A new asymmetric synthesis of optically active allenes via metal catalyzed hydrosilylation

Article abstract of DOI:10.1016/S0022-328X(00)00206-0

The Rh and Ni catalyzed hydrosilylation of butadiynes to chiral allenes in the presence of chiral phosphine ligands is described. For the first time an enantiomeric excess up to 27% was achieved using [Rh(COD)Cl]₂/(-)-PPM and up to 11% using Ni

Full text of DOI:10.1016/S0022-328X(00)00206-0

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 603 (2000) 116–121
A new asymmetric synthesis of optically active allenes via metal
catalyzed hydrosilylationꢀ
Annegret Tillack *, Cornelia Koy, Dirk Michalik, Christine Fischer
Institut fu¨r Organische Katalyseforschung an der Uni6ersita¨t Rostock e.V., Buchbinderstraße 5-6, D-18055 Rostock, Germany
Received 22 November 1999; received in revised form 3 April 2000
Abstract
The Rh and Ni catalyzed hydrosilylation of butadiynes to chiral allenes in the presence of chiral phosphine ligands is described.
For the first time an enantiomeric excess up to 27% was achieved using [Rh(COD)Cl]2/(−)-PPM and up to 11% using
NiCl2[(−)-DIOP]. © 2000 Published by Elsevier Science S.A. All rights reserved.
Keywords: Asymmetric hydrosilylation; Butadiynes; Chiral allenes; Rhodium complexes; Nickel complexes; Chiral phosphines
1. Introduction
butadiynes. In 1985, Kusumoto and Hiyama reported
the first example of hydrosilylation of 1,4-
a
Allenes are of great importance in organic chemistry
as very useful intermediates, their synthesis and applica-
tion are described in detail in the literature [1]. In
particular, allenylsilanes serve as valuable three-carbon
components in a general [3+2] annulation method,
which provides efficient access to a variety of highly
substituted furan derivatives, these again represent im-
portant intermediates for the syntheses of pharmaceuti-
cals and flavors and fragrant compounds [2]. Many
syntheses of chiral allenes of high enantiomeric purity
start from chiral precursors [3], but relatively few syn-
theses are known in which the chirality is induced by a
chiral catalyst. To the best of our knowledge the Palla-
dium catalyzed cross-coupling reaction of 4,4-dimethyl-
1,2-pentadiene and iodobenzene in the presence of
chiral phosphine ligands is the only example of a transi-
tion metal catalyzed enantioselective allene synthesis
[4]. Here we report on a further example of a transition
metal catalyzed synthesis of chiral allenes via asymmet-
ric hydrosilylation. In general, allenes can be synthe-
sized in high yields by hydrosilylation of enynes [5] and
bis(trimethylsilyl)-1,3-butadiyne catalyzed by H2PtCl6,
RhCl(PPh3)3 or Pt(PPh3)4, which gives an enyne (A)
and/or an allene (B) (Scheme 1) [6].
Recently, we reported on the hydrosilylation of
disubstituted butadiynes to allene derivatives in the
presence of achiral L2Ni(0)-butadiyne catalysts [7].
Now we started investigations of asymmetric hydrosily-
lation of substituted 1,3-butadiynes in the presence of
transition metal complexes (e.g. Rh, Ir, Ni, Pd, Pt) and
chiral ligands.
Scheme 1.
ꢀ A preliminary report of this work has been published: A. Tillack,
D. Michalik, C. Koy, M. Michalik, Tetrahedron Lett. 40 (1999) 6567.
* Corresponding author. Tel.: +49-381-4669360; fax: +49-381-
4669324.
E-mail address: annegret.tillack@ifok.uni-rostock.de (A. Tillack)
Scheme 2.
0022-328X/00/$ - see front matter © 2000 Published by Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00206-0

A. Tillack et al. / Journal of Organometallic Chemistry 603 (2000) 116–121
117
Table 1
Results of catalytic hydrosilylation of tBuꢀCꢁCꢀCꢁCꢀtBu with
Me2PhSiH in the presence of [Rh(COD)Cl]2/L at 70°C in toluene
(substrate:silane=1:4, substrate:Rh=50:1, 24 h)
Entry
Ligand
Yield (%)
ee (%) (conf.) a
2
3
1
2
3
4
5
6
7
8
9
(S)-(+)-NMDPP
(2S,3S)-(+)-Norphos
(R)-(+)-QUINAP
(3R,4R)-Pyrphos
(4R,5R)-(−)-DIOP
(R)-(+)-BINAP
(2S,4S)-(−)-BPPM
(3R,4R)-(−)-POP-BZ
(2S,4S)-(−)-PPM
\90
\90
92
67
53
41
56
56
66
B1
B1
7
n.d.
n.d.
n.d.
n.d.
