Chlorination of aromatics with trichloroisocyanuric acid (TCICA) in bronsted-acidic imidazolium ionic liquid [BMIM(SO3H)][OTf]: An economical, green protocol for the synthesis of chloroarenes

Article abstract of DOI:10.1071/CH07261

A survey study on electrophilic chlorination of aromatics with trichloroisocyanuric acid (TCICA) in Bronsted-acidic imidazolium ionic liquid [BMIM(SO₃H)][OTf] is reported. The reactions are performed under very mild conditions (at ～50°C) and give good to excellent yields, depending on the substrates. Chemoselectivity for mono- v. dichlorination can be tuned by changing the arene-to-TCICA ratio and the reaction time. The survey study and competitive experiments suggest that triprotonated/protosolvated TCICA is a selective/moderately reactive transfer-chlorination electrophile. Density functional theory was used as guide to obtain further insight into the nature of the chlorination electrophile and the transfer-chlorination step. CSIRO 2007.

Full text of DOI:10.1071/CH07261

Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2007, 60, 923–927
Chlorination of Aromatics with Trichloroisocyanuric Acid
(TCICA) in Brønsted-Acidic Imidazolium Ionic Liquid
[BMIM(SO3H)][OTf]: an Economical, Green Protocol
for the Synthesis of Chloroarenes∗
Abigail Hubbard,A Takao Okazaki,A and Kenneth K. LaaliA,B
ADepartment of Chemistry, Kent State University, Kent, OH 44242, USA.
BCorresponding author. Email: klaali@kent.edu
A survey study on electrophilic chlorination of aromatics with trichloroisocyanuric acid (TCICA) in Brønsted-acidic
imidazolium ionic liquid [BMIM(SO3H)][OTf] is reported. The reactions are performed under very mild conditions (at
∼50◦C) and give good to excellent yields, depending on the substrates. Chemoselectivity for mono- v. dichlorination can
be tuned by changing the arene-to-TCICA ratio and the reaction time. The survey study and competitive experiments
suggest that triprotonated/protosolvated TCICA is a selective/moderately reactive transfer-chlorination electrophile. Den-
sity functional theory was used as guide to obtain further insight into the nature of the chlorination electrophile and the
transfer-chlorination step.
Manuscript received: 26 July 2007.
Final version: 2 October 2007.
Introduction
system,[2] it becomes necessary to develop strategies to increase
its electrophilicity.
Trichloroisocyanuric acid (TCICA; Scheme 1) is a readily avail-
able, cheap industrial chemical, known for its bleaching and
antibacterial properties. Its utility in synthetic/preparative chem-
istry as a chlorinating agent and oxidant is well recognized and
documented.[1]
TCICA by itself has limited reactivity in chlorination of aro-
matic and heteroaromatic compounds. For it to be used as a
viable and green alternative to the classical chlorine gas/Lewis
acid systems (with HX as by-product), or the more recently stud-
ied and more powerful N-chlorosuccinimide (NCS)/BF3–H2O
TCICA forms a complex with Ph3P (3 equivalents), which
can act as an in situ source of Ph3P–Cl+,[3,4] and was
shown to be effective for chlorination of representative nitro-
gen heterocycles.[4] A more appealing and simpler approach
is by O-protonation with Brønsted acids to form a sol-
vated superelectrophilic trication at the limit (Fig. 1), which
could act as a transfer-chlorinating agent to arene nucleo-
philes, in an analogous fashion to transfer-fluorination with
Umemoto’s N-fluoropyridinium salts[5a] or with F-TEDA-BF4
(Selectfluor).[5b]
An earlier study showed that protonation of TCICA with
H2SO4 greatly increased its reactivity in chlorination of isatin to
5-chloroisatin.[6] Some examples for chlorination of substituted
benzenes were also presented. Chemoselectivity observed with
toluene and chlorobenzene was rather poor and complex mix-
tures consisting of mono-, di-, tri-, and tetrachloro derivatives
were produced.[6]
O
Cl
Cl
O
N
N
O
N
Cl
Scheme 1.
