Selective reduction of 1,4-diarylimidazoline-3-oxides to imidazolidin-1-ols and hydroxylamine derivatives

Article abstract of DOI:10.1007/s00706-010-0344-y

C-2-unsubstituted imidazoline-3-oxides were reduced with NaBH₄ in THF to give the corresponding trans-3,5-diarylimidazolidin-1-ols, while under the same conditions C-2-substituted derivatives gave the corresponding ring-chain-ring tautomers. Tr

Full text of DOI:10.1007/s00706-010-0344-y

Monatsh Chem (2010) 141:901–905
DOI 10.1007/s00706-010-0344-y
ORIGINAL PAPER
Selective reduction of 1,4-diarylimidazoline-3-oxides
to imidazolidin-1-ols and hydroxylamine derivatives
•
Oktay Asutay Necdet Cos¸kun
Received: 1 March 2010 / Accepted: 5 June 2010 / Published online: 27 July 2010
Ó Springer-Verlag 2010
Abstract C-2-unsubstituted imidazoline-3-oxides were
reduced with NaBH4 in THF to give the corresponding
trans-3,5-diarylimidazolidin-1-ols, while under the same
conditions C-2-substituted derivatives gave the corre-
sponding ring–chain–ring tautomers. Treatment of the
crude reaction mixture from the reduction of C-2-unsub-
stituted imidazoline-3-oxides with a MeOH–H2O mixture
provided reductive C–N bond cleavage to give hydroxyl-
amines, while under the same conditions ring–chain–ring
tautomers remained unchanged.
library based on benzylidene exchange reactions of imi-
dazolidin-1-ol, nitrone, and oxadiazinane ring–chain–ring
tautomers at room temperature was created. The probable
mechanism of the reaction was discussed based on Ham-
mett-type correlation analyses [5]. To investigate the effect
of substituents on the N-aromatic ring of 2a–4e we have
subjected a series of C-2-unsubstituted nitrones 1a–1e to
NaBH4 reduction [6–9] in THF at reflux temperature, and
the reduction products were proved to exist only in imi-
dazolidin-1-ol forms 2a–2e.
Here we report on the reduction of cyclic nitrones 1a–1e
to imidazolidine [10] derivatives 2a–2e, which were
selectively reduced to hydroxylamine derivatives 6a–6e
[11–14].
Keywords Nitrones ꢀ Rearrangement ꢀ
Ring–chain–ring tautomers ꢀ Selectivity ꢀ Hydroxylamine
Introduction
Results and discussion
Recently we reported that 1,2,4-triarylimidazolin-3-oxides
[1–3] 1 (R1 = Ar) can be reduced with NaBH4 in THF at
reflux to give the corresponding 2,3,5-triarylimidazolidin-
1-ols 2, which proved to be in a ring–chain–ring tautomeric
equilibrium with N-(2-aminoethyl) nitrones 3 and 3,5,6-
triphenyl-1,2,5-oxadiazinanes 4 (Scheme 1) [4]. The ratios
of the ring and chain form were determined by the sub-
stituent at the reaction center and described by the equation
The reduction of cyclic nitrones 1a–1g with NaBH4 in THF
provides the corresponding imidazolidin-1-ols 2a–2e
(Scheme 1) in the case of R1 = H, and the corresponding
ring–chain–ring tautomeric mixtures 2f–4g [4, 5] in the
case of R1 = Ph.
The infrared (IR) spectra of compounds 2a–2e (KBr)
revealed the presence of OH stretching vibrations at
*3,250 cm-1. Most of the peaks for the imidazolidine
log KX = qr? ? log KX=H
. A dynamic combinatorial
1
hydrogens in the H nuclear magnetic resonance (NMR)
spectra appear as broadened singlets instead of the expected
patterns for AB and ABX systems. The hydroxyl hydrogen
was seen in the case of 2d at 6.08 ppm also as a broad
singlet. Two of the imidazolidine ring protons resonate as
doublet and triplet at *4.49 and *4.43 ppm, respectively;
the heteronuclear multiple quantum coherence (HMQC)
spectrum of 2a shows that they belong to different carbons.
