Synthesis of enantiopure 1-r-alkyl-2-c,5-t-diphenylphospholanes and phospholanium salts through direct alkylation of phospholane

Article abstract of DOI:10.1002/ejoc.200800070

Chiral enantiopure 1-alkyl-2,5-diphenylphospholanium salts were obtained in one step through alkylation of phospholane with alkyl triflates. The resulting air-stable phosphonium salts are electron-rich trialkylphosphane precursor ligands for transition metals, and they offer a convenient route toward chiral quaternary phosphonium salts as phase-transfer agents. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200800070

FULL PAPER
DOI: 10.1002/ejoc.200800070
Synthesis of Enantiopure 1-r-Alkyl-2-c,5-t-Diphenylphospholanes and
Phospholanium Salts through Direct Alkylation of Phospholane
Cristian Dobrota,[a] Amelie Duraud,[a] Martial Toffano,*[a] and Jean-Claude Fiaud[a]
Keywords: Alkylation / Phosphorus heterocycles / P ligands / Phase-transfer catalysis
Chiral enantiopure 1-alkyl-2,5-diphenylphospholanium salts
were obtained in one step through alkylation of phospholane
with alkyl triflates. The resulting air-stable phosphonium
salts are electron-rich trialkylphosphane precursor ligands
for transition metals, and they offer a convenient route to-
ward chiral quaternary phosphonium salts as phase-transfer
agents.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
phosphane borane complex,[7] tris(cyanoethyl)phosphane,[8]
and free secondary phosphane.[9] In the case of 2,5-trans-
diphenylphospholane, the formation of a catalytic amount
of anion could be responsible for epimerization at the ben-
zylic position as a result of the presence of a rather acidic
hydrogen atom.[10] So, the most convenient method is the
alkylation of phosphane without the use of a base. Beller et
al. described the direct alkylation of bis(adamantyl)phos-
phane with an excess amount of alkyl halides.[11] The treat-
ment of the resulting salt with triethylamine gave the phos-
phane. The authors report that no alkylation occurred with
mesylate or more sterically hindered electrophiles.
Introduction
Interest in monophosphanes as ligands for transition
metals but also as organic catalysts has grown recently.[1]
Because organic catalysis mediated by phosphanes involves
their nucleophilic properties, it appears of interest to build
up 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 phosphanes, which often possess two or three
aryl substituents on the phosphorus atom.[2] In a previous
paper, we described the preparation of enantiopure dialkyl-
arylphosphorus compounds derived from 2,5-diphenyl-
phospholane by catalyzed C–P cross coupling.[3] Moreover,
a convenient use of air-stable phosphonium salt as ligand
precursors has been described.[4] With this in mind, we at-
tempted to find a convenient way to obtain basic and nucle-
ophilic chiral phospholanes. Then, electron-rich 1-alkyl-2,5-
diphenylphospholanes became a target of choice. However
these trialkylphosphanes suffer from easy oxidation when
handled in air. It was then desirable to find a convenient
method for the synthesis, protection, storage, and deprotec-
tion of these air-sensitive phosphanes. So, we report here
the synthesis of chiral enantiopure 1-alkyl-2,5-diphenyl-
phospholanes via phospholanium salt derivatives through
alkylation reactions by using alkyl triflate reagents.
Results and Discussion
Although perfluoroalkylsulfonate esters are considered
to be strong alkylating agents,[12] alkyl halides are the usual
alkylating reagents for phosphorus atoms. To the best of
our knowledge, there are only a few examples of addition
reactions of alkyl triflates on phosphane.[13]
In this context, we thought enantiopure trans-2,5-di-
phenylphospholane (1) could be alkylated with simple
electrophiles. This compound is obtained in two steps
from
1-oxo-1-hydroxy-2,5-diphenylphospholanic
acid
(Scheme 1).[14]
The alkylation of a phosphorus atom to introduce an
alkyl chain is one of the principal processes used to generate
1-alkylphosphanes. This process was used with success from
phosphide,[5] secondary phosphane oxide,[6] secondary
[a] Laboratoire de Catalyse Moléculaire (CNRS – UMR 8182),
Institut de Chimie Moléculaire et des Matériaux d’Orsay,
Bâtiment 420, Université Paris Sud,
Scheme 1.
91400 Orsay cedex, France
Fax: +33-1-69154680
E-mail: mtoffano@icmo.u-psud.fr
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
In a first way, we tried to alkylate phospholane 1 in
enantiopure form with methyl iodide (1 equiv.) in toluene
to obtain the resulting phospholanium salt (Scheme 2). The
Eur. J. Org. Chem. 2008, 2439–2445
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C. Dobrota, A. Duraud, M. Toffano, J.-C. Fiaud
FULL PAPER
expected phospholanium salt 2a was obtained as the major
Secondary alkyl triflates are known to be unstable at
product, but it was contaminated by 1 and quaternary di- moderate temperatures[15] and tertiary electrophiles could
methylphospholanium salt 3. Formation of 3 could be the be isolated only if no elimination of triflic acid can occur[16]
result of the weak stability of 2a under the reaction condi- So, alkylation of phospholane with secondary or tertiary
tions. We suppose this salt presumably released free phos- alkyl triflates appears to be difficult. We proposed a proto-
pholane 4b through dissociation, which could then sub- col to generate more sterically hindered triflates in situ,[17]
sequently react with methyl iodide to give the correspond- which could react with the phosphorus center. Alkylation
ing quaternary dimethylphospholanium salt 3.
of (S,S)-1 in the presence of benzhydryl or trityl chloride
and silver triflate in dichloromethane gave 1-alkyl-(2S,5S)-
diphenylphospholanes 2e and 2f in good yields (Scheme 4).
