Facile preparation of 2-imidazolines from aldehydes with tert-butyl hypochlorite

Article abstract of DOI:10.1055/s-2007-983726

An efficient and high-yield preparation of 2-imidazolines was achieved from aldehydes and ethylenediamines in the presence of tert-butyl hypochlorite. By this method, 1,3-bis(imidazolin-2-yl)benzene and 2,6-bis(imidazolin-2-yl) pyridine, which act as chiral ligands, could be prepared directly from the corresponding dialdehydes in high yields. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-983726

PAPER
1939
Facile Preparation of 2-Imidazolines from Aldehydes with tert-Butyl
Hypochlorite
2-Imidazolines from
A
i
ldehyd
d
es with tert-B
o
utyl
H
ypoch
r
lorite i Ishihara, Hideo Togo*
Graduate School of Science, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522, Japan
E-mail: togo@faculty.chiba-u.jp
Received 9 April 2007
Table 1 Preparation of 2-Imidazolines in the Presence of tert-Butyl
Hypochlorite
Abstract: An efficient and high-yield preparation of 2-imidazo-
lines was achieved from aldehydes and ethylenediamines in the
presence of tert-butyl hypochlorite. By this method, 1,3-bis(imida-
zolin-2-yl)benzene and 2,6-bis(imidazolin-2-yl)pyridine, which act
as chiral ligands, could be prepared directly from the corresponding
dialdehydes in high yields.
H2N
NH2
(1.1 equiv)
H
N
t-BuOCl (1.2 equiv)
R
CHO
R
50 °C, 2 h
t-BuOH
R
N
Key words: tert-butyl hypochlorite, 2-imidazoline, aldehydes, eth-
ylenediamine
Entry
Yielda (%)
100
98
1
Ph
The synthetic study of 2-imidazoline units is very impor-
tant because of their potent biological activity1 and syn-
thetic utility as chiral ligands.2 To date, there are several
synthetic methods for the preparation of 2-imidazolines,
mainly starting from nitriles and esters.3 Recently, an ef-
ficient one-pot preparation of 2-imidazolines from alde-
hydes and ethylenediamine with N-bromosuccinimide
was reported.4 We also reported an efficient method for
the preparation of 2-imidazolines from aldehydes and mo-
lecular iodine.5 However, in the method using molecular
iodine, the yield of 2-alkylimidazolines with aliphatic al-
dehydes was rather low, although that of 2-arylimidazo-
lines with aromatic aldehydes was high. Here, as part of
our basic study of molecular iodine and related reagents in
organic synthesis,6 we wish to report another efficient and
practical oxidative conversion of aldehydes together with
ethylenediamine and tert-butyl hypochlorite into 2-imida-
zolines.
2
4-tolyl
3b
PMP
81
4b,c
PMP
99
5
4-BrC6H4
4-O2NC6H4
4-NCC6H4
2-ClC6H4
2-thienyl
2-thienyl
2-pyridyl
1-naphthyl
1-naphthyl
1-adamantyl
cyclohexyl
(CH2)2Ph
(CH2)6Me
CHMePh
100
100
88
6
7
8
99
9
64
10b
91
11
100
81
12b
13b,c
100
99
14b,c
tert-Butyl hypochlorite is an inexpensive and versatile re-
agent, and has been applied to oxidative transformations
such as the oxidation of alcohols to ketones,7 aldehydes to
acid chlorides,8 sulfides to sulfoxides,9 and hydroxyl-
amines to nitroso compounds.10 Furthermore, tert-butyl
hypoiodite is an easily available reagent, which can be
prepared from tert-butyl hypochlorite and metal iodide or
iodine,11 and has recently been developed for the synthesis
of N-heterocycles12 or iodocyclization.13 Thus, the addi-
tion of tert-butyl hypochlorite to a mixture of benzalde-
hyde and ethylenediamine in tert-butyl alcohol provides
the corresponding 2-phenylimidazoline quantitatively
(Table 1, entry 1).
15
79
16
98
17b
95
18b
80
a Isolated yield.
b Reaction time was 10 h.
c KI (1.2 equiv) was added.
tyl hypochlorite in tert-butyl alcohol, and the correspond-
ing 2-aryl- and 2-alkylimidazolines were obtained in good
yields (Table 1). Electron-rich aromatic aldehydes such as
p-methoxybenzaldehyde, thiophenecarboxyaldehyde, and
1-naphthaldehyde require long reaction times (Table 1,
entries 3, 4, 10, 12, and 13). When potassium iodide was
added to the reaction mixture, the yield was improved, be-
cause of the formation of tert-butyl hypoiodite, which was
Under the same conditions, various aromatic and aliphatic
aldehydes were treated with ethylenediamine and tert-bu-
SYNTHESIS 2007, No. 13, pp 1939–1942
x
x.
x
x
.
