A new planar chiral bipyridine ligand

Article abstract of DOI:10.1055/s-1999-3443

Combined methods of cyclophane and bipyridine synthesis open the way to the new planar-chiral 2,2'-bipyridine 1, whose CD spectrum is strongly dependent on metal salts. The absolute configuration of the chiral precursor 2 could be assigned by comparison of experimental and theoretical CD spectra. The usefulness of planar chirality in heterocyclic transition metal ligands is revealed in experiments towards stereoselective catalysis using 1.

Full text of DOI:10.1055/s-1999-3443

PAPER
597
A New Planar Chiral Bipyridine Ligand1
Udo Wörsdörfer,a Fritz Vögtle,*a Martin Nieger,b Mirko Waletzke,c Stefan Grimme,c Frank Glorius,d Andreas Pfaltzd
aKekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Gerhard-Domagk-Str.1, 53121 Bonn, Germany
E-mail: voegtle@uni-bonn.de
bAnorganisch Chemisches Institut der Universität Bonn, Gerhard-Domagk-Str.1, 53121 Bonn, Germany
cInstitut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstr.12, 53115 Bonn, Germany
dMax-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
Received 4 September 1998; revised 7 October 1998
The diol 3, generated by reduction of the ester through so-
Abstract: Combined methods of cyclophane and bipyridine synthe-
dium borohydride/calcium chloride in ethanol,9,10 could
sis open the way to the new planar-chiral 2,2’-bipyridine 1, whose
CD spectrum is strongly dependent on metal salts. The absolute
configuration of the chiral precursor 2 could be assigned by com-
be isolated exclusively by using a strongly acidic cation
exchange resin (e.g. Amberlite IR 200 C)11. After bromi-
parison of experimental and theoretical CD spectra. The usefulness nation of the diol,12 we obtained the dibromide 4. Under
high-dilution conditions13 and by taking advantage of the
of planar chirality in heterocyclic transition metal ligands is re-
cesium effect,14 4 was coupled with 1,4-bis(sulfanylmeth-
vealed in experiments towards stereoselective catalysis using 1.
Keywords: [2.2]paracyclophanes, 2,2’-bipyridine, planar chirality,
stereoselective catalysis, circular dichroism
yl)benzene to yield 2,11-dithia[3](1,4)benzeno[3](2,5)py-
ridinophane 5.
Irradiation of 5 with ultraviolet light (Hg, 180 W) in a
thiophilic solvent generated the [2.2]phane 2, the N-oxide
Chiral ligands are the key compounds in asymmetric ca-
talysis.2 A ligand playing a major role in transition metal
complexation is 2,2’-bipyridine, which has been frequent-
ly provided with stereogenic centres. Chiral bipyridines
are not only used in asymmetric synthesis,3 but also for the
organization of stereochemically defined supramolecular4
structures.5
We combined intramolecularly two structural features
that have always been important in stereochemistry as
well as in coordination chemistry, the [2.2]paracyclo-
phane system and the 2,2’-bipyridine complex ligand, re-
sulting in a planar chiral ligand of a new type, 13-
pyridinyl[2](1,4)benzeno[2](2,5)pyridinophane (1).
The number of planar chiral ligands based on ferrocenes
in catalytic asymmetric synthesis is very high.6
A
[2.2]paracyclophane skeleton, however, has rarely been
described so far in this field.7 We now make use of the
special attributes of the [2.2]paracyclophane type scaffold
as chiral unit. It possesses a high sterical demand that is
particularly effective because of its rigidity. Furthermore,
the chiral information is located near to the metal ion, one
side being shielded by the benzene ring.
