Synthesis of enantiopure 1-r-aryl-2-c,5-t-diphenylphospholane oxides and boranes by Pd-catalyzed C-P bond formation

Article abstract of DOI:10.1002/ejoc.200500577

New chiral enantiopure phospholane oxides 1 and boranes 5 were obtained from efficient carbon-phosphorus bond formation by organocuprate or palladium-catalyzed reactions. C-P cross-coupling reactions between chiral phosphane oxide 3 or borane 4 and variou

Full text of DOI:10.1002/ejoc.200500577

FULL PAPER
DOI: 10.1002/ejoc.200500577
Synthesis of Enantiopure 1-r-Aryl-2-c,5-t-diphenylphospholane Oxides and
Boranes by Pd-Catalyzed C–P Bond Formation
Martial Toffano,[a] Cristian Dobrota,[a] and Jean-Claude Fiaud*[a]
Keywords: Boranes / Cross-coupling / C–P bond formation / Homogeneous catalysis / Ligand design
New chiral enantiopure phospholane oxides 1 and boranes 5
were obtained from efficient carbon–phosphorus bond for-
mation by organocuprate or palladium-catalyzed reactions.
C–P cross-coupling reactions between chiral phosphane ox-
ide 3 or borane 4 and various aryl derivatives are presented.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
framework by substitution of the corresponding phosphin-
oyl chloride 2 with an organocuprate reagent. Since the
phosphorus atom in 1 is not stereogenic, one does not have
to pay attention to the stereochemistry of the substitution.
The results are collected in Table 1.
A large variety of enantiopure P-aryl-2,5-diphenylphos-
pholane oxides were thus obtained. However, since the sub-
stitution of heteroaryl groups such as 2-pyridyl and 2-
benzothiophenyl failed, and the yields of substitution by 1-
and 2-naphthyl groups were only moderate in this stoichio-
metric reaction, we looked for another, preferentially cata-
lytic, procedure.
To the best of our knowledge, most of the coupling part-
ners involved in palladium- or nickel-catalyzed C–P bond
formation are not chiral mono- or diarylphosphanes or
their derivatives (oxides, boranes),[6] and no example of a
coupling reaction with a chiral secondary phosphane oxide
exists.
We report here a palladium-catalyzed C–P bond forma-
tion by coupling a chiral dialkylphosphane oxide 3 with aryl
and heteroaryl iodides, bromides and triflates. The reaction
was carried out in the presence of 10 mol-% of palladium
acetate, 12 mol-% of 1,3-bis(diphenylphosphanyl)propane
(dppp) as ligand, and iPr2NEt as base in DMSO (Table 2).
The synthesis of compound 3 was described in our previous
paper.
The coupling reaction is quite general and clean, and can
be used to prepare a wide variety of P-aryl-2,5-diphenyl-
phospholane oxides. The yields recorded for 1a–f were
lower than those obtained from the method involving orga-
nocopper reagents. However, naphthyl and heteroaryl sub-
strates afforded products 1g–j in good yields. It is note-
worthy that no epimerization at the benzylic carbon atoms
of the phospholane ring, which would have led to dia-
stereomeric or enantiomeric compounds, was observed.
In order to find out a further way of synthesizing P-
arylphospholane compounds, we investigated the secondary
Introduction
The elaboration of new chiral phosphanes is of impor-
tance since they still play a major role as ligands in transi-
tion-metal-based asymmetric catalysis.[1] Although diden-
tate phosphane ligands are the most documented, interest
has grown recently in the use of monophosphanes as li-
gands for transition metals but also as organic catalysts.[2]
Since organic catalysis mediated by phosphanes involves
their nucleophilic properties, it appears of interest to syn-
thesize new dialkylaryl- and trialkylphosphanes. The dialkyl
or trialkyl substitution of the phosphorus atom provides an
electron-rich and basic ligand that differs from the usual
asymmetric mono- or diphosphanes, which possess two or
three aryl substituents on phosphorus.[3]
With this in mind, we designed a new monophosphane
ligand based on the 2,5-disubstituted phospholane frame-
work, namely the new electron-rich, chiral, and enantiopure
1-r,2-c,5-t-triphenylphospholane, which was obtained by re-
duction of the corresponding phospholane oxide 1a.[4] This
monodentate phosphane shows high activity and selectivity
(93% ee) in rhodium-catalyzed hydrogenation of methyl de-
hydrocinnamate.[5]
In order to investigate the influence of the nature of the
P-substituent on the 2,5-diphenylphospholane moiety, we en-
visaged to set up methods to produce a range of enantiopure
substituted P-aryl-2-c,5-t-diphenylphospholane oxides 1 and
boranes 5.
Results and Discussion
We initially developed a method to provide the arylation
of the chiral, enantiopure trans-2,5-diphenylphospholane
[a] Laboratoire de Catalyse Moléculaire (CNRS – UMR 8075), In-
stitut de Chimie Moléculaire et des Matériaux d’Orsay, Bât.
420, Université Paris Sud
91400 Orsay cedex, France
Fax: +33-1-6915-4680
E-mail: fiaud@icmo.u-psud.fr
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New Chiral Enantiopure Phospholane Oxides
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Table 1. Synthesis of (2S,5S)-1-aryl-1-oxo-2,5-diphenylphospholane 1a–j by copper substitution.
[a] Isolated yield. [b] Organolithium reagents were prepared from the corresponding aryl bromide and one equiv. of nBuLi in THF at
–78 °C, except for 1e and 1f, where tBuLi was used.
Table 2. Synthesis of (2S,5S)-1-aryl-1-oxo-2,5-diphenylphospholanes 1a–j by palladium-catalyzed cross-coupling of the secondary phos-
pholane oxide 3.
[a] Isolated yield.
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651

M. Toffano, C. Dobrota, J.-C. Fiaud
FULL PAPER
phosphane–borane complex 4 as a coupling partner.[7] This
phosphane–borane was prepared from the enantiomerically
pure 2,5-diphenylphospholane. The (S,S)-2,5-diphenylphos-
pholane–borane 4 was coupled with various aryl halides
and triflates in the presence of [Pd(PPh3)4] as catalyst pre-
cursor and K2CO3 as base (Table 3).
Table 3. Palladium-catalyzed cross-coupling of secondary trans-2,5-
diphenylphospholane–borane complex 4.
