Synthesis of JOSIPHOS-type ligands via a diastereoselective three-component reaction and their application in asymmetric rhodium-catalyzed hydroborations

Article abstract of DOI:10.1016/j.tetasy.2005.08.051

The recently reported diastereoselective three-component reaction for the synthesis of chiral propargylamines was used for a new stereoselective synthesis of JOSIPHOS-type ligands 2a-d. The present synthesis gives the desired diphosphines in good yields without the need of resolution. Ligands 2a-d were applied to the rhodium-catalyzed hydroboration of styrene.

Full text of DOI:10.1016/j.tetasy.2005.08.051

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 16 (2005) 3385–3393
Synthesis of JOSIPHOS-type ligands via a
diastereoselective three-component reaction and their application
in asymmetric rhodium-catalyzed hydroborations
Shuji Yasuike, Christiane C. Kofink, Ralf J. Kloetzing, Nina Gommermann, Katja Tappe,
Andrei Gavryushin and Paul Knochel*
Department of Chemistry of Ludwig-Maximilians-University, Butenandtstrasse 5-13, 81377 Munich, Germany
Received4 August 2005; accepted30 August 2005
Available online 20 October 2005
Abstract—The recently reporteddiastereoselective three-component reaction for the synthesis of chiral propargylamines was used
for a new stereoselective synthesis of JOSIPHOS-type ligands 2a–d. The present synthesis gives the desired diphosphines in good
yields without the need of resolution. Ligands 2a–d were applied to the rhodium-catalyzed hydroboration of styrene.
Ó 2005 Elsevier Ltd. All rights reserved.
1. Introduction
JOSIPHOS has foundindustrial applications in rho-
8
dium-7 andiridium-catalyzed
hydrogenation reactions
Ferrocenyl ligands occupy a special place in enantio-
while new applications are continuously being devel-
1,2
selective transition-metal catalyzedreactions.
Due to
oped.9 JOSIPHOS is a very versatile ligandsince the
B
their conformational rigidity, the facile combination of
planar chirality andthe presence of stereogenic centers
in side chains, the versatile ferrocene framework
facilitatedthe preparation of very efficient ligands for
asymmetric synthesis. In particular, ferrocene-based
diphosphines were used successfully as ligands for selec-
tive asymmetric reductions.3 UgiÕs amine4 provedto be
an excellent starting point for the synthesis of ferrocenyl
ligands, as was demonstrated by Hayashi and Kumada
(BPPFA).5 In his pioneer investigations, Togni has used
UgiÕs amine to prepare JOSIPHOS,6 one of the most
successful ligands for asymmetric catalysis (Scheme 1).
substituents RA andR
can be varied independently
allowing the modular synthesis of broad libraries of
ligands (Scheme 1).
Recently, we reporteda new copper-catalyzedenantio-
selective three-component reaction for the synthesis of
chiral progargylamines (Scheme 2).10
OMe
N
OMe
+
CuBr (5 mol%)
toluene
R1 CHO
R2
+
N
R1
H
R2
PRB
N(CH3)2
N(CH3)2
2
up to 99% de
Scheme 2. Diastereoselective three-component reaction.
Fe
PRA
2
Fe
Fe
PPh2
PPh2
(R)-(S)-JOSIPHOS
1a: RA: phenyl
RB: cyclohexyl
(R)-(S)-BPPFA
Ugi's amine
Benzaldehyde (R1 = Ph) reacts with phenylacetylene
(R2 = Ph) and( S)-2-(methoxymethyl)pyrrolidine to give
the corresponding progargylamine in high yield and dia-
stereoselectivity (87%, 92% de). This reaction allows the
formation of a new carbon–carbon bondanda stereo-
genic center with excellent control of stereochemistry
in a single step.
Scheme 1. Important ferrocenyl ligands.
*
Corresponding author. Tel.: +49 (0) 89 2180 77681; fax: +49 (0) 89
2180 77680; e-mail: paul.knochel@cup.uni-muenchen.de
0957-4166/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2005.08.051

3386
S. Yasuike et al. / Tetrahedron: Asymmetry 16 (2005) 3385–3393
We herein report the synthesis of JOSIPHOS derivatives
using the new efficient three-component reaction, since
this excellent ligandis a rewarding objective for enantio-
selective organic synthesis.
The copper-catalyzedthree-component reaction of fer-
rocene carbaldehyde 5, (S)-2-(methoxymethyl)-pyrrol-
idine12 6 andseveral terminal alkynes
7a–c gave
amines 4a–c with goodyields andexcellent diastereose-
lectivity. The silyl protection group in 4a was cleaved
hydrolytically by aqueous KOH (Scheme 4).
2. Synthesis
The hydrogenation of acetylene 8 to amine 9 with Pd/C
in methanol was accompaniedby the reductive cleavage
of the C–N bondat the a-position of the ferrocene to
give propyl-ferrocene 10 as a side product. Various addi-
tives andsolvents were examinedin order to improve
the yieldof amine 9 (Scheme 5 and Table 1).
This new approach shouldenable us to prepare an ethyl
analogue of JOSIPHOS in an efficient stereoselective
approach. Compound 2a features an alkyl group in
the side chain whereas JOSIPHOS 1a has a methyl
group at this position.
The key intermediate of this synthesis is amine 3, which
allows the preparation of ligands 2a–d using the same
methods as Togni applied for the synthesis of JOSI-
PHOS 1a starting from UgiÕs amine.6a,11 We planned
to prepare amine 3 by reduction of the triple bond and
substitution of the amine from the ferrocenyl propargyl-
amine 4 according to the retrosynthetic analysis depicted
in Scheme 3.
Without an additive (entry 1 of Table 1), the ratio of
side product 10 andproduct 9 was 2:1. The addition
of sodium hydroxide solution reduced the amount of
side product 10. The yieldof proudct
9 couldbe
improved, but the hydrogenation became less efficient
andthe substantial amounts of olefin 11 were isolated
(entry 2). The addition of amines (entries 3 and 4)
completely inhibitedthe reaction. Other solvents such
OMe
PRB
NMe2
N
2
PRA
TMS
Fe
Fe
Fe
2
2a-d
RA, RB = Ph, cy
3
4
OMe
CHO
TMS
N
H
Fe
5
6
7
Scheme 3. Retrosynthetic analysis.