2
0
0
7
Advanced online publication: 18.06.2007
DOI: 10.1055/s-2007-983726; Art ID: F06607SS
© Georg Thieme Verlag Stuttgart · New York

1940
M. Ishihara, H. Togo
PAPER
Ph
generated from tert-butyl hypochlorite and potassium io-
dide in situ (Table 1, entries 4, 13, and 14). 2-Alkylimida-
zolines were obtained from the corresponding aldehydes
in much high yields (Table 1, entries 15–18) by this meth-
od than by the molecular iodine method.
Ph
HN
HN
Ph
Ph
N
CHO
CHO
(3.0 equiv)
H2N
NH2
t-BuOH
a or b
When 1-methylethylene-1,2-diamine, instead of ethylene-
diamine, was also treated with p-tolualdehyde and tert-bu-
tyl hypochlorite in the presence of potassium iodide, the
corresponding 2-(p-tolyl)imidazoline was formed in good
yield (Table 2, entry 1). The same treatment of p-tolualde-
hyde with (R,R)-(+)-diphenylethylenediamine provided
the corresponding (R,R)-4,5-diphenyl-2-(p-tolyl)imidazo-
line in good yield (Table 2, entry 2).
N
Ph
Ph
Scheme 1 Reagents and conditions: (a) I2 (3.5 equiv), K2CO3 (4.0
equiv), 70 °C, 3 h (98%); (b) t-BuOCl (3.5 equiv), KI (3.5 equiv), 50
°C, 10 h (100%).
Ph
Table 2 Use of Other Diamines for the Preparation of 2-Imidazo-
lines
Ph
HN
Ph
Ph
diamine (1.1 equiv)
N
N
CHO
N
t-BuOCl (1.2 equiv),
KI (1.2 equiv)
H
N
H2N
NH2 (3.0 equiv)
N
Me
CHO
Me
t-BuOH
50 °C, 10 h
t-BuOH
a or b
N
CHO
HN
Entry Diamine
Product
Yielda (%)
100
Ph
H2N
Me
Me
N
Ph
1
Me
Scheme 2 Reagents and conditions: (a) I2 (3.5 equiv), K2CO3 (4.0
equiv), 70 °C, 3 h (92%); (b) t-BuOCl (3.5 equiv), KI (3.5 equiv), 50
°C, 10 h (76%).
N
H
H2N
Ph
2
97
Ph
Ph
Ph
N
Me
H2N
NH2
N
H
study of the present reactions is under way in this labora-
tory.
a Isolated yield.
Melting points were determined on a Yamato MP-21 apparatus and
are uncorrected. IR spectra were recorded on a JASCO FT/IR-200
infrared spectrometer of samples prepared as KBr pellets. NMR
spectra were recorded of samples in CDCl3 (unless stated other-
wise) on a JEOL JNM-LA-400 spectrometer. HRMS–FAB deter-
minations were carried out on a JEOL JMS-AX500 spectrometer,
and HRMS measurements were obtained on a JEOL HX-110 instru-
ment.
Then, benzene-1,3-dicarbaldehyde (Scheme 1) and pyri-
dine-2,6-dicarbaldehyde (Scheme 2) were treated with
(R,R)-(+)-diphenylethylenediamine and tert-butyl hypo-
chlorite in the presence of potassium iodide under the
same conditions; this provided the corresponding 1,3-
bis(imidazolin-2-yl)benzene and 2,6-bis(imidazolin-2-
yl)pyridine (pybim), which are known as chiral ligands, in
good yields. When the reactivities of the molecular iodine
method and the tert-butyl hypochlorite method for the for-
mation of pybim are compared, the former method is bet-
ter than the latter. However, tert-butyl hypochlorite can be
used for both aromatic aldehydes and aliphatic aldehydes
to provide the corresponding 2-substituted imidazolines
in good yields. Moreover, pybim was recently prepared
from 2,6-dicyanopyridine in two steps,14 whereas it could
be obtained in high yield in a single step from the com-
mercially available pyridine-2,6-dicarbaldehyde by the
tert-butyl hypochlorite method presented here.