H
O
H
O
N
ꢀ
Hꢀ
O
Cl
N
Cl
Cl
Cl
ꢀ
N
Cl
Cl
N
Hꢀ
N
ꢀ
N
N
H
H
O
O
O
N
O
ꢀ
Hꢀ
ꢀ
O
N
O
ꢀ
3Nu-Cl
Cl
Cl
H
Cl
H
Nu
Fig. 1. Chlorination involving triprotonated trichloroisocyanuric acid.
∗ Part of undergraduate Honours Thesis of Abigail Hubbard: Halogen Introduction Strategies through Onium Ion Chemistry in Ionic Liquid Solvents (Kent
State University) May 2007.
© CSIRO 2007
10.1071/CH07261
0004-9425/07/120923

924
A. Hubbard, T. Okazaki, and K. K. Laali
Ph
OMe
ꢀ
P
(CH2)4
n-Bu
(CH2)3 SO3ꢁ
N
N
Ph
Ph
ꢀ
SO3ꢁ
Fig. 2. The precursor zwitterions for Brønsted-acidic ionic liquids
1
2
3
4
5
6
O
O
S
Me
F
Cl
NO2
NO2
O
N
N
ꢀ
TfOH
TfOꢁ
Me
(CH2)4
(CH2)4
N
N
ꢀ
SO3ꢁ
OMe
OMe
7
8
9
10
11
12
Me
N
N
ꢀ
Fig. 4. Studied aromatic substrates.
SO3H
Table 1. Chlorination of arenes with TCICA in Brønsted-acidic ionic
liquids
Fig. 3. Synthesis of [BMIM(SO3H)][OTf].
Products confirmed by GC coinjection with authentic samples or by gas
chromatography–mass spectrometry (GCMS). Yields determined by GC.
TCICA, trichloroisocyanuric acid
In 2002, Forbes, Davis and coworkers[7a] reported a facile
two-step process for the synthesis of Brønsted-acidic ionic liq-
uids (ILs), by alkylation of N-alkylimidazole or Ph3P with
sultones, followed by protonation of the resulting zwitterion with
TfOH (Fig. 2).
Substrate Ar:TCICA:IL Time Temp.
Product yields [%]
(mol. ratio)
[h]
[◦C]
Monochlorinated Dichlorinated
The utility of the resulting ILs as dual solvent/catalysts
was demonstrated in representative acid-catalyzed reactions.[7a]
Brønsted-acidic imidazolium ILs, including those bearing other
counterions,[7b,c] have been employed in aromatic nitration,[8a]
alkylation with olefins,[8b] Beckmann rearrangement,[8c]
esterification,[9] olefin oligomerization,[10] and condensation
reactions.[11]
In continuation of our studies focussing on onium ion chem-
istry and electrophilic aromatic substitution in ILs,[12–19] we
report here an efficient, highly economical green process for
chlorination of arenes with good chemoselectivity.The reactions
benefit from high atom economy, producing three moles ofArCl
for each mole of TCICA. They involve a simple extraction step
(with diethyl ether) and a recycling step (adding MeOH) that dis-
solves the IL, leaving behind isocyanuric acid (ICA) by-product,
which, if desired, could be transformed back to TCICA,[1] and
recycled for a large-scale operation. Some insight into the nature
of the chlorination electrophile was gained via competitive reac-
tions and via a model density functional theory (DFT) study
of protonation of TCICA, by examining transfer-chlorination
efficiency of the resulting cationic species. The moderately elec-
trophilic nature of the TCICA–[BMIM(SO3H)][OTf] system is
reflected in lack of reaction with nitrobenzene and nitroanisole.
