Asymmetric synthesis of 1-aryl-1,2-ethanediols from arylacetylenes by palladium-catalyzed asymmetric hydrosilylation as a key step

Article abstract of DOI:10.1021/ja017617g

Double hydrosilylation of arylacetylenes with trichlorosilane catalyzed first by platinum and second by a chiral monophosphine-palladium complex generated the corresponding 1,2-bis(silyl)-1-arylethanes, the oxidation of which with hydrogen peroxide gave 1-aryl-1,2-diols of high enantiomeric purity (94-98% ee) in high yields. Copyright

Full text of DOI:10.1021/ja017617g

Published on Web 02/20/2002
Asymmetric Synthesis of 1-Aryl-1,2-ethanediols from Arylacetylenes by
Palladium-Catalyzed Asymmetric Hydrosilylation as a Key Step
Toyoshi Shimada, Kotaro Mukaide, Akihiro Shinohara, Jin Wook Han, and Tamio Hayashi*
Department of Chemistry, Graduate School of Science, Kyoto UniVersity, Sakyo, Kyoto 606-8502, Japan
Received November 27, 2001; Revised Manuscript Received January 8, 2002
Scheme 1
Methods of transforming alkynes into 1,2-diols have not been
well developed so far due to the difficulty in the addition of water
or its synthetic equivalent twice in a regioselective manner.1
Especially, asymmetric synthesis of 1,2-diols from alkynes by this
transformation is a formidable challenge in organic synthesis.
Recently, Weissensteiner has reported the first example of this type
of asymmetric transformation using rhodium-catalyzed asymmetric
hydroboration of an alkenylboronic ester which is accessible by
hydroboration of phenylacetylene,2 but the selectivity in giving diol
or the enantioselectivity is not high enough despite his extensive
studies on the reaction conditions. Our plan is to use the catalytic
asymmetric hydrosilylation3 as a key step (Scheme 1). If the double
hydrosilylation took place with high regioselectivity and with high
enantioselectivity4 and the oxidation of the resulting 1,2-disilyl-
alkanes into 1,2-diols5 proceeded in a high yield without loss of
their enantiomeric purity, the asymmetric synthesis of 1,2-diols from
alkynes would be successful.
Scheme 2
Our initial studies were focused on the screening of chiral
transition metal catalysts which are capable of promoting double
hydrosilylation of phenylacetylene (1a) giving 1,2-bis(silyl)phen-
ylethane. It was found that the double hydrosilylation takes place
with trichlorosilane in the presence of a palladium complex
coordinated with axially chiral monodentate phosphine ligands
(MOP),6,7 though the selectivity in giving 1,2-bis(trichlorosilyl)-
phenylethane (2a) was not high enough. Thus, as one of the best
examples, the reaction of 1a with 4.5 equiv of trichlorosilane in
the presence of 0.3 mol % (Pd) of a palladium catalyst generated
from [PdCl(π-C3H5)]2 and (R)-2-bis[3,5-bis(trifluoromethyl)phen-
yl]phosphino-1,1′-binaphthyl (3)8 (two equivalents to Pd) at 20 °C
for 72 h (Scheme 2) gave 33% yield of 1,2-bis(trichlorosilyl)-
phenylethane (2a) together with 60% yield of 1-trichlorosilyl-2,4-
diphenyl-1,3-butadiene (4).9 The oxidation of 2a with hydrogen
peroxide in the presence of potassium fluoride10 gave (R)-phenyl-
1,2-ethanediol (5a)11,12 of 95% ee in 91% yield (based on 2a). The
high enantiomeric purity of 5a may demonstrate that the oxidation
of 1,2-bis(trichlorosilyl)alkane 2a proceeded without loss of ster-
eochemistry as has been observed for the oxidation of mono(silyl)-
alkanes.3,10 Monitoring the palladium-catalyzed hydrosilylation of
1a by GLC analysis revealed that most of the phenylacetylene (1a)
is consumed in 24 h to give (E)-1-phenyl-2-trichlorosilylethene (6)
and 4 in a ratio of about 1 to 2 and the mono-hydrosilylation product
6 is slowly converted into the double hydrosilylation product 2a at
the later stage. In a separate experiment, the reaction of mono-
hydrosilylation product 6 with trichlorosilane catalyzed by 0.3 mol
% of the palladium/(R)-3 complex at 20 °C for 42 h gave 96%
yield of 1,2-bis(trichlorosilyl)alkane 2a which is the (R) isomer of
96% ee. It follows that the palladium/(R)-3 complex catalyzes the
second hydrosilylation with perfect regioselectivity and with high
Scheme 3
enantioselectivity13 though the first hydrosilylation is accompanied
by the dimerization-hydrosilylation of alkyne forming 4.
