Synthesis and application of complexes of a novel chiral diphenylphosphino-functionalized N-heterocyclic carbene

Article abstract of DOI:10.1055/s-2004-829548

Complexes of the ligand (S,S)-1-(2-diphenylphosphanylnaphtalen-1-yl)-3-(2- isopropyl-phenyl)-4,5-diphenyl-imidazolin-2-ylidene, a representative of a new class of chiral ligands, were obtained via a short route starting from (S,S)-1,2-diphenyl-ethylen-1,2

Full text of DOI:10.1055/s-2004-829548

LETTER
1789
Synthesis and Application of Complexes of a Novel Chiral Diphenylphosphino-
Functionalized N-Heterocyclic Carbene
Complexes of
a
r
N
ovel
C
h
hiral
D
iphen
a
ylphosphin
r
o-Functi
d
onalized N-Hetero
B
cyclic Carbene appert, Günter Helmchen*
Organisch-Chemisches Institut der Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax +49(6221)544205; E-mail: g.helmchen@urz.uni-heidelberg.de.
Received 14 April 2004
The design of the new ligand C was based on the follow-
Abstract: Complexes of the ligand (S,S)-1-(2-diphenylphosphanyl-
naphtalen-1-yl)-3-(2-isopropyl-phenyl)-4,5-diphenyl-imidazolin-
2-ylidene, a representative of a new class of chiral ligands, were ob-
tained via a short route starting from (S,S)-1,2-diphenyl-ethylen-
ing considerations. Grubbs et al.2a have obtained excellent
results with Ru-complexes of ligand D, the dihydroimida-
zolium salt of which is readily available via a route using
1,2-diamine; a Rh-complex was found to promote catalytic hydro- Buchwald–Hartwig N-arylation of commercially avail-
genation of a,b unsaturated esters with up to 99% ee.
able enantiopure 1,2-diphenyl-ethylen-1,2-diamine as key
step. An interesting aspect of compound D is a relay func-
tion of the i-Pr groups, which are disposed anti to the phe-
nyl groups of the dihydroimidazole moiety. We decided to
combine this structural feature with a rigid 2-(diphen-
ylphosphino)-naphthyl group connected to the dihydro-
imidazole moiety via a stereogenic axis. Realization of
this part of the ligand was expected to be possible by
nucleophilic aromatic substitution as described by Kondo
et al. for a series of P,N-ligands.13
Key words: asymmetric catalysis, chiral N-heterocyclic carbenes,
chiral P ligands, rhodium, enantioselective hydrogenation
N-Heterocyclic carbenes (NHCs) and their transition
metal complexes have recently attracted much interest in
organic and organometallic chemistry.1 Because of strong
carbon-metal s-bonds, NHCs are particularly suited to
act as spectator ligands. An emerging area of application
of NHCs is asymmetric catalysis using chiral NHCs. So
far, only a few reactions catalyzed by complexes of chiral
NHCs gave rise to high enantioselectivity. Examples
include Ru-catalyzed metathesis,2 Ir-catalyzed hydro-
genation of arylalkenes and a,b-unsaturated esters,3
Rh-catalyzed hydrosilylation4 and conjugate addition of
arylboronic acid derivatives to enones5 as well as organo-
catalytic benzoin additions.6 Low degrees of enantio-
selectivity were reported for a Rh-catalyzed hydro-
genation,7 Cu-catalyzed additions of organozinc reagents
to enones,8 and Pd-catalyzed a-arylations of amides.9
N
N
.. N
Ar
PPh2
Fe
N
Ph
PPh2
A
B
Ph
Ph
i-Pr
Ph
Ph
i-Pr
i-Pr
N
N
.. N
.. N
In view of the great importance of phosphines as ligands
in homogeneous catalysis it is astonishing that only a few
mixed donor ligands of general type A (Figure 1) have
been reported.4a,7,10 While many chiral complexes of mo-
nodentate and bidentate N,Ccarb NHCs are known,1,11 only
one nonracemic chiral P,Ccarb ligand (B), incorporating an
imidazolylidene moiety, has been reported.7 Our interest
in P,Ccarb ligands was activated by a report on Ir-catalyzed
hydrogenations with a combination of a monodentate
NHC and a monodentate phosphine.12 As ligand B had
only induced an ee of 12% in catalytic hydrogenation we
decided to develop a new type of ligand. We are now able
to report derivatives of the first chiral P,Ccarb ligand with
a dihydroimidazole moiety, C, and a stereogenic axis.