1
1.0:1.0:25.0
1.0:1.0:25.0
3.0:1.0:25.0
3.0:1.0:25.0
3.0:1.0:25.0
3.0:1.0:25.0
3.0:1.0:25.0
3.0:1.0:25.0
1.0:1.0:25.0
1.0:1.0:25.0
3.0:1.0:25.0
3.0:1.0:25.0
20 48–53
48 48–53
20 55–53
33
69
98
96
97
46
58
72
53
65
37
61
–
24
–
2
–
19
2
14
2
5
<1
<2
2
3
4
5
6
6
49–50
20 48–50
20 50–52
20 51–52
48 56–58
20 52–57
70 55–57
20 41–49
96 49–47
8
9
Chlorination of anisole 3 was nearly complete after 6 h,
whereas for toluene 2 and ethylbenzene 4 near-quantitative
conversions were realized after 20 h. With benzene 1, ethyl-
benzene 4, mesitylene 5, p-xylene 6, p-diethylbenzene 8, and
p-fluoroanisole 9, the reactions had not reached completion after
the specified period (some unreacted starting materials were still
present). Contrary to the earlier reported study in sulfuric acid,[6]
chemoselectivity towards monochlorination was typically very
good in the IL reactions. For benzene 1 and p-xylene 6, with
an arene-to-TCICA ratio of 1:1 and under prolonged reaction
times, it was possible to increase the dichlorination product in
the mixture.
Results and Discussion
The −SO3H tethered ionic liquid [BMIM(SO3H)][OTf] (Fig. 3)
can be prepared in near-quantitative yield and high purity
by reaction of N-methylimidazole with 1,4-butanesultone, fol-
lowed by reaction of the resulting zwitterion with TfOH
(1 equivalent).[7a]
Substrates listed in Fig. 4 were selected for the present survey
study. Table 1 gives a summary of the TCICA chlorinations with
[BMIM(SO3H)][OTf].
As this Brønsted-acidic IL is a viscous liquid at room tem-
perature, chlorination reactions were performed at ∼50◦C to
enable effective magnetic stirring. For most entries, the arene-
to-TCICA-to-IL molar ratio of 3:1:25 was employed.The results
are summarized in Table 1.
In working with the more reactive arenes (mesitylene, durene,
and anisole), by changing the arene-to-TCICA ratio to 1:2 or
to 1:1, and by increasing the reaction time, it was possible
to switch the chemoselectivity in favour of dichlorination (see
Table 2).The observed isomer distribution in the resulting chloro
derivatives (Table 3) is compatible with an electrophilic aromatic
substitution process, with protonatedTCICA acting as a transfer-
chlorinating reagent. Increased formation of the para isomer at
theexpenseoforthoinchlorinationofchlorobenezeneisnotable,
reflecting increased steric crowding at the ortho position.
Isomeric products arising from skeletal rearrangement
(acid-catalyzed methyl migration) and side-chain (benzylic)
chlorination were detected to a minor extent in the mono- and

Chlorination of Aromatics with TCICA
925
Table 2. Chlorination of arenes withTCICA in Brønsted-acidic ionic liquids under conditions favouring
dichlorination
Products confirmed by GC coinjection with authentic samples or by gas chromatography–mass spectrometry
(GCMS). Yields determined by GC (see Experimental). TCICA, trichloroisocyanuric acid
Substrate
Ar:TCICA:IL
(mol. ratio)
Time
[h]
Temp.
[◦C]
Product yields [%]
Dichlorinated
Monochlorinated
Trichlorinated
3
3.0:1.0:25.0
1.0:1.0:25.0
1.0:2.0:25.0
3.0:1.0:25.0
1.0:2.0:25.0
1.0:1.0:25.0
1.0:1.0:25.0
3.0:1.0:25.0
1.0:1.0:25.0
6
20
70
20
70
48
70
20
48
49–50
49–50
52–50
52–50
60–55
56–58
49–54
52–57
42–40
96
<1
4
46
1
72
17
12
2
2
75
20
19
93
14
75
32
74
–
24
76
–
1
–
–
–
–
5
6
7
OH
ꢀ
N
OH
Cl
N
Table 3. Isomer distribution of chlorination products by TCICA
Determined by gas chromatography coinjection with authentic samples.
