Cis-Selective Asymmetric Cyclopropanation
Organometallics, Vol. 20, No. 10, 2001 2107
[Ru Cl2(1a )], 2a . [RuCl2(PPh3)3] (635 mg, 0.66 mmol) and
1a (500 mg, 0.66 mmol) were refluxed in toluene (20 mL)
overnight. Partial evaporation of the solvent gave a bordeaux-
red solid that was recrystallized from CH2Cl2/pentane. Yield:
536 mg (90%). 1H NMR (250 MHz, CDCl3): 8.6 (d, 1H, Nd
CH, J ) 6.2), 7.6-6.7 (m, 34H, arom), 6.0 (d, 1H, J ) 6.2 Hz,
NdCH), 1.9 (s, 6H, 2 CH3). 31P NMR (101 MHz, CDCl3): 46.5
(s, 2P). MS (FAB+) (m/z): 930 ([M + 2 H]+, 100), 928 (M+, 50),
893 [(M - Cl]+, 22). Anal. Calcd for C52H42Cl2N2P2Ru‚0.5CH2-
Cl2: C, 64.92; H, 4.46; N: 2.88. Found: C, 65.10; H, 4.94; N,
2.58.
Ch a r t 2
[Ru Cl(1a )]P F 6, 3a . Complex 2a (185 mg, 0.199 mmol) and
Tl[PF6] (10 mg, 0.20 mmol) were stirred in CH2Cl2 (15 mL)
for 14 h. The precipitated TlCl was filtered off over Celite.
Addition of pentane to the resulting clear solution and partial
evaporation of the solvent gave a brown solid that was
recrystallized from CH2Cl2/pentane. The complex tenaciously
retains variable amounts of crystallization solvents, resulting
1
in erratic elemental analyses. Yield: 124 mg (60%). H NMR
(300 MHz, CDCl3): δ 8.90 (d, 1 H, J H,H′ ) 9.6 Hz, NdCH),
7.9-6.3 (m, 34H, arom), 4.40 (d, 1 H, J H,H′ ) 7.8 Hz, NdCH).
31P NMR: 80.8 (d, 2P, J P,P′ ) 27.6 Hz), 42.9 (d, 2P, J P,P ) 27.6
Hz). MS (FAB+) (m/z): 893 (M+, 100), 858, ([M - Cl]+, 6).
Typ ica l Ca ta lytic Ru n . Complex 3a (20 mg, 21 µmol, 5
mol %) and Tl[PF6] (7.3 mg, 21 µmol) were dissolved in CH2-
Cl2 (1 mL) and stirred overnight, and then TlCl was filtered
off and the resulting red-brown solution was added to the olefin
(0.42 mmol) and decane (50 mg, as internal standard). A
solution of the diazoester (0.42 mmol) in CH2Cl2 (1 mL) was
added with a syringe pump over 6 h. The solution, which was
protected from light throughout the reaction, was stirred for
an additional 14 h at room temperature and then analyzed by
GC. The reactions with a substrate-to-catalyst ratio of 100:1
(1 mol % catalyst) were performed using more olefin (2.1 mmol)
and diazoester (2.1 mmol). Yields were obtained by GC. In
selected instances, we isolated the cyclopropanation product
by column chromatography. The isolated yields are within
(10% of those obtained by GC.
Chart 2, 3b and 12 possess similar steric features
concerning the possible approach trajectories of the
incoming olefin. In both complexes, bulky groups (either
PPh2 or 1-phenyl-naphthyl) block the approach along
the Ru-P or Ru-O vector, and the cyclohexyl moiety
directs the approach along one Ru-N direction. The
presence of the latter stereogenic element is apparently
pivotal for high cis selectivity. Indeed, the apparently
related complex 13, in which the cyclohexenediyl moiety
is missing, prevalently forms the trans cyclopropane
derivative with selectivity in the range 66-98%.29a
Exp er im en ta l P a r t
Gen er a l Com m en ts. Reactions with air- or moisture-
sensitive materials were carried out under an argon atmos-
phere using Schlenk techniques. Styrene, (1S,2S)-(+)-1,2-
diaminocyclohexane, 2,5-dimethyl-2,4-hexadiene, and ethyl
chrysanthemate (30:70 mixture of cis and trans) were obtained
from Fluka AG. 2-(Diphenylphosphino)benzaldehyde was pur-
chased from Aldrich, Tl[PF6] from Strem Chemicals, and ethyl
trans-2-phenylcyclopropane from Lancaster. Enantiomerically
pure (S)-2,2′-diamino-6,6′-dimethylbiphenylene was obtained
from Solvias AG (Basel). Ligand 1b and complexes 2b and 3b
were prepared as previously reported.13b 1H and 31P NMR
A control reaction without the catalyst indicated that the
cyclopropane derivatives 4 and 5 were formed only in traces
under the conditions used. The yields of the uncatalyzed
reaction were 0.03% and 0.13% for the cis and trans products,
respectively.