Highly enantioselective asymmetric hydrogenations were
achieved with a Rh complex of C.
PPh2
D
C
Figure 1 P,Ccarb ligands
Reaction of (S,S)-1,2-diphenyl-ethylen-1,2-diamine with
1-bromo-2-(isopropyl)-benzene under standard Buch-
wald–Hartwig conditions2a gave the monoaryl derivative
1 in 84% yield (Scheme 1). Reaction of 1 with 2 equiva-
lents of n-BuLi–TMEDA at 0 °C for 2 hours and sub-
sequent addition of 1-methoxy-2-(diphenylphos-
phinyl)naphthalene14 yielded diamine 2 in 67% yield. For
the success in this substitution reaction it was important to
add the phosphine oxide at –20 °C, stir the mixture over
night at room temperature and finally heat it at 50 °C for
5 hours.
The phosphine oxide 2 was reduced13 with HSiCl3 in tol-
uene at 110 °C. Reaction of the resultant crude phosphine
2a
3 with HC(OEt)3 and admixed NH4BF4 furnished the
SYNLETT 2004, No. 10, pp 1789–1793
Advanced online publication: 15.07.2004
DOI: 10.1055/s-2004-829548; Art ID: G11404ST
© Georg Thieme Verlag Stuttgart · New York
0
9
.0
8
.2
0
0
4
dihydroimidazolium tetrafluoroborate 4 in 64% overall
yield.15 This compound displayed 31P NMR resonances at
d = –21.80 ppm and –19.52 ppm with an intensity ratio of

1790
E. Bappert, G. Helmchen
LETTER
87:13; 13C and 1H NMR spectra also showed two sets of
lines with the same intensity ratio. In a 1H NMR experi-
ment {[D2]1,1,2,2-tetrachloroethane solution} coales-
cence of NCHN signals at d = 8.08 ppm and 8.05 ppm was
found for a temperature of ca. 135 °C. These results are
indicative of N-Cnaphthyl atropisomerism with a fairly high
barrier to rotation. Atropisomerism with respect to the i-
PrC6H4-N bond can be excluded because this was not dis-
played by Grubb’s dihydroimidazolium tetrafluoroborate
corresponding to D.
Ph
N
Ph
Ar Ar
N
N
Ph
Ph
Ag2O
N
Ag
Ag
(S,S)-4
CH2Cl2,
1 d
P
P
Ph
Ph
Ph Ph
5
–
(BF4
)
2
[Rh(COD)Cl]2
CH2Cl2, 1 h
Ph
Ph
S
S
Ph
Ph
i-Pr
i-Pr
Ph
Ph
HN
a
N
N
H2N
NH2
H2N
Rh
P
Ph
Ph
(S,S)-1
BF4
6
b
Scheme 2 Preparation of the rhodium-complex 6
Ph
Ph
Ph
NH HN
i-Pr
Ph
d
N
N
H
i-Pr
P
R
Ph
Ph
BF4
(S,S)-4
(S,S)-2 : R = POPh2
(S,S)-3 : R = PPh2
c
Scheme 1 Synthesis of the dihydroimidazolium salt (S,S)-4: (a) 1-
Bromo-2-i-propylbenzene, NaOt-Bu, Pd(OAc)2 (2.5 mol%), BINAP
(5 mol%), toluene, 100 °C, 2 d; (b) 1. n-BuLi, TMEDA, r.t., 2 h; 2. 1-
methoxy-2-(diphenylphosphinyl)naphthalene, 50 °C, 5 h; (c) HSiCl3,
Et3N, toluene, 110 °C, 7d; (d) NH4BF4, HC(OEt)3, 120 °C, 1 d.
Figure 2 Stereoview of the crystal structure of the silver carbene
complex 5. Hydrogen atoms, the anion and one P,Ccarb ligand have
been omitted for clarity. Selected bond lengths (Å) and angles (deg)
with estimated standard deviations: Ag(1)-Ccarb 2.104(8), Ag(1)-
Ag(2) 2.7630(13), Ag(2)-P 2.413(2), Ccarb-Ag(1)-Ag(2) 83.8(2), P-
Ag(2)-Ag(1) 94.97(6).