Racemate
Racemate
Racemate
5
4
25
30
21
35
27
22
a The absolute configuration was not determined; optical rotation
sign of crude product: (−) (THF).
Fig. 1. Molecular structure of compound 1 shown by an ORTEP plot
,
at the 30% probability level. Selected bond distances (A) and angles
(°): C(4)ꢀC(5) 1.346(3), C(5)ꢀC(5a) 1.460(4), Si(1)ꢀC(4) 1.886(2),
Si(2)ꢀC(4) 1.880(2); C(4)ꢀC(5)ꢀC(5a) 127.6(2), C(5)ꢀC(4)–Si(1)
121.7(2), Si(2)ꢀC(4)ꢀSi(1) 121.04(11), C(5)ꢀC(4)–Si(2) 117.3(2).
bis(trimethylsilyl)-1,3-butadiene (1) crystallized from
the reaction mixture. The structure was proved by
X-ray analysis (Fig. 1). Compound 1 was formed via
cis-addition of the silane. It was the first time that we
observed addition of both silyl groups at the outer
C-atoms. IR spectroscopy revealed the presence of a
second product in the reaction mixture, which was
proved to be an allene (2) because of the characteristic
absorption at 1883 cm−1 (w(CꢂCꢂC)). However, isola-
tion from the isomeric mixture was not possible.
Thus, as a model reaction the hydrosilylation of
2,2,7,7-tetramethyl-3,5-octadiyne with dimethylphenyl-
silane was studied (Scheme 3). Depending on the reac-
tion conditions the hydrosilylation gives two reaction
products, the monohydrosilylation product 3 and the
dihydrosilylation product (allene) 4.
Scheme 3.
2. Results and discussion
More than 30 chiral phosphine ligands have been
tested in situ in the presence of [Rh(COD)Cl]2; for
instance, monophosphines (e.g. (S)-(+)-NMDPP),
chelate ligands (P/P and P/N ligands, e.g. (2S,3S)-(+)-
2.1. Catalysis with Rh complexes
In order to find an appropriate model reaction, we
investigated the reaction of different butadiynes
(PhꢀCꢁCꢀCꢁCꢀPh, Me3SiꢀCꢁCꢀCꢁCꢀSiMe3, tBuꢀCꢁ
CꢀCꢁCꢀtBu) using different silanes (Ph2SiH2,
Me2PhSiH, Et3SiH) in the presence of [Rh(COD)Cl]2
and DIOP. Me2PhSiH was found to be most suitable.
Formation of disilanes was observed when Ph2SiH2 was
used. Due to the formation of hydrogen, hydrogenation
products could be detected as well as the desired hy-
drosilylation components, and it was not worth work-
ing up the reaction mixture. On the other hand, Et3SiH
was not reactive enough. The investigated butadiynes
showed different behavior. No formation of allenes
could be observed when PhꢀCꢁCꢀCꢁCꢀPh was reacted
in the presence of Me2PhSiH. Two disilylation products
have been found when Me3SiꢀCꢁCꢀCꢁCꢀSiMe3 was
used (Scheme 2). (E,E)-1,4-bis(dimethylphenylsilyl)-1,4-
Norphos,
(2S,3S)-(−)-Chiraphos,
(2S,3S,4S,5S)-
Rophos-benzene [8], (3R,4R)-Pyrphos [9], (R)-(+)-
QUINAP, (S)-(−)-Amphos [9], (2S,3S)-(−)-BDPP,
(4R,5R)-(−)-DIOP, (R)-(+)-BINAP, (2S,4S)-(−)-
BPPM, (2S,4S)-(−)-PPM, (3R,4R)-(−)-POP-BZ [9],
Ph-b-Glup [9], (RC,SFe)-(−)-BPPFA, (S)-(+)-Pro-
lophos [9]. Selected results are given in Table 1 (ligand
structures see Fig. 2). Monophosphines and five- and
six-membered chelates favor the formation of 3.