TCICA, trichloroisocyanuric acid
Cl
Cl
ꢀ
N
ꢀ
ꢁ Clꢀ
Hꢀ
N
HO
N
ꢀ
OH
HO
N
ꢀ
OH
Cl
Substrate Product
ortho [%] para [%] meta [%]
Cl
I
Ia
2
3
4
10
Chlorotoluene
Chloroanisole
Chloroethylbenzene
Dichlorobenzene
58
52
48
39
42
48
52
61
Not detectable
Not detectable
Not detectable
Not detectable
OH
ꢀ
N
OH
Cl
H
ꢀ
ꢀ
N
H
ꢁ Clꢀ
Hꢀ
N
N
HO
N
ꢀ
OH
HO
N
ꢀ
OH
Cl
II
Cl
IIa
Table 4. Isomerization (methyl migration) and benzylic substitution
products present in mono- and dichlorinated fractions
Yields determined by gas chromatography.TCICA, trichloroisocyanuric acid
OH
ꢀ
N
OH
ꢀ
N
H
H
ꢀ
N
ꢀ
N
H
H
ꢁ Clꢀ
Substrate
Methyl migration and benzylic substitution products [%]
HO
N
OH
HO
N
OH
Monochlorinated fraction
Dichlorinated fraction
ꢀ
IIIa
6A
7B
1
21
15
22
Cl
III
Scheme 2. Sequential [N–Cl]+ bond cleavage followed by N-protonation
of trichloroisocyanuric acid.
APercentages listed are from the reaction of p-xylene with an excess of
TCICA after 48 h (see Table 1).
BPercentages listed are from the reaction of durene with a stoichiometric
amount of TCICA after 20 h (see Table 3).
Focussing on the TCICA/[BMIM(SO3H)][OTf] system,
sequential [N–Cl]+ bond cleavage followed by N-protonation
could be considered (Scheme 2).
dichlorination fractions in the case of durene
7 and
p-xylene 6 with TCICA/[BMIM(SO3H)][OTf] (see Table 4). It
is conceivable that the minor presence of benzylic substitution
products stems from single electron transfer (arene radical cation
formation), as the number of methyl substituents is increased.[20]
Whereas attempted halogenations of p-nitroanisole 11 and
nitrobenzene 12 were unsuccessful, p-fluoroanisole 9 was
chlorinated in reasonable yield (Table 1). These observa-
tions imply that the TCICA/[BMIM(SO3H)][OTf] system
produces a moderately reactive chlorination electrophile.
To gain further insight into the relative reactivity of the
chlorination electrophile, substrate selectivity was deter-
mined in competitive reactions (toluene + benzene (1:1)). The
average KT/KB values determined with different arene-to-
TCICA ratios were ∼200. This value is noticeably larger
in comparison with transfer-fluorination with Selectfluor in
[EMIM][OTf] (Kmesitylene/Kdurene = 10)[14] or benzylation with
PhCH2OH/TfOH in [BMIM][OTf] (Ktoluene/Kbenzene = 5),[17]
suggesting a comparatively less reactive, more selective,
electrophile.
Based on DFT calculations (Table S1 in Accessory Pub-
lication), the reactions shown in Scheme 2 are energetically
favourable and exhibit negative enthalpies, which gradually
decrease by 8.37 to 12.55 kJ mol−1. Dication Ia could be in equi-
librium with two other structures (Ib and Ic) that were found to
be minima (Table S2 in Accessory Publication), but these struc-
tures were slightly higher in energy (by 8.78 and 24.26 kJ mol−1
,
respectively). Contrarytothecomputedfavourableenergeticsfor
Cl+ transfer from the trications, transfer-chlorination from the
doubly-charged species (Ia, Ib, and Ic) is noticeably endother-
mic, showing positive ꢀG and ꢀH values, and therefore appears
unlikely. The resulting singly charged species (see Tables S1
and S3) are least likely to act as transfer-chlorinating agents,
given their computed highly unfavourable energies. In line with
the earlier report,[6] these studies underscore the importance of
the triprotonated/protosolvated TCICA as a key intermediate
in transfer-chlorination via TCICA–HX systems. A mechanis-
tic scenario involving sequential chlorine transfer followed by
N-protonation, as outlined in Scheme 2, is compatible with both

926
A. Hubbard, T. Okazaki, and K. K. Laali
the computed energetics and the ability to produce three moles
of ArCl from one mole of TCICA.