Using a procedure of Wang and Lin,16 reaction of the di-
hydroimidazolium salt 4 with Ag2O (1.0 equiv) gave the
silver carbene complex 5 (Scheme 2). With one equiva-
lent of Ag2O full conversion could be achieved. For trans-
metallation a procedure of Crabtree et al. was employed,17
involving reaction of crude 5 with [Rh(COD)Cl]2 which
gave the rhodium complex 6 as a yellow amorphous solid
in 70% overall yield. This compound is stable to air and
moisture and could be purified by chromatography on
silica gel.
to rotation is expected to be higher for 5 then for 4 because
of enhanced steric bulk created by coordination to Ag+.
Transmetallation upon addition of 1.0 equivalent of
[Rh(COD)Cl]2 to a solution of the silver complex 5 in
dichloromethane cleanly gave the rhodium complex 6 af-
ter a reaction time of 1 hour.21 The 31P NMR (CDCl3)
spectrum of 6 also showed two isomers, characterized by
doublets [d = 16.43 (d, JRhP = 167.8 Hz, major isomer),
18.66 (d, JRhP = 162.1 Hz, minor isomer) ppm] with an in-
tensity ratio of 2:1. This indicates that the atropisomers of
5 had been transformed into corresponding atropisomers
of 6. Again, EXSY and ROESY experiments proved that
the isomers do not interconvert at room temperature.
Structures of the new complexes were characterized as
follows. Crystallization of the silver complex from ethyl
acetate–dichloromethane furnished crystalline 5 in 58%
yield. The X-ray crystal structure (Figure 2) of 5 was de-
termined.18 The crystal contained a Ag-Ag core bound to
two ligands in a parallel arrangement. Bond lengths are in
the range found for similar silver NHC complexes (Ag-
C
carb 2.10 Å,16b Ag-Ag 2.8 Å,16a,19 Ag-P 2.38 Å).20 Confor-
mations around the N-CAr bonds are as anticipated, i. e.
(M)-helicities with anti arrangements of the i-Pr as well as
the PPh2 group with respect to the phenyl groups of the
imidazolinylidene moiety.
The 31P NMR (CDCl3) spectrum of 5 displayed a 2:1 mix-
ture of isomers. We assume that these isomers are atropi-
somers with respect to the i-PrC6H4-N bond. The barrier
The rhodium complex (S,S)-6 was tested in several reac-
tions. Interesting results were first obtained in catalytic
hydrogenations, using as benchmark substrates dimethyl
itaconate and N-acetyldehydroamino acid esters
(Scheme 3). In the hydrogenation of dimethyl itaconate
CH2Cl2 was first used as solvent.22 With a catalyst loading
of 0.1 mol% and a pressure of 10 bar conversion was
Synlett 2004, No. 10, 1789–1793 © Thieme Stuttgart · New York

LETTER
Complexes of a Novel Chiral Diphenylphosphino-Functionalized N-Heterocyclic Carbene
1791
Table 1 Rhodium-Catalyzed Hydrogenations According to Scheme 3 (Reaction Time 20 h)
Entry
Mol%
Substrate
p (bar)a
T (°C)b
Solvent
Conv. (%), (yield)c
ee (%)d
of (S,S)-6
1
2
3
0.1
0.1
0.1
7
7
7
10
20
30
25
25
25
CH2Cl2
CH2Cl2
CH2Cl2
19
89 (R)
98 (R)
98 (R)
>99
100
(100%)
4
5
0.1
0.1
1
7
50
100
50
20
20
50
20
20
50
50
25
25
25
25
70
25
25
70
25
70
CH2Cl2
79
49
97 (R)
63 (R)
97 (R)
96 (R)
94 (R)
98 (R)
98 (S)
99 (S)
97 (S)
99 (S)
7
CH2Cl2
6
7
CH2Cl2
100
9
7
0.1
0.1
0.1
1
7
CH2ClCH2Cl
CH2ClCH2Cl
CH2ClCH2Cl
CH2ClCH2Cl
CH2ClCH2Cl
CH2ClCH2Cl
CH2ClCH2Cl
8
7
86
9
7
100
50
10
11
12
13
9a
9a
9a
9a
1
100
92
1
1
100
(99%)
14
15
16
17
1
1
1
1
9b
9b
9b
9b
30
30
50
50
25
70
25
70
CH2ClCH2Cl
CH2ClCH2Cl
CH2ClCH2Cl
CH2ClCH2Cl
98
97
72
98 (S)
97 (S)
99 (S)
97 (S)
100
(97%)
a Pressure of H2.
