The rational design of novel chiral oxovanadium(IV) complexes for highly enantioselective oxidative coupling of 2-naphthols

Article abstract of DOI:10.1039/b201351g

Several novel chiral oxovanadium(IV) complexes have been designed and prepared for the asymmetric catalytic oxidative coupling of 2-naphthols with high enantioselectivities of 83-98% ee.

Full text of DOI:10.1039/b201351g

The rational design of novel chiral oxovanadium(IV) complexes for highly
enantioselective oxidative coupling of 2-naphthols†
Zhibin Luo, Quanzhong Liu, Liuzhu Gong,* Xin Cui, Aiqiao Mi and Yaozhong Jiang
Union Laboratory of Asymmetric Synthesis, Chengdu Institute of Organic Chemistry, Chinese Academy of
Sciences, Chengdu 610041, China. E-mail: gonglz@cioc.ac.cn
Received (in Cambridge, UK) 7th February 2002, Accepted 14th March 2002
First published as an Advance Article on the web 26th March 2002
Several novel chiral oxovanadium(IV) complexes have been
designed and prepared for the asymmetric catalytic oxida-
tive coupling of 2-naphthols with high enantioselectivities of
We prepared complexes 1 and 2 by the condensation of chiral
3,3’-diformyl-2,2’-dihydroxy-1,1’-bi-2-naphthol6 with (S)-
amino acids and vanadyl sulfate, according to the literature
procedure.5 Preliminary study on the characterization of the
complexes by HRMS and IR confirmed their structures.
In the presence of ca. 10 mol% catalyst, the coupling reaction
a
b,7
83–98% ee.
Optically active binaphthol and its derivatives have been
extensively used as chiral auxiliaries and ligands in asymmetric
synthesis, and shown extremely high stereo-control property in
4
of 2-naphthol was carried out in CCl by using molecular
oxygen as oxidant to investigate the effects of the catalyst
structure and reaction temperature on the enantioselectivity, and
the results are summarised in Table 1. The first test of catalyst
1
a wide range of asymmetric transformations. The importance
of such molecules has fuelled the development of efficient
2
methodologies to prepare them. Resolution of racemic bina-
1
(derived from (S)-3,3A-diformyl-2,2A-dihydroxy-1,1A-bi-
phthol has been employed for the scalemic preparation of
2-naphthol and (S)-phenylalanine) in the oxidative coupling of
2-naphthol, gave an acceptable isolated yield, but a very poor
enantioselectivity of only 6% ee with R-configuration (Table 1,
entry 1). However, under similar conditions as used for 1, a
much higher enantioselectivity of 39% ee was induced by 2a
(from (R)-3,3A-diformyl-2,2A-dihydroxy-1,1Abi-2-naphthol and
(S)-phenylalanine) (Table 1, entry 2). This result indicated that
the double chirality in 2a was suited for the oxidative coupling
of 2-naphthol. Fine-tuning the structure of the chiral amino acid
in a catalyst system similar to 2a might result in a good chiral
catalyst. Thus, other catalyst 2b–d were tested for this coupling.
Both oxovanadium(IV) complexes 2b and 2c‡ catalysed the
reaction with similar moderate enantioselectivity of 57% ee
under the same conditions as 2a (Table 1, entries 5 and 8). The
low reaction temperature was beneficial to the enantioselectiv-
ity, but somewhat suppressed the reactivity. For instance,
lowering the reaction temperature from 20 to 10 to 0 °C led to
an obvious improvement of the enantioselectivity for all of the
catalysts 2a–d, but the reactions were prolonged. At a reaction
temperature of 0 °C, catalysts 2b, 2c and 2d provided high
optically pure BINOL on a large scale.2
a–f
However, a
stoichiometric amount of resolving reagent has to be consumed.
This drawback hinders its more practical application. Some
recent studies on the asymmetric catalytic preparation of
BINOLs has given several promising results by using copper
complexes of chiral amines, but a high enantioselectivity has
been obtained only for the coupling of 3-carboalkoxy-2-naph-
3
thols. A photo-activated chiral (NO)Ru(II)–Salen complex has
been evaluated for the aerobic oxidative coupling of 2-napththol
4
derivatives with 33–71% ee. Chen and Uang have independ-
ently developed similar oxovanadium(IV) complexes of chiral
Schiff bases for the asymmetric catalytic coupling of 2-naph-
5
thols to result in moderate enantioselectivities up to 62% ee. In
this catalyst system, the stereo-discrimination depended only on
the chirality in the amino acid. We envisioned that the
enantioselectivity must be improved by introducing another
suitable chiral centre close to the naphthoxy or phenoxy
group(s) in the complex. Based on this idea, we have designed
a novel oxovandium(IV) complexes 1 and 2, as shown in Fig. 1,
which contain double chiral centres (both amino acid and
binaphthyl unit). In addition, these catalysts probably have
helical secondary structures, which might be beneficial for
enantioselectivity.6
a
Table 1 Coupling reaction of 2-naphthol using catalysts 1 and 2a–d
Entry
Catalyst
Time/days Temp./°C Yield (%)b Ee (%)c
1
2
3
4
5
6
7
8
9
1
5
5
5
5
5
5
8
5
5
6
5
8
20
20
10
0
20
10
0
20
10
0
10
0
70
75
74
< 20
84
83
70
90
90
93
6
39
42
50
57
74
81
57
77
83
67
71
2a
2a
2a
2b
2b
2b
2c
2c
2c
2d
2d
10
11
12
a
Fig. 1 The catalysts designed for this study.
86
63
†
Electronic supplementary information (ESI) available: general; repre-
sentative procedure for the preparation of the complexes and coupling of
-naphthols; HRMS spectra of 2b–d; HPLC spectra of 4a–c. See http://
. b Isolated yield. c The ee values were
The reaction was carried out in CCl
4
determined by HPLC on a Kromasil CHI-TBB column, and the absolute
2
configuration is R.
www.rsc.org/suppdata/cc/b201351g/
9
14
CHEM. COMMUN., 2002, 914–915
This journal is © The Royal Society of Chemistry 2002