Reagents and conditions: i, SOCl2, reflux, 8 h, recryst. of acid chlo-
ride (petroleum ether 40/60), then EtOH, reflux, 2 h, 82%; ii, NaBH4
(2 equiv), CaCl2 (1 equiv), EtOH, r.t., 16 h, 67%; iii, HBr/HOAc
(30%), r.t., 6d; iv, sol. A: 4 in EtOH, sol. B: 1,4-bis(sulfanylmeth-
yl)benzene (1 equiv), KOt-Bu (2.3 equiv) in EtOH (85%); Cs2CO3
in mixture, reflux, 16 h, 62%; v, P(OMe)3 , hν (Hg, 180 W), r.t.,
18 h, 84%; vi, MCPBA (2 equiv), CH2Cl2, r.t., 20h, then N,N-
dimethylcarbamoyl chloride (1.3 equiv.), TMSCN (1.3
equiv.), CH2Cl2, r.t., 16 h, 75%; vii, cyclopentadienylcy-
cloocta-1,5-dienecobalt (2 equiv), C2H2 (1.5 bar), toluene,
120 °C, 20 h, 23%.
To obtain the key educt for 1, the [2](1,4)ben-
zeno[2](2,5)pyridinophane (2), which is once mentioned
in literature, but, concerning synthesis and precursors,
was insufficiently described,8 we proceeded from com-
mercially available 2,5-pyridinedicarboxylic acid, which
was converted into the diethyl ester via the acid chloride.
Scheme 1
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598
U. Wörsdörfer et al.
PAPER
of which for the first time was converted into the nitrile 6 To assign these bands to molecular states and to predict
through trimethylsilyl cyanide.15 The hitherto unknown ti- the absolute configuration,17 theoretical calculations of
tle compound 1 (mp 132 °C) was obtained from 6 by ap- the first few singlet excited states and rotatory strengths of
plication of the Bönnemann reaction.16
the corresponding transitions from the ground state have
been performed based on a combination of density func-
tional theory and the singles excitation configuration in-
teraction method (DFT/SCI) which has been proposed by
one of us.18
The enantiomeric resolution of 1 was undertaken by
HPLC on a Daicel Chiralcel OD, 10 x 250 mm semi-
preparative column. A hexane/propan-2-ol mixture was
used as mobile phase, with which complete enantiomeric
separation was achieved. The enantiomers of 2 have been The comparison of theory and experiment allows the as-
separated in a similar way. In order to learn more about signment of the absolute configuration of 2: the (–)-enan-
the chiroptical properties of [2.2]pyridinoparacyclo- tiomer has the (R)-configuration. This result is in
phanes we have investigated the parent compound 2 theo- agreement with the absolute (–)-(R)-configuration of 4-
retically as well and compared theoretical CD spectra with carboxy[2.2]paracyclophane derived independently.19
the experimental data. The experimental CD spectrum of
From similarities between the CD-spectra of 1 and 2, the
2 in methanol shows six resolved CD bands A–F (see Fig-
absolute configuration of 1 can be concluded with high
ure 1).
probability as well. The (–)-enantiomer of 1 has the (R)-
configuration.
The CD spectrum of 1 is strongly dependent on added
metal salts (Figure 2).
Especially with Ag+ and Cu2+ ions, the signal shift is ap-
parent, owing to complex formation in solution. This
demonstrates that the a-substitution of one of the nitrogen
atoms in the 2,2’-bipyridine part does not deteriorate the
coordination properties of the ligand as much as in the
achiral analogue 3,6-dimethyl-2,2’-bipyridine. This also
follows from the X-ray structure of the nitrile 6.20
The boat-shaped distortion of the aromatic rings, typical
for [2.2](1,4)phanes, has the effect that the methylene
group in the a-position to the pyridine nitrogen is distinct-
ly bent out of the plane where metal ion coordination takes
place. So its steric hindrance should be lower in cyclo-
phane-shaped bipyridines compared to planar analogues.
Two orientational catalytic stereoselective reactions were
carried out using the new ligand 1, copper-catalyzed
cyclopropanation21 of styrene with ethyl diazoacetate and
Figure 1 Theoretical and experimental CD spectrum of 2
iridium-catalyzed transfer hydrogenation22 of aceto-
phenone.
Figure 2 Circular dichroism spectrum of 1 depending on added metal salts
Synthesis 1999, No. 4, 597–602 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
A New Planar Chiral Bipyridine Ligand
599
creased ee-values are therefore in progress.
