Novel two-phase oxidative cross-coupling of the two-component molecular crystal of 2-naphthol and 2-naphthylamine

Article abstract of DOI:10.1039/a608256d

Two-phase reaction of a two-component molecular crystal of 2-naphthol and 2-naphthylamine suspended in aqueous Fe³⁺ solutions gives a cross-coupling product, 2-amino-2′-hydroxy-1,1′-binaphthalene, with good selectivity.

Full text of DOI:10.1039/a608256d

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Novel two-phase oxidative cross-coupling of the two-component molecular
crystal of 2-naphthol and 2-naphthylamine
Kuiling Ding,*a Qiguo Xu,a Yang Wang,a Jinxia Liu,a Zhengyan Yu,a Baoshi Du,a Yangjie Wu,*a Hideko
Koshimab and Teruo Matsuurab
a Department of Chemistry, Zhengzhou University, Zhengzhou 450052, P. R. China
b Department of Materials Chemistry, Faculty of Science and Technology, Ryukoku University, Seta, Otsu 520-21, Japan
Two-phase reaction of a two-component molecular crystal of
2-naphthol and 2-naphthylamine suspended in aqueous
Fe3+ solutions gives a cross-coupling product, 2-amino-
2A-hydroxy-1,1A-binaphthalene, with good selectivity.
indicate the formation of a molecular compound between
2-naphthol and 2-naphthylamine. Particularly, the nNH absorp-
tions at 3375, 3290 and 3170 cm21 in the IR spectrum of
2-naphthylamine become two absorption bands at 3350 and
3260 cm21 in the molecular compound 5 and the nOH absorption
at 3250 cm21 for 2-naphthol disappears in the spectrum of 5. It
can be deduced that the formation of the molecular compound
was caused by hydrogen bonding between the OH and NH2
groups.
Solid-state organic reactions occurring in the ground state have
attracted recent attention in organic synthesis.1 For example,
Toda et al. reported that a powdered mixture of 2-naphthol and
FeCl3·6H2O gave 1,1A-bi-2-naphthol 1 in 95% yield.2 We have
developed a two-phase (solid–liquid) oxidative coupling reac-
tion of 2-naphthol and 6-bromo-2-naphthol suspended in
aqueous Fe3+ solutions which gives the corresponding 1,1A-bi-
2-naphthols in up to 95% yield.3 Here we report a novel
oxidative cross-coupling reaction using a two-component
molecular crystal composed of 2-naphthol and 2-naphthylamine
via a similar solid–liquid process leading to 2-amino-2A-hy-
droxy-1,1A-binaphthalene 2, which is a key catalytic ligand for
asymmetric synthesis.4 The present method is the first example
of the ground-state reaction using two-component molecular
crystals, in contrast to their known excited-state (photo)reac-
tions.5
The molecular crystal 5 was obtained by the slow evaporation
of an equimolar solution of 2-naphthol 3 and 2-naphthylamine
4 in methanol–acetone (1:1, v/v) at room temperature or by
melting a 1:1 molar mixture of the component compounds
followed by resolidification of the melt. Elemental analysis of 5
showed the composition of 2-naphthol and 2-naphthylamine
present to be 1:1. The melting point of 5 is 127–129 °C which
is higher than those of 2-naphthol (120–123 °C) and 2-naph-
thylamine (108–110 °C). Powder X-ray diffraction (PXD)
results and the IR spectra of crystal 5 are quite different from
those of the sum of the component compounds. All these results
The oxidative coupling of 2-naphthol 3 reported previously
was carried out using a suspension of the substrate in aqueous
Fe3+ solution.3 We applied this method to the synthesis of
2-amino-2A-hydroxy-1,1A-binaphthalene 2 via oxidative cross-
coupling of molecular crystal 5. In a typical run, a suspension of
finely powdered 5 (2.87 g, 10 mmol) in water (50 ml) containing
FeCl3·6H2O (10.80 g, 40 mmol) was stirred at 55 °C for 6 h
under an argon atmosphere. After cooling, the solid material
was collected quantitatively by filtration and washed with
distilled water to remove Fe3+ and Fe2+. The solid was
chromatographed on an activated charcoal column (100 3 18
mm, 10 g of activated charcoal) using acetone as eluent. The
eluent was evaporated and the residual solid was recrystallized
from benzene to afford pure 2 (2.0 g, 70%) as colourless
1
needles. Elemental analysis, IR, H NMR and 13C NMR data
were consistent with the structure 2. This procedure was also
applied to the large-scale synthesis of 2, using 5 (11.5 g, 40
mmol), FeCl3·6H2O (43.2 g, 160 mmol) and water (200 ml) at
55 °C for 6 h, to gave 7.15 g of 2 (65% isolated yield).
The selectivity and efficiency of the reaction under various
conditions were also examined. The results obtained by the
HPLC analysis of the products are summarized in Table 1. In a
typical run carried out at 55 °C for 6 h (entry 1), the conversion
of 2-naphthol 3 was quantitative and the yield of cross-coupling
product 2 was highest. When the reaction was conducted at
OH
OH
OH
Table 1 Oxidative cross-coupling of 5
NH2
Yield (%)a
Conversion
Entry
Fe3+ :5
T/°C
t/h
of 3 (%)
2
1
1
2
1
2
3
4:1
4:1
4:1
2.2:1
4:1
4:1
4:1
4:1
4:1
4:1
55
55
6
3
6
3
3
3
3
3
5
3
100
82
79
71
71
63
31
42
57
39
78
14
13
14
19
19
23
30
18
39
20
98.0
98.4
94.8
97.0
81.8
77.2
96.8
100
OH
NH2
room temp.
4
55
55
55
55
55
55
55
+
5b
6c
7c
8c
9d
10e
4
3
i
H2
N
96.4
OH
ii
a Yields were obtained by HPLC and based on the amount of consumed 3.
2
+
1
b
c
Ultrasound (25 KHz) was applied.
Fe2(SO4)3·9H2O, NH4Fe-
5
(SO4)2·12H2O and NH4FeCl4·6H2O were used as oxidants. d The reaction
was conducted in the solid state. 3 and 4 were added to aqueous FeCl3
solution separately.
e
Scheme 1 Reagents and conditions: i, acetone–methanol, evaporation,
room temp; ii, Fe3+–H2O, 55 °C
Chem. Commun., 1997
693