Scheme 2. Synthesis of phosphane 5m by Rh-catalyzed hydrogena-
tion of 1a.
Conclusions
In summary, several enantiopure ligand precursors based
on the 1-aryl-trans-2,5-diphenylphospholane structure have
been prepared by C–P bond construction using three ef-
ficient complementary methods from phospholanyl chlo-
ride, secondary phospholane oxide, or borane. The prepara-
tions of the corresponding phosphanes and their applica-
tions in asymmetric catalysis are currently underway.
1
[a] Isolated yield. [b] Conversion determined by H NMR spec-
troscopy.
Experimental Section
1
General Remarks: H NMR spectra were recorded on Bruker 250,
360, or 400 MHz spectrometers. Chemical shifts are reported in
ppm (δ) relative to tetramethylsilane as internal reference (δ =
0.0 ppm). 13C NMR spectra were recorded on Bruker 250 MHz
(62.9 MHz) or 300 MHz (75.45 MHz) spectrometers with complete
proton decoupling. 31P NMR spectra were recorded with a
101.2 MHz spectrometer with complete proton decoupling. The
corresponding chemical shifts are reported in ppm (δ) relative to
the residual deuterated solvent or external phosphoric acid (δ =
0.0 ppm). Flash column chromatography was performed using sil-
ica gel Merck (0.04–0.063 µm). Optical rotations were recorded at
the sodium D line with a Perkin–Elmer 341 polarimeter. [α] is al-
ways given without the units (understood to be degcm2 g–1). High-
resolution mass spectra were obtained with a MAT95 Thermo-Fin-
nigan spectrometer using electrospray analysis. All reactions were
carried out in Schlenk tubes under argon. All solvents were distilled
from appropriate drying agents prior to use. Palladium tetrakis(tri-
phenylphosphane) and 4-bromodibenzothiophene[10] were prepared
as described in the literature. Aryl triflates were prepared from the
corresponding phenol and trifluoromethanesulfonic anhydride. All
other reagents are available commercially and were used without
further purification [CuBr–dimethylsulfide complex (Aldrich), cop-
per iodide (Aldrich), borane–dimethyl sulfide complex (Aldrich),
palladium acetate (Aldrich), RhCl3·4H2O (Prolabo)]. The synthesis
and experimental data of products 1a, 2, and 3 were described in
our previous paper.[4a]
In no case did we observe a total conversion, and the
purification of products 5 was therefore more difficult. This
poor reactivity was attributed to the low degradation of the
substrate under the reaction conditions.
Phosphane–borane 5 could also be obtained by re-
duction of the phosphane oxide following Imamoto’s pro-
cedure.[8] Treatment of the oxide with methyl triflate, fol-
lowed by LiAlH4 and borane, gave the enantiomerically
pure phosphane–borane (Scheme 1).
Scheme 1. Synthesis of phosphane–borane 5.
During the course of our investigation to synthesize
more electron-rich ligands, we found that the phosphane
oxide 1a could be hydrogenated in the presence of
RhCl3·4H2O catalyst under a high pressure of dihydrogen[9]
to give the (2S,5S)-1,2,5-tricyclohexylphosphane oxide 1m
in excellent yield (Scheme 2). Reduction of this phosphane
oxide followed by protection with borane offered enantio-
merically pure electron rich (2S,5S)-1,2,5-tricyclohexyl-
phosphane–borane 5m.
General Procedure for Organocopper Substitution of (S,S)-2: A solu-
tion of the appropriate organolithium reagent in THF (7.3 mmol)
was added slowly to a Schlenk tube containing a suspension of the
CuBr–dimethylsulfide complex (1.5 g, 7.3 mmol) in THF (20 mL)
at –40 °C. The resulting deep yellow solution was stirred for 10 min
at –40 °C and then for 5 min at room temperature. After cooling
down to –60 °C, the phenylcopper solution was added to a preco-
oled (–60 °C) solution of phosphinoyl chloride (2S,5S)-2, prepared
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New Chiral Enantiopure Phospholane Oxides
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from (–)-(2S,5S)-1-hydroxy-l-oxo-2,5-diphenylphospholane[4a] (2 g,
7.34 mmol). The mixture was stirred for 15 min at –60 °C, and
from –60 °C to room temperature overnight. The reaction was
quenched with a 1:1 mixture of a concentrated aqueous solution
of ammonia and saturated NH4Cl aqueous solution (50 mL) and
diluted with dichloromethane. It was vigorously stirred until a dark
blue color appeared. The blue solution was extracted with dichloro-
methane, the organic layer washed with brine, dried with anhydrous
magnesium sulfate, and concentrated. The white solid was sub-
jected to chromatographic purification on silica gel to give a white
product, which was recrystallized from EtOAc/hexane to give the
desired phosphane oxide 1.
(m, 14 H), 3.65–3.90 (m, 2 H), 2.40–2.80 (m, 3 H), 2.20 (s, 3 H),
2.00–2.20 (m, 1 H), 1.45 (m, 2 H) ppm. 13C NMR (75.45 MHz,
CDCl3): δ = 21.5 (s), 30.65 (d, JP,C = 8 Hz), 31.85 (d, JP,C = 8 Hz),
45.40 (d, JP,C = 63 Hz), (s), 52.00 (d, JP,C = 62 Hz), 124.85(d, JP,C
= 12 Hz), 126.35 (d, JP,C = 2.5 Hz), 126.85 (d, JP,C = 1.8 Hz), 127.9
(d, JP,C = 5 Hz), 128.00 (d, JP,C = 1.8 Hz), 128.50 (d, JP,C = 1 Hz),
129.10 (d, JP,C = 5 Hz), 130.60 (d, JP,C = 11.2 Hz), 131.50 (d, JP,C
= 3 Hz), 131.65 (d, JP,C = 10.5 Hz), 136.30 (d, JP,C = 5 Hz), 137.25
(d, JP,C = 3 Hz), 144.00 (d, JP,C = 6.5 Hz) ppm. 31P NMR
(101.2 MHz, CDCl3): δ = 59.4 ppm. HRMS (IE): calcd. for
C23H23OP 346.1487; found 346.1486.