All solvents were freshly distilled before use. The educts were pur-
chased from Fluka, Merck and Aldrich and used without further pu-
rification. Column chromatography was carried out on silica gel 60
(Merck). Mps are uncorrected.
2,5-Bis(hydroxymethyl)pyridine (3)
A patented procedure was modified: To a cooled solution (–10 °C)
of diethyl 2,5-pyridinecarboxylate (25.0 g, 128 mmol) in abs EtOH
(250 mL) NaBH4 (9.70 g, 258 mmol) was added slowly. Then a so-
lution of CaCl2 (14.20 g, 128 mmol) in abs EtOH (88 mL) was add-
ed dropwise into the flask at such a rate that the temperature was
kept below –5 °C. After that, the ice-bath was removed and the mix-
ture was stirred at r.t. for 16 h. Concd H2SO4 (9 ml) was added and
after stirring for 30 min the precipitated CaSO4 was removed by
centrifugation. Now the solvent was evaporated in vacuo and the
colourless oily residue dissolved in H2O (50 mL). This solution was
submitted to ion-exchange chromatography (Amberlite IR 200 C,
900 mL, H+-form). The ion-exchange resin was packed in a column
and washed with H2O. Then, the product solution was put on the
column and it was eluted with water as long as the eluate was acidic.
After that, the column was eluted with diluted NH3 solution (1500
mL, concd NH3 solution/H2O 1/1.5, v/v). This light brown eluate
contains the product. The solvent was removed in vacuo and the res-
idue (brown oil, 12.00 g, 67%) was used for bromination without
further purification.
Figure 3 X-ray Structure of 6
1H NMR (250 MHz, D2O): d = 4.75 (s, 2H; CH2OH), 4.95 (s, 2H;
CH2OH), 7.85 (d, 1H, J = 8.4 Hz, arom), 8.4 (dd, 1H, J = 1.9 Hz and
8.4 Hz, arom), 8.55 (d, 1H, J = 1.9 Hz, arom). EIMS: 140 (5,
[M+H]+), 139 (55, M+), 138 (100, [M–H]+), 122 (13, [M–OH]+).
Experiments on asymmetric synthesis using 1; reagents and condi-
tions: i, 1 (1.3 mol%), Cu(OTf)2, styrene, phenylhydrazine, ethyl di-
azoacetate, CH2Cl2, r.t., 18 h; ii, 1 (2.0 mol%), [IrCODCl]2, HOiPr,
NaOiPr, r.t., 16 h.
2,5-Bis(bromomethyl)pyridine (4)
Compound 3 (12.00 g, 86 mmol) was cooled in an ice-bath and
treated with a solution of HBr in glacial HOAc (30%, 100 mL) and
stirred at r.t. for 6 days. Diluted KOH (25%, 150 mL) was then add-
ed slowly and at pH = 5 a colourless solid precipitated. After filtra-
tion and washing with H2O (100 mL), the product was dried in
vacuo and recrystallized from petroleum ether (40/60). A colourless
solid was obtained, which can be kept in a freezer (–20 °C) for
months, but decomposes slowly to a red solid at r.t.
1H NMR (250 MHz, CDCl3): d = 4.45 (s, 2H; CH2Br), 4.55 (s, 2H;
CH2Br), 7.43 (d, 1H, J = 8.1 Hz, arom), 7.75 (dd, 1H, J = 2.0, 8.0
Hz, arom), 8.6 (d, 1H, J = 1.9 Hz, arom).
Scheme 2
After 18 h (r.t.) the cyclopropanation yielded 47% of the
trans-product with 10% ee (1S,2S) and 25% cis-product
with 23% ee (1S,2R) (1.3 mol% of catalyst). This repre-
sents a trans/cis-ratio of 65:35 (1.86:1). The transfer hy-
drogenation could be carried out at room temperature as
well, in contrast to many other ligands,23 showing the
good activity of the [Ir(1)]-complex. After 16 h, we ob- EIMS: 267 (5, M+), 265 (10, M+), 263 (5, M+), 186 (88, [M–Br]+),
184 (89, [M–Br]+), 105 (100, [M–2Br]+).
tained S-(–)-1-phenylethanol in 91% yield and 31% ee (2
mol% of catalyst).