2-Imidazolines from Aldehydes and Ethylenediamines in the
Presence of tert-Butyl Hypochlorite; Typical Procedure
To a soln of PhCHO (106.0 mg, 1 mmol) in t-BuOH (10 mL) was
added ethylenediamine (66.1 mg, 1.1 mmol). The mixture was
stirred at r.t. under an argon atmosphere for 30 min, and then t-
BuOCl (130.3 mg, 1.2 mmol) was added, and the mixture was
stirred at 50 °C. After 2 h, the mixture was quenched with sat. aq
Na2SO3 (10 mL) and was extracted with CHCl3 (3 × 10 mL). The
organic layer was washed with sat. aq K2CO3 (1 × 10 mL) and brine
(1 × 20 mL), and dried (Na2SO4). After filtration, the mixture was
evaporated; this provided almost pure 2-(phenyl)imidazoline; yield:
100% yield. If necessary, the product can be purified by flash col-
umn chromatography (neutral silica gel, CHCl3–Et3N, 10:1).
In summary, various 2-aryl- and 2-alkylimidazolines
could be obtained easily and in good yields by the reaction
between aldehydes and ethylenediamine in the presence
of tert-butyl hypochlorite. Moreover, 1,3-bis(imidazolin-
2-yl)benzene and 2,6-bis(imidazolin-2-yl)pyridine, a
chiral ligand, could be directly prepared from the corre-
sponding dialdehydes in high yields. Further synthetic
2-(Phenyl)imidazoline
Mp 101.5–102 °C (Lit.15 100–101 °C).
IR (KBr): 3200, 2930, 1600, 1510, 1270, 985, 695 cm–1.
1H NMR (400 MHz, CDCl3): d = 3.90 (s, 4 H), 7.46 (t, J = 7.2 Hz,
2 H), 7.57 (t, J = 7.2 Hz, 1 H), 7.95 (d, J = 7.2 Hz, 2 H).
Synthesis 2007, No. 13, 1939–1942 © Thieme Stuttgart · New York

PAPER
2-Imidazolines from Aldehydes with tert-Butyl Hypochlorite
1941
2-(4-Tolyl)imidazoline
HRMS–FAB: m/z [M + H]+ calcd for C8H10N3: 148.0875; found:
148.0876.
Mp 181–182 °C (Lit.15 181 °C).
IR (KBr): 3140, 2925, 1600, 1495, 985, 830 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.38 (s, 3 H), 3.77 (s, 4 H), 7.21
(d, J = 8.3 Hz, 2 H), 7.67 (d, J = 8.3 Hz, 2 H).
2-(1-Naphthyl)imidazoline
Mp 131–133 °C (Lit.19 134 °C).
IR (KBr): 3140, 2860, 1570, 1515, 1270, 980, 775 cm–1.
2-(4-Methoxyphenyl)imidazoline
1H NMR (400 MHz, CDCl3): d = 3.89 (s, 4 H), 7.45–7.57 (m, 3 H),
7.75 (dd, J = 7.1, 1.2 Hz, 1 H), 7.85–7.91 (m, 2 H), 8.68 (d, J = 8.5
Hz, 1 H).
Mp 136–138 °C (Lit.16 137–139 °C).
IR (KBr): 3120, 2830, 1605, 1490, 1255, 1035, 845 cm–1.
1H NMR (400 MHz, CDCl3): d = 3.77 (s, 4 H), 3.84 (s, 3 H), 6.91
(d, J = 8.9 Hz, 2 H), 7.73 (d, J = 8.9 Hz, 2 H).
2-(1-Adamantyl)imidazoline
Mp 162.5–163.5 °C.
IR (KBr): 3230, 3000, 1590, 1495, 1250, 1085, 980 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.69–1.77 (m, 6 H), 1.86–1.87 (m,
6 H), 2.03 (m, 3 H), 3.56 (s, 4 H).
13C NMR (100 MHz, CDCl3): d = 28.1, 35.1, 36.5, 40.3, 49.4,
174.5.
HRMS–FAB: m/z [M + H]+ calcd for C13H21N2: 205.1705; found:
205.1703.
2-(4-Bromophenyl)imidazoline
Mp 177–177.5 °C.
IR (KBr): 3150, 2930, 1610, 1470, 1270, 1010, 835 cm–1.
1H NMR (400 MHz, CDCl3): d = 3.79 (s, 4 H), 7.54 (d, J = 8.7 Hz,
2 H), 7.65 (d, J = 8.7 Hz, 2 H).
13C NMR (100 MHz, CDCl3): d = 125.0, 128.5, 129.4, 131.6, 163.8.
HRMS–FAB: m/z [M + H]+ calcd for C9H10N2Br: 225.0027; found:
225.0021.
2-Cyclohexylimidazoline
Mp 130.5–131 °C (Lit.15 134 °C).