Scheme 4. Alkylation of phospholane 1 with alkyl chlorides.
Scheme 2.
The presence of small amount of dimethylphospholan-
ium salt 3 (Scheme 1) suggests the possibility to produce
quaternary chiral phospholanium salts by direct alkylation
of 1-alkyl-2,5-diphenylphospholane compounds. These salts
could be used as chiral phosphorus transfer agents. If chiral
quaternary ammonium salts are well known as phase trans-
fer agents,[18] the use of phosphonium salts has not been
well investigated, and in all cases, the chiral part of the
transfer agent is far from the cationic site.[19] With this in
mind, we developed the synthesis of 1-dialkyl-2,5-diphenyl-
phospholanium salts to be used as chiral transfer agents.
The phospholane structure suggests that the cationic phos-
phorus atom would be near the active site and could im-
prove the results in term of reactivity and enantioselectivity
in heterogeneous catalysis.
Attempts to obtain selective formation of 2a failed. Con-
trary, alkylation of phospholane 1 with alkyl triflate gave a
cleaner and more efficient reaction (Table 1).
Table 1. Alkylation of phospholane 1 with alkyl triflates.
Entry
Alk
Product
Yields[a] [%] Reaction conditions
1
2
3
Me
Et
Bu
2b
2c
2d
84
80
92
Et2O/25 °C
Tol./50 °C/12 h
Tol./50 °C/72 h
Simple treatment of enantiopure phospholanes 4b,c with
appropriate alkyl triflates gave the expected quaternary
phospholanium salts 5–11 in good yield (Table 2).
[a] Isolated yields.
Thus, the mixture of phospholane 1 and methyl triflate
in ether resulted in the formation of a white precipitate cor-
responding to the enantiomerically pure 1-methyl-(2S,5S)-
diphenylphospholanium trifluoromethanesulfonate salt (2b)
in excellent yield (Table 1, Entry 1). Addition of ethyl and
butyl triflates was more difficult and required both a higher
temperature and a longer reaction time for completion
(Table 1, Entries 2 and 3). Treatment of the corresponding
phospholanium salt with saturated hydrogen carbonate
solution gave the free 1-alkyl-2,5-diphenylphospholanes 4b–
d quantitatively (Scheme 3).
Table 2. Synthesis of chiral quaternary phospholanium salts 5–11.
Entry Product
R
RЈ
Solvent/
Reaction time Yield[a]
temp. [°C]
[h]
[%]
1
2
3
4
5
6
7
8
5
6
7
8
6
9
10
11
Me
Me
Et
Bu
Oct
Me
Et
Et2O/r.t.
tol./50
tol./60
tol./60
Et2O/r.t.
tol./50
tol./50
tol./50
0.25
24
48
72
0.25
24
87
76
86
84
88
86
61
45
Et
Bu
Oct
24
24
Scheme 3. Deprotection of phospholanium salts 2b–d.
[a] Isolated yields.
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 2439–2445

Enantiopure 1-r-Alkyl-2-c,5-t-Diphenylphospholanes and Phospholanium Salts
For best results, free phospholanes 4b–d must necessarily
Chiral quaternary phospholanium salts 5–11 and 14 were
be generated from tertiary phospholanium salts 2b–d, as de- used in asymmetric phase-transfer benzylation of alkyl-2-
scribed in Scheme 3, before the alkylation step. In most oxo-cyclopentanecarboxylates (Scheme 6).
cases, the alkylation proceeded smoothly in toluene at 50–
60 °C, except for methyl triflate, which proceeded at room
temperature in diethyl ether (Table 2, Entries 1 and 5). Also,
we developed a synthesis of enantiopure 1-aryl-1-alkylphos-
pholanium salt from phospholane 12 (Scheme 5). Phos-
pholane 12[3] was reduced by using the Imamoto pro-
cedure[20] to give free phosphane 13, which was not isolated
Scheme 6. Phase-transfer alkylation.
but treated with methyl triflate to give chiral quaternary
phospholanium salt 14 in good yield (Scheme 5). Prelimi-
nary experiments with tertiary and quaternary phospholan-
ium salts were conducted.
In the presence of potassium carbonate as base and 5–
11, 14 (4 mol-%), benzylation of 12a and 12b was complete
in 2 h. Unfortunately, the enantiomeric excess values did
not exceed 20%ee in all cases. We verified that the presence
of potassium carbonate did not modify the phospholane
structure. In particular, possible epimerization at the ben-
zylic position did not occur. The nature of base is crucial
for activity, as the use of potassium or sodium hydroxide
instead of potassium carbonate led to decomposition of the
catalyst.
Scheme 5. Synthesis of 1-aryl-1-alkylphospholanium salt 14.
The newly prepared chiral tertiary phosphonium salts
2b–d were used in the asymmetric hydrogenation of methyl-
(Z)-2-acetamidocinnamate. The catalyst was generated by
mixing the rhodium precursor (1 mol-%) with phospho-
nium salt 2 (2.2 mol-%) without a base. Because the 2,5-
diarylphospholanes proved to form very active catalytic
species, most of the first tests were performed under an at-
mosphere of hydrogen and at room temperature (Table 3).