0.133 mol (1 equiv); seeTables 1 and 2) and the Schlenk tube was
heated at ∼50◦C for the specified period, during which ICA by-
product appeared as a white solid (see recycling). The reaction
was worked up by addition of diethyl ether (3 × 0.5 mL), which
formed a separate layer from the IL. The biphasic mixture was
stirred vigorously and allowed to separate out before removing
the ether phase. The ether extract was neutralized with sodium
bicarbonate and filtered before analysis by GC or GCMS.
Conclusions
The utility of imidazolium-based Brønsted-acidic IL
[BMIM(SO3H)][OTf] as catalyst and solvent for electrophilic
chlorination of representative aromatic compounds withTCICA
has been demonstrated via a survey study. The reactions were
performed under mild conditions in good to excellent yields,
dependingonthesubstrates.Theabilitytosynthesizethreemoles
of ArCl from one mole of TCICA, the simple product isola-
tion step, facile recovery and recycling of the IL, and the use of
TCICA as a readily available, cheap chlorinating agent, are some
of the positive attributes of this method. The reaction generates
ICA as by-product, which is easily recovered from the IL. The
method avoids the use of chlorine gas and strong/corrosive acids.
Unlike the currently available methods, it does not produce large
quantities of acid by-products that need to be neutralized and dis-
posed of. Chemoselectivity towards mono- and dichlorination
can be controlled by adjusting the reaction conditions. Based
on substrate selectivity measurements, and a model DFT study,
a protosolvated trication is suggested as a key intermediate,
undergoing sequential transfer-chlorination/N-protonation.
Recycling of [BMIM(SO3H)][OTf] IL
Previously used IL containing ICA by-product was extracted
with methanol (3 × 1.0 mL) and transferred into a clean Schlenk
tube via syringe. Methanol was removed from the IL under vac-
uum and the acidity of the IL was checked with litmus paper.
Recycled ILs of pH 3 or lower were reused. Control experi-
ments showed no noticeable decrease in the conversions with
the recycled IL.
Yield Determination by GC
The reaction mixtures were directly analyzed by GC. In each
case, the GC conversions were determined by taking an aver-
age of three injections. Response factors were determined by
using 1:1 equimolar mixtures of authentic samples of products,
formed in various reactions. On this basis, a correction factor
of 3% was applied to the dichloroarene products. The response
factors determined for all other compounds were found to be
good within 1% and did not require correction.
Experimental
General
All reagents employed in the present study were high-purity
commercial samples that were used without further purification.
Reactions were carried out in small Schlenk tubes under a nitro-
gen or argon atmosphere. Diethyl ether used for extraction was
distilled over magnesium sulfate or from benzophenone/sodium
before use.
Gas chromatography analyses were performed on an HP
5890 instrument (using a capillary OV101 column). Gas
chromatography–mass spectrometry (GCMS) analyses were
performed on a Thermoquest Trace gas chromatograph cou-
pled to a Finnigan Polaris mass spectrometer. NMR spectra
were recorded on a 400 MHz Bruker instrument. Infrared (IR)
spectra were obtained on a Perkin Elmer Fourier-transform IR
instrument.
