSO-d6):
δ 10.39 (s, 1H), 8.61 (s, 1H), 8.59 (s, 1H), 7.97−7.91 (m, 4H),
7.84 (d, J = 8.4 Hz, 2H), 7.74−7.70 (m, 2H), 7.64 (t, J = 7.2
Hz, 1H), 4.47 (s, 1H). 13C NMR (100 MHz, DMSO-d6): δ
134.8, 134.7, 133.5, 130.24, 130.16, 123.4, 122.3, 122.10,
1-(Naphthalen-1-yl)-3-phenyl-1H-imidazol-3-ium Tet-
rafluoroborate (3oa). Reacted for 4 h. A gray solid (81 mg,
91% yield); mp 112−114 °C. 1H NMR (400 MHz, DMSO-d6):
δ 10.31 (s, 1H), 8.69 (s, 1H), 8.49 (s, 1H), 8.31 (d, J = 8.0 Hz,
1H), 8.21 (d, J = 7.2 Hz, 1H), 7.99−7.94 (m, 3H), 7.86−7.72
(m, 6H), 7.65 (t, J = 7.2 Hz, 1H). 13C NMR (100 MHz,
DMSO-d6): δ 136.9, 134.8, 133.6, 131.2, 131.1, 130.1, 130.0,
128.5, 128.4, 127.62, 127.57, 125.5, 125.4, 125.1, 122.2, 121.8,
− +
122.07, 121.8, 83.2, 82.1. HRMS (ESI) [M − BF4 ] calcd for
C17H13N2, 245.1073; found, 245.1074.
− +
121.6. HRMS (ESI) [M − BF4 ] calcd for C19H15N2,
1-(4-Acetylphenyl)-3-phenyl-1H-imidazol-3-ium Tet-
rafluoroborate (3ia). Reacted for 4 h. A gray solid (66 mg,
76% yield); mp 208−210 °C. 1H NMR (400 MHz, DMSO-d6):
δ 10.47 (s, 1H), 8.69 (s, 1H), 8.62 (s, 1H), 8.27 (d, J = 8.4 Hz,
2H), 8.09 (d, J = 8.4 Hz, 2H), 7.93 (d, J = 7.6 Hz, 2H), 7.73
(m, 2H), 7.65 (t, J = 7.2 Hz, 1H), 2.68 (s, 3H). 13C NMR (100
MHz, DMSO-d6): δ 197.1, 137.8, 137.5, 135.0, 134.6, 130.2,
130.1, 122.21, 122.15, 122.0, 121.7, 27.0. HRMS (ESI) [M −
271.1230; found, 271.1231.
1-Mesityl-3-phenyl-1H-imidazol-3-ium Tetrafluorobo-
rate (3pa). Reacted for 12 h. A gray solid (75 mg, 86% yield);
mp 166−168 °C. 1H NMR (400 MHz, DMSO-d6): δ 10.05 (s,
1H), 8.66 (s, 1H), 8.21 (s, 1H), 7.93 (d, J = 7.6 Hz, 2H), 7.71
(m, 2H), 7.63 (t, J = 7.2 Hz, 1H), 7.19 (s, 2H), 2.36 (s, 3H),
2.13 (s, 6H). 13C NMR (100 MHz, DMSO-d6): δ 140.6, 136.3,
134.7, 134.5, 131.2, 130.2, 130.1, 129.4, 124.9, 122.1, 121.9,
− +
BF4 ] calcd for C17H15N2O, 263.1179; found, 263.1177.
− +
1-(4-Formylphenyl)-3-phenyl-1H-imidazol-3-ium Tet-
rafluoroborate (3ja). Reacted for 4 h. A gray solid (51 mg,
61% yield); mp 148−150 °C. 1H NMR (400 MHz, DMSO-d6):
δ 10.48 (s, 1H), 10.13 (s, 1H), 8.68 (s, 1H), 8.62 (s, 1H), 8.24
(d, J = 8.8 Hz, 2H), 8.17 (d, J = 8.8 Hz, 2H), 7.93 (d, J = 8.0
Hz, 2H), 7.73 (m, 2H), 7.65 (t, J = 7.2 Hz, 1H). 13C NMR
(100 MHz, DMSO-d6): δ 192.2, 138.6, 136.6, 135.1, 134.6,
20.7, 17.1. HRMS (ESI) [M − BF4 ] calcd for C18H19N2,
263.1543; found, 263.1546.