Conclusions
We described an efficient and simple alkylation of trans-
2,5-diphenylphospholane (1) with alkyl triflate to form di-
rectly some enantiopure tertiary phospholanium salts as a
protected form of electron-rich chiral ligands. A second al-
kylation step of tertiary phospholanes gives a convenient
route to enantiopure quaternary phospholanium salts.
Studies involving chiral 1-alkyl-2,5-diphenylphospholanes
bearing different alkyl groups on the phosphorus atom are
in progress. We are currently exploring the use of these elec-
tron-rich chiral phosphanes as organic catalysts. The aspect
of chiral quaternary phospholanium salt as a viscous paste
suggests that a change in the counterion may potentially
result in ionic liquids; this work is underway.
Table 3. Rh-catalyzed enantioselective hydrogenation of methyl
(Z)-2-acetamidocinnamate by using (S,S)-phospholanium salt 2b–
d[a] and [Rh(cod)2]BF4 as rhodium source.
Ligand
Reaction time [h]
% ee (configuration)[b]
Experimental Section
2b
2c
2d
0.5
1
1
34 (S)
47 (R)
62 (R)
General: Proton NMR spectra were recorded with Bruker 250, 360
or 400 MHz spectrometers. 1H and 13C NMR analysis of free phos-
pholane 1 and 4b–d were realized under argon atmosphere. Proton
chemical shifts are reported in ppm relative to tetramethylsilane as
internal reference (TMS, δ = 0.0 ppm). Carbon NMR spectra were
recorded with Bruker 250 MHz (62.9 MHz) or 300 MHz
(75.45 MHz) spectrometers with complete proton decoupling.
Phosphorus NMR spectra were recorded with a 101.2 MHz spec-
trometer with complete proton decoupling. The corresponding
chemical shifts are reported in ppm relative to the residual deuter-
ated solvent or external phosphoric acid (H3PO4, δ = 0.0 ppm).
Flash column chromatography was performed by using silica gel
Merck (0.04–0.063 µm). Optical rotations were recorded at the so-
dium D line with a Perkin–Elmer 341 polarimeter. The specific
rotation [α] is always given without the units (understood to be
cm2 g–1). High-resolution mass spectra were obtained with a
MAT95 Thermo-Finnigan spectrometer by using electrospray or
GC analysis. All reactions were carried out in Schlenk tubes under
[a] All reactions were carried out under a hydrogen atmosphere
(1 atm.) at room temperature. [b] Determined by chiral HPLC
analysis on a Chiralcel OD-H column, with hexane/2-propanol
(9:1) as eluent.
1-Alkylphospholanium salts 2b–d were excellent ligands
in term of activity. A total conversion was obtained in all
cases in less than 1 h reaction time under atmospheric pres-
sure of hydrogen at room temperature, but with modest en-
antiomeric excess values. We observed an increase in
enantioselectivity with the length of the alkyl chain group
on the phosphorus atom. Surprisingly, there is a clear inver-
sion of configuration of the product for small alkyl groups
(Alk = Me) in comparison to larger alkyl groups (Alk = Et,
Bu).
Eur. J. Org. Chem. 2008, 2439–2445
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C. Dobrota, A. Duraud, M. Toffano, J.-C. Fiaud
FULL PAPER
1
1
an argon atmosphere. All solvents were distilled from appropriate
drying agents prior to use. Ethyl and butyl triflates were prepared
from the corresponding alcohol and triflic anhydride. All other rea-
gents are available commercially and were used without further pu-
rification. tert-Butyl chloride, benhydryl chloride, silver trifluoro-
methanesulfonate were purchased from Acros, and methyl triflate
was purchased from Fluka. The synthesis and experimental data
of (2S,5S)-diphenylphospholane (1) were reported in our previous
papers.[3,14]
(d, JP,C = 42 Hz, PCHPh), 42.98 (d, JP,C = 42 Hz, PCHPh), 121
1
(q, JC,F = 318 Hz, OSO2CF3), 128.27 (d, JP,C = 7 Hz), 128.78 (d,
JP,C = 1 Hz), 128.81 (d, JP,C = 1 Hz), 128.99 (d, JP,C = 5 Hz), 129.62
(d, JP,C = 3 Hz), 129.82 (s), 131.9 (d, JP,C = 5 Hz), 133.35 (d, JP,C
1
= 5 Hz) ppm. 31P NMR (101.2 MHz, CDCl3): δ = 36.00 (d, JP,H
= 486 Hz) ppm. HRMS (IE): calcd. for C20H26P+ 297.1767; found
297.1724.
General Procedure for the Synthesis of 2e,f: To a Schlenk tube con-
taining silver trifuoromethanesulfonate (250 mg, 1.05 mmol) and
phospholane 1 (240 mg, 1 mmol) was added under an argon atmo-
sphere a solution of the appropriate alkyl chloride (1.1 mmol) in
dichloromethane (5 mL). The mixture was stirred for the appropri-
ate time and filtered under an argon atmosphere. The solvent was
evaporated, and the residue was washed with ether/pentane (1: 1)
to give a white powder.