One-dimensional (1D) nuclear Overhauser enhancement
O. Asutay ꢀ N. Cos¸kun
Department of Chemistry, Muratlı Vocational School,
˘
Namık Kemal University, Muratlı-Tekirdag, Turkey
e-mail: asutayoktay@yahoo.com
N. Cos¸kun (&)
Department of Chemistry, Uludag University,
16059 Bursa, Turkey
e-mail: coskun@uludag.edu.tr
˘
123

902
O. Asutay, N. Cos¸kun
Scheme 1
Ph
R1
NaBH4
THF
reflux
Ph
NaBH4
MeOH-H2O
reflux
R1
N
Ph
Ph
O
NH
O
N
N
N
NH
N
NH
N
R
OH
R
R
OH
R
O
N
R
R1 =H
R1
R1
Ph
1
2
3
4
6
a: R = 4-MeO-C6H4, R1 = H, b: R = 4-Me-C6H4, R1 = H, c: R = C6H5, R1 = H, d: R = 4-Br-C6H4,
R1 = H, e: R = 4-Cl-C6H4, R1 = H, f: R = 4-MeO-C6H4, R1 = Ph, g: R = 4-Me-C6H4, R1 = Ph.
spectroscopy (NOESY) experiments revealed that the
doublet is at C-2 while the triplet is at C-5. The NMR
spectra of compounds 2 resembled those of nitrone–
maleimide endo cycloadducts [15], where the presence of a
radical center in the molecule causes pronounced broad-
enings of the neighboring atom signals. However, magnetic
susceptibility measurements for 2a did not confirm the
presence of paramagnetic character of compounds 2. Some
assignments for imidazolidin-1-ols 2a–2e [16–18] based on
1D and two-dimensional (2D) NMR experiments are
exemplified for 2b in Fig. 1.
coplanar with the plane of the imidazolidine ring [torsion
angles involving the atoms C(10)–N(1)–C(1)–C(2) and
C(8)–N(1)–C(1)–C(7) are 13.6(5)° and -21.3(6)°, respec-
tively]. The torsion angle of 162.1(3)° for O(1)–N(2)–
C(9)–C(11) clearly reveals the trans geometry of the
molecule with respect to the hydroxyl at N(2) and the
phenyl at C(9).
Compounds 2a–2e were treated in toluene at room
temperature with phenyl isocyanate to provide the O-car-
bamoylated products 5a–5e [4]. The NMR characteristics
of the latter are similar to those of compounds 2a–2e with
respect to the broadenings of the imidazolidine ring proton
peaks (Fig. 1).
X-ray crystallographic analysis of compound 2b (Fig. 2)
confirmed the assigned structure. The N2–O1 and O1–H
˚
distances are 1.447(5) and 0.880(5) A, respectively, and
It is clear that compounds 2a–2g are not reducible with
NaBH4 in THF; however, treatment of isolated C-2-un-
substituted 2 with the same reducing agent in MeOH–H2O
(2:1) provided selectively the compounds 6 within short
time in excellent yield. The reduction of five-membered
aminals was found to be dependent on the structural nature
of the N,N0-substituents. The presence of an electron-defi-
cient group appears to disfavor formation of the
intermediate iminium ion and consequently lowers the rate
of reduction [19].
are as usually found in similar structures. The N(1)–C(10)
˚
bond [1.451(6) A] is slightly shorter than the N(2)–C(10)
˚
bond [1.455(5) A]. Comparison of the N(1)–C(8) and
N(2)–C(9) bonds reveals that the latter is longer than the
former. All nitrogen-involving bonds except N(2)–C(9) are
˚
smaller than the usual value of 1.48 A. The ring bond
angles at N1, C(1)–N(1)–C(10) = 120.3(3)°, C(1)–N(1)–
C(8) = 123.0(3)°, and C(10)–N(1)–C(8) = 109.6(3)°, are
pointing to a nearly planar nitrogen. The bond angles at
N2, C(10)–N(2)–O(1) = 106.0(3)° and C(9)–N(2)–O(1) =
107.5(3)°, are in agreement with a pyramidal nitrogen. The
angles C(10)–N(2)–C(9) = 102.5(3)°, N(2)–C(9)–C(8) =
104.2(3)°, and C(9)–C(8)–N(1) = 102.9(3)° are shortened,
while N(1)–C(10)–N(2) = 107.1(3)° and C(10)–N(1)–
C(8) = 109.6(3)° are close to the usual tetrahedral angles.