1-(2,6-Diisopropylphenyl)-3-phenyl-1H-imidazol-3-
ium Tetrafluoroborate (3qa). Ph2IBF4 (276.0 mg, 0.75
mmol, 3.0 equiv) was used to react for 12 h. A gray solid (55
mg, 56% yield); mp 210−212 °C. 1H NMR (400 MHz,
DMSO-d6): δ 10.24 (s, 1H), 8.71 (s, 1H), 8.37 (s, 1H), 7.91 (d,
E
dx.doi.org/10.1021/jo400527r | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
− +
J = 7.6 Hz, 2H), 7.74−7.63 (m, 4H), 7.51 (d, J = 7.6 Hz, 2H),
2.47−2.43 (m, 2H), 1.19 (d, J = 8.0 Hz, 6H), 1.17 (d, J = 8.0
Hz, 6H). 13C NMR (100 MHz, DMSO-d6): δ 145.3, 136.3,
134.6, 131.7, 130.5, 130.2, 130.1, 126.0, 124.5, 122.1, 122.0,
28.0, 24.1, 23.8. HRMS (ESI) [M − BF4 ] calcd for C21H25N2,
305.2012; found, 305.2017.
(ESI) [M − BF4 ] calcd for C17H17N2O2, 281.1285; found,
281.1283.
1,3-Bis(4-methoxyphenyl)-1H-imidazol-3-ium Tetra-
fluoroborate (p-3cc). Reacted for 4 h. A gray solid (67 mg,
73% yield); mp 232−234 °C. 1H NMR (400 MHz, DMSO-d6):
δ 10.12 (s, 1H), 8.43 (s, 2H), 7.82 (d, J = 8.8 Hz, 4H), 7.23 (d,
J = 8.8 Hz, 4H), 3.87 (s, 6H). 13C NMR (100 MHz, DMSO-
d6): δ 160.2, 134.0, 127.9, 123.7, 122.0, 115.2, 55.8. HRMS
− +
3-Phenyl-1-(thiophen-2-yl)-1H-imidazol-3-ium Tetra-
fluoroborate (3ra). Reacted for 5 h. A gray solid (69 mg,
88% yield); mp 124−126 °C. 1H NMR (400 MHz, DMSO-d6):
δ 10.31 (s, 1H), 8.56 (s, 1H), 8.49 (s, 1H), 7.89 (d, J = 8.0 Hz,
2H), 7.74−7.62 (m, 5H), 7.23 (t, J = 4.4 Hz, 1H). 13C NMR
(100 MHz, DMSO-d6): δ 135.7, 135.1, 134.5, 130.2, 126.8,
− +
(ESI) [M − BF4 ] calcd for C17H17N2O2, 281.1285; found,
281.1277.
1,3-Bis(3-bromophenyl)-1H-imidazol-3-ium Tetra-
fluoroborate (m-3dd). Reacted for 48 h. A gray solid (54
mg, 46% yield); mp 162−164 °C. 1H NMR (400 MHz,
DMSO-d6): δ 10.44 (s, 1H), 8.61 (s, 2H), 8.26 (s, 2H), 7.95 (d,
J = 8.0 Hz, 2H), 7.86 (d, J = 8.0 Hz, 2H), 7.69 (t, J = 8.0 Hz,
2H). 13C NMR (100 MHz, DMSO-d6): δ 135.7, 135.3, 132.9,
132.1, 124.9, 122.6, 121.9, 121.1. HRMS (ESI) [M − BF4 ]
calcd for C15H11Br2N2, 376.9283; found, 376.9275.
