Reaction of 1,3,5-tri-tert-butylbenzene with 2,4,6,8-tetraiodo- 2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione

Article abstract of DOI:10.1134/S107042801206005X

Reactions of 1,3,5-tri-tert-butylbenzene with 2,4,6,8-tetraiodo-2,4,6,8- tetraazabicyclo[3.3.0]octane-3,7-dione in acetic and trifluoroacetic acids involve substitution of one or two tert-butyl groups in the aromatic ring with formation of mono-, di-, and

Full text of DOI:10.1134/S107042801206005X

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2012, Vol. 48, No. 6, pp. 780–782. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © Kh.M. Nguen, V.K. Chaikovskii, V.D. Filimonov, A.A. Funk, 2012, published in Zhurnal Organicheskoi Khimii, 2012, Vol. 48,
No. 6, pp. 784–786.
Reaction of 1,3,5-Tri-tert-Butylbenzene with 2,4,6,8-Tetraiodo-
2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione
Kh. M. Nguen, V. K. Chaikovskii, V. D. Filimonov, and A. A. Funk
Tomsk Polytechnical University, pr. Lenina 30, Tomsk, 634050 Russia
e-mail: clg@mail.ru
Received December 27, 2011
Abstract—Reactions of 1,3,5-tri-tert-butylbenzene with 2,4,6,8-tetraiodo-2,4,6,8-tetraazabicyclo[3.3.0]octane-
3,7-dione in acetic and trifluoroacetic acids involve substitution of one or two tert-butyl groups in the aromatic
ring with formation of mono-, di-, and triiodo-substituted derivatives. No iodo derivatives are formed in
acetonitrile.
DOI: 10.1134/S107042801206005X
Iodo derivatives of trialkylbenzenes are convenient
models for studying steric effects of substituents and
deformations of the benzene ring. Direct iodination of
trimethylbenzene (mesitylene) readily occurs with
formation of iodo derivatives in high yield, whereas
introduction of iodine into benzene ring containing
tert-butyl groups involves some specificity. Monosub-
stituted tert-butylbenzene undergoes smooth iodination
[1–6], while iodination of di-tert-butylbenzenes is not
selective, and it leads to the formation of a consider-
able amount of ipso-substitution products [1, 5]. This
is especially typical of 1,4-di-tert-butylbenzene [1, 5].
Direct iodination of 1,3,5-tri-tert-butylbenzene (I) was
not studied.
ipso-iodination is thermodynamically more favorable
than electrophilic iodination. We examined the be-
havior of compound I in reaction with 2,4,6,8-tetra-
iodo-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione
(II) in acetonitrile and organic acids, acetic (in the
presence of sulfuric) and trifluoroacetic. We previously
showed that tetraiodoglycoluril II is a soft iodinating
agent which readily reacts with polyalkylbenzenes in
the temperature range from 0 to 20°C [9].
I
I
N
N
N
N
O
O
I
I
II
tert-Butyl groups in compound I can be replaced
even in the bromination process, in particular in acid
medium. According to [7], the bromination of I with
acetyl hypobromite generated in situ by reaction of
bromine with silver perchlorate in acetic acid yields
not only 1,3,5-tri-tert-butyl-2-bromobenzene but also
acetoxylation product, 2,4,6-tri-tert-butylphenyl
acetate and products of replacement of one tert-butyl
group by the halogen atom or acetoxy group, the
substrate conversion being 55%. Even more complex
mixture of compounds, including ipso-substitution and
diarylation products, was obtained in the bromination
of I with 2,4,6,8-tetrabromo-2,4,6,8-tetraazabicyclo-
[3.3.0]octane-3,7-dione [8].
In order to avoid ipso-substitution, we tried to react
trialkylbenzene I with glycoluril II in acetonitrile in
the absence of acid. However, stirring of the reaction
mixture for 24 h at room temperature (~20°C),
followed by heating for 5 h under reflux, did not result
in any transformation of the substrate (GC–MS data).
The iodination occurred in acid medium, namely in
acetic acid containing sulfuric acid, but the process
was necessarily accompanied by ipso-substitution of
one tert-butyl group even in 10 min. The reaction of I
with II at a molar ratio of 1:0.25 resulted in 18.3%
conversion of the substrate into 1,3-di-tert-butyl-5-
iodobenzene (IIIa), whereas the other part of I re-
mained unchanged. In the presence of excess reagent
(ratio I :II 1 :1.5), the reaction mixture contained
compound IIIa and a hydroxy derivative, assumingly,
The calculated (PM3) enthalpies of electrophilic
(SE) and ipso-iodination (Si) of compound I, ΔH =
500.90 and –258.95 kJ/mol, respectively, indicate that
780