OMe
R
N
CuBr (5 mol %)
CHO
OMe
Fe
R
+
+
Fe
MS 4Å, toluene
rt, 5 d
N
H
5
4a-c
6
7a-c
7a
7b
7c
R = SiMe3
CH2OMe
tert-Butyl
4a: 74%, de >98%
4b: 86%, de 95%
4c: 80%, de >98%
OMe
OMe
TMS
N
N
1 M KOH aq.
MeOH
rt, 1.5 h
Fe
Fe
H
4a
Scheme 4. Three-component reaction anddeprotection.
8: 93%

S. Yasuike et al. / Tetrahedron: Asymmetry 16 (2005) 3385–3393
3387
sample preparedfrom the alcohol (by CBS-reduction
of the corresponding ferrocenyl ketone)13 andshowed
essentially the same specific rotation. This provedthat
our procedure furnishes amine 3 in an enantiomerically
pure form as the (R)-enantiomer. The overall yieldstart-
ing from propargylamine 4 was 68% (four steps).
OMe
OMe
H
N
N
H2
Fe
Pd/C (1 mol %)
1 bar, rt
Fe
8
9
Like UgiÕs amine,14 ferrocenyl amine 3 can undergo a
diastereoselective ortho-lithiation. This reaction was
carriedout with tert-butyllithium in ether at 0 °C. The
OMe
reaction with two different chlorophosphines (RA = Ph,
N
15
c-Hex) andprotection
ledto the borane complexes
Fe
13a,b in good yields. Only one diastereomer was
observedby NMR spectroscopy ( Scheme 7). Unlike
JOSIPHOS, these ethyl derivatives can be easily oxi-
dized by air during work-up. Their purification requires
a borane protection.
Fe
11
10
Scheme 5. Hydrogenation of alkyne 8.
Nucleophilic substitution of amines 13a and b with
phosphines (RB = Ph, c-Hex) andprotection gave the
borane complexes 14a–d. These stable complexes can
be easily hanleddin air andpurifiedvia flash-
chromatography.
Table 1. Hydrogenation of alkyne 8a
Solvent Additive
Time (h) Yield (%)b
9
1
0
1
1
1
2
3
4
5
MeOH
EtOH
EtOH
EtOH
—
1.5
2
3
3
2
28 56
43 24 32
—
2.0 M NaOH (10 mol %)
Et3N (15 mol %)
Quinoline (15 mol %)
3. Catalysis
—
—
—
—
—
—
Prior to their use as ligands for asymmetric metal catal-
ysis, the borane complexes 14a–d needed to be deprotec-
ted. Since the usual reagents such as diethylamine16 or
DABCO failedto perform this transformation in high
yields, we used N,N0-bis(3-aminopropyl)piperazine 15
at an elevatedtemperature (100 °C) for the deprotection
(Scheme 8).17
EtOH– 2.0 M NaOH (10 mol %)
toluene
CH2Cl2 0.2 M NaOH (5 mol %)
EtOH
EtOH
20 12 65
6
7
8
1.5
1.5
31 26 24
0.2 M NaOH (20 mol %)
0.2 M NaOH (20 mol %) 14
36
6
38
—
83 12
a Reaction performedat room temperature.
b Isolatedyield.
The conversion of borane complexes 14a–d to the
diphosphines 2a–d was monitoredby 31P NMR spec-
troscopy. After complete deprotection, the amine was
removedby filtration through silica unedr Ar and
ligands 2a–d were obtainedin quantitative yield.
as toluene or CH2Cl2 (entries 5 and6) gave an unfavor-
able ratio of 9 and 10 andeven larger amounts of olefin
11 were isolated. Finally, the use of sodium hydroxide at
a lower concentration alloweda to rise in the product
yieldto 83% (entries 7 and8). No reaction was observed
with the Wilkinson catalyst.
We have now examinedthe scope of ligands 2a–d in the
Rh-catalyzedhydroboration of styrene 16 with catechol-
borane 17.18 After oxidation with aqueous hydrogen
peroxide, alcohols 18 and 19 were obtained( Scheme 9
and Table 2).
The conversion of amine 9 into key-intermediate 3 was
performedvia acetate 12 (Scheme 6). Nucleophilic sub-
stitution at the a-position to ferrocene usually proceeds
with complete retention of configuration.4 Thus, the chi-
ral amine usedas an auxiliary in compound 9 was
substitutedby an acetoxy group upon treatment with
acetic anhydride. Acetate 12 reacts with dimethylamine
in aqueous solution to give ferrocenyl derivative 3 in
excellent yield. Amine 3 was comparedto another
Surprisingly, the results with ligands 2a–d indicate that
the introduction of an ethyl substituent in JOSIPHOS-
type diphosphines decreases the enantioselectivity in
the asymmetric Rh-catalyzedhydroboration. The best
results were achievedwith ligand 2a (RA = Ph, RB = cy,
OMe
N
NMe2
Et
OAc
Et
Ac2O
Et
HNMe2
Fe
Fe
Fe
70 ˚C, 12 h
H2O, CH3CN
60 ˚C, 20 h
9
12: 91%
3: 96%
Scheme 6. Substitution of the chiral auxiliary.

3388
S. Yasuike et al. / Tetrahedron: Asymmetry 16 (2005) 3385–3393
1) t-BuLi, 0 ˚C, 3 h
NMe2
NMe2
2) RA2PCl, 0 ˚C, 1 h
RA
13a Ph
Yield (%)
Et2O
Et
Et
76
64
PHRA
Fe
Fe
2
13b cy
3) BH3·SMe2, rt,12 h
BH3
THF
3
13a, b
BH3
PRB
RA
RB
2
Yield (%)
1) RB2PH, 70 ˚C, 6 h
14a
14b
14c
14d
cy
Ph
cy
Ph
69
83
63
86
Ph
Ph
cy
cy
AcOH
Et
PHRA
13a, b
Fe
2
2) BH3·SMe2, rt,12 h
THF
BH3
14a-d
Scheme 7. Synthesis of the ferrocenyl ligands 14a–d.
BH3
N
NH2
PRB
PRB
H2N
N
2
2
15
Et
Et
PHRA
PHRA
Fe
Fe
2
2
toluene,
100 ˚C, 10-17 h
BH3
14a-d
2a-d
Scheme 8. Deprotection of ferrocenyl diphosphines 14a–d.
1) Ligand 2 (2.2 mol %)
OH
*
[Rh(nbd)2]BF4 (2 mol %)
OH
O
+
B
H
(1.1 equiv.)
O
16
18 : branched
19 : linear
17
2) NaOH, H2O2 (30% aq.)
DME
Scheme 9. Asymmetric hydroboration catalyzed by Rh(I)-complexes.