1,3-Bis(4-bromophenyl)-1H-imidazol-3-ium Tetra-
fluoroborate (p-3dd). Reacted for 48 h. A gray solid (55
mg, 47% yield); mp > 250 °C. H NMR (400 MHz, DMSO-
− +
126.2, 123.7, 123.3, 122.2, 122.0. HRMS (ESI) [M-BF4 ]
calcd for C13H11N2S, 227.0637; found, 227.0641.
3-Phenyl-1-(pyridin-2-yl)-1H-imidazol-3-ium Tetra-
fluoroborate (3sa). Reacted for 4 h. A gray solid (66 mg,
86% yield); mp 162−164 °C. 1H NMR (400 MHz, DMSO-d6):
δ 10.60 (s, 1H), 8.75 (s, 1H), 8.71 (d, J = 4.4 Hz, 1H), 8.58 (s,
1H), 8.30−8.26 (m, 1H), 8.16 (d, J = 8.0 Hz, 1H), 7.95 (d, J =
8.0 Hz, 2H), 7.74−7.69 (m, 3H), 7.65 (t, J = 7.6 Hz, 1H). 13C
NMR (100 MHz, DMSO-d6): δ 149.3, 146.3, 140.7, 134.7,
134.3, 130.2, 130.1, 125.5, 122.3, 120.0, 114.8. HRMS (ESI)
− +
1
d6): δ 10.39 (s, 2H), 8.58 (s, 2H), 7.97 (d, J = 8.4 Hz, 4H), 7.88
− +
(d, J = 8.4 Hz, 4H). 13C NMR (100 MHz, DMSO-d6): δ 135.0,
[M − BF4 ] calcd for C14H12N3, 222.1026; found, 222.1030.
− +
1-Isopropyl-3-phenyl-1H-imidazol-3-ium Tetrafluoro-
borate (3ta). Reacted for 5 h. A semisolid (59 mg, 86% yield).
1H NMR (400 MHz, CDCl3): δ 9.19 (s, 1H), 7.69 (s, 1H), 7.64
(s, 1H), 7.61 (d, J = 7.2 Hz, 2H), 7.50−7.43 (m, 3H), 4.83
(septet, J = 6.4 Hz, 1H), 1.58 (d, J = 6.4 Hz, 6H). 13C NMR
(100 MHz, CDCl3): δ 134.7, 133.1, 130.6, 130.4, 122.1, 121.8,
133.9, 133.1, 124.1, 123.1, 121.9. HRMS (ESI) [M − BF4 ]
calcd for C15H11Br2N2, 376.9283; found, 376.9283.
1,3-Di(naphthalen-1-yl)-1H-imidazol-3-ium Tetra-
fluoroborate (3oo). Reacted for 6 h. A gray solid (89 mg,
88% yield); mp 146−148 °C. 1H NMR (400 MHz, DMSO-d6):
δ 10.23 (s, 1H), 8.60 (s, 2H), 8.32 (d, J = 8.4 Hz, 2H), 8.22 (d,
J = 8.0 Hz, 2H), 8.11 (d, J = 7.6 Hz, 2H), 7.98 (d, J = 7.6 Hz,
2H), 7.84−7.76 (m, 6H). 13C NMR (100 MHz, DMSO-d6): δ
139.2, 133.7, 131.3, 131.2, 128.6, 127.7, 127.6, 125.5, 125.4,
− +
121.3, 54.1, 22.7. HRMS (ESI) [M − BF4 ] calcd for
C12H15N2, 187.1230; found, 187.1232.
1-tert-Butyl-3-phenyl-1H-imidazol-3-ium Tetrafluoro-
borate (3ua). Reacted for 5 h. A gray solid (67 mg, 90%
− +
125.3, 121.9. HRMS (ESI) [M − BF4 ] calcd for C23H17N2,
321.1386; found, 321.1386.
1
yield); mp 146−148 °C. H NMR (400 MHz, DMSO-d6): δ
9.69 (s, 1H), 8.38 (s, 1H), 8.28 (s, 1H), 7.85 (d, J = 7.6 Hz,
2H), 7.69−7.65 (m, 2H), 7.59 (t, J = 7.2 Hz, 1H), 1.66 (s, 9H).