b Reaction temperature.
c Conversion was measured by GC (cf. footnoted).
d The ee was determined by GC using a Chrompack CP-Chiralsil-L-Val column (25 m × 0.25 mm), flow 100 mL·h–1, 105 °C, tR[(+)-(R)-
10a] = 4.5 min, tR[(–)-(S)-10a] = 4.9 min, tR(9a) = 3.0 min; 150 °C: tR[(–)-(R)-10b] = 11.5 min, tR[(+)-(S)-10b] = 12.3 min, tR(9b) = 21.6 min;
and a Chrompack CP-g-Cyclodextrin-TA column (30 m × 0.25 mm), flow 60 mL·h–1, 65 °C, tR[(–)-(S)-8] = 26.6 min, tR[(+)-(R)-8] = 29.1 min,
tR(7) = 46.6 min. Absolute configurations see ref.25
incomplete and an ee of 89% was obtained (Table 1, entry In summary, we have prepared a novel chiral P,Ccarb
1).23 Optimization of pressure (entries 2–5) revealed an ligand giving rise to high enantioselectivity in Rh-cata-
optimum of enantioselectivity at 20 bar. Surprisingly, at lyzed enantioselective hydrogenations with benchmark
higher pressures than 30 bar conversion was incomplete, substrates dimethyl itaconate and N-acetyldehydroamino
and at 100 bar the ee was extremely low, indicating for- acid derivatives.24
mation of a catalytically inactive rhodium hydride spe-
cies. A further solvent screening showed, that 1,2-
dichloroethane was also a suitable solvent (entries 7–9).
(S,S)-6 (0.1–1 mol%)
MeO2C
MeO2C
CO2Me
CO2Me
10–100 bar H2, 1 d
The hydrogenation of enamides 9 required 1 mol% of the
rhodium complex (S,S)-6. As solvent 1,2-dichloroethane
led to the best results. In the case of methyl N-acetami-
doacrylate (9a), full conversion could be only achieved by
heating the reaction mixture under a pressure of 50 bar at
70 °C (Table 1, entry 11). Remarkably, use of these con-
ditions gave rise to perfect enantioselectivity (entry 13).
In contrast, enantioselectivity of the hydrogenation of
methyl (Z)-N-acetamidocinnamate (9b) was practically
independent of pressure and temperature (entries 14–17).
7
8
CO2Me
NHAc
CO2Me
NHAc
(S,S)-6 (1 mol%)
R
R
20-50 bar H2, 1 d,
1,2-dichloroethane
10a: R = H
10b: R = Ph
9a: R = H
9b: R = Ph
Scheme 3 Hydrogenations performed with complex (S,S)-6 as
catalyst
Synlett 2004, No. 10, 1789–1793 © Thieme Stuttgart · New York

1792
E. Bappert, G. Helmchen
LETTER
(13) Kondo, K.; Kazuta, K.; Fujita, H.; Sakamoto, Y.; Murakami,
Y. Tetrahedron 2002, 58, 5209.
(14) Hattori, T.; Sakamoto, J.; Hayashizaka, N.; Miyano, S.
Synthesis 1994, 199.
Acknowledgment
This work was supported by the EC (RTNHPRN-CT-2001-00172)
and the Fonds der Chemischen Industrie. We thank Dr. Frank
Rominger for the X-ray crystal structure analysis of complex 5 and
Prof. H. Wadepohl for an EXSY experiment.