enantioselectvities of 81% (entry 7), 83% (entry 10) and 71% ee
entry 12), respectively. To the best of our knowledge, these are
the best results so far reported for this oxidative coupling of
In summary, we have designed novel chiral oxovanadium(IV)
(
complexes for the asymmetric catalytic oxidative coupling of
2-naphthols which results in high yields of 86–99%, and with
high enantioselectivities of 83–98% ee.
2
-naphthols. Catalyst 2c is the best reported system for the
catalytic asymmetric coupling of 2-naphthol.
We are grateful for financial support from the National
Science Foundation of China (20102005).
With comparably better chiral catalysts 2b and 2c in hand, we
extended their applications in catalysing the oxidative coupling
of other 2-naphthol derivatives 3b–d and results are shown in
Table 2. In all cases, catalyst 2c, on average, exhibited higher
enantioselectivity than 2b. For the 2-naphthol derivatives 3b–d
tested, the corresponding coupling products 4b–d were afforded
in 86–99% yields and with 83–98% ee. The best enantiose-
lectivity of 98% ee was obtained with 7,7A-dimethoxy-BINOL
Notes and references
‡ General procedure: a two-neck round bottom flask (5 mL) was charged
with a solution of catalyst 2c (16 mg, 0.02 mmol) in anhydrous CCl
The solution was stirred for 10 min under an oxygen atmosphere, and then
treated with a solution of 2-naphthol (29 mg, 0.2 mmol) in CCl (1 mL). The
reaction mixture was stirred at 0 °C until the reaction was complete
monitored by TLC). The crude mixture was concentrated under reduced
4
(1 mL).
4
4
b (Table 2, entry 4) and is the best result among catalytic
(
asymmetric preparations of this type. Optically pure 4b is very
pressure and the residue purified by column chromatography (ethyl acetate–
light petroleum (bp 60–90 °C) (1/3)) to give the desired compound.
useful for the preparation of some novel chiral ligands, such as
8
a multifunctional polymeric catalyst. 3,3A-Dimethoxy-BINOL
was not produced by oxidative coupling in the presence of either
1 (a) L. Pu, Chem. Rev., 1998, 98, 2405; (b) R. Noyori, Asymmetric
Catalysis in the Organic Synthesis, Wiley, New York, 1994; (c) R.
Noyori and H. Takaya, Acc. Chem. Res., 1990, 23, 345.
For resolution of binaphthols, see:(a) B. Feringa and H. Wynberg,
Bioorg. Chem., 1978, 7, 397; (b) F. Toda and K. Tanaka, J. Org. Chem.,
2
b or 2c. Substitution with a methoxy group at C3 suppressed
5b
the coupling reactivity.
2
1
988, 53, 3607; (c) S. Miyano, K. Kawahara, Y. Inoue and H. Hashimoto,