13C NMR (100 MHz, DMSO-d6): δ 135.0, 133.7, 130.0, 129.7,
1,3-Dimesityl-1H-imidazol-3-ium Tetrafluoroborate
(3pp).20 [Mesityl]2IBF4 (339.0 mg, 0.75 mmol, 3.0 equiv)
was used to react for 6 h. A gray solid (81 mg, 83% yield); mp
206−208 °C. 1H NMR (400 MHz, DMSO-d6): δ 9.64 (s, 1H),
8.28 (s, 2H), 7.21 (s, 4H), 2.36 (s, 6H), 2.12 (s, 12H).
1,3-Di(thiophen-2-yl)-1H-imidazol-3-ium 4-Methyl-
benzenesulfonate (3rr). Reacted for 5 h. A gray solid (87
mg, 86% yield); mp 154−156 °C. 1H NMR (400 MHz,
DMSO-d6): δ 10.28 (s, 1H), 8.46 (s, 2H), 7.73 (d, J = 5.2 Hz,
2H), 7.64 (d, J = 2.8 Hz, 2H), 7.47 (d, J = 8.0 Hz, 2H), 7.22−
7.20 (m, 2H), 7.11 (d, J = 8.0 Hz, 2H), 2.29 (s, 3H). 13C NMR
(100 MHz, DMSO-d6): δ 145.6, 137.7, 136.7, 134.9, 128.1,
126.8, 126.3, 125.5, 123.7, 123.4, 20.8. HRMS (ESI) [M −
OTs−]+ calcd for C11H9N2S2, 233.0202; found, 233.0202.
1,3-Diphenyl-1H-benzo[d]imidazol-3-ium Tetrafluoro-
borate (4). Reacted for 4 h. A gray solid (81 mg, 91% yield);
− +
122.2, 121.5, 121.2, 60.3, 29.0. HRMS (ESI) [M − BF4 ] calcd
for C13H17N2, 201.1386; found, 201.1386.
1-(1-Adamantyl)-3-phenyl-1H-imidazol-3-ium Tetra-
fluoroborate (3va). Reacted for 6 h. A gray solid (86 mg,
90% yield); mp 163−165 °C. 1H NMR (400 MHz, CDCl3): δ
9.11 (s, 1H), 7.67−7.66 (m, 4H), 7.55−7.46 (m, 3H), 2.29 (s,
3H), 2.33 (s, 6H), 1.78 (s, 6H). 13C NMR (100 MHz, CDCl3):
δ 134.8, 131.7, 130.5, 130.3, 122.3, 121.7, 120.3, 61.5, 42.3,
− +
35.3, 29.6. HRMS (ESI) [M − BF4 ] calcd for C19H23N2,
279.1856; found, 279.1857.
1,3-Bis(2-methoxyphenyl)-1H-imidazol-3-ium Tetra-
fluoroborate (o-3cc). Reacted for 5 h. A gray solid (83 mg,
90% yield); mp 178−180 °C. 1H NMR (400 MHz, DMSO-d6):
δ 9.90 (s, 1H), 8.25 (s, 2H), 7.72 (d, J = 7.6 Hz, 2H), 7.66−
7.62 (m, 2H), 7.41 (d, J = 8.4 Hz, 2H), 7.25−7.21 (m, 2H),
3.93 (s, 6H). 13C NMR (100 MHz, DMSO-d6): δ 152.3, 138.1,
132.0, 126.4, 123.7, 123.3, 121.1, 113.3, 56.4. HRMS (ESI) [M
1
mp > 250 °C. H NMR (400 MHz, DMSO-d6): δ 10.58 (s,
1H), 7.98−7.93 (m, 6H), 7.83−7.74 (m, 8H). 13C NMR (100
MHz, DMSO-d6): δ 142.8, 133.0, 131.2, 130.8, 130.5, 127.8,
− +
125.4, 113.8. HRMS (ESI) [M − BF4 ] calcd for C19H15N2,
271.1230; found, 271.1234.
− +
− BF4 ] calcd for C17H17N2O2, 281.1285; found, 281.1284.