Allene 4 is obtained by using ligands forming seven-
membered chelates. For the first time an enantiomeric
excess of 5% and 22% was obtained in the presence of
ligands POP-BZ and PPM. In contrast to PPM, no
enantioselection was obtained with BPPM, a ligand
with an electron-withdrawing substituent at the pyrro-
lidine nitrogen atom.

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A. Tillack et al. / Journal of Organometallic Chemistry 603 (2000) 116–121
Both ligands differ in the substituent at the nitrogen
substantial difference in the yield or in the enantiomeric
excess. The conversion is too low when the temperature
is decreased down to 50°C. Also THF and chloroform
as solvents cause a drastic lowering in conversion.
Without any solvent, but an excess of silane, the con-
version increases, followed by a decrease in the ee
values.
We observed a slight increase of the ee values with
Et3N as solvent. However, due to the lower solubility of
the starting compounds, the yields turned to be much
lower.
atom. Achiwa [10] showed that an additional coordina-
tion of the nitrogen to the rhodium atom exists in the
non-substituted PPM. This hemilabile effect seems to
influence positively the induction of chirality. The role
of this N-substituent must still be clarified.
Furthermore, the effect of different reaction condi-
tions such as temperature, reaction time, solvents, and
additives on the enantiomeric excess was investigated
(Table 2). An increase in temperature up to 90°C or a
decrease in reaction time down to 8 h did not show a
Fig. 2. Selected phosphine ligands (see Table 1).
Table 2
Hydrosilylation of BuꢀCꢁCꢀCꢁCꢀtBu with Me2PhSiH in the presence of [Rh(COD)Cl2]/PPM under different reaction conditions
t
Entry
Solvent
Temperature (°C)
t (h)
Yield (%)
ee (%) a
2
3
1
2
3
4
5
6
7
Toluene
Toluene
Toluene
THF
CHCl3
Et3N
70
70
90
70
70
70
70
24
8
6
24
24
24
24
66
58
73
83
47
80
51
27
21
23
6
2
15
39
22
23
21
n.d.
n.d.
25
Without
15
a Optical rotation sign of crude product: (−) (THF).

A. Tillack et al. / Journal of Organometallic Chemistry 603 (2000) 116–121
119
Table 3
added at the inner or outer C-atoms depends on the
substrate, the silane, and the catalyst.
Effect of Et3N as additive at the hydrosilylation of
tBuꢀCꢁCꢀCꢁCꢀtBu with Me2PhSiH in the presence of [Rh(COD)Cl2]/
PPM (toluene; 70°C; 24 h; substrate:silane=1:4, substrate:Rh=50:1)
2.2. Catalysis with Ir, Pd and Pt complexes
Entry
n(NEt3) (mmol)
Yield (%)
ee (%) a
Besides Rh catalysts, (COD)PtCl2, (COD)PdCl2 and
[Ir(COD)Cl]2 with PPM were also investigated as pre-
2
3
t
catalysts with BuꢀCꢁCꢀCꢁCꢀtBu in the presence of the
1
2
3
4
0.02
0.05
0.07
0.10
60
53
50
54
35
31
34
30
22
25
20
27
silanes Me2PhSiH and Ph2SiH2. The Pd complex de-
composed with precipitation of metal during the reac-
tion after the silanes have been added. On the other
hand, when the Ir complex was used no reaction oc-
curred in the presence of Me2PhSiH, whereas the Pt
complex only formed the enyne 3. With Ph2SiH2 as
reagent, in both cases, formation of the allene was not
observed.
a Optical rotation sign of crude product: (−) (THF).
2.3. Catalysis with Ni complexes
Scheme 4.
For the investigation of hydrosilylation with chiral
Ni(II) complexes, such as NiCl2[(−)-DIOP] and
NiCl2[(−)-PPM], Me3SiꢀCꢁCꢀCꢁCꢀSiMe3 was chosen
as substrate and Ph2SiH2 as silane component (Scheme
4).
Neither formation of disilane or hydrogen nor reac-
tion to the enyne was observed in the presence of
Ph2SiH2.
In contrast to the Rh catalyzed reaction, ee values
were found in both cases (Table 4). We were able to
show that besides Rh complexes, it is also possible to
induce chirality using chiral Ni complexes.
It is known that achiral additives can influence dras-
tically the enantioselectivity and yields [11]. We investi-
gated this effect in the case of Et3N. A remarkable
influence could not be observed (Table 3). The ee values
reached 27% when 0.1 mmol Et3N was added to the
reaction mixture (Table 3, entry 4). Small amounts of
additives did not change the solubility considerably,
and that is why yields were not affected compared with
the reaction when using Et3N as solvent. Now the
influence of other achiral amine additives is investi-
gated.