Table 2. Enantioselective hydroboration of styrene
LigandReaction time (h)
Temperature (
°C)
Conv.a (%)
Regioselectivitya 18:19
Enantioselectivityb (% ee)
2a
2b
2c
2d
6
24
20
20
ꢀ40
ꢀ40
ꢀ40
ꢀ70
71
72
58
52
92:8
46
6
34
15
53:47
71:29
92:8
a The ratio of isomers andconversion were determinedby GC.
b The enantiomeric excess was determined by HPLC (column: Chiracel OD-H). The absolute configuration was established by comparison with
literature data.
Table 2, entry 1). Better selectivities were obtained
with the JOSIPHOS ligand(65% yiel;d 18:19 > 99:1;
91.5% ee).6a In analogy with JOSIPHOS, the ligandwith
RA = Ph andR B = cy gave the best results for this reac-
tion. An electron-rich phosphine in the side chain (RB =
cy) provedto be especially important. Thus, with
ligands 2b and d (entries 2 and4) only very low enantio-
selectivities were obtained, whereas with ligand 2c (entry
3), a moderate enantioselectivity with a reduced regio-
selectivity was achieved.
4. Conclusion
In conclusion, we have reporteda new andefficient syn-
thesis for JOSIPHOS-type ligands. The diastereoselec-
tive three-component reaction avoids the need for
resolution processes. Unfortunately, ligands 2a–d did
not give as high selectivities as JOSIPHOS 1a in the
Rh-catalyzedhyrdoboration. Changing the original
methyl group to ethyl reduced the performance of the
new ligands in asymmetric hydroboration. Further

S. Yasuike et al. / Tetrahedron: Asymmetry 16 (2005) 3385–3393
3389
˚
applications of this approach to prepare ferrocenyl
ligands of interest for asymmetric catalysis are underway.
0.2 mmol, 5 mol %), andMS 4 A (2 g) in toluene
(8 mL). The crude product was purified by column chro-
matography (n-pentane/ether 10:1). Diastereomerically
pure 4b was isolatedas a redoil (1.31 g, 3.44 mmol,
~
5. Experimental
86%). [a]D = +134.4 (c 4.15, CHCl3); IR (KBr): m 3094
(m), 2925 (s), 2874 (s), 2820 (s), 1610 (w), 1449 (m),
All reactions were carriedout under argon using stan-
dard Schlenk techniques. 1H and 13C NMR spectra were
recorded on a Bruker AMX 300 instrument. 31P NMR
spectra were recorded on a VARIAN Mercury 200
instrument. Chemical shifts (d) are given as parts per
million relative to the residual solvent peak. IR spectra
were recorded on a PERKIN ELMER 1420 Infrared
Spectrometer. Mass spectra were recorded on a FINNI-
GAN MAT 95 Q spectrometer. Optical rotations were
measuredon a PERKIN ELMER 241 polarimeter. Col-
umn chromatography was performedon MERCK silica
gel 60 (230–400 mesh ASTM). Thin layer chromatogra-
phy was performedon MERCK TLC-plates silica gel 60
F-254. Enantiomeric excesses were determined by
HPLC. A Chiralcel OD-H (Daicel Chemical Industries)
column was usedwith n-heptane/i-propanol as a mobile
phase and detection by a diode array UV–vis detector at
214 nm.
1357 (m), 1187 (m), 1106 (vs), 1001 (m), 906 (m), 819
(s), 502 (s); H NMR (CDCl3): d 4.84 (s, 1H), 4.35 (s,
1
1H), 4.27–4.21 (m, 3H), 4.16 (s, 5H), 4.09 (t,
J = 1.8 Hz, 2H), 3.47 (s, 3H), 3.41–3.38 (m, 4H), 3.30
(dd, J = 9.2 Hz, 5.9 Hz, 1H), 3.10–3.05 (m, 1H), 2.62
(t, J = 6.6 Hz, 2H), 1.88–1.79 (m, 1H), 1.67–1.52 (m,
3H); 13C NMR (CDCl3): d 86.4, 83.3, 80.3 (CH2), 76.3,
68.6 (CH3), 68.2 (CH), 67.9 (CH), 67.7 (CH), 67.0
(CH), 59.7 (CH2), 59.6 (CH3), 58.7 (CH), 57.0 (CH),
53.2 (CH), 48.1 (CH2), 28.2 (CH2), 22.3 (CH2); MS
(EI, 70 eV) m/z (%): 381 (M+, 19), 268 (23), 267 (100),
252 (16), 236 (9), 186 (4); HRMS calcdfor C 21H27Fe-
NO2: 381.1391. Observed: 381.1423.
5.1.3. (R)-1-Ferrocenyl-1-[(S)-2-methoxymethyl-1-pyrrol-
idinyl]-4,4-dimethyl-2-pentyne 4c. Preparedaccoridng
to the procedure described above from 3,3-dimethyl-1-
butyne 7c (0.49 mL, 329 mg, 4.0 mmol), ferrocene carb-
aldehyde
5
(856 mg, 4.0 mmol), (S)-2-(methoxy-
5.1. Diastereoselective three-component reaction
methyl)pyrrolidine 6 (0.49 mL, 461 mg, 4.0 mmol),
CuBr (29 mg, 0.2 mmol, 5 mol %), andMS 4 A (2 g) in
˚
5.1.1. (R)-1-Ferrocenyl-1-[(S)-2-methoxymethyl-1-pyrrol-
idinyl]-3-trimethylsilyl-2-propyne
toluene (8 mL). The crude product was purified by col-
umn chromatography (n-pentane/ether 10:1). Diastereo-
merically pure 4c was isolatedas a redoil (1.25 g,
3.17 mmol, 80%). [a]D = +139.4 (c 0.49, CHCl3); IR
4a. Trimethylsilyl-
acetylene 7a (1.40 mL, 982 mg, 10.0 mmol), ferrocene
carbaldehyde 5 (2.14 g, 10.0 mmol) and( S)-2-(meth-
oxymethyl)pyrrolidine 6 (1.23 mL, 1.15 g, 10.0 mmol)
were added to a suspension of CuBr (72 mg, 0.5 mmol,
~
(KBr): m 3096 (m), 2967 (vs), 2926 (s), 2824 (m), 2226
(w), 1620 (w), 1455 (m), 1361 (m), 1259 (s), 1106 (vs),
1
˚
5 mol %) andMS 4 A (5 g) in toluene (20 mL) at rt.
1001 (s), 817 (s), 504 (s); H NMR (CDCl3): d 4.65 (s,
The reaction mixture was stirredat rt andafter 5 days
the solids were filteredoff andwashedwith diethyl ether.