2,11-Dithia[3](1,4)benzeno[3](2,5)pyridinophane (5)
Solution A: Compound 4 (2.65 g, 10 mmol) in EtOH (270 mL); So-
The rather positive results with the unsubstituted 1 with-
out any optimization by additional substituents demon-
strate again that planar chirality in heterocyclic ligands is
an interesting future option for the design of new chiral
ligands. 1 can be used as a lead structure for a variety of
new, additionally substituted chiral bipyridine ligands and
therewith offers future potential. Studies leading to more
sophisticated planar chiral heterocyclic ligands and in-
lution B: 1,4-Bis(sulfanylmethyl)benzene (1.70 g, 10 mmol) (Ald-
rich) and KOt-Bu (2.50 g, 22 mmol) in a mixture of EtOH (250 mL)
and H2O (20 mL). Both solutions were dropped simultaneously into
a 2 L flask containing EtOH (1 L) and Cs2CO3 (0.20 g). After that,
the mixture was kept under reflux for 16 h and then the solvent was
evaporated in vacuo. The residue was dissolved in CH2Cl2 (150
mL), filtered and purified by column chromatography (silica gel,
Table Selected Bord Lengths (Å), Angles (º) and Torsion Angles (º) of Nitrite 6
C1–C2
C1–C14
1.590 (2)
1.509 (2)
C14–C1–C2
C11–C10–C9
112.90 (10)
112.01 (11)
C3–C4
1.390 (2)
1.390 (2)
1.395 (2)
1.378 (2)
C13–C14–C15
114.17 (11)
120.63 (11)
–17.78 (18)
–17.44 (17)
C4–C5
N12–C11–C16
C14–C15
C15–C16
N12–C11–C16–C15
N12–C13–C14–C15
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U. Wörsdörfer et al.
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CH2Cl2/acetone = 10/1 v/v, Rf = 0.4). A colourless solid melting at
13-Cyano[2](1,4)benzeno[2](2,5)pyridinophane (6)
204 °C (Lit.8 204–205 °C) was obtained (1.70 g, 62%).
To a solution of [2](1,4)benzeno[2](2,5)pyridinophane N-oxide
(0.60 g, 2.67 mmol) in CH2Cl2 (20 mL) was slowly added N,N-dim-
ethylcarbamoyl chloride (0.39 g, 3.7 mmol) in CH2Cl2 (5 mL). After
stirring for 30 min at r.t., TMSCN (0.33 g, 3.3 mmol) in CH2Cl2
(5mL) was added and stirring was continued for 16 h. The mixture
was extracted with aq NaHCO3 (15 mL) and CH2Cl2 (4 x 20 mL).
The organic layer was washed with brine (2 x 30 mL), dried
(Na2SO4) and freed from the solvent in vacuo. Compound 6 was iso-
lated by column chromatography (silica gel; CH2Cl2/MeOH = 30/1
v/v; Rf = 0.5) as a colourless solid melting at 136 °C (0.47 g, 75%).
1H NMR (250 MHz, CDCl3): d = 3.7–4.0 (m, 8H; CH2S), 6.77 (d,
1H, J = 7.8 Hz, arom), 6.86 (d, 1H, J = 7.8 Hz, arom), 6.97 (s, 2H;
arom), 7.0 (d, 1H, J = 8.1 Hz, arom, Py.), 7.42 (dd, 1H, J = 2.0, 8.1
Hz, arom, Py.), 7.9 (d, 1H, J = 1.9 Hz, arom, Py.).
13C NMR (62.86 MHz, CDCl3): d = 34.91, 37.91, 38.3, 39.56 (CH2),
123.61, 129.23, 129.54, 129.77, 129.95, 130.86, 135.24, 135.75,
137.16, 148.69, 155.48 (arom C).
GCMS: Rt= 10.1 min, m/z = 273.