Hiyama [6b] discussed the fact that hydrosilylation of
butadiynes proceeds stepwise. The first addition of hy-
dridosilane leads to the cis-product with a regioselectiv-
ity that hydrogen adds at C(1) and silicon at C(2) to
give products of type 3 (enynes). The second addition
of hydridosilane leads to products of 1,3-butadiynes via
another 1,2-addition of CꢁC bond of enyne but with
different regioselectivity or, alternatively, to allene via
1,4-addition. We assume that the hydrosilylation does
not proceed in a two-step mechanism. It is likely to be
a concerted reaction because the allene did not form
3. Experimental
All operations were carried out in an inert atmo-
sphere (argon). Toluene and THF were freshly distilled
from sodium tetraethylaluminate under argon prior to
use. Chloroform was distilled from CaH2. The starting
materials, metal complexes, butadiynes, silanes and lig-
ands (NMDPP, Norphos, Chiraphos, QUINAP,
BDPP, DIOP, BINAP, BPPM, PPM, BPPFA), were
commercially available (STREM, Fluka, Aldrich).
NiCl2[(−)-DIOP] was synthesized according to the
literature method [12]. The following spectrometer were
when the enyne
3
was used instead of the
tBuꢀCꢁCꢀCꢁCꢀtBu under the same conditions de-
scribed above. We also observed only cis-addition of
the silanes in the reaction. Whether the silyl groups are
Table 4
Results of catalytic hydrosilylation of Me3SiꢀCꢁCꢀCꢁCꢀSiMe3 with Ph2SiH2 in toluene (substrate:silane=1:4, substrate:Ni=50:1, 24 h)
Entry
Catalyst
Temperature (°C)
Yield (%)
ee (%) (sign of rot.)
1
2
3
4
NiCl2[(−)-DIOP]
NiCl2[(−)-DIOP] a
NiCl2[(−)-DIOP]
NiCl2[(−)-PPM]
70
70
90
70
9
8
11
49
9 (+)
8 (+)
11 (+)
7 (+)
a Without solvent.

120
A. Tillack et al. / Journal of Organometallic Chemistry 603 (2000) 116–121
used: NMR, Bruker ARX 400; IR, Nicolet Magna 550;
MS, AMD 402; C,H-analysis, Leco CHNS 932-Ana-
lyzer. Melting points were measured on a Bu¨chi 535
apparatus. HPLC was performed with a Liquid Chro-
matograph 1090 series II equipped with DAD
(Hewlett–Packard) and Chiralyser (IBZ Messtechnik
GmbH, Hanover). Separations were carried out on
CHIRALCEL OD-H analytical column 4.6×250 mm
I.D (Daicel).
298 (23) [M+], 283 (20) [M+−Me], 241 (9) [M+−
tBu], 163 (4) [M+−SiMe2Ph], 135 (100) [(SiPhMe2)+],
57 (6) [tBu+]. IR (neat, cm−1): 1428 and 1113
(w(PhꢀSi)), 1249 (ls(MeꢀSi)). Anal. Calc. for C20H30Si
(298.54): C, 80.46; H, 10.13. Found: C, 80.35; H,
10.59%.
3.2.3. 3,5-Bis(dimethylphenylsilyl)-
2,2,7,7-tetramethyl-3,4-octadiene (4) [7]
1H-NMR (CDCl3): l (ppm) 0.34, 0.36, 0.39, 0.43 (4s,
12H, SiMe2Ph); 0.89, 1.01 (2s, 18H, CMe3); 1.70 (d,
3.1. General procedures of hydrosilylation
1H, JHa,Hb:14.5 Hz, Hb, CH2); 1.83 (d, 1H, JHa,Hb
:
Under inert conditions, a mixture of 1 mmol of
butadiyne, 0.02 mmol of the ligand and 0.01 mmol of
[Rh(COD)Cl]2 (or 0.02 mmol of L2NiCl2) were dis-
solved in 1 ml of solvent and stirred for 10 min at room
temperature.
A certain amount of amine was added in the case
when additives were used (see Table 3). Then 4 mmol of
silane were added and the mixture was stirred for 24 h
at 70°C. The yields were determined by gas chromatog-
raphy and dodecane was used as internal standard.