It is most noteworthy that the N(1) aromatic ring is
Compounds 6a–6e were prepared according to a one-pot
procedure involving the treatment of compounds 1a–1e
with NaBH4 in THF for 4 h and heating the crude reaction
mixture in MeOH–H2O (2:1) in a water bath for 0.5 h. We
assume that compounds 6a–6e arise from reduction of the
ring-opened unstable nitrones 3a–3e, although they do not
form at room temperature in solvents such as CDCl3 and
Fig. 1 Characteristic NMR
data for 2b and 5b
50.2;
3.69;
3.98
51.3;
3.45;
3.76
71.7; 4.82
71.7; 4.43
H
H
H
H
H
H
H
H
N
N
N
N
O
OH
H
H
O
112.2; 6.52
NH
111.8; 6.42
128.2; 7.35
71.3;
4.63;
4.76
73.1;
4.49;
4.21
8.32
152.6
5b
2b
123

Selective reduction of 1,4-diarylimidazoline-3-oxides to imidazolidin-1-ols
903
Fig. 2 X-ray crystal structure
of compound 2b, showing atom
numbering scheme. Thermal
ellipsoids are drawn at 50%
probability level for clarity
dimethyl sulfoxide (DMSO)-d6. Tautomeric mixtures
2f–4g were treated with NaBH4 in MeOH–H2O (2:1) at
1
reflux for 19 h. H NMR investigations of the crude reac-
was crystallized from toluene/petroleum ether (ca. 1:5) at
room temperature. The formed white crystals were filtered
and dried under vacuum.
tion mixtures revealed that no reduction products were
formed. The starting materials were isolated and proved to
be identical to the starting compounds 2f–4g.
trans-3-(4-Methoxyphenyl)-5-phenylimidazolidin-1-ol
(2a, C16H18N2O2)
Yield 0.303 g (80%); white crystals; m.p.: 107–108 °C; IR
(KBr): m = 3,250 (N–OH) cm-1 1H NMR (400 MHz,
;
CDCl3): d = 3.44 (1H, brs), 3.75 (3H, s), 3.76 (1H, brs),
4.27 (1H, brs), 4.43 (1H, t, J = 6.8 Hz), 4.49 (1H, d,
J = 7.2 Hz), 6.48 (2H, d, J = 8.4 Hz), 6.86 (2H, d,
J = 8.4 Hz), 7.32–7.39 (5H, m) ppm; 13C NMR
(100 MHz, CDCl3): d = 55.9, 71.8, 72.0, 112.7, 115.1,
128.1, 128.6, 141.1, 151.7 ppm.
Experimental
Solvents and reagents were Aldrich or Merck quality and
were used without additional purification. Melting points
were taken using an electrothermal digital melting point
apparatus. Infrared spectra were recorded on a Thermo-
Nicolet 6700 FTIR. H and 13C NMR as well as 2D NMR
trans-3-(4-Methylphenyl)-5-phenylimidazolidin-1-ol
(2b, C16H18N2O)
1
experiments as correlation spectroscopy (COSY), HMQC,
heteronuclear multiple-bond correlation (HMBC), and 1D
NOESY were performed using a Varian Mercury Plus 400-
MHz spectrometer. Elemental analyses were conducted
using a EuroEA 3000 CHNS elemental analyzer. The
results were found to be in good agreement ( 0.2%) with
the calculated values.
Yield 0.285 g (80%); white crystals; m.p.: 123-124 °C; IR
(KBr): m = 3,250 (N–OH) cm-1 1H NMR (400 MHz,
;
CDCl3): d = 2.26 (3H, s), 3.44 (1H, brs), 3.76 (1H, brs),
4.21 (1H, brs), 4.39 (1H, t, J = 6.8 Hz), 4.49 (1H, d,
J = 7.6 Hz), 6.42 (2H, d, J = 7.6 Hz), 7.06 (2H, d,
J = 7.6 Hz), 7.35 (5H, s) ppm; 13C NMR (100 MHz,
CDCl3): d = 20.4, 51.3 (CH2), 71.7 (CH), 73.1 (CH2),
111.8, 126.0, 128.2, 128.6, 129.3 ppm.