1H NMR (400 MHz, CDCl3): d = 2.95–3.1 (m, 3H; CH2), 3.12–3.31
(m, 4H; CH2), 3.35–3.43 (m, 1H; CH2), 6.39 (dd, 1H, J = 2.0, 7.9
Hz, arom), 6.44 (dd, 1H, J = 1.7, 7.9 Hz, arom), 6.56 (d, 1H, J = 7.9
Hz, arom, Py.), 6.73 (dd, 1H, J = 1.7, 7.9 Hz, arom), 6.87 (d, 1H, J
= 7.9 Hz, arom, Py.), 6.9 (dd, 1H, J = 2.0, 7.9 Hz, arom).
13C NMR (100.6 MHz, CDCl3): d = 32.43, 34.32, 34.48, 37.07
(CH2), 116.86 (CN), 127.24, 130.41, 132.55, 133.35, 133.4, 134.83,
138.18, 138.96, 139.14, 140.78, 162.33 (arom C).
EIMS: 276 (1, M+), 275 (5, M+), 274 (10, M+), 273 (48, M+), 169 (4,
[M–C8H8]+), 139, 138, 137 (15, 10, 5, [M–C8H8S]+), 107, 106 (10,
100, [C7H7N]+).
[2](1,4)Benzeno[2](2,5)pyridinophane (2)8
Compound 5 (3.0 g, 11 mmol) was suspended in P(OMe)3 (300 mL)
and irradiated with UV (Hg, 180 W) at r.t. for 20 h. The trimethyl
phosphite was removed in vacuo and 2 was isolated from the yel-
lowish residue by flash chromatography (silica gel; CH2Cl2/acetone
= 10/2 v/v; Rf = 0.35). A colourless solid was obtained (1.94 g,
84%), mp 147 °C. Enantiomeric resolution: Daicel Chiralcel OD
semipreparative column, 10 x 250 mm (hexane/propan-2-ol = 100/
GCMS: Rt = 8.6 min, m/z = 234.
EIMS: 235 (5, [M+H]+), 234 (32, M+), 104 (100, [C8H8]+), 78 (8,
[C5H4N]+).
1 v/v; 3 mL/min; Rt = 67 and 87 min; [a]D = +176 (1. fraction);
25
HRMS (C16H14N2): calcd 234.1091, found 234.1151.
[a]D25 = –177 (2. fraction); c = 0.0475, CH2Cl2).
1H NMR (400 MHz, CDCl3): d = 2.8–3.3 (m, 8H; CH2), 6.33 (dd,
1H, J = 1.97, 7.87 Hz, arom), 6.36 (d, 1H, J = 7.63 Hz, arom, Py.),
6.38 (dd, 1H, J = 1.97, 7.38 Hz, arom), 6.54 (dd, 1H, J = 1.72, 7.87
Hz, arom), 6.75 (dd, 1H, J = 2.22, 7.63 Hz, arom, Py.), 6.77 (dd, 1H,
J = 1.97, 7.88 Hz, arom), 7.66 (d, 1H, J = 2.22 Hz, arom, Py.).
13C NMR (100.6 MHz, CDCl3): d = 32.79, 34.59, 35.43, 37.12
(CH2), 124.21, 131.69, 132.29, 132.34, 133.53, 133.56, 138.97,
139.07, 139.64, 152.45, 159.78 (arom C).
13-Pyridinyl[2](1,4)benzeno[2](2,5)pyridinophane (1)
An autoclave was charged with a solution of 6 (0.48 g, 2.05 mmol)
and cyclopentadienyl-1,5-cyclooctadienecobalt16 (0.5 g, 2.2 mmol)
in toluene (200 mL). The mixture was stirred at 120 °C under an
acetylene pressure of 1.5 bar for 20 h, during which the acetylene
pressure was kept constant. After cooling to r.t. the solvent was
evaporated in vacuo, the residue dissolved in CH2Cl2 (75 mL), fil-
tered (Celite) and washed with H2O (30 mL). The solution was dried
(Na2SO4) and purified by flash chromatography (silica gel;
CH2Cl2/MeOH/NH3 = 100/10/1 v/v/v). From this raw product 1 was
isolated by column chromatography (silica gel; CH2Cl2/MeOH =
10/1 v/v; Rf = 0.4) to obtain colourless crystals melting at 132 °C
(130 mg, 23%). Enantiomeric resolution: Daicel Chiralcel OD, 10 x
250 mm semipreparative column (hexane/propan-2-ol = 95/10 v/v;
GCMS: Rt= 7.4 min, m/z = 209.