Product Confirmation
Isocyanuricacid:[21] δH ([D6]DMSO)11.16(s, 3H). Chloroethyl-
benzene: GCMS m/z 140.0, 142.0 (M+), 125.1 (M+ − CH3),
105.2 (M+ − Cl). Dichloroanisole: GCMS m/z 176.0, 178.0,
180.0 (M+). Trichloroanisole: GCMS m/z 209.9, 211.9,
213.9 (M+). Chloro-p-xylene: GCMS m/z 140.0, 142.0
(M+), 105.1 (M+ − Cl). Dichloro-p-xylene: GCMS m/z
174.0, 175.9, 178.0 (M+), 139.1, 141.0 (M+ − Cl), 103.1
(M+ − HCl2). Chloro-p-fluoroanisole: GCMS m/z 160.1, 162.1
(M+). Dichloro-p-fluoranisole: GCMS m/z 193.9, 196.0,
198.0 (M+). Chloro-p-diethylbenzene: GCMS m/z 168.1,
170.1 (M+), 133.1 (M+ − Cl). Dichloro-p-diethylbenzene:
GCMS m/z 202.1, 204.1, 206.0 (M+), 187.0, 189.0 (M+ − CH3),
167.1, 169.1 (M+ − Cl). Chlorodurene: GCMS m/z 168.0,
170.0 (M+), 133.1 (M+ − Cl). Dichlorodurene: GCMS m/z
202.0, 204.0, 206.0 (M+), 167.1, 169.1 (M+ − Cl). Trichloro-
durene: GCMS m/z 236.0, 238.0, 240.0 (M+), 201.0,
203.0, 204.0 (M+ − Cl). Chloromesitylene: GCMS m/z 154.0,
156.0 (M+), 119.1 (M+ − Cl). Dichloromesitylene: GCMS
m/z 188.0, 190.0, 192.1 (M+), 153.3, 155.1 (M+ − Cl),
115.2 (M+ − H3Cl2). Trichloromesitylene: GCMS m/z 222.0,
224.0/226.0(M+), 187.0, 189.0(M+ − Cl), 151.0(M+ − HCl2),
115.1 (M+ − H2Cl3).
Synthesis of Brønsted-Acidic IL [BMIM(SO3H)][OTf][7]
N-Methylimidazole (98.2 mmol, 7.8 mL) was stirred (with-
out any added solvent) with 1,4-butane sultone (98.2 mmol,
10.0 mL) at room temperature for 2 days, whereby a solid
mass was formed. It was washed repeatedly with diethyl ether
and with toluene, and dried under vacuum to give the corre-
sponding zwitterion in 94.7% yield. A stoichiometric amount
of triflic acid (92.9 mmol, 8.2 mL) was added and the reac-
tion mixture was stirred at 40◦C for 2 days during which time
the zwitterion dissolved/liquefied, resulting in the formation of
[BMIM(SO3H)][OTf] in near-quantitative yield. The IL was
washed repeatedly with toluene and with ether and dried under
Identity of all other products was confirmed by GC co-
injection with authentic samples. Isomer distributions were
confirmed by GC coinjection with authentic samples.
1
vacuum. The purity of the IL was assessed by H NMR spec-
troscopy. Its NMR data were in agreement with the reported
values.[7b,10b]
Computational Protocols
Structures were optimized by the DFT method at B3LYP/
6–31+G(d,p) level using the Gaussian 03 package.[22,23] All
computed geometries were verified by frequency calculations
to have no imaginary frequencies. Global minima were located
by changing the conformation (by varying the directions of the
OH groups), and by comparing the energies of the optimized
TCICA Chlorination Procedure
The IL (3.33 mmol, 1.23 g) was charged into a Schlenk tube
equipped with a magnetic stirring bar under a nitrogen atmos-
phere and TCICA (0.133 mmol, 31.0 mg) was added. The aro-
matic substrate was then introduced (0.40 mmol (3 equiv) or

Chlorination of Aromatics with TCICA
927
structures. Reaction enthalpies and Gibbs free energies for Cl+
generation from various triprotonated, diprotonated, and mono-
protonated TCICA, and the energies of various cationic species
are summarized in Tables S1–S4 (Accessory Publication).
[10] (a)Y. Gu, F. Shi,Y. Deng, Catal. Commun. 2003, 4, 597. doi:10.1016/
J.CATCOM.2003.09.004
(b) Y. Gu, F. Shi, Y. Deng, J. Mol. Catal. A–Chem. 2004, 212, 71.
doi:10.1016/J.MOLCATA.2003.10.039
[11] T. M. Potewar, R. J. Lahoti,T. Daniel, K.V. Srinivasen, Synth. Commun.
2007, 37, 261. doi:10.1080/00397910601033534
[12] K. K. Laali, V. J. Gettwert, J. Fluorine Chem. 2001, 107, 31.
doi:10.1016/S0022-1139(00)00337-7
[13] K. K. Laali, V. J. Gettwert, J. Org. Chem. 2001, 66, 35. doi:10.1021/
JO000523P
[14] K. K. Laali, G. I. Borodkin, J. Chem. Soc., Perkin Trans. 2 2002, 953.
doi:10.1039/B111725D
[15] V. D. Sarca, K. K. Laali, Green Chem. 2004, 6, 245. doi:10.1039/
B400113C
[16] K. K. Laali, V. D. Sarca, T. Okazaki, A. Brock, P. Der, Org. Biomol.