General procedure for the synthesis
of trans-3,5-diarylimidazolidin-1-ols 2a–2e
A colorless platelet crystal of 2b (C16H18N2O) having
approximate dimensions of 0.60 9 0.40 9 0.10 mm3 was
mounted on a glass fiber. All measurements were made on
a Rigaku RAXIS RAPID imaging plate area detector with
graphite monochromated Mo Ka radiation. Cell constants
and an orientation matrix for data collection corresponded
to a primitive monoclinic cell with dimensions: a =
To a solution of nitrone 1a–1e (1.4 mmol) in 40 cm3 THF,
0.5296 g NaBH4 (14 mmol) was added, and the reaction
mixture was refluxed under stirring for 4 h. The solvent
was evaporated under vacuum, and the residue suspended
in water and extracted with chloroform (2 9 15 cm3). The
combined extracts were washed with water (2 9 15 cm3),
dried over anhydrous Na2SO4, and filtered, and the solvent
evaporated under reduced pressure. The nearly pure residue
˚
˚
˚
8.3634(3) A, b = 9.9982(3) A, c = 16.4784(6) A, m =
3
˚
1,377.90(8) A , and b = 90.131(2)°. For Z = 4 and
F.W. = 254.33, the calculated density is 1.23 g/cm3. The
123

904
O. Asutay, N. Cos¸kun
systematic absences of h0l: h 2n and 0k0: k 2n
uniquely determine the space group to be P21/a. Data were
collected at temperature of 20 1 °C to a maximum 2h
value of 50.2°. A total of 135 oscillation images were
collected. The crystal-to-detector distance was 127.40 mm.
Readout was performed in the 0.100-mm pixel mode.
6.56 (2H, d, J = 8.4 Hz), 6.89 (2H, d, J = 8.4 Hz), 7.09–
7.45 (10H, m), 8.32 (1H, brs, NH) ppm; 13C NMR
(100 MHz, CDCl3): d = 50.9, 55.9, 71.4, 72.3, 113.2,
115.2, 115.4, 119.3, 124.2, 127.8, 128.9, 129.1, 136.8,
140.2, 152.2, 152.6 ppm.
Phenylcarbamic acid 3-(4-methylphenyl)-
5-phenylimidazolidin-1-yl ester (5b, C23H23N3O2)
Yield 0.088 g (78%); white crystals; m.p.: 146 °C; IR
trans-3,5-Diphenylimidazolidin-1-ol (2c, C15H16N2O)
Yield 0.313 g (93%); white crystals; m.p.: 107–108 °C; IR
(KBr): m = 3,250 (N–OH) cm-1
;
1H NMR (400 MHz,
(KBr): m = 3,300 (NH), 1,722 (C=O) cm-1 1H NMR
;
CDCl3): d = 3.48 (1H, brs), 3.81 (1H, brs), 4.30 (1H, brs),
4.44 (1H, brs), 4.57 (1H, d, J = 7.6 Hz), 6.52 (2H, d,
J = 6.8 Hz), 6.75 (1H, d, J = 7.2 Hz), 7.24–7.26 (2H, m),
7.34–7.38 (5H, m) ppm; 13C NMR (100 MHz, CDCl3):
d = 51.2, 71.6, 72.8, 111.7, 116.8, 127.9, 128.3, 128.7,
129.4, 137.9, 146.0 ppm.