The organic layers were washedwith satdNH 4Cl and
25% NH3 solution (2:1), water, andbrine anddriedover
MgSO4. The crude material was purified by column
chromatography (n-pentane/triethylamine 20:1). The
product 4a was obtaineddiastereomerically pure as a
redoil (3.03 g, 7.40 mmol, 74%). [ a]D = +181.9 (c 1.56,
1H), 4.34–4.33 (m, 1H), 4.22–4.20 (m, 1H), 4.16 (s,
5H), 4.07 (t, J = 1.9 Hz, 2H), 3.38–3.36 (m, 4H), 3.27
(dd, J = 9.4 Hz, 6.8 Hz, 1H), 3.11–3.04 (m, 1H), 2.65–
2.55 (m, 2H), 1.82–1.77 (m, 1H), 1.66–1.56 (m, 3H),
1.31 (s, 9H); 13C NMR (CDCl3): d 93.8, 87.7, 76.7
(CH2), 75.2, 68.9 (CH3), 68.6 (CH), 68.2 (CH), 68.0
(CH), 67.3 (CH), 59.9 (CH), 59.1 (CH), 53.5 (CH),
48.2 (CH2), 31.5 (CH3), 28.9 (CH2), 27.5, 23.1 (CH2);
MS (EI, 70 eV) m/z (%): 393 (M+, 10), 280 (22), 279
(100), 264 (20), 186 (14), 121 (19); HRMS calcdfor
C23H31FeNO: 393.1755. Observed: 393.1764.
~
CHCl3); IR (KBr): m 3096 (m), 2960 (s), 2873 (s), 2825
(m), 2161 (m), 1449 (m), 1249 (s), 1106 (vs), 999 (s),
842 (vs); 1H NMR (CDCl3): d 4.72 (s, 1H), 4.43 (s,
1H), 4.20 (s, 1H), 4.16 (s, 5H), 4.08 (s, 2H), 3.39 (s,
3H), 3.38 (dd, J = 9.2 Hz, 5.9 Hz, 1H), 3.28 (dd,
J = 9.2 Hz, 6.3 Hz, 1H), 3.11–3.07 (m, 1H), 2.66–2.61
(m, 2H), 1.86–1.80 (m, 1H), 1.67–1.56 (m, 3H), 0.24 (s,
9H); 13C NMR (CDCl3): d 103.0 (CH), 88.8, 86.1,
76.6, 76.2 (CH2), 68.6 (CH3), 68.3 (CH), 67.8 (CH),
67.1 (CH), 59.5 (CH), 58.7 (CH), 53.9 (CH), 48.1
(CH2), 26.3 (CH2), 22.5 (CH2), 0.12 (CH3); MS (EI,
70 eV) m/z (%): 410 ([M+1]+, 10), 409 (31), 296 (33),
295 (100); HRMS calcdfor C 22H31FeNOSi: 409.1524.
Observed: 409.1544.
5.2. (R)-1-Ferrocenyl-1-[(S)-2-methoxymethyl-1-pyrrol-
idinyl]-2-propyne 8
KOH in methanol (1.0 m, 12 mL, 12 mmol, 1.5 equiv)
was added to a stirred solution of (R)-1-ferrocenyl-1-
[(S)-2-methoxymethyl-1-pyrrolidinyl]-3-trimethylsilyl-2-
propyne 4a (3.15 g, 7.7 mmol) in methanol (20 mL) at rt.
After 1.5 h, the solvent was evaporated, water (30 mL)
was added, and the mixture extracted with ether
(40 mL). The organic layers were washedwith brine
anddriedover MgSO 4. The crude product was purified
by column chromatography (n-pentane/diethyl ether
3:2). The product 8 was isolatedas a redsolid(2.43 g,
7.21 mmol, 94%). Mp 44.5–45.5 °C; [a]D = +87.3 (c
5.1.2. (R)-1-Ferrocenyl-1-[(S)-2-methoxymethyl-1-pyrrol-
idinyl]-4-methoxy-2-butyne 4b. Preparedaccording to
the procedure described above from methyl propargyl
ether 7b (0.39 mL, 280 mg, 4.0 mmol), ferrocene carbal-
dehyde 5 (856 mg, 4.0 mmol), (S)-2-(methoxymethyl)-
pyrrolidine 6 (0.49 mL, 461 mg, 4.0 mmol), CuBr (29 mg,
~
3.29, CHCl3); IR (KBr): m 3296 (s), 3096 (m), 2960 (s),
2873 (s), 2826 (m), 1450 (m), 1233 (m), 1193 (m), 1106
1
(m), 1001 (m), 820 (m); H NMR (CDCl3): d 4.83 (d,

3390
S. Yasuike et al. / Tetrahedron: Asymmetry 16 (2005) 3385–3393
J = 2.0 Hz, 1H), 4.36 (dd, J = 3.2 Hz, 1.6 Hz, 1H), 4.25
(s, br, 1H), 4.10 (s, 5H), 4.08 (t, J = 1.9 Hz, 2H), 3.47
(dd, J = 12.1 Hz, 6.0 Hz, 1H), 3.39 (s, 3H), 3.33 (dd,
J = 10.2 Hz, 5.9 Hz, 1 H), 3.13–3.04 (m, 1H), 2.64–
2.60 (m, 2H), 2.41 (d, J = 2.2 Hz, 1 H), 1.89–1.83 (m,
1H), 1.68–1.56 (m, 3H); 13C NMR (CDCl3): d 86.4,
80.6, 76.8 (CH), 72.9 (CH), 69.1 (CH3), 68.9 (CH),
68.6 (CH), 68.2 (CH), 67.5 (CH), 59.9 (CH), 59.1
(CH), 53.4 (CH), 48.3 (CH2), 28.5 (CH2), 22.7 (CH2);
MS (EI, 70 eV) m/z (%): 338 (M+, 2), 337 (10), 223
CHCl3); 1H NMR (CDCl3): d 4.05–3.97 (m, 8H),
3.96–3.94 (m, 1H), 3.18 (dd, J = 11.0 Hz, 3.4 Hz, 1H),
2.03–1.89 (m, 1H), 1.93 (s, 6 H), 1.73–1.57 (m, 1H),
1.03 (t, J = 7.4 Hz, 3H); 13C NMR (CDCl3): d 85.6,
69.3 (CH), 68.5 (CH), 67.4 (CH), 67.1 (CH), 66.8
(CH), 64.9 (CH), 40.5 (CH3), 24.4 (CH2), 12.3 (CH3);
HRMS calcdfor C 15H21FeN: 271.1023. Observed:
271.1003. Further analytical data is in accordance with
the literature.13
(100), 120 (19); HRMS calcdfor
337.1129. Observed: 337.1100.
C
19H23FeNO:
5.5. Synthesis of the protected monophosphines 13a,b
5.5.1. (SFc)-1-Diphenylphosphano-2-[a-(R)-(N,N-dimethyl-
amino)propyl]ferrocene borane complex 13a. A solution
of (R)-[3-(N,N-dimethylamino)propyl]ferrocene 3 (204
mg, 0.75 mmol) in diethyl ether (6 mL) was cooled to
0 °C. tert-BuLi in pentane (1.45 m, 0.57 mL, 0.82 mmol,
1.1 equiv) was added dropwise and the mixture stirred
for 3 h at 0 °C. Chlorodiphenylphosphine (0.17 mL,
0.97 mmol, 1.3 equiv) was added at 0 °C. The reaction
mixture was stirredfor 1 h at rt, then a borane dimethyl
sulfide complex (0.70 mL, 0.75 mmol, 10 equiv) added
dropwise and the mixture stirred for 13 h at rt. After
careful addition of water, the mixture was extracted with
CH2Cl2 (30 mL) andthe organic layers washedwith
water andbrine anddriedover MgSO 4. The crude prod-
uct was purifiedby column chromatography ( n-pentane/
CH2Cl2 2:3). Compound 13a was obtainedas an orange
solid(267 mg, 0.569 mmol, 76%). Mp 204.2–205.1 °C
(decomp.); [a]D = ꢀ304.7 (c 0.54, CH2Cl2); IR: (Film):
1063 (m), 823 (m), 743 (m), 699 (m); 1H NMR (CDCl3):
d 7.87–7.50 (m, 4H), 7.48–7.35 (m, 6H), 4.84 (s, br, 1H),
4.61 (s, br, 1H), 4.30 (s, br, 1H), 4.19 (s, br, 1H), 3.94 (s,
5H), 2.59–2.45 (m, 1H), 2.24–2.18 (m, 1H), 2.15 (s, 3H),
1.83 (s, 3H), 1.70 (s, br, 3H), 1.35 (t, J = 7.6 Hz, 3H);
13C NMR (75 MHz, CDCl3): d 133.8 (CH), 133.6
(CH), 132.9 (CH), 132.8 (CH), 131.5 (CH), 131.4
(CH), 131.2, 130.3, 129.0 (CH), 128.9 (CH), 128.8
(CH), 128.6 (CH), 74.5 (CH), 73.4 (CH), 72.2 (CH),
71.7, 71.5 (CH), 69.2 (CH), 53.1 (CH3), 50.0 (CH3),
28.9 (CH2), 16.0 (CH3); 31P NMR (81 MHz, CDCl3):
d +10.8 (s, br); MS (EI, 70 eV) m/z (%): 469 (M+, 2),
455 (49), 440 (19), 426 (100), 412 (32), 226 (42), 183
5.3. (R)-1-Ferrocenyl-1-[(S)-2-methoxymethyl-1-pyrrol-
idinyl]-2-propane 9
A mixture of (R)-1-ferrocenyl-1-[(S)-2-methoxymethyl-
1-pyrrolidinyl]-2-propyne
8
(674 mg, 2.00 mmol),
NaOH in ethanol (0.2 m, 2 mL, 0.4 mmol, 20 mol %),
andpallaidum on charcoal (10%, 24 mg) in ethanol
(4 mL) was stirred at rt under a hydrogen atmosphere
(1 bar) for 14 h. The reaction mixture was filtered. After
removal of the solvent, the crude product was purified
by column chromatography (n-pentane/diethyl ether
2:1 + 0.5% NEt3). The product 9 was obtainedas a
redoil (574 mg, 1.68 mmol, 83%). [ a]D = ꢀ61.8 (c 0.86,
~
CHCl3); IR (KBr): m 3094 (m), 2959 (s), 2928 (s), 2872
(s), 1674 (m), 1453 (m), 1383 (w), 1195 (w), 1106 (vs),
1057 (s), 1001 (w), 817 (m); 1H NMR (CDCl3): d
4.10–4.08 (m, 1H), 4.06–4.00 (m, 8H), 3.47 (dd,
J = 9.4 Hz, 4.0 Hz, 1H), 3.29 (s, 3H), 3.14 (dd,
J = 9.7 Hz, 4.3 Hz, 1H), 3.00 (t, J = 8.6 Hz, 1H), 2.70–
2.60 (m, 2H), 2.01–1.89 (m, 2H), 1.79–1.34 (m, 5H),
1.05 (t, J = 7.4 Hz, 3H); 13C NMR (CDCl3): d 90.2,
77.4 (CH), 77.2 (CH2), 68.53 (CH3), 68.52 (CH), 67.06
(CH), 67.05 (CH), 61.4 (CH), 58.9 (CH), 57.2 (CH),
51.0 (CH2), 29.0 (CH2), 25.7 (CH2), 23.8 (CH2), 12.5
(CH3); MS (EI, 70 eV) m/z (%): 341 (M+, 15), 315
(15), 312 (84), 290 (48), 246 (13), 227 (100), 212 (30),
186 (24), 121 (44); HRMS calcdfor C 19H27FeNO:
341.1442. Observed: 341.1459.
~
m 3436 (s), 2388 (m), 1629 (w), 1437 (m), 1173 (m),
5.4. (R)-[3-(N,N-Dimethylamino)propyl]ferrocene 3
A solution of (R)-1-ferrocenyl-1-[(S)-2-methoxymethyl-
1-pyrrolidinyl]-2-propane 9 (682 mg, 2.00 mmol) in
freshly distilled acetic anhydride (10 mL) was stirred
for 12 h at 70 °C. The reaction mixture was cooledto
0 °C and water added carefully. The mixture was neu-
tralizedwith 2 M NaOH solution andextractedwith
ether (40 mL). The organic layers were washedwith
(32), 121 (34); HRMS calcdfor
469,1793. Observed: 469.1802.
C 27H33BFeNP:
5.5.2.
(SFc)-1-Dicyclohexylphosphano-2-[a-(R)-(N,N-
dimethylamino)propyl]ferrocene borane complex 13b.