(2S,5S)-(–)-1-Methyl-2,5-diphenylphospholanium Trifluoromethane-
sulfonate (2b): MeOTf (0.12 mL, 1.1 equiv.) was added dropwise
to a solution of phospholane 1 (0.36 g, 1.5 mmol) in diethyl ether
(10 mL). After 10 min at ambient temperature, the white precipitate
was filtered and washed with diethyl ether. The phospholanium salt
was obtained as a white powder. M.p. 110–111 °C. [α]2D0 = –6 (c =
0.5, THF). 1H NMR (250 MHz, CDCl3): δ = 2.04 (dd, 2JP,H = 15.1,
3JH,H = 5.4 Hz, 3 H, PCH3), 2.39–2.90 (m, 4 H, PCHPhCH2), 4.14–
4.31 (m, 1 H, PCHPh), 4.73–4.90 (m, 1 H, PCHPh), 6.68 (dm, 1JP,H
= 499 Hz, 1 H), 7.30–7.55 (m, 10 H, C6H5) ppm. 13C NMR
(50 MHz, CDCl3): δ = 0.88 (d, 1JP,C = 46 Hz, PCH3), 32.67 [d, 2JP,C
(2S,5S)-(+)-1-(Benzhydryl)-2,5-diphenylphospholanium
Trifluoro-
methanesulfonate (2e): M.p. 58–60 °C. [α]2D0 = +72.5 (c = 1.05,
CH2Cl2). 1H NMR (250 MHz, CDCl3): δ = 2.49–2.9 (m, 4 H), 3.89
(m, 1 H, PCHPh), 4.65 (m, 1 H, PCHPh), 4.97 (m, 1 H, PCHPh),
1
6.55 (dm, JP,H = 488 Hz, 1 H), 6.91–7.44 (m, 20 H, C6H5) ppm.
2
13C NMR (50 MHz, CDCl3): δ = 33.22 (d, JP,C = 6 Hz, CH2), 34.84
= 6 Hz, PCH(Ph)CH2], 33.33 [d, JP,C = 9.2 Hz, PCH(Ph)CH2],
1
1
39.32 (d, JP,C = 44.6 Hz, PCHPh), 42.98 (d, JP,C = 45.5 Hz,
PCHPh), 121 (q, 1JC,F nd, OSO2CF3), 127.93 (s), 128.06 (s), 128.98
(s), 129.09 (s), 129.12 (d, JP,C = 2.5 Hz) 129.18 (d, JP,C = 2.8 Hz),
129.83 (d, JP,C = 2.8 Hz), 130.02 (d, JP,C = 2.8 Hz), 131.84 (d, JP,C
= 5.5 Hz), 133.24 (d, JP,C = 4.6 Hz) ppm. 31P NMR (101.2 MHz,
CDCl3): δ = 32.3 (d, JP,H = 500 Hz) ppm. 19F NMR (235 MHz,
CDCl3): δ = –19.54 (s) ppm. LRMS (ES): m/z (%) = 269.2 [M +
NH4]+, 255.1 (100) [M]+, 121.1. HRMS (ES): calcd. for C17H20P+
255.1297; found 255.1301.
1
(d, JP,C = 10 Hz, CH2), 40.48 (d, JP,C = 37 Hz, PCHPh2), 42.84
1
1
(d, JP,C = 5 Hz, PCHPh), 43.63 (d, JP,C = 11 Hz, PCHPh),
127.79–128.25 (m, 5 C), 128.61–129.29 (m, 9 C), 129.64 (s, 2 C),
131.51 (d, JP,C = 6 Hz), 132.82 (d, JP,C = 5 Hz), 133.11 (d, JP,C
=
4 Hz), 133.6 (d, JP,C = 6 Hz) ppm. 31P NMR (101.2 MHz, CDCl3):
δ = 34.81 (d, JP,H = 468 Hz) ppm. 19F NMR (235 MHz, CDCl3):
1
δ = –78.03 (s) ppm. MS (ES): m/z (%) = 407.2 (24) [Mcat]+, 320.1
(8), 295.0 (5), 279.1 (15), 257.1 (16), 215.1 (13), 168 (15), 167 (100).
HRMS (IE): calcd. for C29H28P+ 407.1929; found 407.1935.
General Procedure for the Synthesis of 2c,d: A mixture of phos-
pholane 1 (240 mg, 1 mmol) and alkyl triflate (1.1 mmol) was
stirred at 50 °C in toluene for the appropriate time under an argon
atmosphere. After removal of the solvent, diethyl ether was added.
The residue was filtered and washed with diethyl ether to give salts
2c,d as white solids.
(2S,5S)-(+)-1-Triphenylmethyl-2,5-diphenylphospholanium Trifluoro-
methanesulfonate (2f): M.p. 92–95 °C. [α]2D0 = +35.4 (c = 0.74,
CH2Cl2). 1H NMR (250 MHz, CDCl3): δ = 2.26–2.82 (m, 4 H), 4.0
(m, 1 H, PCHPh), 5.4 (m, 1 H, PCHPh), 6.91–7.44 (m, 20 H),
6.79–6.88 (m, 7 H), 6.95–7.02 (m, 2 H), 7.07–7.29 (m, 16 H), 8.02
1
(d, JP,H = 500 Hz, 1 H) ppm. 13C NMR (62.9 MHz, CDCl3): δ =
33.89 (d, JP,C = 6 Hz, CH2), 34.77 (d, JP,C = 8 Hz, CH2), 44.96 (d,
JP,C = 29 Hz, PCHPh), 46.04 (d, JP,C = 38 Hz, PCHPh), 61.1 (d,
(2S,5S)-(+)-1-Ethyl-2,5-diphenylphospholanium Trifluoromethane-
sulfonate (2c): [α]2D0 = +5.24 (c = 0.53, CHCl3). 1H NMR
(250 MHz, CDCl3): δ = +0.85 (dt, 3JP,H = 20.7 Hz, 2JH,H = 7.6 Hz,
JP,C = 30 Hz, PCHPh), 127.34 (s), 127.99 (s), 128.15 (d, JP,C
=
2
2
3 Hz), 128.29 (d, JP,C = 2 Hz), 128.46 (s), 128.57–128.61 (m), 129.07
(m), 129.22 (s), 129.55 (d, JP,C = 5 Hz), 129.58 (s), 129.92–130.03
(m), 130.79 (d, JP,C = 6 Hz), 134.79 (d, JP,C = 5 Hz) ppm. 31P NMR
(101.2 MHz, CDCl3): δ = 41.58 (d, 1JP,H = 495 Hz) ppm. 19F NMR
(235 MHz, CDCl3): δ = –77.99 (s) ppm. MS (ES): m/z (%) = 521.2
(4), 259.1 (8), 244.1 (13), 243.1 (63.4), 229.1 (4), 228.1 (21), 216.1
(3), 215.1 (10), 166.0 (15), 165.0 (100). HRMS (IE): calcd. for
C35H32P+ 483.2242; found 483.2246.