(2S,5S)-(–)-1-Oxo-2,5-diphenyl-1-(p-tolyl)phospholane (1c): The
product was purified by flash chromatography on silica gel using
CH2Cl2/MeOH (95:5) as eluent. Recrystallization from EtOAc/hex-
General Procedure for Palladium-Catalyzed Cross-Coupling of Sec-
ondary Phospholane Oxide 3: Palladium acetate (22.5 mg,
0.1 mmol) and 1,3-bis(diphenylphosphanyl)propane (dppp) (62 mg,
0.15 mmol) were dissolved in DMSO (1 mL) in a Schlenk tube un-
der argon. The yellow solution was stirred for 15 min at room tem-
perature. The solution was added to a solution of (S,S)-3 (1 mmol),
diisopropylethylamine (4 mmol), and the appropriate aryl halide or
triflate (1.2 mmol) in DMSO (2 mL). The mixture was heated at
100–110 °C for the appropriate time. After cooling and hydrolysis
with water, the aqueous phase was extracted with dichloromethane.
The organic layer was washed with water (2×10 mL) and then
dried with MgSO4. Evaporation of the solvent gave a residue that
was purified by flash chromatography on silica gel. The white prod-
uct was recrystallized from EtOAc/hexane to give the desired phos-
phane oxide 1.
ane gave the desired phosphane oxide as white crystals. [α]2D0
=
1
–156 (c = 1, CHCl3). H NMR (250 MHz, CDCl3): δ = 7.40–7.15
(m, 8 H), 7.10–7.95 (m, 6 H), 3.85 (ddd, J = 6.8, 12.7, 25.39 Hz, 1
H), 3.55 (s, 1 H), 2.80–2.40 (m, 3 H), 2.25 (m, 3 H), 2.30–2.10 (m,
1 H) ppm. 13C NMR (62.9 MHz, CDCl3): δ = 21.3 (d, JP,C
=
1.5 Hz), 27.80 (d, JP,C = 8.5 Hz), 31.35 (d, JP,C = 7 Hz), 46.80 (d,
JP,C = 62 Hz), 51.1 (d, JP,C = 61.5 Hz), 126.20 (d, JP,C = 2 Hz),
126.40 (s), 126.80 (d, JP,C = 2 Hz), 127.10 (d, JP,C = 5 Hz), 128.10
(d, JP,C = 2.5 Hz), 128.4 (d, JP,C = 1.5 Hz), 128.60 (d, JP,C = 4.5 Hz),
128.70 (d, JP,C = 3 Hz), 131.10 (d, JP,C = 9 Hz), 135.70 (d, JP,C
=
5 Hz), 136.00 (d, JP,C = 3 Hz), 141.70 (d, JP,C = 3 Hz) ppm. 31P
NMR (101.2 MHz, CDCl3): δ = 53.4 ppm. HRMS (IE): calcd. for
C23H23OP 346.1487; found 346.1480.
General Procedure for Palladium-Catalyzed Cross-Coupling of Sec-
ondary Phospholane–Borane Complex 4: Tetrakis(triphenylphos-
phane)palladium (58 mg, 0.05 mmol), 2,5-diphenylphospholane–
borane (4; 253 mg, 1 mmol), and the appropriate aryl triflate
(1.2 mmol) were dissolved in CH3CN (5 mL) in a Schlenk tube
under argon. The solution was stirred for 5 min at room tempera-
ture and was then added to a solution of K2CO3 (2 mmol) in 5 mL
of acetonitrile. The mixture was heated at 40 °C for 16 h. After
cooling and hydrolysis with HCl solution (3 n), the aqueous phase
was extracted with dichloromethane. The organic layer was washed
with brine (10 mL) and then dried with MgSO4. Evaporation of
the solvent gave a residue that was purified by flash chromatog-
raphy on silica gel using pentane/ethyl acetate (90:10) as eluent to
give the desired phosphane–borane 5.
(2S,5S)-(–)-1-(o-Anisyl)-1-oxo-2,5-diphenylphospholane (1d): The
product was purified by flash chromatography on silica gel using
CH2Cl2/MeOH (95:5) as eluent. Recrystallization from EtOAc/hex-
ane gave the desired phosphane oxide as colorless needles. [α]2D0
=
1
–140 (c = 1, CHCl3). H NMR (250 MHz, CDCl3): δ = 7.80 (ddd,
J = 12.7, 8, 2 Hz, 1 H), 6.80–7.40 (m, 12 H), 6.5 (dd, J = 8, 5.5 Hz,
1 H), 3.70–3.40 (m, 2 H), 2.35–3.80 (m, 1 H) ppm. 13C NMR
(62.9 MHz, CDCl3): δ = 26.00 (d, JP,C = 7.6 Hz), 30.75 (d, JP,C
=
7 Hz), 45.00 (d, JP,C = 63 Hz), 50.00 (d, JP,C = 64 Hz), 54.2 (s),
109.30 (d, JP,C = 6.5 Hz), 117.8 (s), 120.30 (d, JP,C = 10.5 Hz), 125.5
(d, JP,C = 2.4 Hz), 126 (s), 126.1(s), 127.00 (d, JP,C = 2 Hz), 127.8
(d, JP,C = 2 Hz), 128.3 (d, JP,C = 5 Hz), 133.40 (d, JP,C = 2 Hz),
135.10 (d, JP,C = 5 Hz), 135.70 (d, JP,C = 5.8 Hz), 135.9 (d, JP,C
=
4 Hz), 158.3 (d, JP,C = 5 Hz) ppm. 31P NMR (101.2 MHz, CDCl3):
δ = 56.5 ppm. C23H23O2P: calcd. C 76.23, H 6.40, P 8.55; found C
75.98, H 6.39, P 8.49. MS (IE): 385 [M + Na+], 747 [2M + Na+].
General Procedure for Preparation of Phosphane–Borane 5 by Phos-
phane Oxide Reduction: Methyl trifluoromethanesulfonate (125 µL,
1.1 mmol) was added to the appropriate phosphane oxide 3
(1 mmol) dissolved in DME (10 mL) under argon. After 2 h the
mixture was cooled down to 0 °C and lithium aluminum hydride
(57 mg, 1.5 mmol) was added. The mixture was warmed to room
temperature and stirred for an additional 15 h. After hydrolysis
with a minimum amount of water, the mixture was filtered under
argon through Celite via a cannula. Borane–dimethylsulfide com-
plex (0.379 mL) was then added to the resulting solution at 0 °C
and stirred for 2 h. After hydrolysis with HCl solution (1 n), the
aqueous phase was extracted with dichloromethane. The organic
layer was washed with brine (10 mL) and then dried with MgSO4.