Prepared according to the procedure described above
from (R)-[3-(N,N-dimethylamino)propyl]ferrocene 3 (196
mg, 0.72 mmol), tert-BuLi (1.45 m, 0.55 mL, 0.79 mmol,
1.1 equiv), chlorodicyclohexylphosphine (0.2 mL, 0.94
mmol, 1.3 equiv), and borane dimethyl sulfide complex
(0.70 mL, 0.73 mmol, 10 equiv). The crude product
was purifiedby column chromatography ( n-pentane/
CH2Cl2 2:3). Compound 13b was obtainedas an orange
solid(222 mg, 0.461 mmol, 64%). Mp 166–167.5 °C
(decomp.); [a]D = ꢀ144.8 (c 0.29, CH2Cl2); IR (KBr):
water andbrine anddriedover MgSO
4. The solvents
were distilled off and the product dried under vacuum
(10ꢀ3 mbar). The acetamido derivative of the chiral aux-
iliary was efficiently removedudring work-up. No
attempts were made to isolate it. The remaining acetate
12 (521 mg, 1.82 mmol) was dissolved in acetonitrile
(6 mL) without further purification. Dimethylamine
(6 mL, 40% solution in water) was added and the reac-
tion mixture stirredfor 20 h at 60 °C in a sealedtube.
After purification by acid–base work-up, amine 3 was
obtainedas a yellow solid(471 mg, 1.73 mmol, 87% over
two steps). mp 66.0–67.5 °C; [a]D = ꢀ57.5 (c 0.5,
~
m 3436 (w), 2931 (s), 2852 (m), 2388 (s), 1636 (w), 1449
1
(m), 1173 (m), 1064 (m), 822 (m); H NMR (CDCl3):
d 4.71 (s, br, 1H), 4.66 (s, br, 2H), 4.34 (s, 5H), 3.76
(s, br, 1H), 2.66–2.52 (m, 1H), 2.40 (s, 3H), 2.34 (s,

S. Yasuike et al. / Tetrahedron: Asymmetry 16 (2005) 3385–3393
3391
3H), 2.29–1.01 (m, 26H), 1.46 (t, J = 7.6 Hz, 3H); 13C
NMR (CDCl3): d 76.5 (CH), 74.7, 74.1, 73.4 (CH),
73.1 (CH), 71.8 (CH), 53.9 (CH3), 48.7 (CH3), 37.1
(CH, d, J = 30.4 Hz), 32.3–28.1 (m, CH2), 18.2 (CH3);
31P NMR (81 MHz, CDCl3): d +27.6 (s, br); MS (EI,
70 eV) m/z (%): 481 (M+, 15), 467 (31), 452 (89), 424
(61), 384 (52), 341 (52), 259 (100), 226 (58), 121 (22);
HRMS calcdfor C 27H45BFeNP: 481.2732. Observed:
481.2734.
J = 3.5 Hz), 66.8 (d, J = 3.5 Hz), 32.5 (CH2,
d
,
J = 19.9 Hz), 15,2 (CH3, d ,J = 6.6 Hz); 31P NMR
(CDCl3): d +26.3 (s, br), +12.5 (s, br); MS (EI, 70 eV)
m/z (%): 624 (M+, 0.3), 596 (15), 411 (91), 334 (11),
226 (100), 183 (17), 108 (11); HRMS calcdfor
C37H40B2FeP2: 624.2141. Observed: 624.2179.
5.6.3. (SFc)-1-Dicyclohexylphosphano-2-[a-(R)-(dicyclo-
hexylphosphano)propyl]ferrocene bis-borane complex
14c. Prepared according to the procedure described
above from 13b (86 mg, 0.18 mmol) anddiphenylphos-
phine (45 mg, 0.22 mmol, 1.2 equiv). The crude product
was purifiedby column chromatography ( n-pentane/
CH2Cl2 3:2). Compound 14c was isolatedas an orange
solid(73 mg, 0.113 mmol, 63%). Mp 118.3–122.4 °C
5.6. Synthesis of the protected diphosphines 14a–d
5.6.1. (SFc)-1-Diphenylphosphano-2-[a-(R)-(dicyclohexyl-
phosphano)propyl]ferrocene bis-borane complex 14a.
Dicyclohexylphosphine (40 mg, 0.20 mmol, 1.2 equiv)
was added to a solution of 13a (80 mg, 0.17 mmol) in
degassed acetic acid (3.5 mL). The mixture was heated
to 60 °C for 6 h. After the mixture hadbeen cooledto
rt, the solvent was removed under reduced pressure
andthe residual oil dissolvedin THF (2 mL). Borane
dimethyl sulfide complex (0.16 mL, 1.7 mmol, 10 equiv)
was added dropwise and the mixture stirred for 14 h at
rt. After careful addition of water, the mixture was
~
(decomp.); [a]D = ꢀ29.9 (c 0.36, CH2Cl2); IR (KBr): m
3436 (w), 2930 (s), 2852 (m), 2385 (m), 1630 (m), 1449
1
(m), 1062 (m), 1003 (m), 824 (m); H NMR (CDCl3):
d 5.01 (s, br, 1H), 4.41 (t, J = 2.3 Hz, 1H), 4.22 (s, br,
1H), 4.18 (s, 5H), 3.32 (ddd, J = 10.6 Hz, 6.6 Hz,
4.0 Hz, 1H), 2.35–0.76 (m, 52H), 1.32 (t, J = 7.5 Hz,
3H); 13C NMR (CDCl3): d 70.4, 70.2 (CH), 69.7 (CH),
69.2 (CH), 69.0, 52.1, 38.5 (CH, d, J = 33.5 Hz), 35.4
(CH, d, J = 34.0 Hz), 34.2 (CH, d, J = 27.9 Hz), 33.2
(CH, d, J = 28.0 Hz), 31.4–24.5 (m), 13.5 (CH3); 31P
NMR (CDCl3): d +39.8 (s, br), +22.6 (s, br); MS (EI,
70 eV) m/z (%): 648 (M+, 0.2), 633 (6), 537 (100), 371
(52), 289 (6), 257 (9), 121 (2); HRMS calcdfor
C37H64B2FeP2: 648.4019. Observed: 648.4025.
extractedwith CH Cl2 (20 mL) andthe organic layers
2
were washedwith water andbrine andrdiedover
MgSO4. The crude product was purified by column chro-
matography (n-pentane/CH2Cl2 3:2). Compound 14a
was obtainedas an orange solid(75 mg, 0.112 mmol,
69%). Mp 230.3–232.6 °C (decomp.); [a]D = ꢀ196.4 (c
~
0.39, CH2Cl2); IR: (KBr): m 3436 (w), 2931 (s), 2390
1
(m), 1630 (w), 1437 (m), 1062 (m), 741 (m), 698 (m); H
5.6.4. (SFc)-1-Dicyclohexylphosphano-2-[a-(R)-(diphenyl-
phosphano)propyl]ferrocene bis-borane complex 14d.