3 H, PCH2CH3), 2.04 (dm, JP,H = 66.2 Hz, JH,H = 7.6 Hz, 2 H,
PCH2CH3), 2,44–2.82 (m, 4 H, PCHPhCH2), 4.23–4.40 (m, 1 H,
1
PCHPh), 4.70–4.87 (m, 1 H, PCHPh), 6.44 (dm, JP,H = 490 Hz, 1
H), 7.16–7.50 (m, 10 H, C6H5) ppm. 13C NMR (62.9 MHz,
2
1
CDCl3): δ = 6.97 (d, JP,C = 5.9 Hz, PCH2CH3), 11.09 (d, JP,C
=
41.2 Hz, PCH2CH3), 32.96 [d, 2JP,C = 5.9 Hz, PCH(Ph)CH2], 34.33
[d, JP,C = 8 Hz, PCH(Ph)CH2], 39.6 (d, JP,C = 42.4 Hz, PCHPh),
2
1
1
1
42.2 (d, JP,C = 44.1 Hz, PCHPh), 120.8 (q, JC,F = 320 Hz,
OSO2CF3), 127.54 (d, JP,C = 6.8 Hz), 128.2 (d, JP,C = 6.8 Hz),
128.89 (d, JP,C = 4.2 Hz), 129.69 (d, JP,C = 2.2 Hz), 129.88 (d, JP,C
= 1.7 Hz), 130.17 (d, JP,C = 2.6 Hz), 131.69 (d, JP,C = 5.1 Hz),
133.23 (d, JP,C = 4.7 Hz) ppm. 31P NMR (101.2 MHz, CDCl3): δ
= 40.6 (d, 1JP,H = 487 Hz) ppm. 19F NMR (235 MHz, CDCl3): δ =
–79.53 (s) ppm. HRMS (ES): calcd. for C18H22P+ 269.1454; found
269.1442.
General Procedure for the Deprotection of Phospholanium Salts 2b–
d: In a Schlenk tube placed under an argon atmosphere a solution
of phospholanium salts 2b–d (1 mmol) in dichloromethane (10 mL)
was treated with a saturated solution of NaHCO3. When the effer-
vescence stopped, the mixture was stirred vigorously under an ar-
gon atmosphere for 20 min and decanted. The organic phase was
dried with sodium sulfate under an argon atmosphere, and the sol-
vents were evaporated. Free phospholanes 4b–d were obtained and
stored in a glove box without purification.
(2S,5S)-(–)-1-(n-Butyl)-2,5-diphenylphospholanium Trifluorometh-
anesulfonate (2d): M.p. 132–135 °C. [α]2D0 = –8 (c = 1.2, CH2Cl2).
1H NMR (200 MHz, CDCl3): δ = 0.59 (t, J = 7 Hz, 3 H), 1.0–1.26 (2S,5S)-(+)-1-Methyl-2,5-diphenylphospholane (4b): [α]2D0 = +142.6
(m, 4 H), 1.91 (m, 1 H), 2.17 (m, 1 H), 2.42–2.85 (m, 4 H), 4.38 (c = 0.70, CH2Cl2). 1H NMR (250 MHz, CDCl3): δ = 0.77 (d, 2JP,H
(m, 1 H, PCHPh), 4.90 (m, 1 H, PCHPh), 6.55 (dm, 1JP,H = 488 Hz, = 4 Hz, 3 H, PCH3), 1.86–2.03 (m, 1 H, PCHPhCH2), 2.22–2.45
1 H), 7.33–7.53 (m, 10 H) ppm. 13C NMR (50 MHz, CDCl3): δ = (m, 2 H, PCHPhCH2), 2.52–2.67 (m, 1 H, PCHPhCH2), 3.15 (dt,
12.93 (s), 16.59 (d, JP,C = 39 Hz), 23.25 (d, JP,C = 14 Hz), 24.62 (d,
JP,C = 6 Hz), 33.09 (d, JP,C = 6 Hz), 34.43 (d, JP,C = 8 Hz), 39.64
J = 11 Hz, J = 7 Hz, 1 H, PCHPh), 3.71 (td, J = 13 Hz, J = 6 Hz,
1 H, PCHPh), 7.18–7.42 (m, 10 H) ppm. 13C NMR (62.9 MHz,
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Enantiopure 1-r-Alkyl-2-c,5-t-Diphenylphospholanes and Phospholanium Salts
1
2
CDCl3): δ = 9.45 (d, JP,C = 25 Hz, PCH3), 31.48 [d, JP,C = 5 Hz,
sphere of argon. The solvent was removed under reduced pressure.