REACTION OF 1,3,5-TRI-tert-BUTYLBENZENE WITH 2,4,6,8-TETRAIODO-...
781
Scheme 1.
I
OH
CH3COOH–H2SO4
I:II = 1:1.5
OH
+
Bu-t
t-Bu
Bu-t
t-Bu
Bu-t
IIIa
IIIb
20°C
I
I
t-Bu
Bu-t
CF3COOH
I:II = 1:1.5
I
I
I
I
I
I
IIIa
+
+
+
t-Bu
Bu-t
t-Bu
t-Bu
IIIc
IIId
IIIe
3,5-di-tert-butylbenzene-1,2-diol (IIIb, 14.8%), and
46.7% of I remained intact (Scheme 1). By replacing
AcOH–H2SO4 by CF3COOH (molar ratio I:II 1:0.25)
we succeeded in increasing the conversion of I, but the
major product was 3,5-di-tert-butyl-5-iodobenzene
(IIIa) (see table). The higher activity of the system II–
CF3COOH follows not only from the higher conver-
sion of substrate I into iodo derivative IIIa but also
from the formation of a number of other iodination
products with different degrees of substitution as the
amount of iodinating agent II increased.
MS 1,3-di-tert-butyl-5-iodobenzene (IIIa, 28.7%),
3,5-di-tert-butyl-1,2-diiodobenzene (IIIc, 15.9%),
4-tert-butyl-1,2-diiodobenzene (IIId, 1.6%), and
(assumingly), 5-tert-butyl-1,2,3-triiodobenzene (IIIe,
53.8%) (Scheme 1, see table). Neither expected
1,3,5-tri-tert-butyl-2-iodobenzene nor acetylation
products were detected.
EXPERIMENTAL
Gas chromatographic–mass spectrometric analysis
was performed on an Agilent-7890A gas chroma-
tograph coupled with an Agilent-5975C mass-selective
In the reaction mixture obtained from compound I
and 1.5 equiv of II in CF3COOH we detected by GC–
Reaction of 1,3,5-tri-tert-butylbenzene (I) with 2,4,6,8-tetraiodo-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione (II) in
AcOH–H2SO4 and CF3COOH (20°C, 10 min; GC–MS data)
Solvent,
molar ratio I:II
Compound Fraction,
Mass spectrum, m/z (Irel, %)
246 (11) [M]+, 231 (100), 57 (19), 41(7)
316 (32) [M]+, 301 (100), 273 (7), 159 (11), 127 (7), 115 (7), 57 (16),
no.
%
AcOH–H2SO4, 1:0.25
I
81.7
18.3
IIIa
41(8)
AcOH–H2SO4, 1:1.5
I
46.7
38.5
246 (11) [M]+, 231 (100), 57 (19), 41 (7)
316 (32) [M]+, 301 (100), 273 (7), 159 (11), 127 (7), 115 (7), 57 (16),
IIIa
41(8)
IIIb
I
14.8
36.1
63.9
222 (19) [M]+, 207(100), 191 (5), 179 (5), 96 (6), 82 (7), 57(16)
246 (11) [M]+, 231 (100), 57 (19), 41 (7)
CF3COOH, 1:0.25
CF3COOH, 1:1.5
IIIa
316 (30) [M]+, 301 (100), 273 (6), 159 (11), 127 (6), 115 (5), 57 (15),
41 (6)
IIIa
IIIc
IIId
IIIe
28.7
15.9
01.6
53.8
316 (30) [M]+, 301 (100), 273 (6), 159 (11), 127 (6), 115 (5), 57 (15),
41(6)
442 (88) [M]+, 427 (100), 399 (45), 285 (11), 143 (6), 129 (8), 115 (17),
91 (5), 57 (24), 41 (11)
386 (57) [M]+, 371 (100), 343 (17), 254 (5), 244 (13), 127 (6), 117 (17),
89 (7)
512 (79) [M]+, 497 (100), 469 (21), 370 (21), 258 (9), 234 (10), 215 (5),
127 (7), 115 (19), 74 (8), 41 (7)
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 6 2012

NGUEN et al.
782
detector (HP-5MS capillary column, 5.30 m×0.25 mm,
film thickness 0.25 μm; electron impact, 70 eV).
Commercial 1,3,5-tri-tert-butylbenzene, mp 70–71°C
(Aldrich), was used. 2,4,6,8-Tetraiodo-2,4,6,8-tetraaza-
bicyclo[3.3.0]octane-3,7-dione (II) was prepared ac-
cording to the procedure described in [10].
acetic acid, and the mixture was stirred for 10 min
at 20°C.
When the reaction was complete, the mixture was
diluted with 20 ml of water and extracted with
methylene chloride (3×10 ml), the extracts were
washed with water and a 5% solution of NaHCO3 until
neutral reaction, dried over Na2SO4, and evaporated
under reduced pressure, and the residue was analyzed
by GC–MS (see table).
Reaction of 1,3,5-tri-tert-butylbenzene (I) with
2,4,6,8-tetraiodo-2,4,6,8-tetraazabicyclo[3.3.0]oc-
tane-3,7-dione (II). a. Compound II, 0.97 g
(1.5 mmol), was added to a solution of 0.247 g
(1 mmol) of I in 5 ml of acetonitrile, and the mixture
was stirred for 24 h at room temperature and heated for
5 h under reflux. According to the GC–MS data, the
mixture contained only initial compound I.
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trifluoroacetic acid, and the mixture was stirred for
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 6 2012