Prepared according to the procedure described above
from 13b (80 mg, 0.16 mmol) anddiphenylphosphine
(40 mg, 0.20 mmol, 1.2 equiv). The crude product was
purifiedby column chromatography ( n-pentane/CH2Cl2
3:2). Compound 14d was isolatedas a redsolid(87 mg,
0.136 mmol, 86%). Mp 175 °C (decomp.); [a]D = ꢀ44.4
NMR (CDCl3): d 7.79–7.70 (m, 4H), 7.43–7.19 (m,
6H), 4.85 (s, br, 1H), 4.48 (t, J = 2.6 Hz, 1H), 4.16 (s,
br, 1H), 3.91 (s, 5H), 3.33–3.25 (m, 1H), 2.34–2.22 (m,
2H), 1.95–0.42 (m, 28H), 1.37 (t, J = 7.2 Hz, 3H);
13C NMR (CDCl3): d 133.6 (CH), 133.5 (CH), 133.4
(CH), 133.3 (CH), 131.9, 131.5, 131.3 (CH), 129.1
(CH), 129.0 (CH), 128.7 (CH), 128.6 (CH), 74.1 (CH),
72.4 (CH), 71.2 (CH), 70.8 (CH), 68.8, 68.0, 34.1 (CH,
d, J = 28.2 Hz), 32.0 (CH, d, J = 28.0 Hz), 29.3 (CH,
d, J = 26.5 Hz), 28.6–25.9 (CH2, m), 15.3 (CH3, d ,
J = 8.1 Hz); 31P NMR (CDCl3): d +41.6 (s, br), +10.5
(s, br); MS (EI, 70 eV) m/z (%): 636 (M+, 0.2), 621 (6),
525 (100), 411 (80), 226 (30); HRMS calcdfor
C37H52B2FeP2: 636.3080. Observed: 636.3045.
~
(c 0.27, CH2Cl2); IR (KBr): m 3435 (w), 2930 (s), 2851
(m), 2383 (s), 1637 (w), 1437 (s), 1060 (s), 736 (m), 700
1
(s); H NMR (C6D6): d 8.05–7.90 (m, 4H), 7.18–7.12
(m, 6H), 5.19 (s, br, 1H), 4.27 (s, br, 1H), 3.90 (s, 5H),
3.87–3.79 (m, 1H), 2.78–2.62 (m, 1H), 2.51–2.31 (m,
2H), 2.19–0.63 (m, 28H), 1.73 (t, J = 7.1 Hz, 3H); 13C
NMR (CDCl3): d 134.0, 133.9 (CH), 133.7 (CH), 133.6
(CH), 131.3 (CH), 131.2 (CH), 129.2 (CH), 129.6,
129.4, 129.1 (CH), 128.7 (CH), 128.6 (CH), 72.9 (CH),
70.7 (CH), 69.8 (CH), 69.4 (CH), 67.3, 66.5, 33.0 (CH,
d, J = 27.5 Hz), 31.5 (CH, d, J = 28.2 Hz), 30.6 (CH),
28.2 (CH, d, J = 24.1 Hz), 27.2 (CH, d, J = 35.8 Hz),
26.6–24.6 (m), 14.0 (CH3); 31P NMR (CDCl3): d +26.4
(s, br), +22.4 (s, br); MS (EI, 70 eV) m/z (%): 636
(M+, 0.2), 621 (4), 525 (100), 442 (8), 423 (12), 257
5.6.2. (SFc)-1-Diphenylphosphano-2-[a-(R)-(diphenylphos-
phano)propyl]ferrocene bis-borane complex 14b. Pre-
pared according to the procedure described above
from 13a (96 mg, 0.20 mmol) andidcyclohexylphos-
phine (45 mg, 0.24 mmol, 1.2 equiv). The crude product
was purifiedby column chromatography ( n-pentane/
CH2Cl2 3:2). Compound 14b was isolatedas a redsolid
(104 mg, 0.167 mmol, 83%). Mp 222.1–224.3 °C
(decomp.); [a]D = ꢀ212.1 (c 0.43, CH2Cl2); IR (KBr):
(18), 226 (12); HRMS calcdfor
636.3080. Observed: 636.3116.
C 37H52B2FeP2:
~
m 3438 (w), 2379 (m), 1636 (w), 1438 (m), 1104 (m),
1
1060 (m), 744 (m), 699 (s); H NMR (CDCl3): d 8.05–
5.7. Deprotection
7.96 (m, 2H), 7.76–7.66 (m, 2H), 7.46–7.18 (m, 14H),
6.81–6.78 (m, 2H), 5.15 (s, br, 1H), 4.44 (t, J = 2.6 Hz,
1H), 4.31 (dt, J = 6.5 Hz, 5.4 Hz, 1H), 4.30 (s, br, 1H),
3.79 (s, 5H), 2.44–2.17 (m, 2H), 1.35 (s, br, 6H), 1.02
(t, J = 7.6 Hz, 3H); 13C NMR (CDCl3): d 133.6–128.0
(m), 72.7 (CH), 72.1 (CH), 71.1 (CH), 67.7 (d,
Prior to use in catalysis, the requiredquantity of the pro-
tectedligand 14a–d (12–15 mg) was dissolved in toluene
(0.8 mL). To the solution, 1,4-bis(3-aminopropyl)piper-
azine (15, 45–50 mg, excess) was added. The reaction
mixture was heatedat 100 °C for 10–17 h, cooledand

3392
S. Yasuike et al. / Tetrahedron: Asymmetry 16 (2005) 3385–3393
2. (a) Togni, A.; Hayashi, T. Ferrocenes: Homogeneous
Catalysis, Organic Synthesis, Material Science; VCH:
Weinheim, 1995; (b) Perseghini, M.; Togni, A. Sci. Synth.
2002, 1, 889.
diluted with ether (5–10 mL). The solution was filtered
under an Ar atmosphere through a pad of previously
dried silica gel. Solvents were removed under vacuum.
The deprotection can be monitored by 31P NMR.
3. For recent reviews see: (a) Atkinson, R. C. J.; Gibson, V.
C.; Long, N. J. Chem. Soc. Rev. 2004, 33, 313; (b) Colacot,
T. J. Chem. Rev. 2003, 103, 3101; for further examples see:
(c) Sturm, T.; Weissensteiner, W.; Spindler, F. Adv. Synth.