Evaporation of the solvent gave a residue that was purified by flash
chromatography on silica gel with heptane/ethyl acetate (95:5) to
give the desired phosphane–borane 5.
(2S,5S)-(–)-1-(3,5-Dimethylphenyl)-1-oxo-2,5-diphenylphospholane
(1e): The product was purified by flash chromatography on silica
gel using CH2Cl2/MeOH (98:2) as eluent. Recrystallization from
EtOAc/hexane gave the desired phosphane oxide as fine colorless
needles. [α]2D0 = –136 (c = 1, CHCl3). 1H NMR (250 MHz, CDCl3):
δ = 7.20–7.30 (m, 5 H), 6.80–7.10 (m, 8 H), 3.8 (m, 1 H), 3.55 (m,
1 H), 2.40–2.80 (m, 3 H), 2.30 (m, 1 H), 2.15 (s, 6 H) ppm. 13C
NMR (62.9 MHz, CDCl3): δ = 21.00 (s), 27.80 (d, JP,C = 8 Hz),
31.30 (d, JP,C = 7 Hz), 46.70 (d, JP,C = 61 Hz), 51.00 (d, JP,C
=
61 Hz), 126.25 (d, JP,C = 3 Hz), 126.80 (d, JP,C = 3 Hz), 127.10 (d,
JP,C = 4.5 Hz), 128.00 (d, JP,C = 2 Hz), 128.40 (d, JP,C = 2 Hz),
128.75 (d, JP,C = 2 Hz), 128.80 (s), 133.15 (d, JP,C = 3 Hz), 135.70
(d, JP,C = 5.5 Hz), 136.00 (d, JP,C = 3 Hz), 137.40 (d, JP,C = 13Hz)
ppm. 31P NMR (101.2 MHz, CDCl3): δ = 53.8 ppm. HRMS (IE):
calcd. for C24H25OP 360.1632; found 360.1643.
(2S,5S)-(–)-1-Oxo-2,5-diphenyl-1-(o-tolyl)phospholane (1b): The
product was purified by flash chromatography on silica gel using
CH2Cl2/MeOH (95:5) as eluent. Recrystallization from EtOAc/hex-
(2S,5S)-(+)-1-(3,5-Di-tert-butylphenyl)-1-oxo-2,5-diphenylphosphol-
ane (1f): The product was purified by flash chromatography on
silica gel using CH2Cl2/MeOH (98:2) as eluent. Recrystallization
from EtOAc/hexane gave the desired phosphane oxide as a white
ane gave the desired phosphane oxide as colorless needles. [α]2D0
–135 (c = 1, CHCl3). H NMR (300 MHz, CDCl3): δ = 6.90–7.60
=
1
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solid. [α]2D0 = +103 (c = 1, CHCl3). H NMR (250 MHz, CDCl3):
1
5.5 Hz), 135.25 (d, JP,C = 8 Hz), 136.15 (d, JP,C = 5 Hz), 149.10 (d,
δ = 7.10–7.40 (m, 8 H), 7.05 (m, 5 H), 3.70–4.00 (m, 1 H), 3.50– JP,C = 20 Hz), 153.55 (s), 155.70 (s) ppm. 31P NMR (101.2 MHz,
3.60 (m, 1 H), 2.40–2.80 (m, 3 H), 2.15–2.35 (m, 1 H), 1.2 (s, 18
H) ppm. 13C NMR (50 MHz, CDCl3): δ = 28.28 (d, JP,C = 8.5 Hz),
31.40 (s), 31.60 (d, JP,C = 7.5 Hz), 35.00 (s), 46.50 (d, JP,C = 62 Hz),
CDCl3): δ = 54.5 ppm. HRMS (IE): calcd. for C21H20NOP
333.1279; found 333.1279.
(2S,5S)-(–)-1-(4-Dibenzothiophenyl)-1-oxo-2,5-diphenylphospholane
(1j): The product was purified by flash chromatography on silica
gel using heptane/EtOAc (50:50) as eluent. Recrystallization from
EtOAc/hexane gave the desired phosphane oxide as colorless crys-
tals. [α]1D8 = –193 (c = 0.425, CHCl3). 1H NMR (250 MHz, CDCl3):
δ = 8.00–8.20 (m, 2 H), 7.80 (m, 1 H), 7.10–7.50 (m, 11 H), 6.80–
7.00 (m, 3 H), 3.70–4.15 (m, 2 H), 2.30–2.90 (m, 4 H) ppm. 13C
NMR (62.9 MHz, CDCl3): δ = 27.85 (d, JP,C = 8 Hz), 31.25 (d,
JP,C = 8 Hz), 46.00 (d, JP,C = 62 Hz), 51.00 (d, JP,C = 62 Hz), 121.2
(s), 122.30 (s), 123.40 (d, JP,C = 11.5 Hz), 124.90 (s), 126.30 (s),
51.20 (d, JP,C = 61 Hz), 125.30 (d, JP,C = 9 Hz), 125.70 (d, JP,C
=
3.5 Hz), 126.35 (d, JP,C = 3 Hz), 127.10 (d, JP,C = 3 Hz), 127.35 (d,
JP,C = 4.5 Hz), 128.35 (d, JP,C = 2 Hz), 128.75 (d, JP,C = 2 Hz),
129.10 (d, JP,C = 5.5 Hz), 130.50 (s), 136.15 (d, JP,C = 5.5 Hz),
136.70 (d, JP,C = 3.5 Hz). 150.65 (d, JP,C = 11 Hz) ppm. 31P NMR
(101.2 MHz, CDCl3): δ = 55.0 ppm. HRMS (IE): calcd. for
C30H37OP 444.2582; found 445.2576.
