Nonenzymatic kinetic resolution of 1,2-diols catalyzed by an organotin compound

Article abstract of DOI:10.1021/ol9908373

(matrix presented) A new nonenzymatic kinetic resolution method of 1,2-diols 1 using chiral organotin catalyst A with benzoyl chloride was developed. A remarkable effect due to an inorganic base such as sodium carbonate and a small portion of water on the ee of the main products 2 was observed. The reaction showed high enantio-and chemoselectivities to 1,2-diols 1.

Full text of DOI:10.1021/ol9908373

ORGANIC
LETTERS
1
999
Vol. 1, No. 7
69-972
Nonenzymatic Kinetic Resolution of
,2-Diols Catalyzed by an Organotin
9
1
Compound
Fumiaki Iwasaki, Toshihide Maki, Waka Nakashima, Osamu Onomura, and
†
‡
‡
‡
,§
Yoshihiro Matsumura*
Tsukuba Research Laboratory, Tokuyama Corporation, 40 Wadai,
Tsukuba 300-4247, Japan, Faculty of Pharmaceutical Sciences, Nagasaki UniVersity,
1-14 Bunkyo-machi, Nagasaki 852-8131, Japan, and Institute for Fundamental
Research of Organic Chemistry, Kyushu UniVersity, 6-10-1 Hakozaki, Higashi-ku,
Fukuoka 812-8581, Japan
matumura@ms.ifoc.kyushu-u.ac.jp
Received June 10, 1999
ABSTRACT
A new nonenzymatic kinetic resolution method of 1,2-diols 1 using chiral organotin catalyst A with benzoyl chloride was developed. A remarkable
effect due to an inorganic base such as sodium carbonate and a small portion of water on the ee of the main products 2 was observed. The
reaction showed high enantio- and chemoselectivities to 1,2-diols 1.
Nonenzymatic kinetic resolution is emerging as an important
field of organic chemistry. Some effective catalysts for
Recently, we reported a catalytic monobenzoylation of
diols with benzoyl chloride where a catalytic amount (∼1
mol %) of dimethyltin dichloride selectively worked to
activate the diols, giving monobenzoylated products quan-
1
asymmetric acylation of racemic secondary alcohols or
2
desymmetrization of meso diols have been reported for this
purpose. On the other hand, there is no precedent for the
kinetic resolution of racemic diols using chiral catalysts,
4
titatively (Scheme 1) The successful result of the catalytic
3
except enzymatic methods, despite its synthetic importance.
†
Tokuyama Corporation.
Nagasaki University.
Kyushu University.
Scheme 1. Selective Monobenzoylation of 1,2-Diols
‡
§
Catalyzed by Organotin Compounds
(
1) (a) Vedejs, E.; Daugulis, O.; Diver, S. T. J. Org. Chem. 1996, 61,
4
30. (b) Ruble, J. C.; Fu, G. C. J. Org. Chem. 1996, 61, 7230. (c) Oriyama,
T.; Hori, Y.; Imai, K.; Sasaki, R. Tetrahedron Lett. 1996, 37, 8543. (d)
Ruble, J. C.; Latham, H. A.; Fu, G. C. J. Am. Chem. Soc. 1997, 119, 1492.
(
1
1
e) Kawabata, T.; Nagao, M.; Takasu, K.; Fuji, K. J. Am. Chem. Soc. 1997,
19, 3169. (f) Copeland, G. T.; Jarvo, E. R.; Miller, S. J. J. Org. Chem.
998, 63, 6784.
(
2) (a) Oriyama, T.; Imai, K.; Hosoya, T.; Sano, T. Tetrahedron Lett.
1
998, 39, 397. (b) Oriyama, T.; Imai, K.; Sano, T.; Hosoya, T. Tetrahedron
process prompted us to extend the reaction to an asymmetric
version. We present herein the first chemoselective kinetic
Lett. 1998, 39, 3529. (c) Otera, J.; Sakamoto, K.; Tsukamoto, T.; Orita, A.
Tetrahedron Lett. 1998, 39, 3201.
1
0.1021/ol9908373 CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/31/1999