Catal. 2003, 345, 160; (d) Ireland, T.; Grossheimann, G.;
Wieser-Jeunesse, C.; Knochel, P. Angew. Chem., Int. Ed.
1999, 38, 3212; (e) Lotz, M.; Polborn, K.; Knochel, P.
Angew. Chem., Int. Ed. 2002, 41, 4708; (f) Lotz, M.;
Kramer, G.; Knochel, P. Chem. Commun. 2002, 2546; (g)
Almena Perea, J. J.; Lotz, M.; Knochel, P. Tetrahedron:
Asymmetry 1999, 10, 375; (h) Enders, D.; Peters, R.;
Lochtman, R.; Raabe, G.; Runsink, J.; Bats, J. W. Eur. J.
Org. Chem. 2002, 3399; (i) Berens, U.; Burk, M. J.;
Gerlach, A.; Hems, W. Angew. Chem., Int. Ed. 2000, 39,
1981.
5.7.1. (SFc)-1-Diphenylphosphano-2-[a-(R)-(dicyclohexyl-
phosphano)propyl]ferrocene 2a. 31P NMR (Et2O): d
+21.7 (d, J = 21 Hz), ꢀ24.7 (d, J = 21 Hz).
5.7.2. (SFc)-1-Diphenylphosphano-2-[a-(R)-(diphenylphos-
phano)propyl]ferrocene 2b. 31P NMR (Et2O): d +3.1
(d, J = 14 Hz), ꢀ24.4 (d, J = 14 Hz).
5.7.3. (SFc)-1-Dicyclohexylphosphano-2-[a-(R)-(dicyclo-
hexylphosphano)propyl]ferrocene 2c. 31P NMR (Et2O):
+13.1 (d, J = 16 Hz), ꢀ14.7 (d, J = 16 Hz).
5.7.4. (SFc)-1-Dicyclohexylphosphano-2-[a-(R)-(diphenyl-
phosphano)propyl]ferrocene 2d. 31P NMR (Et2O):
+21.0 (d, J = 22 Hz), ꢀ25.8 (d, J = 22 Hz).
4. (a) Gokel, G. W.; Marquarding, D.; Ugi, I. K. J. Org.
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Klusacek, H.; Marquarding, D.; Ugi, I. Angew. Chem.
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5.8. Hydroboration of styrene
The freshly deprotected ligand 2a–d and[Rh(nbd) 2]BF4
(7.5 mg, 0.020 mmol, 2 mol %) were dissolved in DME
(2 mL) andstirredfor 20 min at rt. Styrene
16
(0.11 mL, 1.0 mmol) andtetradecane as internal stan-
dard were added and the mixture cooled to the indicated
temperature (Table 2) before catechol borane 17
(0.11 mL, 1.1 mmol) was added. The reaction was fol-
lowedby GC. Aliquots were treatedwith a mixture of
2 M sodium hydroxide solution and hydrogen peroxide
solution (30%). After the indicated time (Table 2) meth-
anol (1 mL), 2 M sodium hydroxide solution (1.5 mL),
and hydrogen peroxide solution (30%, 0.1 mL) were
added subsequently to the reaction mixture. The mixture
was warmedup to rt andthen extractedwith diethyl
ether (60 mL) andthe organic layers washedwith 1 M
sodium bisulfite solution, water, and brine and dried
over MgSO4. The crude product was dissolved in diethyl
ether andfilteredthrough a short padof silica gel. The
enantiomeric excess was determined by HPLC (OD-H,
95% n-heptane, 5% i-propanol, 0.6 mL/min); retention
time (min): 1-phenylethanol: 15.0 (R), 17.5 (S); 2-phenyl-
ethanol: 16.1.
´
9. (a) Lopez, F.; Harutyunyan, S. R.; Meetsma, A.; Minaard,
A. J.; Feringa, B. L. Angew. Chem., Int. Ed. 2005, 44,
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Am. Chem. Soc. 2004, 126, 8352; (c) Lipshutz, B. H.;
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H.; Gommermann, N.; Knochel, P. Synthesis 2004, 2015;
(c) Gommermann, N.; Knochel, P. Chem. Commun. 2004,
2324.
11. Hayashi, T.; Mise, T.; Fukushima, M.; Kagotani, M.;
Nagashima, N.; Hamada, Y.; Matsumoto, A.; Kawakami,
S.; Konishi, M. Bull. Chem. Soc. Jpn. 1980, 53, 1138.
12. Corey, E. J.; Gross, A. W. Tetrahedron Lett. 1984, 25, 495.
13. Tappe, K.; Knochel, P. Tetrahedron: Asymmetry 2004, 15,
91.
14. (a) Marquarding, D.; Klusacek, H.; Gokel, G.; Hoffmann,
P.; Ugi, I. J. Am. Chem. Soc. 1970, 92, 5389; (b) Ohno, A.;
Yamane, M.; Hayashi, T. Tetrahedron: Asymmetry 1995,
6, 2495.
15. Pellon, P. Tetrahedron Lett. 1992, 33, 4451.
16. Imamoto, T.; Kusumoto, T.; Suzuki, N.; Sato, K. J. Am.
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Acknowledgements
We thank Degussa AG (Frankfurt) for generous sup-
port, S.Y. thanks the Humboldt Foundation for a fel-
lowship, N.G. thanks the DFG (SPP 1118 ÔSekunda¨re
Wechselwirkungen als Steuerungsprinzip zur gerichteten
Funktionalisierung reaktionstra¨ger SubstrateÕ) and
R.J.K. thanks the Stiftung Stipendien-Fonds des VCI
17. Gavryushin, A.; Polborn, K.; Knochel, P. Tetrahedron:
Asymmetry 2004, 15, 2279.
18. For general reviews see: (a) Carroll, A.-M.; OÕSullivan, T.
P.; Guiry, P. J. Adv. Synth. Catal. 2005, 347, 609; (b)
(Frankfurt) andthe Bunedsministerium fu r Bildung
¨
undForschung for a scholarship.
`
Chelucci, G.; Orru, G.; Pinna, G. Tetrahedron 2003, 59,
9471; (c) Beletskaya, I.; Pelter, A. Tetrahedron 1997, 53,
4957; For further examples: (d) Kno¨pfel, T. F.; Aschwan-
den, P.; Ichikawa, T.; Watanabe, T.; Carreira, E. M.
Angew. Chem., Int. Ed. 2004, 43, 5971; (e) Segarra, A. M.;
Claver, C.; Fernandez, E. Chem. Commun. 2004, 464; (f)
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