Although the asymmetric double hydrosilylation catalyzed by
the palladium/(R)-3 complex gave the diol 5a with high enantio-
selectivity, the yield is not high enough. On the basis of the report
that the platinum-catalyzed hydrosilylation of 1-alkynes gives a high
yield of (E)-1-(silyl)-1-alkenes,14 [PtCl2(C2H4)]215 was used for the
hydrosilylation of phenylacetylene (1a) with trichlorosilane. At 20
°C for 16 h, the reaction with 0.01 mol % of the platinum catalyst
gave 97% yield of 6 together with a small amount of its regioisomer,
1-phenyl-1-trichlorosilylethene (1%), and 1-phenyl-2-trichloro-
silylethane (2%). It is important that the selectivity in forming 6 is
high and the platinum does not catalyze the second hydrosilylation
under the reaction conditions. These results indicate that the high-
yield asymmetric double hydrosilylation of acetylene 1a in one pot
should be realized by use of the platinum catalyst for the first-step
hydrosilylation and the palladium/(R)-3 catalyst for the second-
step16 (Scheme 3). Thus, to a mixture of phenylacetylene (1a) (1.02
g, 10.0 mmol) and [PtCl2(C2H4)]2 (0.3 mg, 1 µmol Pt) was added
trichlorosilane (4.5 mL, 45 mmol), and the mixture was stirred at
20 °C. After consumption of 1a (24 h), a solution of [PdCl(π-
C3H5)]2 (5.5 mg, 30 µmol Pd) and (R)-3 (43 mg, 60 µmol) in toluene
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1584 VOL. 124, NO. 8, 2002 J. AM. CHEM. SOC.
10.1021/ja017617g CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
Scheme 4
provides a new efficient and practical route to enantiomerically
enriched 1,2-diols, which have been mainly prepared from alkenes
by the catalytic asymmetric oxidation reactions.17,18
Acknowledgment. This work was supported by the Research
for the Future program, the Japan Society for the Promotion of
Science, and a Grant-in-Aid for Scientific Research, the Ministry
of Education, Japan.
Table 1. Catalytic Asymmetric Synthesis of 1,2-Diols 5 Starting
from Arylacetylenes 1 by Successive Platinum- and
Palladium-Catalyzed Hydrosilylationa
Supporting Information Available: Experimental procedures and
spectroscopic and analytical data for the substrates and products (PDF).
This material is available free of charge via the Internet at http://
pubs.acs.org.
time (h)
c
acetylene
yieldb (%)
of 5
%ee of
[R]20D of
5 (c 1.0)
entry
1
Ptd
Pde
5 (config)
1f
2
3
1a
1a
1b
1c
1d
1e
24
24
18
24
24
20
48
48
24
72
168
72
87 (5a)
75 (5a)
83 (5b)
75 (5c)
50 (5d)
67 (5e)
95 (R)
95 (R)
95 (R)
94 (R)
96 (R)
98 (R)
References
-36.4 (EtOH)
-64.9 (CHCl3)
-57.0 (CHCl3)
-46.0 (CHCl3)
-26.8 (MeOH)
(1) This transformation has been attempted by double hydroboration followed
by oxidation, but the selectivity in giving 1,2-diols is very low because
of the low regioselectivity at the hydroboration: (a) Brown, H. C.; Zweifel,
G. J. Am. Chem. Soc. 1961, 83, 3834. (b) Pasto, D. I. J. Am. Chem. Soc.
1964, 86, 3039.