resolution of racemic 1,2-diols using a chiral organotin
catalyst.
recovered 1a was enriched with the (R)-enantiomer in a 36-
87% yield. A small amount of 1-benzoylated diol 3a (0-
8
1
0%) was found, but no dibenzoylated product.
Racemic 1-phenyl-1,2-ethanediol (1a) was used as a
The results showed the remarkable effects of chiral tin
representative example of 1,2-diols, and (S)-4,4-dibromo-
5
catalyst A, the type of base, and water on the ee of 2a.
Namely, the absence of A in the reaction system did not
result in resolution of 1a (runs 1 and 2), though 2a was
formed in moderate yields (theoretically, the maximum yield
is 50% since the amount of benzoyl chloride was 0.5 equiv
to 1a). On the other hand, the presence of A afforded a result
with a resolution of 1a (runs 4-12). Although triethylamine
4
,5-dihydro-3H-dinaphtho[2,1-c:1′,2′-e]stannepin (A) syn-
6
thesized according to the reported method was employed
as a chiral organotin catalyst (Scheme 2).
Scheme 2. Kinetic Resolution of 1-Phenyl-1,2-ethanediol (1a)
with Catalyst A
gave an unsuccessful result with respect to the ee of 2a (run
9
3
), sodium carbonate as a suspended state gave an ap-
preciable degree of ee (32%) of 2a (run 4), which was
improved to 58% ee if a small amount of water was present
(run 5). However, the ee decreased in the presence of a large
amount of water (run 6), where sodium carbonate was
completely dissolved to give a homogeneous solution. In
contrast, with sodium carbonate, triethylamine was not
effective even though water was present (run 7).
1
0
Although the selectivity (s value) did not vary much in
the temperature range of 0 to -30 °C (runs 8-11), the yield
of 2a dropped when the reaction was carried out at -30 °C
(
run 11). The reaction at -40 °C resulted in both low ee
The reaction was carried out under a variety of conditions,
and the results are summarized in Table 1. The main product
was (S)-enantiomer-enriched 2-benzoyloxy-1-phenylethanol
1
1
and low yield (run 12). The best selectivity was obtained
when the reaction was performed using sodium carbonate
in the presence of a small amount of water at -10 °C (run
9
).
The procedure for the best result (run 9) is as follows.
Table 1. Kinetic Resolution of Diol 1a by Benzoylation with
Catalyst Aa
Sodium carbonate (1.5 mmol) as a base was suspended in
THF (5 mL) containing 1a (1 mmol), water (100 µL, 5.5
mmol), and 0.25 mol % of A. Then into the suspension was
added benzoyl chloride (0.5 mmol) at -10 °C, and the
resulting solution was stirred at that temperature for 14 h.
After the usual workup, a mixture of 2a (86% ee, 38% yield)
and recovered 1a (46% ee, 58% yield) was obtained with a
trace amount of 3a.
On the basis of these results, we applied this method to
various 1-substituted 1,2-ethanediols 1b-e. The results are
summarized in Table 2.
(
3) (a) Chenault, H. K.; Chafin, L. F.; Liehr, S. J. Org. Chem. 1998, 63,
4
039. (b) Egri, G.; Baitzz-G a´ cs, E.; Poppe, L. Tetrahedron: Asymmetry
1996, 7, 1437. (c) Theil, F.; Weidner, J.; Ballschuh, S.; Kunath, A.; Schick,
H. J. Org. Chem. 1994, 59, 388. (d) Weidner, J.; Theil, F.; Schick, H.
Tetrahedron: Asymmetry 1994, 5, 751. (e) Theil, F.; Weidner, J.; Ballschuh,
S.; Kunath, A.; Schick, H. Tetrahedron Lett. 1993, 34, 305. (f) Theil, F.;
Ballschuh, S.; Kunath, A.; Schick H. Tetrahedron: Asymmetry 1991, 2,
1
031.
(4) Maki, T.; lwasaki, F.; Matsumura, Y. Tetrahedron Lett. 1998, 39,
5
601.
(5) Noyori, R.; Kitamura, M.; Takemoto, K. Japan Kokai Tokkyo Koho
JP 04-91093, 1992; Chem. Abstr. 1992, 117, 171695u.
(6) (a) Nanni, D.; Curran, D. P. Tetrahedron: Asymmetry 1996, 7, 2417.
(b) Maigrot, N.; Mazaleyrat, J.-P. Synthesis 1985, 317.
(7) Brown, J. M.; Murrer, B. A. J. Chem. Soc., Perkin Trans. 2 1982,
489.
a
Reaction conditions: 1a (1.0 mmol), BzCl (0.5 mmol), THF (5 mL).
b
Determined by CSP HPLC analysis (for 2a, Chiralcel OB column; 254
nm; n-hexane:i-PrOH ) 9:1). Corrected value based on the ee of used A
91%). Isolated yield based on starting 1a. (+); (S)-isomer. See ref 10.
c
d
e
f
(
(
8) (R)-Enantiomer-enriched 3a with 0-59% ee was generated.
(
9) Potassium carbonate was usable. Satisfactory results were obtained
by using solid bases pulverized as small as possible.
(
10) Kagan, H. B.; Fiaud, J. C. Top. Stereochem. 1988, 18, 249.
(2a), and its ee was determined by CSP HPLC analysis. The
(11) There has recently appeared an interesting temperature-dependent
absolute configuration of 2a was confirmed by alkaline
switching of enantioselectivity (<42.3% ee) in a desymmetric carbam-
oylation of 2-substituted 1,3-propanediol using catalyst A; see ref 2c.
However, the enantioselectivity in A-catalyzed benzoylation of the 1,3-
diol was 0% in our hand.
hydrolysis followed by comparison of the specific rotation
7
of the resulting 1a with that of an authentic sample. The
970
Org. Lett., Vol. 1, No. 7, 1999