Afterwards, toluene and silane were removed in
vacuo. The residue was purified by column chromatog-
raphy (eluent: n-hexane; Silica Gel 60 (Merck)).
14.5 Hz, Ha, CH2); 7.30–7.35, 7.45-7.55 (m, 10H, Ph).
13C-NMR (CDCl3): l (ppm) −2.8, −2.3, 0.0, 0.1
(SiPhMe2); 29.7, 31.5 (CMe3); 32.3, 35.0 (CMe3); 42.5
(CH2); 85.7, 96.9 (CꢂCꢂC); 128.5, 128.7 (p-Ph); 127.3,
127.4, 134.0, 134.1, (2m-Ph, 2o-Ph); 138.4, 140.0 (i-Ph);
206.9 (CꢂCꢂC). 29Si-NMR (CDCl3): l (ppm) −9.6,
−7.2 (SiPhMe2). MS (70 eV): m/z (rel. int. (%)) 434
(19) [M+], 419 (9) [M+−Me], 377 (5) [M+−tBu], 135
(100) [(SiPhMe2)+], 57 (12) [tBu+]. IR (neat, cm−1):
1880 (w(CꢂCꢂC)), 1428 and 1111 (w(PhꢀSi)), 1246
(ls(MeꢀSi)). Anal. Calc. for C28H42Si2 (434.81): C,
77.35; H, 9.74. Found: C, 77.52; H, 9.97%.
3.2.4. 1,3-Bis(diphenylsilyl)-1,4-bis(trimethylsilyl)-
1,2-butadiene (5) [7]
3.2. Characterization of reaction products
1H-NMR: l (ppm) −0.07 (s, 9H, 1-SiMe3); −0.04
(s, 9H, 4-SiMe3); 1.07 (d, 1H, JHa,Hb:15.0 Hz, Hb,
CH2); 1.31 (d, 1H, JHa,Hb:15.0 Hz, Ha, CH2); 5.09 (s,
1H, 3-SiH); 5.11 (s, 1H, 1-SiH); 7.27–7.52 (m, 20H,
Ph). 13C-NMR: l (ppm) −0.8 (4-SiMe3); −0.1 (1-
3.2.1. (E,E)-1,4-Bis(dimethylphenylsilyl)-1,4-
bis(trimethylsilyl)-1,3-butadiene (1)
Colorless crystals (n-hexane); yield 10%; m.p. 93–
1
94°C. H-NMR (CDCl3): l (ppm) 0.00 (s, 18H, SiMe3);
0.39 (s, 12H, SiMe2); 7.33 (m, 4H, m-Ph); 7.33 (m, 2H,
p-Ph); 7.42 (s, 2H, CH); 7.46 (m, 4H, o-Ph). 13C-NMR
(CDCl3): l (ppm) −1.0 (2SiMe2); 1.6 (2 SiMe3); 127.8
(4m-Ph); 128.8 (2p-Ph); 134.0 (4o-Ph); 139.6 (2i-Ph);
147.8 (2CSi2); 154.9 (2CH). 29Si-NMR (CDCl3):
l(ppm) −8.9 (2JSiꢀH:6.5 Hz, 2SiMe3); −4.1
(2JSiꢀH:6.5 Hz, 2SiMe2). MS (70 eV): m/z (rel. int.
(%)) 466 (4) [M+], 316 (31), 243 (34), 135 (100)
[(SiPhMe2)+], 73 (66) [(SiMe3)+]. IR (KBr, cm−1):
1428 and 1114 (w(PhꢀSi)), 1251 (ls(CH3ꢀSi)). Anal.
Calc. (%) for C26H42Si4 (466.96): C, 66.88; H, 9.07.
Found: C, 66.72; H, 9.18%.