2-Phenylimidazo[1,5-a]pyridin-2-ium Tetrafluorobo-
rate (5). Reacted for 4 h. A gray solid (63 mg, 89% yield);
mp 154−156 °C. 1H NMR (400 MHz, DMSO-d6): δ 10.30 (s,
1H), 8.75 (s, 1H), 8.58 (d, J = 6.8 Hz, 1H), 7.94−7.90 (m,
3H), 7.76−7.66 (m, 3H), 7.38−7.34 (m, 1H), 7.29−7.26 (m,
1H). 13C NMR (100 MHz, DMSO-d6): δ 135.1, 130.6, 130.4,
129.8, 125.9, 125.3, 124.3, 122.9, 118.4, 118.3, 112.3. HRMS
1,3-Bis(3-methoxyphenyl)-1H-imidazol-3-ium Tetra-
fluoroborate (m-3cc). Reacted for 4 h. A gray solid (76
mg, 83% yield); mp 117−119 °C. 1H NMR (400 MHz,
DMSO-d6): δ 10.32 (s, 1H), 8.59 (s, 2H), 7.62 (t, J = 8.0 Hz,
2H), 7.54 (s, 2H), 7.49 (d, J = 8.0 Hz, 2H), 7.21 (d, J = 8.0 Hz,
2H), 3.89 (s, 6H). 13C NMR (100 MHz, DMSO-d6): δ 160.4,
135.7, 134.6, 131.2, 121.9, 115.7, 113.9, 108.1, 55.9. HRMS
F
dx.doi.org/10.1021/jo400527r | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
− +
Thomas, A. W. Angew. Chem., Int. Ed. 2003, 42, 5400. (d) Monnier, F.;
Taillefer, M. Angew. Chem., Int. Ed. 2009, 48, 6954. (e) Senra, J. D.;
Aguiar, L. C. S.; Simas, A. B. C. Curr. Org. Chem. 2011, 8, 53.
(2) Zhu, Z.-Q.; Xiang, S.; Chen, Q.-Y.; Chen, C.; Zeng, Z.; Cui, Y.-P.;
Xiao, J.-C. Chem. Commun. 2008, 5016.
(ESI) [M − BF4 ] calcd for C13H11N2, 195.0917; found,
195.0916.
1,3-Dimesityl-4,5-dihydro-1H-imidazol-3-ium Tetra-
fluoroborate (6).21 [Mesityl]2IBF4 (339.0 mg, 0.75 mmol,
3.0 equiv) was used to react for 6 h. A gray solid (72 mg, 74%
(3) Benhamou, L.; Chardon, E.; Lavigne, G.; Bellemin-Laponnaz, S.;
1
yield); mp > 250 °C. H NMR (400 MHz, DMSO-d6): δ 8.99
Ces
́
ar, V. Chem. Rev. 2011, 111, 2705.
(s, 1H), 7.10 (s, 4H), 4.45 (s, 4H), 2.36 (s, 12H), 2.30 (s, 6H).
(4) Furstner, A.; Alcarazo, M.; Ces
Commun. 2006, 2176.
́
ar, V.; Lehmann, C. W. Chem.
̈
13C NMR (100 MHz, DMSO-d6): δ 160.3, 139.7, 135.5, 130.9,
− +
129.5, 50.9, 20.6, 17.2. HRMS (ESI) [M − BF4 ] calcd for
C21H27N2, 307.2169; found, 307.2166.
1,3-Diphenyl-1H-1,2,3-triazol-3-ium Tetrafluorobo-
(5) (a) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290.
(b) Bellemin-Laponnaz, S.; Despagnet-Ayoub, E.; Díez-Gonzalez, S.;
́
Gade, L. H.; Glorius, F.; Louie, J.; Nolan, S. P.; Peris, E.; Ritter, T.;
Rogers, M. M.; Stahl, S. S.; Tekavec, T. N. N-Heterocyclic Carbenes in
Transition Metal Catalysis, Topics in Organometallic Chemistry, Vol.