A Schlenk tube was charged with the tertiary phosphane obtained
in freshly distilled toluene, and alkyl triflate (0.8 mmol) was then
added at room temperature. The mixture was stirred at 60 °C for
the appropriate time, and the solvent was removed under reduced
pressure. The crude product was purified by flash column
chromatography (CH2Cl2/MeOH, 97:3) to give the product as a
viscous paste.
1
PCH(Ph)CH2], 37.46 [s, PCH(Ph)CH2], 45.83 (d, JP,C = 14 Hz,
1
PCHPh), 52.22 (d, JP,C = 14.7 Hz, PCHPh), 125.76 (d, JP,C
=
2 Hz) 125.92 (d, JP,C = 2 Hz), 127.66 (d, JP,C = 4 Hz), 127.77 (s),
128.36 (s), 128.57 (s), 139.19 (s, Cq), 144.78 (d, JP,C = 16 Hz, Cq)
ppm. 31P NMR (101.2 MHz, CDCl3): δ = 0.59 ppm. LRMS (ES):
m/z (%) = 255.1 (100) [M + H]+, 223.1 (3), 215 (16), 207.1 (3), 155
(11), 151 (7), 131 (4), 129 (17). HRMS (IE): calcd. for C17H19P
254.1219; found 254.1206.
(2R,5R)-(–)1-Methyl-1-ethyl-2,5-diphenylphospholanium Trifuoro-
methanesulfonate (6): [α]2D0 = –5.3 (c = 0.515, CHCl3). 1H NMR
(2S,5S)-1-Ethyl-2,5-diphenylphospholane (4c): 1H NMR (200 MHz,
CD6D6): δ = 0.65 (dt, 3JP,H = 16 Hz, JH,H = 8 Hz, 3 H, PCH2CH3), (250 MHz, CDCl3): δ = 0.95 (dt, 3 H, J = 7.5 Hz, JP,H = 18 Hz,
0.92–1.05 (m, 2 H, PCH2CH3), 1.52–1.62 (m, 1 H, PCHPhCH2), PCH2CH3), 1.78 (d, JP,H = 13 Hz, 3 H, PCH3), 1.91–2.06 (m, 1 H),
1.74–1.86 (m, 2 H, PCHPhCH2), 2.09–2.33 (m, 1 H, PCHPhCH2), 2.30–2.47 (m, 1 H), 2.72–2.82 (m, 4 H, PCHPhCH2), 4.51–4.67 (m,
2.76–2.89 (m, 1 H, PCHPh), 3.38–3.54 (m, 1 H, PCHPh), 7.05–
2 H, PCHPh), 7.43–7.63 (m, 10 H) ppm. 31P NMR (101.2 MHz,
CDCl3): δ = 49.17 ppm. 13C NMR (62.9 MHz, CDCl3): δ = 3.26
7.33 (m, 10 H) ppm. 13C NMR (50 MHz, CD6D6): δ = 10.17 (d,
2JP,C = 18.5 Hz, PCH2CH3), 18.62 (d, JP,C = 22.5 Hz, PCH2CH3), (d, JP,C = 47 Hz, CH3), 5.07 (d, JP,C = 6 Hz, CH3), 14.73 (d, JP,C
1
2
32.16 (d, JP,C = 4 Hz, PCHPhCH2), 38.19 (s, PCHPhCH2), 46.64
(d, JP,C = 16.3 Hz, PCHPh), 51.16 (d, JP,C = 17.8 Hz, PCHPh),
125.96 (d, JP,C = 2 Hz), 126.09 (d, JP,C = 2 Hz), 127.89 (d, JP,C
3.3 Hz), 128.49 (s), 128.6 (d, JP,C = 1 Hz), 128.8 (s), 139.66 (d, JP,C
= 1.5 Hz), 145.69 (d, JP,C = 16.6 Hz) ppm. 31P NMR (101.2 MHz,
CD6D6): δ = 1.2 ppm. HRMS (IE): calcd. for C18H21P 268.1375;
found 268.1360.
= 44.5 Hz, CH2), 30.49 (d, JP,C = 6.5 Hz, CH2), 31.44 (d, JP,C
6.5 Hz, CH2), 42.80 (d, JP,C = 45 Hz, PCHPh), 43.64 (d, JP,C
=
=
1
1
=
45 Hz, PCHPh), 128.22 (d, JP,C = 5 Hz), 128.64 (d, JP,C = 3 Hz),
128.71 (d, JP,C = 5 Hz), 129.64 (d, JP,C = 3 Hz), 129.68 (d, JP,C
=
3 Hz), 131.74 (d, JP,C = 5.5 Hz, Cq), 132.39 (d, JP,C = 7 Hz, Cq)
ppm. 19F NMR (235 MHz, CDCl3): δ = –78.23 ppm. (s). HRMS
(ES): calcd. for C19H24P 283.1610; found 283.1619.