Table 5
Crystallographic data for compound 1
1
Formula
C26H42Si4
466.96
Prism
Colorless
0.5×0.3×0.2
P1
Formula weight (g mol−1
)
Crystal
Color
Crystal size (mm)
Space group
Z
(
2
,
a (A)
6.6070(10)
11.134(2)
11.960(2)
117.42(3)
104.14(3)
91.49(3)
747.4(2)
1.037
0.209
2225
2225
1818
,
b (A)
,
c (A)
3.2.2. (E)-4-Dimethylphenylsilyl-2,2,7,7-tetramethyl-
3-octen-5-yne (3) [7]
h (°)
i (°)
k (°)
1H-NMR (CDCl3): l (ppm) 0.38 (s, 6H, SiMe2Ph);
1.18 and 1.19 (s, 18H, CMe3); 5.92 (s, 1H, CH); 7.33
(m, 3H, m-/p-Ph); 7.56 (m, 2H, o-Ph). 13C-NMR
(CDCl3): l (ppm) −3.1 (SiMe2); 28.5 (CꢁCꢀCMe3);
29.6 (Me3CꢀCꢂ); 30.8 (Me3CꢀCꢁ); 35.7 (Me3CꢀCꢂ);
78.6 (CꢁCꢀCMe3); 109.6 (CꢁCꢀCMe3); 120.2
(ꢂCꢀSiMe2Ph); 127.5 (m-Ph); 128.9 (p-Ph); 134.1 (o-
Ph); 138.2 (i-Ph); 159.2 (CH). 29Si-NMR (CDCl3): l
(ppm) −7.3 (SiPhMe2). MS (70 eV): m/z (rel. int. (%))
3
,
V (A )
Dcalc (g cm−3
)
Absorption coefficient (mm−1
Reflection measured
Unique reflections
Observed reflection (I]2|I)
No. of parameters
R1
)
140
0.0372
0.1366
wR2 (all data)

A. Tillack et al. / Journal of Organometallic Chemistry 603 (2000) 116–121
121
SiMe3); 16.0 (4-C); 69.1 (3-C); 73.9 (1-C); 127.7 (2m-Ph);
Acknowledgements
127.79, 127.82 (m-Ph); 129.5 (4p-Ph); 133.4, 133.5 (3-i-
Ph); 134.2, 134.5 (1-i-Ph); 135.6 (3o-Ph); 135.8 (o-Ph);
210.7 (2-C). 29Si-NMR: l (ppm) −20.5 (1JSiꢀH:189.9
Hz, 1-SiPh); −13.9 (1JSiꢀH:192.0 Hz, 3-SiPh); −1.6
(2JSiꢀH:23.7 Hz, 1-SiMe3); 2.5 (2JSiꢀH:22.6 Hz, 4-
SiMe3).
The authors wish to thank the Deutsche Forschungs-
gemeinschaft for financial support, Professor Dr M.
Beller for helpful discussions, Professor Dr H. Brunner
and co-workers of the IfOK for a gift of ligands,
especially Dr V. Tararov for the ligand POP-BZ, and Dr
A. Spannenberg for the X-ray analysis of 1. Furthermore,
we thank Ch. Mewes, A. Modler, and B. Harzfeld for
technical assistance.
3.2.5. Preparation of NiCl2[(−)-PPM]
NiCl2[(−)-PPM] was prepared according to the pro-
cedure for the synthesis of NiCl2[(−)-DIOP] [12b].
Green solid; MS (FAB): m/z (rel. int. (%)) 546 [90,
M+−Cl], 511 [34, M+−2Cl].
References
3.2.6. X-ray structure determination of 1
X-ray diffraction data were collected on a STOE-IPDS
diffractometer using Mo–Ka radiation (u=0.71073 A).
The structure was solved by direct methods [13a] and
refined by full-matrix least-squares techniques against F2
[13b]. Crystallographic data for 1 are given in Table 5.
[1] (a) D.J. Pasto, Tetrahedron 40 (1984) 2805. (b) H.F. Schuster,
G.M. Coppola, Allenes in Organic Synthesis, Wiley, New York,
1984. (c) C. Bruneau, P.H. Dixneuf, A.R. Katritzky, O. Meth-
Cohn, C.W. Rees (Eds.), Comprehensive Organic Functional
Group Transformations, vol. 1, Pergamon, Oxford, 1995 (Chapter
20). (d) M. Manoharan, P. Venuvanalingen, J. Chem. Soc. Perkin
Trans. 2 (1996) 1423. (e) I. Ikeda, K. Honda, E. Osawa, M. Shiro,
M. Aso, K. Kanematsu, J. Org. Chem. 61 (1996) 2031. (f) R.
Lunkwitz, K. Zab, C. Tschierske, J. Prakt, Chem.-Chem. Ztg. 340
(1998) 662. (g) M. Purpura, N. Krause, Eur. J. Org. Chem. (1999)
267 and refs therein.
