A practical synthesis of 2-amino-2′-hydroxy-1,1′-binaphthyl (NOBIN)

Article abstract of DOI:10.1016/S0040-4039(02)01674-X

A practical synthesis of 2-amino-2′-hydroxy-1,1′-binaphthyl (NOBIN) was realized from BINOL through a single step. Its facile purification procedure makes the process amenable for large scale synthesis of NOBIN.

Full text of DOI:10.1016/S0040-4039(02)01674-X

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 7163–7165
A practical synthesis of 2-amino-2%-hydroxy-1,1%-binaphthyl
NOBIN)
(
Karsten K o¨ rber, Wenjun Tang, Xinquan Hu and Xumu Zhang*
Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
Received 25 July 2002; accepted 9 August 2002
Abstract—A practical synthesis of 2-amino-2%-hydroxy-1,1%-binaphthyl (NOBIN) was realized from BINOL through a single step.
Its facile purification procedure makes the process amenable for large scale synthesis of NOBIN. © 2002 Elsevier Science Ltd. All
rights reserved.
Chiral 2-amino-2%-hydroxy,-1,1%-binaphthyl (NOBIN),
1
first developed by Ko cˇ ovsk y´ , has proven to be an
excellent framework for constructing chiral ligands (Fig.
1
). For example, ligand 1, made from NOBIN by
Carreira, has been successfully applied in Ti-catalyzed
asymmetric aldol reactions. We have recently developed
2
a NOBIN-derived N,P ligand 2, which has shown high
enantioselectivities in the Cu-catalyzed Michael addi-
3
tion. A Ru complex derived from an N,O-mixed
polydentate ligand 3 has been applied as an excellen4t
catalyst for intermolecular cyclopropanation reactions.
Hoveyda has developed an excellent asymmetric
5
metathesis catalyst based on the NOBIN motif. In
addition, NOBIN itself has been used as a good phase
6
transfer catalyst by Kagan. However, despite many
excellent applications of NOBIN and its derived ligands,
a practical synthesis of NOBIN is still not available.
Figure 1.
Several methods have been reported for the synthesis of
NOBIN. Koc' ovsk y´ employed a Cu(II)Cl -mediated cou-
2
pling reaction of 2-naphthylamine and 2-naphthol to
1
yield NOBIN in 43% yield (Scheme 1). Ding et al.
reported improved conditions for the above coupling
reaction by employing the two-component molecular
crystal 6 in aqueous solution. The coupling yield
increased to 65% when 10 g of molecular crystal was
7
,8
employed. Buchwald et al. offered an attractive route
to synthesize chiral NOBIN from optically pure BINOL
9
via a palladium-catalyzed amination reaction. However,
this process requires several protection and deprotection
steps.
*
Corresponding author. Tel.: 1-814-863-5614; fax: 1-814-863-8403;
e-mail: xumu@chem.psu.edu
Scheme 1.
0
040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01674-X

7
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K. K o¨ rber et al. / Tetrahedron Letters 43 (2002) 7163–7165
We used both Ko cˇ ovsk y´ and Ding’s methods to synthe-
size NOBIN in a 20 g scale. By using Kocovsk y´ ’s
method, a mixture of NOBIN, BINOL, and 1,1%-
binaphthyl-2,2%-diamine (BINAM) was obtained.
Although the ratio of NOBIN in the mixture was
relatively high, the isolated yield decreased to around
was observed during the reaction. We assumed that the
strong internal hydrogen bond between the hydroxy
group and the amino group of NOBIN prevented its
further conversion to BINAM.
'
A detailed procedure is as follows. To a 125 mL Teflon
lined autoclave was added 5.0 g (17.5 mmol) of 1,1%-bi-
4
0% due to the difficult separation of NOBIN from
2
6
-naphthol, 23.5 g (175 mmol) of (NH ) SO ·H O, and
5 mL of concentrated aqueous ammonia. The mixture
BINOL and especially BINAM. Using Ding’s method
also resulted in formation of a mixture of three prod-
ucts. However, since less BINAM was formed in Ding’s
method, an easier purification procedure allowed us to
obtain NOBIN in 58% yield. It is likely that the forma-
tion of BINOL and BINAM is unavoidable in the
cross-coupling reaction between 2-naphthol and 2-
naphthylamine. Since removal of the two by-products
from NOBIN is tedious due to their similar properties,
a higher yield of NOBIN is unlikely to be obtained.
4 2 3 2
was stirred at 200°C in an oil-bath for 5 days. It was
then cooled down to ambient temperature and filtered.
The resulting solid was washed with water followed by
recrystallization from benzene to afford 4.5 g (15.8
mmol, 91%) of pure 2-amino-2%-hydroxy-1,1%-
binaphthyl.
In summary, we have discovered a practical procedure
for the synthesis of NOBIN. This single-step prepara-
tion of NOBIN from BINOL is simple and offers high
yield. This method may be applicable for a large-scale
synthesis of NOBIN. The enantiomerically pure
NOBIN can be obtained from racemic NOBIN by the
We have made 2-naphthylamine in high yield from
1
0
2
-naphthol via a Bucherer reaction. We proposed that
NOBIN might be synthesized from BINOL in a similar
way (Scheme 2). It was reported that 2-naphthylamine
was obtained in high yield when 2-naphthol was heated
at 150°C in the presence of concentrated aqueous
2e,12
reported resolution methods.
1
1
ammonia and ammonium sulfite for 8 h. However, no
reaction was observed when the same conditions were
subjected to BINOL. When the temperature was
increased to 200°C and more ammonium sulfite was
employed, NOBIN was exclusively formed without
detectable amounts of BINAM. By extending the reac-
tion time to 5 days and increasing the amount of
ammonium sulfite to 10 equiv., the starting material
disappeared completely. The produced solid was simply
filtered and washed with water. A 91% isolated yield of
NOBIN was obtained by recrystallization from benzene
Acknowledgements
This work was supported by the National Institute of
Health.
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7165
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