(400 MHz, CDCl3): d = 2.29 (3H, s), 3.69 (1H, brs), 3.98
(1H, brs), 4.63 (1H, brs), 4.76 (1H, brs), 4.82 (1H, brs),
6.52 (2H, d, J = 8.0 Hz), 7.10 (2H, d, J = 8.0 Hz), 7.09–
7.45 (10H, m), 8.31 (1H, brs, NH) ppm; 13C NMR
(100 MHz, CDCl3): d = 20.4 (CH3), 50.2 (CH2), 71.3
(CH2), 71.7 (CH), 112.2, 119.3, 124.2, 126.9, 127.8, 128.9,
129.1, 130.0, 136.8, 143.4, 152.6 ppm.
trans-3-(4-Bromophenyl)-5-phenylimidazolidin-1-ol
(2d, C15H15BrN2O)
Phenylcarbamic acid 3,5-diphenylimidazolidin-1-yl ester
(5c, C22H21N3O2)
Yield 0.398 g (71%); white crystals; m.p. 120–122 °C; IR
(KBr): m = 3,256 (N–OH) cm-1
;
1H NMR (400 MHz,
Yield 0.055 g (51%); white crystals; m.p.: 121 °C; IR
CDCl3): d = 3.45 (1H, brs), 3.78 (1H, brs), 4.27 (1H, brs),
4.46 (1H, brs), 4.53 (1H, d, J = 7.6 Hz), 6.08 (1H, brs),
6.44 (2H, d, J = 7.6 Hz), 7.19 (2H, d, J = 7.6 Hz), 7.34–
7.38 (5H, m) ppm; 13C NMR (100 MHz, CDCl3):
d = 51.2, 71.6, 72.8, 112.7, 127.8, 128.3, 128.7, 129.2,
137.9, 146.0 ppm.
(KBr): m = 3,298 (NH), 1,724 (C=O) cm-1 1H NMR
;
(400 MHz, CDCl3): d = 3.72–3.75 (1H, m), 4.01 (1H,
brs), 4.66 (1H, brs), 4.79–4.86 (2H, m), 6.59 (2H, d,
J = 8.0 Hz), 6.82 (1H, d, J = 8.0 Hz), 7.10–7.45 (12H,
m), 8.32 (1H, brs, NH) ppm; 13C NMR (100 MHz, CDCl3):
d = 50.9, 71.3 (2C), 112.1, 117.0, 119.3, 124.2, 127.8,
128.9, 129.1, 129.5, 136.8, 152.6 ppm.
trans-3-(4-Chlorophenyl)-5-phenylimidazolidin-1-ol
(2e, C15H15ClN2O)
Phenylcarbamic acid 3-(4-bromophenyl)-
5-phenylimidazolidin-1-yl ester (5d, C22H20BrN3O2)
Yield 0.114 g (86%); white crystals; m.p.: 114 °C; IR
Yield 0.342 g (89%); white crystals; m.p.: 128 °C; IR
(KBr): m = 3,243 (N–OH) cm-1 1H NMR (400 MHz,
;
CDCl3): d = 3.45 (1H, brs), 3.78 (1H, brs), 4.27 (1H, brs),
4.47 (1H, brs), 4.54 (1H, d, J = 7.6 Hz), 6.40 (2H, d,
J = 7.6 Hz), 7.33 (2H, d, J = 7.6 Hz), 7.34-7.38 (5H, m)
ppm; 13C NMR (100 MHz, CDCl3): d = 51.2, 71.7, 72.6,
113.2, 114.2, 127.8, 128.3, 128.7, 132.0, 137.9, 145.0 ppm.
(KBr): m = 3,335 (NH), 1,741 (C=O) cm-1 1H NMR
;
(400 MHz, CDCl3): d = 3.72 (1H, brs), 3.98 (1H, brs),
4.61 (1H, brs), 4.73 (1H, brs), 4.85 (1H, brs), 6.46 (2H, d,
J = 8.4 Hz), 7.09–7.45 (12H, m), 8.24 (1H, brs, NH) ppm;
13C NMR (100 MHz, CDCl3): d = 51.2, 71.2 (2C), 110.0,
113.6, 119.3, 124.3, 127.7, 129.1, 132.2, 136.7, 144.4,
152.4 ppm.
General procedure for the synthesis of phenylcarbamic
acid 3,5-diarylimidazolidin-1-yl esters 5a–5e
Phenylcarbamic acid 3-(4-chlorophenyl)-
5-phenylimidazolidin-1-yl ester (5e, C22H20ClN3O2)
Yield 0.060 g (51%); white crystals; m.p.: 111 °C; IR
To a solution of 3,5-diarylimidazolidin-1-ol 2 (0.3 mmol)
in 30 cm3 toluene was added 0.048 g phenyl isocyanate
(0.4 mmol), and the reaction mixture was stirred at
room temperature for 18 h. The solvent was evaporated
under vacuum, and the residue dissolved in petroleum
ether under heating and left to crystallize at room
temperature.