(15) Physical data of (S,S)-4: mp 195–197 °C; [a]D24 –297 (c
1.13, CHCl3). 1H NMR (300 MHz, CDCl3) for the major
isomer of (S,S)-4: d = 0.93 (d, J = 6.6 Hz, 3 H, CH3), 1.02 (d,
J = 6.6 Hz, 3 H, CH3), 3.45 [sept, J = 7.0 Hz, 1 H,
CH(CH3)2], (dd, J = 13.6 Hz, JPH = 5.2 Hz, 1 H, CHN), 6.57
(d, J = 13.6 Hz, 1 H, CHN), 6.92–7.79 (m, 27 H, CHAr), 7.82
(d, J = 8.5 Hz, 1 H, CHNaph), 7.99 (d, J = 7.7 Hz 1 H, CHNaph),
8.11 (br s, 1 H, NCHN), 8.54 (d, J = 8.8 Hz, 1 H, CHNaph).
13C NMR (125.8 MHz, CDCl3) for the major isomer of (S,S)-
4: d = 23.60, 24.96, 27.70, 74.97, 79.00 (d, J = 14.1 Hz),
124.36, 126.18, 126.88, 127.26, 127.54, 128.54, 128.87,
128.94, 129.11, 129.13, 129.24 (d, J = 6.6 Hz), 129.39 (d,
J = 7.5 Hz), 129.56, 129.72, 129.77, 129.98, 130.08, 130.15,
130.26, 130.66 (d, J = 4.7 Hz), 130.96, 131.42, 132.23,
132.38 (d, J = 14.1 Hz), 132.68 (d, J = 18.8 Hz), 133.30 (d,
J = 19.8 Hz), 133.76 (d, J = 18.8 Hz), 134.05 (d, J = 6.6 Hz),
134.30, 134.73 (d, J = 5.7 Hz), 136.41 (d, J = 25.4 Hz),
144.35, 157.38. 31P NMR (121.5 MHz, CDCl3): d = –19.52
(s, minor isomer, 13%), –21.80 (s, major isomer, 87%).
HRMS (FAB+, direct insert): m/z calcd for C46H40N2P [M –
BF4]+: 651.2929. Found: 651.2936.
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colorless crystal (polyhedron), dimensions 0.12 × 0.17 × 0.2
mm3, crystal system orthorhombic, space group P21212,
Z = 2, a = 16.730 (2) Å, b = 22.902 (3) Å, c = 11.2472 (15)
Å, V = 4309.3 (10) Å3, r = 1.303 g/cm3, T = 200(2) K,
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(software package SHELXTL V5.10 for structure solution
and refinement, G. M. Sheldrick, Bruker Analytical X-ray-
Division, Madison, Wisconsin 1997), 525 parameters
refined, hydrogen atoms were treated using appropriate
riding models, Flack absolute structure parameter 0.07 (6),
goodness of fit 1.21 for observed reflections, final residual
values R1 (F) = 0.077, wR2 (F2) = 0.167 for observed
reflections, residual electron density –1.14 to 1.10 eÅ–3.
CCDC 236937 contains the supplementary crystallographic
data for this structure. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html [or
from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK;
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0.30, CHCl3). 1H NMR (300 MHz, CDCl3, signals of major
and minor isomer are distinguished by indices a and i,
respectively): d = 0.52 (d, J = 6.4 Hz, 3 Ha, CH3), 1.15 (d,
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Synlett 2004, No. 10, 1789–1793 © Thieme Stuttgart · New York

LETTER
Complexes of a Novel Chiral Diphenylphosphino-Functionalized N-Heterocyclic Carbene
1793
J = 6.6 Hz, 3 Ha, CH3), 1.11–1.23 (m, COD-CH2), 1.29 (d,
Hz), 142.32 (d, JCP = 13.2 Hz), 143.70, 144.32 (d, JCP = 12.3
Hz), 144.78, 207.67 (d, JRhC = 44.4 Hz, only visible in
13C{31P}), 209.87 (d, JRhC = 43.5 Hz, only visible in
13C{31P}). 31P NMR (202.47 MHz, CDCl3, 253 K): d = 17.89
(d, JRhP = 168.1 Hz, major isomer, 66%), 19.90 (d,
JRhP = 162.0 Hz, minor isomer, 33%). HRMS (FAB+, direct
insert): m/z calcd for C54H51N2PRh [M – BF4]+: 861.2844.
Found: 861.2820.