2-(4-Nitrophenyl)imidazoline
IR (paraffin): 3085, 1600, 1510, 1275, 1060, 980 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.16–1.43 (m, 5 H), 1.67–1.92 (m,
5 H), 2.22 (tt, J = 11.5, 3.4 Hz, 1 H), 3.56 (s, 4 H).
Mp 235–237 °C (Lit.17 231 °C).
IR (KBr): 3180, 2935, 1580, 1520, 1335, 1105, 855 cm–1.
1H NMR (400 MHz, CDCl3): d = 3.85 (s, 4 H), 7.95 (d, J = 8.9 Hz,
2 H), 8.27 (d, J = 8.9 Hz, 2 H).
2-Phenethylimidazoline
Mp 101–103 °C.
IR (KBr): 3160, 2925, 1605, 1500, 1285, 960, 700 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.54 (t, J = 8.0 Hz, 2 H), 2.96 (t,
J = 8.0 Hz, 2 H), 3.55 (br s, 4 H), 7.21–7.36 (m, 5 H).
13C NMR (100 MHz, CDCl3): d = 31.3, 32.9, 126.3, 128.3, 128.6,
141.1, 167.2.
HRMS–FAB: m/z [M + H]+ calcd for C11H15N2: 175.1235; found:
175.1237.
2-(4-Cyanophenyl)imidazoline
Mp 195–196 °C.
IR (KBr): 3160, 2230, 1595, 1490, 1275, 985, 850 cm–1.
1H NMR (400 MHz, CDCl3): d = 3.83 (s, 4 H), 7.70 (d, J = 8.5 Hz,
2 H), 7.88 (d, J = 8.5 Hz, 2 H).
13C NMR (100 MHz, CDCl3): d = 114.2, 118.4, 127.7, 132.4, 134.7,
163.2.
HRMS–FAB: m/z [M + H]+ calcd for C10H10N3: 172.0875; found:
172.0883.
4-Methyl-2-(4-tolyl)imidazoline
Mp 162–164 °C.
IR (paraffin): 3400, 1590, 1540, 1330, 1015, 830, 730 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.29 (d, J = 6.3 Hz, 3 H), 2.38 (s,
3 H), 3.36 (br s, 1 H), 3.91 (br s, 1 H), 4.11 (br s, 1 H), 7.20 (d,
J = 8.0 Hz, 2 H), 7.66 (d, J = 8.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): d = 21.3, 22.0, 51.2, 53.2, 118.3,
129.7, 130.0, 146.4, 164.1.
HRMS–FAB: m/z [M + H]+ calcd for C11H15N2: 175.1235; found:
2-(2-Chlorophenyl)imidazoline
Mp 83 °C (Lit.18 69–70 °C).
IR (KBr): 3100, 2920, 1610, 1505, 1260, 985, 765 cm–1.
1H NMR (400 MHz, CDCl3): d = 3.80 (s, 4 H), 7.28–7.41 (m, 3 H),
7.78 (dd, J = 7.5 and 1.9 Hz, 1 H).
2-(2-Thienyl)imidazoline
Mp 175 °C (Lit.16 175–177 °C).
175.1236.
IR (KBr): 3150, 2935, 1595, 1495, 1270, 985, 710 cm–1.
1H NMR (400 MHz, CDCl3): d = 3.78 (s, 4 H), 7.06 (dd, J = 4.9, 3.7
Hz, 1 H), 7.36 (dd, J = 3.7, 0.9 Hz, 1 H), 7.40 (dd, J = 4.9, 0.9 Hz,
1 H).
(4R,5R)-4,5-Diphenyl-2-(4-tolyl)imidazoline
Mp 146.5 °C.
IR (paraffin): 3150, 1600, 1130, 1020, 830, 765, 700 cm–1.
2-(2-Pyridyl)imidazoline
Mp 95–96 °C.
IR (KBr): 3270, 1595, 1505, 1280, 975, 805, 750 cm–1.
1H NMR (400 MHz, CDCl3): d = 3.85 (s, 4 H), 7.36 (dd, J = 4.8, 1.2
Hz, 1 H), 7.77 (td, J = 7.8, 0.7 Hz, 1 H), 8.14 (d, J = 7.8 Hz, 1 H),
8.57 (dt, J = 4.8, 0.7 Hz, 1 H).
1H NMR (400 MHz, CDCl3): d = 2.43 (s, 3 H), 4.75 (br s, 1 H), 5.07
(br s, 1 H), 5.33 (br s, 1 H), 7.26–7.37 (m, 12 H), 7.84 (d, J = 8.2
Hz, 2 H).