(KBr): m = 3,335 (NH), 1,742 (C=O) cm-1 1H NMR
;
(400 MHz, CDCl3): d = 3.73 (1H, brs), 3.99 (1H, brs),
4.61 (1H, brs), 4.74 (1H, brs), 4.85 (1H, brs), 6.51 (2H, d,
J = 8.4 Hz), 7.09–7.40 (12H, m), 8.24 (1H, brs, NH) ppm;
13C NMR (100 MHz, CDCl3): d = 51.2, 71.3 (2C), 113.1,
119.3, 124.3, 127.7, 129.1, 129.3, 136.7, 144.4, 152.4 ppm.
Phenylcarbamic acid 3-(4-methoxyphenyl)-
5-phenylimidazolidin-1-yl ester (5a, C23H23N3O3)
Yield 0.053 g (45%); white crystals; m.p.: 134 °C; IR
General procedure for the synthesis of N-(2-arylamino-
1-phenylethyl)-N-methylhydroxylamines 6a–6e
(KBr): m = 3,299 (NH), 1,731 (C=O) cm-1 1H NMR
;
(400 MHz, CDCl3): d = 3.66 (1H, brs), 3.78 (3H, s), 3.96
(1H, brs), 4.63 (1H, brs), 4.75 (1H, brs), 4.82 (1H, brs),
To a solution of nitrone 1 (1.4 mmol) in 40 cm3 THF,
NaBH4 (14 mmol) was added and the reaction mixture was
123

Selective reduction of 1,4-diarylimidazoline-3-oxides to imidazolidin-1-ols
905
(400 MHz, CDCl3): d = 2.53 (3H, s), 3.36-3.40 (1H, m),
3.75–3.80 (2H, m), 4.04 (1H, brs, NH), 6.10 (1H, brs, OH),
6.47 (2H, d, J = 8.0 Hz), 7.22 (2H, d, J = 8.0 Hz), 7.29–
7.37 (5H, m) ppm; 13C NMR (100 MHz, CDCl3): d = 46.5
(CH3), 47.2 (CH2), 72.1 (CH), 109.1, 114.7, 128.3, 128.7,
132.0 (2C), 138.0, 146.9 ppm.
refluxed under stirring for 4 h. The solvent was evaporated
under vacuum, the residue dissolved in 10 cm3 water and
20 cm3 methanol, and the mixture stirred under reflux for
0.5 h. The solvent was evaporated under vacuum, and the
residue extracted with chloroform (2 9 15 cm3). The
combined extracts were dried over Na2SO4 and filtered,
and the solvent evaporated. The residue was dissolved in
ether/petroleum ether mixture (10 cm3, 2:1) and left to
crystallize in a refrigerator.
N-[2-(4-Chlorophenylamino)-1-phenylethyl]-
N-methylhydroxylamine (6e, C15H17ClN2O)
Yield 0.263 g (68%); white crystals; m.p.: 134 °C; IR
1
(KBr): m = 3,385 (NH), 3,197 (N–OH) cm-1; H NMR
N-[2-(4-Methoxyphenylamino)-1-phenylethyl]-
N-methylhydroxylamine (6a, C16H20N2O2)
(400 MHz, CDCl3): d = 2.53 (3H, s), 3.37–3.40 (1H, m),
3.75–3.82 (2H, m), 4.04 (1H, brs), 6.50 (2H, d,
J = 8.0 Hz), 7.08 (2H, d, J = 8.0 Hz), 7.29–7.37 (5H,
m) ppm; 13C NMR (100 MHz, CDCl3): d = 46.5 (CH3),
47.2 (CH2), 72.2 (CH), 114.2, 122.1, 128.3, 128.7, 128.8,
129.1, 137.8, 146.5 ppm.