21; Glorius, F., Ed.; Springer: Berlin, Germany, 2007.
rate (7). Reacted for 4 h. A gray solid (71 mg, 91% yield);
1
mp 158−160 °C. H NMR (400 MHz, DMSO-d6): δ 9.83 (s,
2H), 8.16 (d, J = 6.4 Hz, 4H), 7.82−7.76 (m, 6H). 13C NMR
(100 MHz, DMSO-d6): δ 134.9, 132.1, 130.5, 129.9, 121.8.
(6) (a) Boydston, A. J.; Vu, P. D.; Dykhno, O. L.; Chang, V.; Wyatt,
A. R., II; Stockett, A. S.; Ritschdorff, E. T.; Shear, J. B.; Bielawski, C.
W. J. Am. Chem. Soc. 2008, 130, 3143. (b) Giernoth, R. Angew. Chem.,
Int. Ed. 2010, 49, 5608. (c) Park, J. S.; Karnas, E.; Ohkubo, K.; Chen,
P.; Kadish, K. M.; Fukuzumi, S.; Bielawski, C. W.; Hudnall, T. W.;
Lynch, V. M.; Sessler, J. L. Science 2010, 329, 1324. (d) Hutt, J. T.; Jo,
J.; Olasz, A.; Chen, C.-H.; Lee, D.; Aron, Z. D. Org. Lett. 2012, 14,
3162.
− +
HRMS (ESI) [M − BF4 ] calcd for C14H12N3, 222.1026;
found, 222.1026.
1,4-Diphenyl-1H-1,2,4-triazol-4-ium Tetrafluorobo-
rate (8). Ph2IBF4 (184.0 mg, 0.50 mmol, 2.0 equiv) was
used to react for 6 h. A gray solid (74 mg, 94% yield); mp 166−
1
168 °C. H NMR (400 MHz, DMSO-d6): δ 11.43 (s, 1H),
10.02 (s, 1H), 8.04 (d, J = 7.6 Hz, 2H), 7.94 (d, J = 7.6 Hz,
2H), 7.79−7.75 (m, 4H), 7.71−7.67 (m, 2H). 13C NMR (100
MHz, DMSO-d6): δ 143.3, 140.5, 135.0, 132.1, 130.8, 130.4,
́
(7) For selected reviews, see (a) Cesar, V.; Bellemin-Laponnaz, S.;
Gade, L. H. Chem. Soc. Rev. 2004, 33, 619. (b) Enders, D.; Balensiefer,
T. Acc. Chem. Res. 2004, 37, 534. (c) Wang, F.; Liu, L.-J.; Wang, W.; Li,
S.; Shi, M. Coord. Chem. Rev. 2012, 256, 804.
− +
122.6, 120.8. HRMS (ESI) [M − BF4 ] calcd for C14H12N3,
222.1026; found, 222.1024.
(8) For selected recent examples, see (a) Zhao, Y.-M.; Cheung, M.
S.; Lin, Z.; Sun, J. Angew. Chem., Int. Ed. 2012, 51, 10359. (b) Yoshida,
M.; Ohmiya, H.; Sawamura, M. J. Am. Chem. Soc. 2012, 134, 11896.
(c) Ortega, N.; Urban, S.; Beiring, B.; Glorius, F. Angew. Chem., Int. Ed.
2012, 51, 1710. (d) DiRocco, D. A.; Rovis, T. J. Am. Chem. Soc. 2012,
134, 8094. (e) Cohen, D. T.; Eichman, C. C.; Phillips, E. M.; Zarefsky,
E. R.; Scheidt, K. A. Angew. Chem., Int. Ed. 2012, 51, 7309. (f) Piel, I.;
1-(4-bromophenyl)-3-(4-methoxyphenyl)-1H-imida-
zol-3-ium Tetrafluoroborate (p-3dc). Reacted for 5 h. A
gray solid (97 mg, 93% yield); mp 179−181 °C. 1H NMR (400
MHz, DMSO-d6): δ 10.24 (s, 1H), 8.52 (s, 1H), 8.47 (s, 1H),
7.94 (d, J = 8.8 Hz, 2H), 7.88 (d, J = 8.8 Hz, 2H), 7.82 (d, J =
8.8 Hz, 2H), 7.24 (d, J = 8.8 Hz, 2H), 3.87 (s, 3H). 13C NMR
(100 MHz, DMSO-d6): δ 160.3, 134.4, 134.1, 133.1, 127.7,
124.2, 123.7, 123.0, 122.3, 121.7, 115.2, 55.8. HRMS (ESI) [M
Steinmetz, M.; Hirano, K.; Frohlich, R.; Grimme, S.; Glorius, F. Angew.