(2S,5S)-1-Butyl-2,5-diphenylphospholane (4d): 1H NMR (250 MHz,
(2R,5R)-(+)-1-Methyl-1-butyl-2,5-diphenylphospholanium Trifuoro-
1
CDCl3): δ = 0.69 (t, J = 7 Hz, 3 H), 0.78–0.88 (m, 1 H), 1.04–1.19 methanesulfonate (7): [α]2D0 = +12.6 (c = 0.975, CHCl3). H NMR
(m, 4 H), 1.21–1.27 (m, 1 H), 1.79–1.97 (m, 1 H), 2.17–2.4 (m, 4 (250 MHz, CDCl3): δ = 0.68 (t, J = 7 Hz, 3 H), 1.05–1.27 (m, 4
H), 2.46–2.62 (m, 1 H), 3.12 (dt, J = 12 Hz, J = 7 Hz, 1 H,
H), 1.62 (d, JP,H = 13 Hz, 3 H, PCH3), 1.76–1.92 (m, 1 H), 2.06–
PCHPh), 3.68 (td, J = 12 Hz, J = 6 Hz, 1 H, PCHPh), 7.15–7.35 2.23 (m, 1 H), 2.54–2.70 (m, 4 H, PCHPhCH2), 4.36–4.54 (m, 2 H,
(m, 10 H) ppm. 13C NMR (62.9 MHz, CDCl3): δ = 13.77 (s), 24.38
PCHPh), 7.29–7.51 (m, 10 H) ppm. 31P NMR (101.2 MHz,
CDCl3): δ = 50.72 ppm. 13C NMR (62.9 MHz, CDCl3): δ = 3.84
(d, JP,C = 12 Hz), 25.32 (d, JP,C = 22 Hz), 28.22 (d, JP,C = 17 Hz),
1
32.15 (d, JP,C = 4 Hz), 37.9 (s), 46.33 (d, JP,C = 15 Hz, PCHPh), (d, JP,C = 47 Hz, PCH3), 13.05 (s, CH3), 20.39 (d, JP,C = 43 Hz,
51.1 (d, 1JP,C = 16 Hz, PCHPh), 125.79 (d, JP,C = 2 Hz), 125.86 (d,
JP,C = 2 Hz), 127.64 (d, JP,C = 3 Hz), 127.95 (d, JP,C = 5 Hz), 128.36
CH2), 22.92 (d, JP,C = 6 Hz, CH2), 23.60 (d, JP,C = 15 Hz, CH2),
43.00 (d, JP,C = 45 Hz, PCHPh), 43.76 (d, JP,C = 45 Hz, PCHPh),
(s), 128.59 (s), 139.15 (s), 145.15 (d, JP,C = 16.5 Hz) ppm. 31P NMR 128.27–128.74 (m), 129.57 (s), 132.06 (d, JP,C = 5.5 Hz, Cq), 132.44
(101.2 MHz, CDCl3): δ = 10.83 (s) ppm. MS (ES): m/z (%) = 297.1
(100) [M + H]+, 241.1 (2), 215.1 (4), 155 (3), 141 (3), 137 (4), 131
(10), 129 (28). HRMS (IE): calcd. for C20H25P 296.1688; found
296.1684.
(d, JP,C = 5.5 Hz, Cq) ppm. 19F NMR (235 MHz, CDCl3): δ =
–78.17 ppm. (s). HRMS (ES): calcd. for C21H28P 311.1923; found
311.1925.
(2R,5R)-(+)-1-Methyl-1-octyl-2,5-diphenylphospholanium Trifuoro-
1
(2R,5R)-(–)-1,1-Dimethyl-2,5-diphenylphospholanium Trifuorometh-
anesulfonate (5): phospholanium salt 2b (0.8 mmol) was treated
with a saturated solution of NaHCO3, extracted with freshly dis-
tilled methylene chloride and dried with Na2SO4 under an argon
atmosphere. The solvent was removed under reduced pressure. A
Schlenk tube was charged with the tertiary phosphane obtained
in freshly distilled diethyl ether, and then methyl triflate (90 µL,
0.8 mmol) was added at room temperature. The mixture was stirred
for 15 min, and the solvent was removed under reduced pressure.
The crude product was purified by flash column chromatography
(CH2Cl2/MeOH, 97:3) to give the product as a viscous paste. [α]2D0
methanesulfonate (8): [α]2D0 = +15.6 (c = 1.075, CHCl3). H NMR
(250 MHz, CDCl3): δ = 0.84 (t, J = 7 Hz, 3 H), 1.11–1.24 (m, 12
H), 1.62 (d, JP,H = 13 Hz, 3 H, PCHPhCH3), 1.77–1.93 (m, 1 H),
2.06–2.22 (m, 1 H), 2.54–2.69 (m, 4 H, PCHPhCH2), 4.38–4.53 (m,
2 H, PCHPh), 7.29–7.51 (m, 10 H) ppm. 31P NMR (101.2 MHz,
CDCl3): δ = 47.41 ppm. 13C NMR (62.9 MHz, CDCl3): δ = 3.84
(d, JP,C = 47 Hz, PCH3), 14.00 (s, CH3), 20.70 (d, JP,C = 40 Hz,
CH2), 21.08 (d, JP,C = 3 Hz, CH2), 22.50 (s, CH2), 28.63 (s, CH2),
28.67 (s, CH2), 30.69 (d, JP,C = 7 Hz, PCHPhCH2), 31.33 (d, JP,C
= 7 Hz, PCHPhCH2), 31.50 (s, CH2), 43.03 (d, JP,C = 44 Hz,
PCHPh), 43.74 (d, JP,C = 44 Hz, PCHPh), 128.34 (d, JP,C = 5 Hz),
1
= –3.9 (c = 0.595, CHCl3). H NMR (250 MHz, CDCl3): δ = 1.59
128.52 (d, JP,C = 2 Hz), 128.60 (d, JP,C = 3 Hz), 128.72 (d, JP,C =
(d, JP,H = 14 Hz, 6 H, P-CH3), 2.56–2.74 (m, 4 H, P-CHPh-CH2),
4.31–4.45 (m, 2 H, P-CHPh), 7.33–7.40 (m, 10 H) ppm. 31P NMR
(101.2 MHz, CDCl3): δ = 47.58 ppm. 13C NMR (62.9 MHz,
CDCl3): δ = 6.48 (d, JP,C = 49 Hz, PCH3), 30.58 (d, JP,C = 7 Hz,
5.5 Hz), 129.55 (d, JP,C = 2 Hz), 129.59 (d, JP,C = 3 Hz), 132.13 (d,
JP,C = 5.5 Hz, Cq), 132.45 (d, JP,C = 5.5 Hz, Cq) ppm. 19FNMR
(235 MHz, CDCl3): δ = –78.14 ppm. (s). HRMS (ES): calcd. for
C25H36P 367.2549; found 367.2540.