J = 6.8 Hz, 3 Hi, CH3), 1.41 (d, J = 6.6 Hz, 3 Hi, CH3), 1.34–
1.77 (m, COD-CH2), 2.00–2.34 (m, COD-CH2), 2.37 (br s, 1
Hi, COD-CH2), 2.86 [sept, J = 6.7 Hz, 1 Ha, CH(CH3)2], 3.18
[sept, J = 6.8 Hz, 1 Hi, CH(CH3)2], 3.62–3.78 (m, 1 Ha + 1
Hi, COD-CH), 3.91–4.05 (m, 1 Ha + 1 Hi, COD-CH), 4.59 (d,
J = 10.7 Hz, 1 Hi, CHN), 4.96 (d, J = 5.1 Hz, 1 Ha, CHN),
5.36–5.48 (m, 1 Ha + 1 Hi, COD-CH), 5.50–5.60 (m, 1 Hi,
COD-CH), 5.79–5.90 (m, 2 Ha + 1 Hi, 2 CHN, COD-CH),
6.16 (d, J = 7.4 Hz, 1 Ha, CHAr), 6.23 (d, J = 7.4 Hz, 1 Hi,
CHAr), 6.67 (t, J = 7.8 Hz, 1 Ha, CHAr), 6.84 (t, J = 7.6 Hz, 1
Hi, CHAr), 6.89–7.97 (m, 28 Ha + 28 Hi, CHAr). 13C NMR
(125.67 MHz, CDCl3, 253 K, major and minor isomer): d =
23.58, 23.83, 25.30, 25.32, 25.75, 25.95, 26.04, 28.42, 29.03
(2 C), 34.19, 34.26, 35.77, 36.57, 75.24, 76.70, 78.69, 81.60,
88.31 (dd, JCP = 15.5 Hz, JCRh = 6.2 Hz), 88.57 (dd,
(22) With PhCF3, n-hexane, MeOH, and THF enantioselectivities
were lower.
(23) Representative Procedure for Catalytic Hydrogenation:
Preparation of (R)-8: An autoclave was charged with
dimethyl itaconate (158 mg, 1.00 mmol), (S,S)-6 (0.9 mg,
1.0 mmol) and CH2Cl2 (15 mL). The autoclave was then
sealed and pressurized to 30 bar of H2. The reaction mixture
was stirred for 20 h at r.t. The solution was passed over a
short plug of silica gel with CH2Cl2 as eluent. After
evaporation of the solvent, 2-methyl-succinic acid dimethyl
ester was obtained in quantitative yield. The ee value was
determined to be 98.2% ee by GC on a chiral phase
(analytical data cf. Table 1).
(24) (a) The rhodium complex (S,S)-6 was also tested in the
catalytic asymmetric addition of phenylboronic acid to
enones. Using 3 mol% of the complex (S,S)-6
enantioselectivities up to 94% could be achieved (b) J.-M.
Becht and E. Bappert, unpublished results.
(25) Ostermeier, M.; Brunner, B.; Korff, C.; Helmchen, G. Eur.
J. Org. Chem. 2003, 17, 3453.
JCP = 14.5 Hz, JCRh = 6.4 Hz), 93.03 (m), 94.39 (dd,
JCP = 10.3 Hz, JCRh = 4.7 Hz), 100.46 (d, JCP = 6.0 Hz),
101.05 (d, JCP = 6.4 Hz), 102.81 (d, JCP = 5.2 Hz), 104.06 (d,
JCP = 6.0 Hz), 121.31 (d, JCP = 49.9 Hz), 122.86 (d,
JCP = 49.0 Hz), 122.86, 123.95, 124.64 (m), 125.17, 125.41,
125.77, 126.15, 126.49, 126.54, 126.74 (d, JCP = 4.3 Hz),
127.10 (d, JCP = 6.6 Hz), 127.35, 127.43, 127.69, 127.74,
127.86, 128.33–128.63 (several signals are overlapping in
this range), 128.78, 128.88 (d, JCP = 34.9 Hz), 129.11,
129.27, 129.44, 129.66, 130.16, 130.26, 130.56, 130.63,
130.75 (d, JCP = 37.2 Hz), 131.38, 131.53, 132.03, 132.53 (d,
JCP = 11.3 Hz), 132.78, 133.52 (d, JCP = 44.26 Hz), 133.75,
133.91, 134.46, 134.95, 135.53, 137.21, 139.14 (d, JCP = 2.1
Synlett 2004, No. 10, 1789–1793 © Thieme Stuttgart · New York