(2S,5S)-(–)-1-(2-Naphthyl)-1-oxo-2,5-diphenylphospholane (1g): The
product was purified by flash chromatography on silica gel using
CH2Cl2/MeOH (98:2) as eluent. Recrystallization from EtOAc/hex-
ane gave the desired phosphane oxide as a white solid. [α]2D0 = –148
(c = 1, CHCl3). 1H NMR (250 MHz, CDCl3): δ = 8.15 (d, J =
13 Hz, 1 H), 7.60–7.80 (m, 3 H), 7.40–7.60 (m, 2 H), 7.10–7.40 (m,
8 H), 6.80–7.10 (m, 3 H), 3.40–4.10 (m, 1 H), 3.50–3.70 (m, 1 H),
2.50–2.90 (m, 3 H), 2.35 (m, 1 H) ppm. 13C NMR (50 MHz,
CDCl3): δ = 28.35 (d, JP,C = 8 Hz), 31.60 (d, JP,C = 7 Hz), 47.65
(d, JP,C = 62 Hz), 51.15 (d, JP,C = 62 Hz), 125.60 (d, JP,C = 10 Hz),
126.85 (s), 126.95 (s),127.95 (s), 128.50 (s), 128.85 (d, JP, C
=
5.25 Hz), 129.20 (d, JP,C = 9.5 H), 133.45 (s), 135.40 (s), 136.50 (d,
JP,C = 9 Hz), 140.85 (s), 143.60 (d, JP,C = 5 Hz) ppm. 31P NMR
(101.2 MHz, CDCl3): δ = 57.6 ppm. HRMS (IE): calcd. for
C28H23OPS 438.1207; found 438.1207.
(2S,5S)-(+)-1,2,5-Tricyclohexyl-1-oxophospholane (1m): A solution
of (2S,5S)-1-oxo-1,2,5-triphenylphospholane 1a (1 mmol),
RhCl3·4H2O (0.05 mmol), and aliquot 336 (0.0625 mmol) in
dichloromethane (10 mL) and water (2 mL) was placed in an auto-
clave under 80 bar of dihydrogen for two days. The aqueous phase
was then extracted with dichloromethane. The organic layer was
washed with water (2×10 mL) and then dried with MgSO4. Evapo-
ration of the solvent gave a residue that was purified by flash
chromatography on silica gel using heptane/ethyl acetate (40:60)
as eluent. Recrystallization from EtOAc/hexane gave the desired
phosphane oxide as fine, colorless needles. [α]2D0 = +20.8 (c = 0.52,
CHCl3). 1H NMR (250 MHz, CDCl3): δ = 2.00–2.3 (m, 4 H), 1.45–
2.00 (m, 19 H), 1.10–1.50 (m, 12 H), 0.80–1.10 (m, 4 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 50.50 (d, JP,C = 59 Hz), 39.45 (s),
38.45 (s), 38.10 (s), 37.70 (d, JP,C = 2 Hz), 37.50 (s), 36.51 (s), 33.60
(d, JP,C = 1.5 Hz), 33.30 (d, JP,C = 3 Hz), 32.40 (d, JP,C = 11 Hz),
126.70 (d, JP,C = 3 Hz), 126.90 (d, JP,C = 1.5 Hz), 127.30 (d, JP,C
2 Hz), 127.45 (d, JP,C = 4.5 Hz), 127.85 (d, JP,C = 1 Hz), 127.90 (s),
128.00 (s), 128.25 (s), 128.55 (d, JP,C = 2 Hz), 128.85 (d, JP,C
=
=
2 Hz), 129–129.10 (2C, m), 132.40 (d, JP,C = 12 Hz), 134.40 (d, JP,C
= 6.5 Hz). 134.5 (d, JP,C = 2 Hz), 135.75 (d, JP,C = 5.5 Hz), 136.00
(d, JP,C = 3 Hz) ppm. 31P NMR (101.2 MHz, CDCl3): δ =
53.4 ppm. HRMS (IE): calcd. for C26H23OP 382.1487; found
382.1480.
(2S,5S)-(–)-1-(1-Naphthyl)-1-oxo-2,5-diphenylphospholane (1h): The
product was purified by flash chromatography on silica gel using
CH2Cl2/MeOH (95:5) as eluent. Recrystallization from EtOAc/hex-
ane gave the desired phosphane oxide as colorless crystals. [α]2D0
=
1
–206 (c = 1, CHCl3). H NMR (250 MHz, CDCl3): δ = 8.60 (d, J
= 9 Hz, 1 H), 7.80 (d, J = 8.2 Hz, 1 H), 7.65 (ddd, J = 14, 6.75,
1 Hz, 1 H), 7.45 (d, J = 8.25 Hz, 1 H), 7.20–7.40 (m, 6 H), 7.00
(m, 2 H), 6.85 (m, 3 H), 4.05 (m, 1 H), 3.80 (m, 1 H), 2.50–2.90
(m, 3 H), 2.10–2.40 (m, 1 H) ppm. 13C NMR (50 MHz, CDCl3): δ
31.25 (d, JP,C = 9 Hz), 27.95 (d, JP,C = 6.5 Hz), 27.60 (d, JP,C
=
2.25 Hz), 26.60 (d, JP,C = 12 Hz), 26.50 (d, JP,C = 12.5 Hz), 26.20
(s), 26.15 (s), 26.05 (s), 26.00 (s), 25.95 (s), 25.93 (s), 25.90 (s), 25.80
(d, JP,C = 4 Hz), 25.65 (s) ppm. 31P NMR (101.2 MHz, CDCl3): δ
= 66.8 ppm. HRMS (IE): calcd. for C22H40OP [MH+] 351.2811;
found 351.2815.
= 29.50 (d, JP,C = 8.5 Hz), 31.80 (d, JP,C = 8 Hz), 46.00 (d, JP,C
=
63 Hz), 52.00 (d, JP,C = 62 Hz), 123.70 (d, JP,C = 14 Hz), 126.15
(s), 126.20 (d, JP,C = 2.8 Hz), 126.65 (s), 126.95 (d, JP,C = 2 Hz),
(2S,5S)-(–)-2-c,5-t-Diphenylphospholane–Borane (4): BH3·SMe2
(3 mmol) was added at 0 °C to a Schlenk tube containing a solution
of (2S,5S)-(+)-2,5-diphenylphospholane (1 mmol) in Et2O (10 mL).