Table 2. Kinetic Resolution of Diols 1b-e by Benzoylation
Scheme 4. Enantioselective Benzoylation of 1,2-Diol by a
with Catalyst Aa
Chiral Organotin Catalyst
Since the observed ee was strongly dependent on the type
of base (Table 1) and it has been well documented that
stannylene acetals are easily acylated without bases by
1
2
various acid chlorides, the first step may be responsible
for the enantiodiscrimination of racemic 1, which may occur
on the surface of sodium carbonate.
Thus, we propose a mechanism for the kinetic resolution
of 1a using A as depicted in Scheme 5. That is, when amine
a
Determined by CSP HPLC analysis. b Isolated yield. c See ref 10.
Scheme 5. A Mechanism for Resolution of 1a with Catalyst
A
Moderate selectivities were also observed for the A-
catalyzed benzoylation of 1b-e in which the 2-benzoylated
diols 2b-e were enriched with (S)-enantiomer and 1-ben-
zoylated products were found in trace amounts. Other 1,2-
diols such as trans-1,2-cyclohexanediol afforded poor results
under similar reaction conditions.
The other remarkable property of our method was its 1,2-
diol selectivity. That is, 1a was efficiently resolved even in
the presence of an equimolar amount of cyclohexanol (1f)
(Scheme 3). The ee of 2a in the reaction was almost
Scheme 3. Chemoselective Kinetic Resolution of 1a in the
Presence of Cyclohexanol (1f)
unaffected by the presence of 1f, though a small amount of
cyclohexyl benzoate (2f) was formed. This result suggests
that the initiation step involves formation of stannylene acetal
as an intermediate as described below.
The resolution reaction presented here may involve two
crucial steps: formation of stannylene acetal B by the
reaction of 1 with chiral tin catalyst A (first step) and
benzoylation of B with benzoyl chloride (second step)
is used as a base, stannylene acetals B may be formed in a
solution phase (THF) in which A approaches the primary
hydroxyl group of 1a from as far away as possible from a
bulky phenyl group (route a in Scheme 5). According to this
hypothesis, there seems to be no significant difference
between the accessibility of A toward (S)-1a and (R)-1a.
On the contrary, when sodium carbonate is used as the
base, the hydrophilic 1,2-diol moiety of 1a may be adsorbed
(Scheme 4). The formation of B is supported by the high
chemoselective formation of 2a with a high ee from a mixture
of 1a and 1f (Scheme 3).
Org. Lett., Vol. 1, No. 7, 1999
971

on the surface of the sodium carbonate, directing the
hydrophobic phenyl group toward the solution phase (THF)
required. On the other hand, our method was based on the
selective activation of 1,2-diols by a chiral organotin catalyst
and therefore the process could possess not only a high
enantioselectiVity but also a high chemoselectiVity.
Our report presents complementary information for the
design of new artificial enzymes to allow for the recognition
of both acylating reagents and substrates.
(route b in Scheme 5). In the presence of a small amount of
water, a thin aqueous phase is formed on the surface of the
sodium carbonate and, as the result, the adsorption of 1a is
assisted by hydrogen bonding as depicted in Scheme 5.
Provided that this hypothesis is true, A should approach from
the solution phase in a manner that allows the steric repulsion
between A and the phenyl group to be as small as possible.
Thus, the discrimination of (S)-1a from (R)-1a takes place
since a steric repulsion between the methylene group of A
and the phenyl group of (S)-1a is less than that between A
and (R)-1a.
A detailed mechanistic study and development of new
chiral organotin catalysts are under investigation.
Acknowledgment. This study was supported by a Grant-
in-Aid for Scientific Research on Priority Areas No. 706
(Dynamic Control of Stereochemistry) and No.11771414
In conclusion, we report the first catalytic system for
nonenzymatic kinetic resolution of 1,2-diols. Since the known
acylating catalysts for 1,2-diols work by activating acylating
reagents, further modification to recognize substrates is
from the Ministry of Education, Science, and Culture, Japan.
One of the authors (T.M.) also thanks Daicel Chemical
Industries for general financial support.
Supporting Information Available: Full experimental
and analytical data for all new compounds; the conditions
of HPLC analysis for 2b-e; the specific rotations of 2b-e.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(
12) Acylation of dibutylstannylene acetals was well documented, for
example: (a) Hanessian, S.; David, S. Tetrahedron 1985, 41, 643 and
references therein. (b) Ricci, A.; Roelens, S.; Vannucchi, A. J. Chem. Soc.,
Chem. Commun. 1985, 1457. (c) Roelens, S. J. Chem. Soc., Perkin Trans
1988, 1617. (d) Reginato, G.; Ricci, A.; Roelens, S.; Scapecchi, S. J.
Org. Chem. 1990, 55, 5132. (e) Roelens, S. J. Org. Chem. 1996, 61, 5257.
f) Hanessian, S.; Reinhold, U.; Gentile, G. Angew. Chem., Int. Ed. Engl.
997, 36, 1881.
2
(
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