Table 2 Coupling reaction of 2-naphthol and derivatives using catalysts 2b
and 2c
a
Tetrahedron Lett., 1987, 28, 355; (d) W. H. Pirkle and J. L. Schreiner, J.
Org. Chem., 1981, 46, 4988; (e) Q. S. Hu, D. Vitharana and L. Pu,
Tetrahedron: Asymmetry, 1995, 6, 2123; (f) D. Cai, D. L. Hughes, T. R.
Verhoeven and P. J. Reider, Tetrahedron Lett., 1995, 35, 7991; for non-
oxidative methods of chiral binaphthyl synthesis, see; (g) T. Hayashi, K.
Hayashizaki, T. Kiyoi and Y. Ito, J. Am. Chem. Soc., 1988, 110, 8153; (h)
M. Shindo, K. Koga and K. Tomioka, J. Am. Chem. Soc., 1992, 114,
8732; (i) A. N. Cammidge and K. V. L. Crepy, Chem. Commun., 2000,
1723; (j) J. Yin and S. L. Buchwald, J. Am. Chem. Soc., 2000, 122,
12051.
3
(a) M. Nakajima, I. Miyoshi, K. Kanayama and S.-i. Hashimoto, J. Org.
Chem., 1999, 64, 2264; (b) X. Lin, J. Yang and M. C. Kozlowski, Org.
Lett., 2001, 3, 1137 and references therein.
4
5
R. Irie, K. Masutani and T. Katsuki, Synlett, 2000, 1433.
(a) C. Y. Chu, D. R. Hwang, S. K. Wang and B. J. Uang, Chem.
Commun., 2001, 980; (b) S. W. Hon, C. H. Li, J. H. Kuo, N. B. Barhate,
Y. H. Liu, Y. Wang and C. T. Chen, Org. Lett., 2001, 3, 869.
For the studies on the helical polymeric salen complexes, see: (a) H. C.
Zhang, W. S. Huang and L. Pu, J. Org. Chem., 2001, 66, 481; (b) Y. Dai,
T. J. Katz and D. A. Nichols, Angew. Chem., Int. Ed. Engl., 1996, 35,
2109; for helical chiral Lewis acid, see; (c) K. Maruoka, N. Murase and
H. Yamamoto, J. Org. Chem., 1993, 58, 2938; for other chiral catalysts
based on peptides with secondary structures, see; (d) S. J. Miller, G. T.
Copeland, N. Papaioannou, T. E. Horstmann and E. M. Ruel, J. Am.
Chem. Soc., 1998, 120, 1629; (e) S. R. Gilbertson, S. E. Collibee and A.
Agarkov, J. Am. Chem. Soc., 2000, 122, 6522.
Entry
Catalyst
Product
Time/days Yield (%)b Ee (%)c
6
1
2
3
4
5
6
7
8
a
2b
2c
2b
2c
2b
2c
2b
2c
4a
4a
4b
4b
4c
4c
4d
4d
8
6
5
5
5
5
7
7
86
95
85
88
98
99
trace
trace
81
83
97
98
87
88
ND
ND
7 (a) L. J. Theriot, G. O. Carlisle and H. J. Hu, J. Inorg. Nucl. Chem., 1969,
31, 2841; (b) J. J. R. Frausto da Silva, R. Wootton and R. D. Gillard, J.
Chem. Soc. A, 1970, 3369.
The reaction was carried out at 0 °C in the presence of 10 mol% catalyst
b
c
using CCl
4
as solvent. Isolated yield. The ee values were determined by
HPLC on a Kromasil CHI-TBB column.
8
H. B. Yu, Q. S. Hu and L. Pu, J. Am. Chem. Soc., 2000, 122, 6500.
CHEM. COMMUN., 2002, 914–915
915
Typeset and printed by Black Bear Press Limited, Cambridge, England