Chem. 2005, 3, 1034. doi:10.1039/B416997B
[17] V. D. Sarca, K. K. Laali, Green Chem. 2006, 8, 615. doi:10.1039/
B603176E
[18] K. K. Laali, in Ionic Liquids in Organic Synthesis: ACS Symposium
Ser. 950 (Ed. S. V. Malhotra) 2006, Ch. 2 (ACS: Washington, DC).
[19] K. K. Laali, T. Okazaki, S. D. Bunge, J. Org. Chem. 2007, 72, 6758.
doi:10.1021/JO0708801
[20] P. Kralj, M. Zupan, S. Stavber, J. Org. Chem. 2006, 71, 3880.
doi:10.1021/JO060213S
Accessory Publication
B3LYP/6–31+G(d,p) energies and reaction energies for TCICA
are available from the author or, until December 2012, the
Australian Journal of Chemistry.
References
[1] J. C. Barros, Synlett 2005, 2115. doi:10.1055/S-2005-872237
[2] G. K. S. Prakash, T. Mathew, D. Hoole, P. M. Esteves, Q. Wang,
G. Rasul, G. A. Olah, J. Am. Chem. Soc. 2004, 126, 15770.
doi:10.1021/JA0465247
[3] G. A. Hiegel, J. Ramirez, R. K. Barr, Synth. Commun. 1999, 29, 1415.
doi:10.1080/00397919908086119
[4] O. Sugimoto, K. Tanji, Heterocycles 2005, 65, 181.
[5] (a) T. Umemoto, in Advances in Organic Synthesis (Ed. K. K. Laali)
2006, Vol. 2, pp. 159–181 (Bentham: the Netherlands).
(b) S. Stavber, M. Zupan, in Advances in Organic Synthesis (Ed.
K. K. Laali) 2006, Vol. 2, pp. 213–268 (Bentham: the Netherlands).
[6] G. F. Mendonça, R. R. Magalhães, M. C. S. de Mattos, P. M. Esteves,
J. Braz. Chem. Soc. 2005, 16, 695.
[21] A. J. Bellamy, N. V. Latypov, P. Goede, J. Chem. Res., Miniprint 2003,
9, 943.
[22] W. Koch, M. C. Holthausen, A Chemist’s Guide to Density Functional
Theory, 2nd edn 2000 (Wiley–VCH: Weinheim).
[7] (a) 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. 2002, 124, 5962.
doi:10.1021/JA026290W
[23] M. J. Frisch, G. W.Trucks, H. B. Schlegel, G. E. Scuseria, M.A. Robb,
J. R. Cheeseman, J. A. Montgomery, Jr, T. Vreven, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul,
S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith,
M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe,
P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez,
J. A. Pople, Gaussian 03, Revision B.05 2003 (Gaussian Inc.:
Pittsburgh, PA).
(b) Z. Du, Z. Li, Y. Deng, Synth. Commun. 2005, 35, 1343.
doi:10.1081/SCC-200057264
(c) S. Chowdhury, R. S. Ram, J. L. Scott, Tetrahedron 2007, 63, 2363.
doi:10.1016/J.TET.2006.11.001
[8] (a) K. Qiao, C. Yokoyama, Chem. Lett. (Jpn.) 2004, 33, 1350.
doi:10.1246/CL.2004.808
(b) K. Qiao, C. Yokoyama, Chem. Lett. (Jpn.) 2004, 33, 472.
doi:10.1246/CL.2004.472
(c) K. Qiao, Y. Deng, C. Yokoyama, H. Sato, M. Yamashima, Chem.
Lett. (Jpn.) 2004, 33, 472. doi:10.1246/CL.2004.472
[9] H.-P. Zhu, F. Yang, M. Y. He, Green Chem. 2003, 5, 38. doi:10.1039/
B209248B