13C NMR (100 MHz, CDCl3): d = 21.4, 126.7, 127.3, 127.4, 128.6,
129.2, 143.6, 163.0.
HRMS–FAB: m/z [M + H]+ calcd for C22H21N2: 313.1705; found:
313.1676.
13C NMR (100 MHz, CDCl3): d = 50.4, 122.2, 125.0, 136.5, 148.5,
148.6, 164.2.
1,3-Bis[(4R,5R)-4,5-diphenyl-2-imidazolin-2-yl]benzene
Mp 136.5–138 °C.
Synthesis 2007, No. 13, 1939–1942 © Thieme Stuttgart · New York

1942
M. Ishihara, H. Togo
PAPER
IR (neat): 3062, 1570, 1493, 1452, 1270, 754, 696 cm–1.
1H NMR (400 MHz, CDCl3): d = 4.93 (br s, 4 H), 7.28–7.37 (m, 20
H), 7.57 (t, J = 7.8 Hz, 1 H), 8.11 (d, J = 7.8 Hz, 2 H), 8.50 (s, 1 H).
13C NMR (100 MHz, CDCl3): d = 126.1, 126.6, 127.6, 128.7, 128.9,
129.0, 130.4, 143.1, 162.4.
(3) For examples, see: (a) Ferm, R. J.; Riebsomer, J. L. Chem.
Rev. 1954, 54, 593. (b) Hughey, J. L. IV.; Knapp, S.;
Schugar, H. Synthesis 1980, 489. (c) Quaglia, W.;
Bousquet, P.; Pigini, M.; Carotti, A.; Carrieri, A.;
Dontenwill, M.; Gentili, F.; Giannella, M.; Maranca, F.;
Piergentili, A.; Brasili, L. J. Med. Chem. 1999, 42, 2737.
(d) Anastassiadou, M.; Baziard-Mouysset, G.; Payard, M.
Synthesis 2000, 1814. (e) Neef, G.; Eder, U.; Sauer, G. J.
Org. Chem. 1981, 46, 2824. (f) Mitchell, J. M.; Finney, N.
S. Tetrahedron Lett. 2000, 41, 8431. (g) Peddibhotla, S.;
Tepe, J. J. Synthesis 2003, 1433. (h) You, S.; Kelly, J. W.
Org. Lett. 2004, 6, 1681.
(4) (a) Fujioka, H.; Murai, K.; Ohba, Y.; Hiramatsu, A.; Kita, Y.
Tetrahedron Lett. 2005, 46, 2197. (b) Fujioka, H.; Murai,
K.; Kubo, O.; Ohba, Y.; Kita, Y. Tetrahedron 2007, 63, 638.
(5) Ishihara, M.; Togo, H. Synlett 2006, 227.
(6) For a review, see: (a) Togo, H.; Iida, S. Synlett 2006, 2159.
For other papers, see: (b) Mori, N.; Togo, H. Synlett 2004,
880. (c) Mori, N.; Togo, H. Tetrahedron 2005, 61, 5915.
(d) Mori, N.; Togo, H. Synlett 2005, 1456. (e) Iida, S.;
Togo, H. Synlett 2006, 2633. (f) Iida, S.; Togo, H. Synlett
2007, 407.
HRMS–FAB: m/z [M + H]+ calcd for C36H31N4: 519.2549; found:
519.2513.
2,6-Bis[(4R,5R)-4,5-diphenyl-2-imidazolin-2-yl]pyridine
Mp 124–125 °C (Lit.14 123–126 °C).
IR (neat): 3028, 1606, 1564, 1452, 999, 752, 698 cm–1.
1H NMR (400 MHz, CDCl3): d = 4.79 (d, J = 8.7 Hz, 2 H), 5.20 (d,
J = 8.7 Hz, 2 H), 6.42 (br s, 2 H), 7.25–7.35 (m, 20 H), 7.98 (t,
J = 7.8 Hz, 1 H), 8.48 (d, J = 7.8 Hz, 2 H).
Acknowledgment
Financial support from a Grant-in-Aid for Scientific Research (No.
16655012) from the Ministry of Education, Science, Sports, and
Culture of Japan is gratefully acknowledged.
(7) Stevens, R. V.; Gaeta, F. C. A. J. Am. Chem. Soc. 1977, 99,
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(8) Bergmann, F.; Weizmann, M.; Dimant, E.; Patai, J.;
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1109.
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Synthesis 2007, No. 13, 1939–1942 © Thieme Stuttgart · New York