An a lyt ic Det a ils (GC, ee, Ab solu t e Con figu r a t ion ).
Eth yl 2-P h en yl-cylopr opan ecar boxylate. Achiral GC analy-
sis: Macherey-Nagel SE 54, 30 m, He carrier (92 kPa).
Temperature program: 50 °C isotherm for 5 min, then to 200
°C at 5 °C min-1. Rt (min): styrene, 10.2; decane, 14.25; ethyl
cis-2-phenylcyclopropanecarboxylate, 28.2; ethyl trans-2-phe-
nylcyclopropanecarboxylate, 29.7. Chiral GC analysis: Supelco
Beta Dex 120, 1.4 mL He min-1; temperature program: 110
°C for 10 min, 5 °C min-1 to 150 °C, isotherm for 20 min. Rt
(min): cis-(1R,2S), 26.0; cis-(1S,2R), 26.38; trans-(1R,2R),
28.09; trans-(1S,2S), 28.34. The GC peaks were attributed by
comparison with an authentic sample with a known E/Z ratio
(99:1, Lancaster). The absolute configurations are (1R,2S) for
4 and (1S,2S) for 5 (by the sign of the optical rotation of the
isolated products).30
1
spectra were recorded on Bruker DPX spectrometers. H and
13C positive chemical shifts in ppm are downfield from tet-
ramethylsilane. 31P NMR spectra were referenced to external
85% H3PO4. Mass spectra were measured by the MS service
of the Laboratorium fu¨r Organische Chemie (ETH Zu¨rich). A
3-NOBA (3-nitrobenzyl alcohol) matrix and a Xe atom beam
with a translational energy of 8 keV were used for FAB+ MS.
Optical rotations were measured using a Perkin-Elmer 341
polarimeter with a 1 dm cell. Elemental analyses were carried
out by the Laboratory of Microelemental Analysis (ETH
Zu¨rich). Molecular modeling calculations were performed on
a Silicon Graphics O2 platform with the Cerius2 program (MSI)
using standard UFF settings.
ter t-Bu tyl 2-P h en ylcyclop r op a n eca r boxyla te. Achiral
GC analysis: Macherey-Nagel SE 54, 30 m, He carrier (92
kPa). Temperature program: 50 °C isotherm for 5 min, then
to 200 °C at 5 °C min-1. Rt (min): styrene, 10.0; decane, 14.10;
tert-butyl cis-2-phenylcyclopropanecarboxylate, 29.95; tert-
butyl trans-2-phenylcyclopropanecarboxylate, 31.29. Chiral GC
analysis: Supelco Beta Dex 120, 1.4 mL He min-1; tempera-
ture program: 110 °C for 10 min, 5 °C min-1 to 150 °C,
isotherm for 20 min. Rt (min): cis-(1R,2S), 27.68; cis-(1S,2R),
28.06; trans-(1R,2R), 31.08; trans-(1S,2S), 31.26. Product
isolated from a catalysis run was used for GC calibration. The
(S)-N,N′-Bis[2-(d ip h en ylp h osp h in o)ben zylid en e]-2,2′-
d ia m in o-6,6′-d im eth ylbip h en ylen e, (S)-1a . (S)(-)-2,2′-Di-
amino-(S)-6,6′-dimethylbiphenylene (292 mg, 1.38 mmol) and
2-diphenylphosphinobenzaldehyde (800 mg, 2.76 mmol) were
refluxed in toluene (15 mL) in a Dean-Stark apparatus for 14
h. Evaporation of the solvent in a vacuum and recrystallization
of the resulting yellow oil from toluene/MeOH (4:1) gave a
yellow solid. Yield: 998 mg (96%). Mp: 69 °C. [R]D20: -224.9
1
( 2 (c ) 1, CHCl3). H NMR: δ 8.9 (d, 2H, NdCH, J P,H ) 5.5
Hz), 7.7-6.75 (m, 32H, arom.), 6.3 (d, 2H, arom.), 1.9 (s, 6H,
2CH3). 31P NMR: δ -13.6 (s, 2P). IR (KBr, cm-1): 1624 (s,
ν
CN). MS (FAB+) (m/z): 757 ([M + H]+, 61), 756 (M+, 24), 468
([M + H - NdCPPh2]+, 100).
(30) Krieger, P. E.; Landgrebe, J . A. J . Org. Chem. 1978, 43, 4447.