EIMS: 210 (8, [M+H]+), 209 (40, M+), 105 (12 [M–C8H8]+), 104
(100, [C8H8]+), 78 (12, [C5H4N]+).
HRMS (C15H15N): calcd 209.1215, found 209.1205.
2 mL/min; Rt = 28 and 39 min; [a]D25 = –151 (1. fraction); [a]D
+ 151 (2. fraction); c = 0.09, CHCl3).
=
25
[2](1,4)Benzeno[2](2,5)pyridinophane N-Oxide
Compound 2 (0.30 g, 1.43 mmol) was dissolved in CH2Cl2 (25 mL)
and MCPBA (0.55 mg, 3.2 mmol) was added slowly. The mixture
was stirred at r.t. for 20 h. Then it was diluted with CH2Cl2 (15 mL),
washed with 5% NaOH solution (5 x 12 mL) and brine (2 x 12 mL)
and dried (Na2SO4). The solvent was evaporated in vacuo and the
residue purified by column chromatography (silica gel; CH2Cl2/
MeOH = 10/1 v/v; Rf = 0.4) to obtain colourless crystals melting un-
der decomposition at 220 °C (0.27 g, 82%).
1H NMR (400 MHz, CDCl3): d = 2.52 (m, 1H; CH2), 2.65 (m, 1H;
CH2), 2.82–3.14 (m, 4H; CH2), 3.35 (m, 1H; CH2), 3.7 (m, 1H;
CH2), 6.34 (dd, 1H, J = 1.72, 7.87 Hz, arom), 6.4 (d, 1H, J = 8.12
Hz, arom, Py.), 6.44 (dd, 1H, J = 1.96, 7.87 Hz, arom), 6.54 (dd, 1H,
J = 1.97, 7.87 Hz, arom), 6.59 (dd, 1H, J = 1.73, 7.87 Hz, arom),
6.72 (d, 1H, J = 1.48 Hz, arom, Py.), 7.53 (dd, 1H, J = 1.96, 7.87
Hz, arom, Py.).
1H NMR (400 MHz, CDCl3): d = 2.6–2.7 (m, 1H; CH2), 2.8–3.0 (m,
3H; CH2), 3.1–3.3 (m, 3H; CH2), 3.9–4.0 (m, 1H; CH2), 6.38 (dd,
1H, J = 1.7, 7.9 Hz, arom), 6.41 (d, 1H, J = 7.6 Hz, arom, Py.), 6.45
(dd, 1H, J = 1.7, 7.9 Hz, arom), 6.5 (dd, 1H, J = 1.7, 7.9 Hz, arom),
6.7 (dd, 1H, J = 1.7, 7.9 Hz, arom), 6.87 (d, 1H, J = 7.6 Hz, arom,
Py.), 7.23 (ddd, 1H, J = 1.3, 4.7, 7.5 Hz, arom, Bpy.), 7.83 (ddd, 1H,
J = 2.0, 7.6, 7.9 Hz, arom, Bpy.), 8.14 (ddd, 1H, J = 1.0, 1.3, 7.9 Hz,
arom, Bpy.), 8.6 (ddd, 1H, J = 1.0, 2.0, 4.7 Hz, arom, Bpy.).
13CNMR (100.6 MHz, CDCl3): d = 33.74, 34.5, 34.87, 37.09 (CH2),
122.86, 123.52, 123.99, 129.68, 132.02, 132.09, 132.2, 133.1,
136.88, 138.63, 140.22, 142.88, 148.87, 155.72, 158.25, 158.43
(arom C).
GCMS: Rt = 9.9 min, m/z = 286.