The resulting solution was stirred for 16 h until it reached room
temperature. The solvent was then evaporated and the residue was
purified by flash chromatography on silica gel using pentane/di-
ethyl ether (90:10) as eluent. The product was isolated as a white
127.25 (d, JP,C = 4 Hz), 127.50 (d, JP,C = 5 Hz), 127.85 (d, JP,C
=
5 Hz), 128.15 (d, JP,C = 2.5 Hz), 128.55 (d, JP,C = 2 Hz), 129.20 (d,
JP,C = 5.2 Hz), 130.60 (d, JP,C = 10 Hz), 132.75 (d, JP,C = 3 Hz),
133.35 (d, JP,C = 12 Hz), 134.00 (d, JP,C = 7 Hz). 136.30 (d, JP,C
=
5 Hz), 136.80 (d, JP, C = 3 Hz) ppm. 31P NMR (101.2 MHz,
CDCl3): δ = 59.0 ppm. C26H23O2P: calcd. C 81.66, H 6.06, P 8.10;
found C 82.24, H 6.08, P 8.05. MS (IE): m/z = 383 [MH+], 405 [M
+ Na+], 787 [2M + Na+].
1
solid. [α]1D8 = –15.5 (c = 1, CHCl3). H NMR (250 MHz, CDCl3):
δ = 7.20–7.40 (m, 10 H), 4.80 (d, JP,H = 360 Hz), 3.80–4.15 (m, 1
H), 3.50 (m, 1 H), 2.50–2.70 (m, 2 H), 2.15–2.25 (m, 2 H), 0.1–0.9
(broad, 3 H, BH3) ppm. 13C NMR (62.9 MHz, CDCl3): δ = 33.80
(d, JP,C = 1 Hz), 34.50 (d, JP,C = 4 Hz), 40.50 (d, JP,C = 29 Hz),
(2S,5S)-(–)-1-Oxo-2,5-diphenyl-1-(2-pyridyl)phospholane (1i): The
product was purified by flash chromatography on silica gel using
CH2Cl2/MeOH (98:2) as eluent. Recrystallization from EtOAc/hex-
44.40 (d, JP,C = 33 Hz), 127.15 (d, JP,C = 2.5 Hz), 127.25 (d, JP,C
=
ane gave the desired phosphane oxide as colorless crystals. [α]2D0
=
2 Hz), 127.28 (d, JP,C = 5 Hz), 128.40 (d, JP,C = 2 Hz), 128.60 (d,
JP,C = 5.25 Hz), 128.90 (d, JP,C = 2 Hz), 136.50 (d, JP,C = 2 Hz),
137.70 (d, JP,C = 5.25 Hz) ppm. 31P NMR (101.2 MHz, CDCl3): δ
= 29.4 (d, JP,B = 46 Hz) ppm. HRMS (IE): calcd. for C16H20BP
254.1396; found 240.1063 (corresponding to C16H17P, i.e. [M –
BH3]).
1
–136 (c = 1, CHCl3). H NMR (250 MHz, CDCl3): δ = 8.60 (m, 1
H), 7.65 (m, 1 H), 6.80–7.50 (m, 12 H), 4.20–4.50 (s, 1 H), 3.60–
3.90 (m, 1 H), 2.60–2.90 (m, 1 H), 2.20–2.60 (m, 3 H) ppm. 13C
NMR (50 MHz, CDCl3): δ = 27.60 (d, JP,C = 8.3 Hz), 32.10 (d,
JP,C = 7.5 Hz), 42.80 (d, JP,C = 63Hz), 51.50 (d, JP,C = 59 Hz),
120.80 (s), 123.45 (s), 124.75 (d, JP,C = 3.2 Hz), 126.00 (d, JP,C
3 Hz), 126.55 (d, JP,C = 2 Hz), 127.15 (d, JP,C = 4.5 Hz), 127.75 (d,
JP,C = 3 Hz), 128.30 (d, JP,C = 2 Hz), 128.50 (s), 128.90 (d, JP,C
=
(2S,5S)-(+)-2,5-Diphenylphospholane:[11] (2S,5S)-(–)-1-Chloro-1-
oxo-2,5-diphenylphospholane (2; 1 mmol) was suspended in freshly
=
654
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Eur. J. Org. Chem. 2006, 650–656

New Chiral Enantiopure Phospholane Oxides
FULL PAPER
distilled diethyl ether (10 mL) after sonication and cooled to 0 °C.
Lithium aluminum hydride (1.5 mmol) was then added portion-
wise. The solution was stirred at room temperature for 16 h, then
hydrolyzed with a minimum of water and filtered under argon to
give a colorless solution. The solvent was removed in vacuo and
the phospholane was obtained as a white solid that was stored in
a glove box without further purification. [α]2D0 = +104 (c = 0.95,
136.20 (d, JP,C = 5 Hz), 136.60 (d, JP,C = 2 Hz), 137.50 (d, JP,C =
10 Hz), 147.15 (s) ppm. 31P NMR (101.2 MHz, CDCl3): δ = 40.90
(d, J = 46 Hz) ppm. HRMS (IE): calcd. for C24H25P 344.1688;
found 344.1684.
(2R,5R)-(+)-1-(3Ј,5Ј-Di-tert-butylphenyl)-2,5-diphenylphospholane–
Borane (5f): [α]2D0 = +81.9 (c = 0.77, CH2Cl2). 1H NMR (250 MHz,
CDCl3): δ = 0.10–0.97 (m, 3 H, BH3), 1.28 (s, 18 H), 2.38–2.76 (m,
4 H), 3.88–3.96 (m, 1 H), 4.09–4.15 (m, 1 H), 6.95–7.11 (m, 5 H),
7.32–7.47 (m, 8 H) ppm. 13C NMR (62.9 MHz, CDCl3): δ =
1
CHCl3). H NMR (360 MHz, CDCl3): δ = 7.25 (m, 9 H), 7.10 (m,
1 H), 3.90 (m, 1 H), 3.35 (ddd, JP,H = 190, JH,H = 11 and 11 Hz, 1
H), 3.35 (m, 1 H), 2.45–2.55 (m, 2 H), 2.00–2.15 (m, 1 H), 1.75–
1.90 (m, 1 H) ppm. 13C NMR (62.9 MHz, CDCl3): δ = 38.80 (d,
JP,C = 5 Hz), 39 (s), 41.10 (d, JP,C = 9 Hz), 44.80 (d, JP,C = 12 Hz),
126.00 (d, JP,C = 13 Hz), 127.15 (d, JP,C = 14 Hz), 127.65 (d, JP,C
= 8 Hz), 128.55 (s) ppm. 31P NMR (101.2 MHz, CDCl3): δ = –17.8
(d, JP,H = 190 Hz) ppm. HRMS (IE): calcd. for C16H17P 240.1068;
found 240.1063.