4
5g
6g
(2) Wiesauer, C.; Weissensteiner, W. Tetrahedron: Asymmetry 1996, 7, 5.
(3) For reviews on catalytic asymmetric hydrosilylation of alkenes see: (a)
Nishiyama, H.; Itoh, K. In Catalytic Asymmetric Synthesis, 2nd ed.; Ojima,
I., Ed.; VCH: New York, 2000; pp 111-143. (b) Hayashi, T. In
ComprehensiVe Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A.,
Yamamoto, H., Eds.; Springer: Berlin, Germany, 1999; Vol. 1, Chapter
7. (c) Hayashi, T. Acta Chem. Scand. 1996, 50, 259.
(4) There have been no reports on the asymmetric synthesis of 1,2-
disilylalkanes to our best knowledge.
(5) Oxidation of a 4,5-bis(silyl)oxacyclohexan-2-one and a 3,4-bis(silyl)-
cyclohexene into the corresponding diols with retention of configuration
at the stereogenic carbon atoms has been reported: (a) Fleming, I.; Ghosh,
S. K. J. Chem. Soc., Chem. Commun. 1992, 1777. (b) Chen, R.-M.; Weng,
W.-W.; Luh, T.-Y. J. Org. Chem. 1995, 60, 3272.
a The double hydrosilylation was carried out at 20 °C in a one-pot
reaction. The platinum catalyst [PtCl2(C2H4)]2 and the palladium catalyst
generated from [PdCl(π-C3H5)]2 and (R)-3 were used for the first-step and
the second-step hydrosilylation, respectively. The hydrogen peroxide
oxidation was carried out for the crude hydrosilylation products 2. The ratio
of 1/HSiCl3/Pt/Pd/(R)-3 is 1/4.5/0.0001/0.003/0.006. b Isolated yield. c De-
termined by HPLC analysis with chiral stationary phase columns: Daicel
Chiralcel OB-H (5a) (eluent, hexane/2-propanol ) 90/10), double OB-H
(5b, 5e) (eluent, hexane/2-propanol ) 90/10), AS (5c, 5d) (eluent, hexane/
2-propanol ) 90/10). d Reaction time for the platinum-catalyzed hydrosi-
lylation. e Reaction time for the palladium/3-catalyzed hydrosilylation.
f After the second-step hydrosilylation, the oxidation was carried out for
the distilled 2a. g With 0.006 equiv (to arylacetylene) of [PdCl(π-C3H5)]2
and 0.012 equiv of (R)-3.
(6) For a review of MOP ligands see: Hayashi, T. Acc. Chem. Res. 2000,
33, 354.
(7) With chelating bisphosphine ligands such as binap or chiraphos the
hydrosilylation did not take place, the starting acetylene being recovered.
(8) The MOP ligand 3 is the most enantioselective ligand for the asymmetric
hydrosilylation of styrene derivatives: (a) Hayashi, T.; Hirate, S.;
Kitayama, K.; Tsuji, H.; Torii, A.; Uozumi, Y. J. Org. Chem. 2001, 66,
1441. (b) Hayashi, T.; Hirate, S.; Kitayama, K.; Tsuji, H.; Torii, A.;
Uozumi, Y. Chem. Lett. 2000, 1272.
(1 mL) was added, and the whole mixture was stirred at the same
temperature for 48 h. Distillation under reduced pressure gave 3.60
g (96% yield) of 1,2-bis(trichlorosilyl)phenylethane (2a), which was
subjected to the oxidation with hydrogen peroxide in the presence
of potassium fluoride and potassium hydrogen carbonate to give
1.20 g (87% yield from 1a) of (R)-phenyl-1,2-ethanediol (5a) whose
enantiomeric purity is 95%.12 Oxidation of the double hydrosily-
lation product 2a without isolation is also possible, though the
overall yield is somewhat lower, probably due to the decomposition
of hydrogen peroxide during the oxidation by the platinum and/or
palladium catalysts used for the hydrosilylation (entries 1 and 2 in
Table 1).