,
3.2.7. Methods of determination of enantiomeric excess
In general, enantiomeric excesses are determined by
gas chromatography and HPLC, respectively. The deter-
mination of enantiomers of allene 5 was carried out by
HPLC (see Table 4). In order to achieve the enantiomeric
resolution normal phase systems with different chiral
stationary phases were used. A Chiralcel OD-H column
showed the best results. Baseline resolution was obtained
with an 100% n-hexane eluent. Various chiral columns
were tested to separate both enantiomers of allene 4. In
the case of GC no separation could be observed whereas
a partial separation could be achieved by means of
HPLC, which was unfortunately too inaccurate for an ee
determination. Therefore, investigations with shift
reagents were carried out to determine the enantiomeric
purity by NMR spectroscopy. It is known that certain
chiral lanthanoid shift reagents (CLSR) together with
silver(I) complexes induce a signal separation in several
alkenes [14]. In the 1H-NMR spectra of 4 with Yb(hfc)3/
Ag(fod) the signals of both the CH2 and the tert-butyl
group were separated. Details will be given in [15]. The
enantiomeric excess was determined using the tert-butyl
signals. The results are given in Tables 1–3.
[2] R.L. Danheiser, E.J. Stoner, H. Koyama, D.S. Yamashita, C.A.
Klade, J. Am. Chem. Soc. 111 (1989) 4407.
[3] (a) C.J. Elsevier, in: G. Helmchen, R.W. Hoffmann, J. Mulzer, E.
Schumann (Eds.), Houben-Weyl series Methods of Organic Chem-
istry, vol. E21a, Thieme Verlag, Stuttgart, 1995, pp. 537. (b) A.G.
Myers, B. Zheng, J. Am. Chem. Soc. 118 (1996) 4492. (c) P.H.
Dixneuf, T. Guyot, M.D. Ness, S.M. Roberts, Chem. Commun.
(1997) 2083.
[4] W. de Graaf, G. van Knoten, C.J. Elsevier, J. Organomet. Chem.
378 (1989) 115.
[5] (a) Y. Maruyama, K. Yoshiuchi, F. Ozawa, Y. Wakatsuki, Chem.
Lett. (1997) 623. (b) Y. Maruyama, K. Yamamura, I. Nakayama,
K. Yoshiuchi F. Ozawa, J. Am. Chem. Soc. 120 (1998) 1421, and
refs therein.
[6] (a) T. Kusumoto, T. Hiyama, Chem. Lett. (1985) 1405. (b) T.
Kusumoto, K. Ando, T. Hiyama, Bull. Chem. Soc. Jpn. 65 (1992)
1280.
[7] A. Tillack, S. Pulst, W. Baumann, H. Baudisch, K. Kortus, U.
Rosenthal, J. Organomet. Chem. 532 (1997) 117.
[8] J. Holz, M. Quirmbach, U. Schmidt, D. Heller, R. Stu¨rmer, A.
Bo¨rner, J. Org. Chem. 63 (1998) 8031.
[9] H. Brunner, W. Zettlmeier, Handbook of Enantioselective Catal-
ysis, vol. II, VCH, Weinheim, 1993, and refs therein.
[10] Y. Ohga, Y. Iitaka, K. Achiwa, Chem. Lett. (1980) 861.
[11] E.M. Vogl, H. Gro¨ger, M. Shibasaki, Angew. Chem. 111 (1999)
1672; Angew. Chem. Int. Ed. 38 (1999) 1570.
[12] V. Gramlich, G. Consiglio, Helv. Chim. Acta 62 (1979) 1016. (b)
A. Wille, Dissertation, Universita¨t Gesamthochschule Kassel,
1997.
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited at the Cambridge Crystallographic Data
Centre, CCDC no. 136870 for compound 1. Copies of
this information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ,
UK (Fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
[13] (a) G.M. Sheldrick, SHELXS-86, Acta Crystallogr. Sect. A 46 (1990)
467. (b) G.M. Sheldrick, SHELXL-93, University of Go¨ttingen,
Germany, 1993, unpublished.
[14] (a) A. Mannschreck, W. Munninger, T. Burgemeister, J. Gore, B.
Cazes, Tetrahedron 42 (1986) 399. (b) T.J. Wenzel, R.E. Sievers,
J. Am. Chem. Soc. 104 (1982) 382. (c) T.J. Wenzel, NMR Shift
Reagents, CRC Press, Boca Raton, FL, 1987 (Chapter 3).
[15] M. Michalik, C. Koy, D. Michalik, A. Tillack, submitted.