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room temperature for 6 h (entry 3), the yield and the selectivity
for the formation of 2 apparently decreased in comparison with
those at 55 °C. At the lower molar ratio of FeCl3·6H2O to 5
(entry 4) the yields of 2 and 1 were unaltered. Under ultrasonic
application (entry 5) no improvement of the yield and
selectivity of the formation of 2 were observed. Although three
other kinds of Fe3+ salts were also used as oxidants (entries 6, 7
and 8), the yield and the selectivity for the formation of 2 were
poor in every case. A total solid-state reaction was carried out
by grinding a mixture of FeCl3·6H2O and 5 (4:1) in a mortar at
55 °C for 5 h (entry 9), the conversion of 2-naphthol 3 was
quantitative, but the yield and the selectivity of the formation of
2 were low. This is interpreted by the fact that with the progress
of the reaction the powdered mixture became glassy, a state in
which the original arrangement of the component molecules in
the crystal lattice may be altered.
It is interesting to note that when the crystals of 2-naphthol 3
and 2-naphthylamine 4 were separately added to the solution of
FeCl3·6H2O in water and the suspension was stirred at 55 °C for
3 h (entry 10), the yield of 2 was comparable to that obtained by
the reaction of molecular 5 (entry 2). In order to clarify this
phenomenon, a suspension of a mixture of 2-naphthol and
2-naphthylamine in water without the presence of oxidant was
stirred at 55 °C for 1 h. The solid collected by filtration showed
the same melting point and IR spectrum as those of 5. It can be
concluded that in the case of entry 10 the actual reacting species
is molecular 5 and as a result it gave the same yield and
selectivity of the product as those obtained from the reaction of
5.
We are grateful to the Research Foundation of National
Education Committee and the Natural Science Foundation of
Henan Province for Outstanding Young Scientists for financial
support of this work.
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Received, 9th December 1996; Com. 6/08256D
694
Chem. Commun., 1997