(9) The formation of dimerization-hydrosilylation product 4 has been reported
in palladium-catalyzed hydrosilylation of terminal alkynes with trichlo-
rosilane: Kawanami, Y.; Yamamoto, K. Synlett 1995, 1232.
(10) (a) Tamao, K. In AdVances in Silicon Chemistry; Larson, G. L., Ed.; JAI
Press: Greenwich, 1996; Vol. 3, pp 1-62. (b) Tamao, K. In Organosilicon
and Bioorganosilicon Chemistry; Sakurai, H., Ed.; Halsted Press: New
York, 1985; pp 231-242.
(11) [R]20 -36.4 (c 1.00, EtOH) (ref 12; [R]20 -38.4 (c 1.12, EtOH) for
D
D
(R)-5a). The enantiomeric purity was determined by HPLC analysis with
a chiral stationary phase column, Chiralcel OB-H (hexane/2-propanol )
90/10).
(12) Becker, H.; King, B. S.; Taniguchi, M.; Vanhessche, K. P. M.; Sharpless,
K. B. J. Org. Chem. 1995, 60, 3940.
The catalytic asymmetric synthesis of 1-aryl-1,2-diols 5b-e
containing substituents on the phenyl ring was also successful from
the corresponding arylacetylenes 1b-e. The results obtained for
the successive platinum- and palladium-catalyzed hydrosilylation
followed by oxidation of the crude bis(silyl)ethanes are summarized
in Table 1. The enantioselectivity is all high (ranging between 94%
and 98% ee) irrespective of the electron-donating or -withdrawing
characters of the substituents on the phenyl (entries 3-6). It also
should be noted that the hydrosilylation was carried out (1) without
solvent, (2) in the presence of a very small amount of the catalysts,
and (3) at room temperature (20 °C). Unfortunately, alkyl-
substituted acetylenes cannot be converted into the corresponding
1,2-diols by the present method because the second palladium-
catalyzed hydrosilylation is very slow.
(13) The hydrosilylation of styrenes substituted with alkyl groups at the
â-position in the presence of Pd/3 catalyst gave high yields of benzylic
silanes of over 97% ee (ref 8).
(14) Tamao, K.; Yoshida, J.; Yamamoto, H.; Kakui, T.; Matsumoto, H.;
Takahashi, M.; Kurita, A.; Murata, M.; Kumada, M. Organometallics
1982, 1, 355.
(15) (a) Buss, P. J.; Greene, B.; Orchin, M. Inorg. Synth. 1980, 20, 181. (b)
Buss, P.; Orchin, M. J. Organomet. Chem. 1977, 128, 85.
(16) The hydrosilylation in the presence of both the platinum and the palladium/
(R)-3 catalysts at the same time was not successful, which resulted in the
formation of the hydrosilylation products of the same composition as the
palladium/(R)-3-catalyzed reaction, because the platinum does not catalyze
the hydrosilylation in the presence of phosphine ligands.
(17) Asymmetric dihydroxylation: (a) Hentges, S. G.; Sharpless, K. B. J. Am.
Chem. Soc. 1980, 102, 4263. (b) Kolb, H. C.; VanNieuwenhze, M. S.;
Sharpless, K. B. Chem. ReV. 1994, 94, 2483. (c) Jonsson, S. Y.;
Fa¨rnegårdh, K.; Ba¨ckvall, J.-E. J. Am. Chem. Soc. 2001, 123, 1365.
(18) Asymmetric epoxidation: (a) Katsuki, T.; Sharpless, K. B. J. Am. Chem.
Soc. 1980, 102, 5974. (b) Zhang, W.; Loebach, J. L.; Wilson, S. R.;
Jacobsen, E. N. J. Am. Chem. Soc. 1990, 112, 2801. (c) Katsuki, T. J.
Mol. Catal. A: Chem. 1996, 113, 87. (d) Wong, M.-K.; Ho, L.-M.; Zheng,
Y.-S.; Ho, C.-Y.; Yang, D. Org. Lett. 2001, 3, 2587.
In summary, we have realized the asymmetric synthesis of 1,2-
diols from arylacetylenes by use of the palladium-catalyzed
asymmetric hydrosilylation as a key step. The present method
JA017617G
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