Yield 0.290 g (76%); white crystals; m.p.: 87 °C; IR
1
(KBr): m = 3,365 (NH), 3,243 (N–OH) cm-1; H NMR
(400 MHz, CDCl3): d = 2.53 (3H, s), 3.38 (1H, dd,
J = 14.4, 8.0 Hz), 3.74 (3H, s), 3.76–3.81 (2H, m), 6.57
(2H, d, J = 9.2 Hz), 6.76 (2H, d, J = 9.2 Hz), 7.31–7.37
(5H, m) ppm; 13C NMR (100 MHz, CDCl3): d = 46.4
(CH3), 48.3 (CH2), 55.8 (CH3O), 72.3 (CH), 114.7, 114.9,
128.1, 128.8, 142.1, 152.3 ppm.
˘
Acknowledgments Uludag University Research Fund is gratefully
acknowledged for its financial support (project no. 2001-2).
N-Methyl-N-[2-(4-methylphenylamino)-
1-phenylethyl]hydroxylamine (6b, C16H20N2O)
Yield 0.319 g (89%); white crystals; m.p.: 113–114 °C; IR
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synthesis of imidazolidines. Chem Rev 54:593
11. Stanek J, Frei J, Mett H, Schneider P, Regenass U (1992) J Med
Chem 35:1339
(KBr): m = 3,384 (NH), 3,199 (N–OH) cm-1; H NMR
(400 MHz, CDCl3): d = 2.31 (3H, s), 2.53 (3H, s), 3.36–
3.42 (1H, m, part of an ABC system), 3.76–3.83 (2H, m,
part of an ABC system), 6.53 (2H, d, J = 8.8 Hz), 6.97
(2H, d, J = 8.8 Hz), 7.31–7.37 (5H, m) ppm; 13C NMR
(100 MHz, CDCl3): d = 20.4 (CH3), 46.3 (CH3), 47.6
(CH2), 72.2 (CH), 113.4, 126.9, 128.1, 128.6, 128.8, 129.8,
138.0, 145.6 ppm.
N-Methyl-N-[1-phenyl-2-(phenylamino)ethyl]-
hydroxylamine (6c, C15H18N2O)
Yield 0.258 g (76%); white crystals; m.p.: 118–119 °C; IR
12. Sosnovskikh VY, Moshkin VS, Kodess MI (2008) Tetrahedron
64:7877
1
(KBr): m = 3,387 (NH), 3,195 (N–OH) cm-1; H NMR
13. Filimonov SI, Filimonova SA, Shashkov AS, Firgang SI, Stashina
GA (2006) Mendeleev Commun 16:328
14. Smith DG, Gribble AD, Haigh D, Ife RJ, Lavery P, Skett P,
Slingsby BP, Stacey R, Ward RW, West A (1999) Bioorg Med
Chem Lett 9:3137
¨
15. Cos¸kun N, Oztu¨rk A (2007) Tetrahedron 63:1402
16. Osiecki JH, Ullman EF (1968) J Am Chem Soc 90:1078
17. Keana JFW (1978) Chem Rev 78:37
18. Kroll C, Schwarz KH, Surmann P, Borchert HH (1999) Bio-
electrochem Bioenerg 48:233
19. Boyd E, Coumbarides GS, Eames J, Jones RVH, Stenson RA,
Suggate MJ (2005) Tetrahedron Lett 46:3479
(400 MHz, CDCl3): d = 2.54 (3H, s), 3.40–3.44 (1H, dd,
J = 14.4, 8.0 Hz), 3.78–3.86 (2H, m), 4.01 (1H, brs), 6.60
(2H, d, J = 8.0 Hz), 6.70 (1H, t, J = 8.0 Hz), 7.16 (2H, t,
J = 8.0 Hz), 7.32–7.37 (5H, m) ppm; 13C NMR
(100 MHz, CDCl3): d = 46.4 (CH3), 47.2 (CH2), 72.2
(CH), 113.2, 117.6, 128.2, 128.7, 128.8, 129.3, 138.0,
147.9 ppm.
N-[2-(4-Bromophenylamino)-1-phenylethyl]-
N-methylhydroxylamine (6d, C15H17BrN2O)
Yield 0.279 g (62%); white crystals; m.p. 135 °C; IR
1
(KBr): m = 3,387 (NH), 3,206 (N–OH) cm-1; H NMR
123