2
31.00(s, 6C), 31.10 (d, JP,C = 6 Hz), 31.65 (d, JP,C = 6 Hz), 34.65
1
1
(s, 2 C), 44.75 (d, JP,C = 29 Hz), 47.25 (d, JP,C = 31 Hz), 124.92
1
(d, JP,C = 3 Hz), 125.50 (d, JP,C = 44 Hz), 126.17 (d, JP,C = 2 Hz),
126.66 (d, JP,C = 9 Hz), 126.82 (d, JP,C = 3 Hz), 127.36 (d, JP,C
=
4 Hz), 127.86 (d, JP,C = 3 Hz), 128.08 (d, JP,C = 2 Hz), 128.24 (d,
JP,C = 4 Hz), 136.46 (d, JP,C = 5 Hz), 136.59 (d, JP,C = 2 Hz), 150.39
(d, JP,C = 9 Hz) ppm. 31P NMR (101.2 MHz, CDCl3): δ = 42.70
(broad) ppm. HRMS (IE): calcd. for C30H37P: 428.2627; found
428.2629.
(2R,5R)-(+)-2,5-Diphenyl-1-(o-tolyl)phospholane–Borane (5b): [α]2D0
= +75.6 (c = 1, CHCl3). 1H NMR (250 MHz, CDCl3): δ = 2.05 (s,
3 H), 2.15–2.80 (m, 4 H), 3.80–4.25 (m, 2 H), 6.86–7.30 (m, 13 H),
7.60 (m, 1 H) ppm. 13C NMR (62.9 MHz, CDCl3): δ = 22.80 (s),
31.20 (s), 32.65 (d, JP,C = 6.5 Hz), 45.20 (d, JP,C = 30.5 Hz), 47.85
(d, JP,C = 32 Hz), 125.50 (d, JP,C = 9 Hz), 126.55 (s), 127.00 (s),
(2S,5S)-(–)-1-(2-Naphthyl)-2,5,-diphenylphospholane–Borane (5g):
[α]2D0 = –147 (c = 1, CHCl3). 1H NMR (250 MHz, CDCl3): δ =
0.30–1.40 (broad, 3 H, BH3) 2.40–2.90 (m, 4 H), 3.90–4.20 (m, 2
H), 6.80–7.10 (m, 3 H), 7.10–7.40 (m, 8 H), 7.40–7.60 (m, 2 H),
7.70 (m, 1 H), 7.75 (m, 2 H), 8.15 (d, J = 13 Hz, 2 H) ppm. 13C
NMR (62.9 MHz, CDCl3): δ = 31.00 (s), 31.45 (d, JP,C = 6 Hz),
127.80 (d, JP,C = 5 Hz), 128.00 (s), 128.25 (s), 128.40 (d, JP,C
=
5 Hz), 131.20 (s), 131.50 (d, JP,C = 9 Hz), 133.55–133.70 (m, 2 C),
136.65 (m, 1 C), 137.50 (d, JP, C = 5 Hz) ppm. 31 P NMR
(101.2 MHz, CDCl3): δ = 40.00 (d, J = 61 Hz) ppm. HRMS (IE):
calcd. for C23H23P 330.1532; found 330.1518.
46.20 (d, JP,C = 30 Hz), 47.00 (d, JP,C = 31 Hz), 124.20 (d, JP,C
43 Hz), 126.30 (d, JP,C = 3 Hz), 126.45 (s), 126.80 (d, JP,C = 3 Hz),
127.25 (d, JP,C = 4 Hz), 127.35 (s), 127.60 (s), 127.90 (d, JP,C
=
=
(2R,5R)-(+)-2-c,5-t,-Diphenyl-1-r-(p-tolyl)phospholane–Borane (5c):
[α]2D0 = +131 (c = 1, CHCl3). 1H NMR (250 MHz, CDCl3): δ =
0.30–1.40 (broad, 3 H, BH3), 2.05 (s, 3 H, CH3), 2.05–2.70 (m, 4
H), 3.50–4.00 (m, 2 H), 6.70–7.15 (m, 12 H), 7.15–7.30 (m, 2 H)
ppm. 13C NMR (62.9 MHz, CDCl3): δ = 21.00 (s), 3.80 (s), 31.30(d,
JP,C = 6 Hz), 45.70 (d, JP,C = 30 Hz), 47.00 (d, JP,C = 31 Hz), 123.15
(d, JP,C = 45 Hz), 126.40 (d, JP,C = 28 Hz), 127.20 (d, JP,C = 4 Hz),
3 Hz), 127.95 (s), 128.00 (s), 128.05 (s), 128.35 (s), 132.05 (d, JP,C
= 11 Hz), 133.80 (d, JP,C = 3 Hz), 135.50 (d, JP,C = 11 Hz), 135.85
(d, JP,C = 5 Hz), 136.25 (d, JP, C = 2 Hz) ppm. 31 P NMR
(101.2 MHz, CDCl3): δ = 41.76 (broad) ppm. HRMS (IE): calcd.
for C26H23P 366.1532; found 366.1519.
(2S,5S)-(–)-1-(1-Naphthyl)-2,5-diphenylphospholane–Borane (5h):
[α]D = –136 (c = 1, CHCl3). 1H NMR (250 MHz, CDCl3): δ =
0.10–1.10 (broad, 3 H, BH3), 2.55–2.89 (m, 4 H), 4.20–4.38 (m, 2
H), 6.88 (d, JH,H = 7 Hz, 3 H), 7.10 (d, JH,H = 7 Hz, 2 H), 7.20–
7.50 (m, 8 H), 7.70 (d, JH,H = 7 Hz, 1 H), 7.85 (d, JH,H = 7 Hz, 1
H), 7.95 (dd, JH,H = 15, JH,H = 7 Hz, 1 H), 8.15 (d, JH,H = 7 Hz,
127.70–128.00 (m, 5 C), 128.70 (d, JP,C = 9 Hz), 135.90 (d, JP,C
=
5 Hz), 136.40 (s), 141.20 (s) ppm. 31P NMR (101.2 MHz, CDCl3):
δ = 40.54 (s large) ppm. HRMS (IE): calcd. for C23H23P 330.1532;
found 330.1519.