̈
Chem., Int. Ed. 2011, 50, 4983. (g) Liu, F.; Bugaut, X.; Schedler, M.;
Frohlich, R.; Glorius, F. Angew. Chem., Int. Ed. 2011, 50, 12626.
̈
− +
− BF4 ] calcd for C16H14BrN2O, 329.0284; found, 329.0287.
(h) Vora, H. U.; Rovis, T. J. Am. Chem. Soc. 2010, 132, 2860.
(9) Yoshida, H.; Sugiura, S.; Kunai, A. Org. Lett. 2002, 4, 2767.
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2009, 48, 9052. (d) Yusubov, M. S.; Maskaev, A. V.; Zhdankin, V. V.
Arkivoc 2011, 1, 370. (e) Kita, Y.; Koser, G. F.; Ochiai, M.; Tohma, H.;
Varvoglis, A.; Wirth, T.; Zhdankin, V. V. Hypervalent Iodine Chemistry :
Modern Developments in Organic Synthesis; Topics in Current
Chemistry, Vol. 224; Wirth, T., Ed.; Springer: Berlin, Germany, 2003.
(11) (a) Wang, L.; Chen, Z.-C. J. Chem. Res. (S) 2000, 367. (b) Kang,
S.-K.; Lee, S.-H.; Lee, D. Synlett 2000, 7, 1022.
3-(4-bromophenyl)-1-(4-methoxyphenyl)-1H-imida-
zol-3-ium Tetrafluoroborate (p-3cd). Reacted for 48 h. A
gray solid (79 mg, 76% yield). p-3cd and p-3dc are the same
compound.
ASSOCIATED CONTENT
* Supporting Information
Data and copies of NMR for compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: gg2b@scu.edu.cn (G.G.); jsyou@scu.edu.cn (J.Y.)
(12) Zhang, B.-X.; Nuka, T.; Fujiwara, Y.; Yamaji, T.; Hou, Z.;
Kitamura, T. Heterocycles 2004, 64, 199 and references therein.
(13) The BF4 salt could be easily metathesized to the corresponding
Cl salt by using Dowex 1 × 4-50 anion exchange resin following a
literature procedure. see Higgins, E. M.; Sherwood, J. A.; Lindsay, A.
G.; Armstrong, J.; Massey, R. S.; Alder, R. W.; O’Donoghue, A. C.
Chem. Commun. 2011, 47, 1559.
(14) Deprez, N. R.; Sanford, M. S. Inorg. Chem. 2007, 46, 1924.
(15) Canty, A. J.; Rodemann, T.; Ryan, J. H. Transition Metal
Organometallic Synthesis Utilising Diorganoiodine(III) Reagents In
Advances in Organometallic Chemistry, Vol. 55; West, R.; Hill, A. F.;
Fink, M. J., Eds.; Elsevier: Amsterdam, The Netherlands, 2008.
(16) Phipps, R. J.; Grimster, N. P.; Gaunt, M. J. J. Am. Chem. Soc.
2008, 130, 8172.
■
Notes
The authors declare no competing financial interest
ACKNOWLEDGMENTS
■
This work was financially supported by the NSFC (Grants
20902063, 21172159, 21025205, and 21021001) and the SRF
for ROCS, SEM (Grant 20111568-8-2). We thank the Centre
of Testing & Analysis, Sichuan University, for NMR measure-
ments.
(17) Lin, D. W.; Masuda, T.; Biskup, M. B.; Nelson, J. D.; Baran, P. S.
J. Org. Chem. 2011, 76, 1013.
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