EIMS: 287 (4, [M+H]+), 286 (21, M+), 183 (12), 182 (100, [M–
C8H8]+), 181 (50), 155 (2), 154 (3), 104 (6, [C8H8]+), 103 (2), 78 (3,
[C5H4N]+), 77 (2).
13C NMR (100.6 MHz, CDCl3): d = 31.84, 31.89, 32.08, 35.00
(CH2), 127.52, 128.58, 129.66, 130.68, 130.99, 134.55, 137.26,
138.38, 138.45, 144.82, 149.49 (arom C).
HRMS (C20H18N2): calcd 286.1492, found 286.1472. Anal. calcd
for C20H18N2: C 83.88, H 6.34, N 9.78; found C 83.05, H 6.15, N
9.53.
GCMS: Rt = 9.3 min, m/z = 225.
EIMS: 226 (6, [M+H]+), 225 (35, M+), 209 (20, [M–O]+), 165 (4),
119 (6), 104 (100, [C8H8]+), 78 (15, [C5H4N]+).
Copper(I)-Catalyzed Cyclopropanation of Styrene with 1
Cu(OTf)2 (3.6 mg, 0.01 mmol) and 1 (5.7 mg, 0.02 mmol) were dis-
solved in CH2Cl2 (1 mL), giving a green solution. After stirring for
HRMS (C15H15NO): calcd 225.1153, found 225.1153.
Synthesis 1999, No. 4, 597–602 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
A New Planar Chiral Bipyridine Ligand
eds., VCH: Weinheim 1995.
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601
30 min the solution was filtered. Then styrene (88 µL, 0.77 mmol)
and phenylhydrazine (2 µL, 0.02 mmol) were added, resulting in a
brown solution. A solution of ethyl diazoacetate (88 µL, 0.84
mmol) in CH2Cl2 (1 mL) was added dropwise over a period of 5 h.
The reaction was then stirred for 13 h at r.t. Purification was
achieved by flash chromatography (silica gel; pentane/Et2O = 10/1
v/v). To check the results of the asymmetric catalysis reaction, a
GC-system with chiral columns was used (Restek Rtx-1701, 30 m
x 0.25 mm, 0.25 µm, 0.6 bar H2, injector: 220 °C, detector: 320 °C.
Temperature programme: 120–140 °C, 1 °C per min; tR = 14.5 min
(cis-product), tR = 16.9 min (trans-product). Chrompack b-CD-per-
methylated, 25 m x 0.25 mm, 0.5 bar, Injector: 200 °C, Detector:
300 °C. Temperature programme: 90 –120 °C, 0.3 °C per min.; tR =
68.6 / 71.9 min (cis-product: 1S,2R / 1R,2S), tR = 75.5 / 77.1 min
(trans-product: 1R,2R / 1S,2S)). In the reaction 47% of the trans-
product was formed with 10% ee (1S, 2S) and 25% of the cis-prod-
uct with 23% ee (1S, 2R). This corresponds to a trans/cis- ratio of
65:35 or 1.86:1.
Togni, A. Angew. Chem. 1996, 108, 1581; Angew. Chem., Int.
Ed. Engl. 1996, 35, 1475.
(7) Pye, P. J.; Rossen, K.; Reamer, R. A.; Tsou, N. N.; Volante,
R. P.; Reider, P. J. J. Am. Chem. Soc. 1997, 119, 6207.
Pye, P. J.; Rossen, K.; Reamer, R. A.; Volante, R. P.; Reider,
P. J. Tetrahedron Lett. 1998, 4441.
Vetter, A. H.; Berkessel, A. Tetrahedron Lett. 1998, 1741.
(8) Bruhin, J.; Jenny, W. Chimia 1972, 26, 420.
Bruhin, J.; Jenny, W. Tetrahedron Lett. 1973, 1215.
(9) Matsumoto, I.; Yoshizawa, Y. Japan Kokai, 1973, 7329794;
Chem. Abstr. 1973, 79, 31912j.