(2S,5S)-(–)-1-(o-Anisyl)-2,5-diphenylphospholane–Borane (5d): [α]2D0
= –99.4 (c = 0.68, CH2Cl2). 1H NMR (250 MHz, CDCl3): δ = 0.10–
0.91 (m, 3 H, BH3), 2.46–2.72 (m, 4 H), 3.61 (s, 3 H), 3.96–4.07
(m, 1 H), 4.38–4.53 (m, 1 H), 6.58 (dd, J = 8, 3 Hz, 1 H), 6.85–
7.19 (m, 12 H), 7.81 (dd, J = 14, 7 Hz, 1 H) ppm. 13C NMR
1 H) ppm. 13C NMR (62.9 MHz, CDCl3): δ = 31.80 (d, JP,C
=
7 Hz), 31.92 (s), 45.57 (d, JP,C = 30 Hz), 47.53 (d, JP,C = 32 Hz),
124.34 (s), 124.55 (d, JP,C = 11 Hz), 124.65 (d, JP,C = 34 Hz), 124.93
(s), 126.06 (d, JP,C = 6 Hz), 126.39 (d, JP,C = 2 Hz), 126.99 (d, JP,C
= 3 Hz), 127.05 (s), 127.52 (d, JP,C = 4 Hz), 127.84 (d, JP,C = 2 Hz),
128.22 (d, JP,C = 2 Hz), 128.58 (d, JP,C = 11 Hz), 128.73 (s), 132.6
(d, JP,C = 3 Hz), 133.36 (s), 133.50 (s), 133.34 (d, JP,C = 9 Hz),
136.76 (d, JP,C = 2 Hz), 137.13 (d, JP,C = 5 Hz) ppm. 31P NMR
(101.2 MHz, CDCl3): δ = 42.00 ppm. HRMS (IE): calcd. for
C26H23P 366.1532; found 366.1534.
2
2
(62.9 MHz, CDCl3): δ = 29.80 (d, JP,C = 6 Hz), 31.27 (d, JP,C
=
1
1
6.6 Hz), 42.50 (d, JP,C = 31 Hz), 45.51 (d, JP,C = 35 Hz), 54.77
(s), 109.75 (d, JP,C = 4 Hz), 113.79 (d, JP,C = 40.3 Hz), 121.00 (d,
1
JP,C = 12.6 Hz), 126.02 (d, JP,C = 2 Hz), 126.8 (d, JP,C = 2 Hz),
126.83 (d, JP,C = 4.5 Hz), 127.49 (d, JP,C = 1.8 Hz), 128.14 (d, JP,C
= 3 Hz), 128.2 (d, JP,C = 4.5 Hz), 133.94 (d, JP,C = 2 Hz), 137.00
(d, JP,C = 1.5 Hz), 137.36 (d, JP,C = 19.5 Hz), 138.20 (d, JP,C
=
(2R,5R)-(–)-1,2,5-Tricyclohexylphospholane–Borane (5m): [α]2D0
–40.8 (c = 0.805, CHCl3). H NMR (250 MHz, CDCl3): δ = 0.10–
0.80 (broad, 3 H, BH3), 0.75–1.00 (m, 4 H), 1.00–1.35 (m, 14 H),
1.35–1.50 (m, 1 H), 1.50–1.85 (m, 15 H), 1.85–1.95 (m, 1 H), 1.95–
=
15.5 Hz), 160.27 (d, JP,C = 2.6 Hz) ppm. 31P NMR (101.2 MHz,
CDCl3): δ = 43.05 (d, J = 71 Hz) ppm. HRMS (IE): calcd. for
C23H23OP 346.1481; found 346.1483.
1
(2S,5S)-(–)-1-(3,5-Dimethylphenyl)-2,5-diphenylphospholane–Borane 2.15 (m, 4 H) ppm. 13C NMR (90.5 MHz, CDCl3): δ = 47.60 (d, J
1
(5e): [α]2D0 = –101 (c = 1, CHCl3). H NMR (250 MHz, CDCl3): δ
= 33 Hz, CH), 40.00 (d, JP,C = 29 Hz, CH), 37.50 (d, JP,C = 4 Hz,
= 0.20–0.90 (broad, 3 H, BH3), 2.15 (s, 6 H), 2.30–2.80 (m, 4 H), CH), 34.45 (d, JP,C = 3 Hz), 34.25 (s), 32.60 (d, JP,C = 24.5 Hz,
3.70–4.10 (m, 2 H), 6.90–7.20 (m, 7 H), 7.20–7.60 (m, 6 H) ppm.
13C NMR (62.9 MHz, CDCl3): δ = 21.00 (s, 2 C), 30.90 (s), 31.60
(d, JP,C = 5 Hz), 45.60 (d, JP,C = 30 Hz), 47.30 (d, JP,C = 32 Hz),
126.00 (s), 126.35 (d, J = 2.5 Hz), 126.70 (s), 126.90 (d, J = 2.5 Hz),
CH), 32.30 (d, JP,C = 9 Hz), 31.25 (d, JP,C = 9 Hz), 30.95 (s), 29.65
(d, JP,C = 2.5 Hz), 29.25 (d, JP,C = 5 Hz), 27.85 (s), 27.20 (d, JP,C
= 12 Hz), 26.85(d, JP,C = 8.5 Hz), 26.10 (s), 26.00 (s), 25.95 (s),
25.93 (s), 25.85 (s, 2 C), 25.75 (s) ppm. 31P NMR (101.2 MHz,
127.45 (d, JP,C = 4 Hz), 127.85 (d, J = 2.5 Hz), 128.15 (s), 128.20 CDCl3): δ = 36.55 ppm. HRMS (IE): calcd. for C22H39P [MH+]
(d, J = 3 Hz), 130.50 (d, JP,C = 9 Hz), 132.80 (d, JP,C = 3 Hz),
334.2784, found 344.2783.
Eur. J. Org. Chem. 2006, 650–656
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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655

M. Toffano, C. Dobrota, J.-C. Fiaud
FULL PAPER
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Acknowledgments
We wish to thank L’Agence Universitaire de la Francophonie and
the Romanian Ministry of Education for financial support.
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Received: July 29, 2005
Published Online: November 25, 2005
656
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