Transfer-Hydrogenation using [Ir(1)] as Catalyst
Compound 1 (6.0 mg, 0.021 mmol) and [IrCODCl]2 (5.9 mg, 0.009
mmol) were placed in a sealed tube which was flushed with Ar. Af-
ter addition of isopropanol (5 mL) the resulting mixture was stirred
for 1 h. The resulting orange solution was degassed. A 0.10 M solu-
tion of sodium isopropylate in isopropanol (1.3 mL, 0.13 mmol)
was added followed by the addition of acetophenone (103 µL, 0.9
mmol). The mixture was degassed once again and the tube was
sealed. The mixture was stirred at r.t. For GC-analysis an aliqout
was taken and filtered through a small pad of basic alumina. (Chira-
dex g-CD-TA, 30 m x 0.25 mm, 0.5 bar, injector: 200 °C, detector:
300 °C, temperature programme: 5 min isothermal at 50 °C, 50–100
°C, 1 °C per min; tR = 49.1 min (acetophenone), tR = 50.8 min (S-(–
)-1-phenylethanol), tR = 52.1 min (R-(+)-1-phenylethanol)). After 2
h, 49% 1-phenylethanol with 25% ee, after 4 h, 70% 1-
phenylethanol with 31% ee, after 16 h, 91% 1-phenylethanol with
31% ee and after 40 h, 96% 1-phenylethanol with 29% ee (S-(–)-
enantiomer) were formed.
(10) Dawson, M. I.; Chan, R.; Hobbs, P. D.; Chao, W.; Schiff, L. J.
J. Med. Chem. 1983, 26, 1282.
(11) We are grateful to Röhm & Haas AG, Frankfurt, for providing
a free sample of Amberlite IR 200 C.
(12) We thank Prof. T. Shinmyozu, Institute for Fundamental
Research of Organic Chemistry, Kyushu University, Fukuoka,
Japan, for providing this synthetic procedure.
(13) Rossa, L.; Vögtle, F. Top. Curr. Chem. 1983, 113, 1.
Knops, P.; Sendhoff, N.; Mekelburger, H.-B.; Vögtle, F. Top.
Curr. Chem. 1991, 161, 3.
(14) Ostrowicki, A.; Koepp, E.; Vögtle, F. Top. Curr. Chem. 1991,
161, 37.
(15) Modified Reissert-Henze reaction, see e.g.: Fife, W. K. J. Org.
Chem. 1983, 48, 1375.
(16) Bönnemann, H.; Bogdanovic, B.; Brinkmann, R.; He, D.;
Spliethoff, B. Angew. Chem. 1983, 95, 749; Angew. Chem.,
Int. Ed. Engl. 1983, 22, 728.
(17) The agreement of theoretical and experimental CD data is
good, i.e. with the exception of bands C and D all bands are
predicted with the correct sign, good relative intensities and
low errors for the band positions (i.e.< 0.3 eV). The error in
the CD signs of bands C and D may be caused by solvation
effects (pyridine derivative in polar methanol), absent in the
theoretical treatment.
(18) Grimme, S. Chem. Phys. Lett. 1996, 259, 128.
Pischel, I.; Grimme, S.; Kotila, S.; Nieger, M.; Vögtle, F.
Tetrahedron: Asymmetry 1996, 7, 109.
References
(1) A part of this work has been presented at the Symposium of
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(20) X-ray data of 6: C16H14N2, Mr= 234.29, monoclinic, space
group P21/n (No.14), colourless crystals, dimensions 0.25 x
0.30 x 0.40 mm3, a = 7.4660(2), b = 17.5470(6), c = 9.1913(2)
Å, b = 96.366(2)°, U = 1196.69(6) Å3, Dc = 1.30 Mg m–3, Z =
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0.118 {R1 = 0.041 for I > 2 σ(I)}.
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Atomic coordinates, bond lengths and angles, and thermal
parameters have been deposited at the Cambridge
Synthesis 1999, No. 4, 597–602 ISSN 0039-7881 © Thieme Stuttgart · New York

602
U. Wörsdörfer et al.
PAPER
Crystallographic Data Centre. Any request to the CCDC for
this material should quote the full literature citation and the
reference number 102794.
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Synthesis 1999, No. 4, 597–602 ISSN 0039-7881 © Thieme Stuttgart · New York