PCHPhCH2), 43.43 (d, JP,C = 46.5 Hz, PCHPh), 128.44 (d, JP,C
=
(2R,5R)-1-Ethyl-1-methyl-2,5-diphenylphospholanium Trifuorometh-
anesulfonate (6): Phospholanium salt 2c (0.24 mmol) was treated
with a saturated solution of NaHCO3, extracted with freshly dis-
tilled methylene chloride, and dried with Na2SO4 under an atmo-
18.4 Hz), 128.78 (d, JP,C = 61.6 Hz), 132.20 (d, JP,C = 5 Hz) ppm.
19F NMR (235 MHz, CDCl3): δ = 78.23 (s) ppm. HRMS (ES):
calcd. for C18H22P 269.1454; found 269.1464.
(2R,5R)-1,1-Methyl,alkyl-2,5-diphenylphospholanium Trifuorometh- sphere of argon. The solvent was removed under reduced pressure.
anesulfonate (5–8): Phospholanium salt 2b (0.8 mmol) was treated
with a saturated solution of NaHCO3, extracted with freshly dis-
tilled methylene chloride, and dried with Na2SO4 under an atmo-
A Schlenk tube was charged with tertiary phosphane 4c in freshly
distilled diethyl ether, and methyl triflate (33 µL, 0.29 mmol) was
then added at room temperature. The mixture was stirred at room
Eur. J. Org. Chem. 2008, 2439–2445
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2443

C. Dobrota, A. Duraud, M. Toffano, J.-C. Fiaud
FULL PAPER
temperature for 15 min, and the solvent was removed under re-
duced pressure. The crude product was purified by flash column
chromatography (CH2Cl2/MeOH, 97:3) to give the product as a
viscous paste.
mosphere of argon. After 2 h, the mixture was cooled down to 0 °C
and lithium aluminium hydride (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 mix-
ture was filtered under an argon atmosphere through Celite by can-
nula, and the solvent was evaporated. The tertiary phosphane ob-
tained was diluted in dry toluene (5 mL) and methyl trifluorome-
thanesulfonate (1.2 mmol) was added. The mixture was stirring at
room temperature overnight. Evaporation of the solvent gave a res-
idue, which was purified by flash column chromatography (CH2Cl2/
(2S,5S)-1-Ethyl-1-alkyl-2,5-diphenylphospholanium Trifuorometh-
anesulfonate (9–11): Phospholanium salt 2c (0.24 mmol) was
treated with a saturated solution of NaHCO3, extracted with
freshly distilled methylene chloride, and dried with Na2SO4 under
an atmosphere of argon. The solvent was removed under reduced
pressure. A Schlenk tube was charged with the tertiary phosphane
in freshly distilled toluene, and alkyl triflate (0.29 mmol) was then
added at room temperature. The mixture was stirred at 60 °C for
the appropriate time, and the solvent was removed under reduced
pressure. The crude product was purified by flash column
chromatography (CH2Cl2/MeOH, 97:3) to give the product as a
viscous paste.
MeOH, 97:3) to give salt 14 as a viscous paste. [α]2D0 = +90.8 (c =
1
1.225, CHCl3). H NMR (400 MHz, CDCl3): δ = 1.98 (d, JP,H
=
13.3 Hz, 3 H, PCH3), 2.41–2.93 (m, 4 H), 3.45 (s, 3 H, OCH3),
4.59–4.83 (m, 2 H), 6.70–7.75 (m, 14 H) ppm. 31P NMR (162 MHz,
CDCl3): δ = 45.59 ppm. 13C NMR (62.9 MHz, CDCl3): δ = 6.29
(d, JP,C = 53 Hz, PCH3), 29.37 (d, JP,C = 8.75 Hz), 31.74 (d, JP,C
6.5 Hz), 41.36 (d, JP,C = 47 Hz, PCHPh), 45.37 (d, JP,C = 47 Hz,
PCHPh), 55.72 (s), 104.23 (d, JP,C = 77 Hz), 111.54 (d, JP,C
=
(2S,5S)-(+)-1,1-Diethyl-2,5-diphenylphospholanium Trifuorometh-
anesulfonate (9): [α]2D0 = +17 (c = 0.575, CHCl3). 1H NMR
(250 MHz, CDCl3): δ = 0.68–0.81 (dt, JP,C = 17.6 Hz, J = 7.5 Hz,
6 H, CH3), 1.75–1.90 (m, 2 H), 2.25–2.39 (m, 2 H), 2.48–2.56 (m,
4 H), 4.39–4.54 (m, 2 H, PCHPh), 7.24–7.44 (m, 10 H) ppm. 31P
NMR (101.2 MHz, CDCl3): δ = 49.72 ppm. 13C NMR (62.9 MHz,
CDCl3): δ = 5.07 (d, JP,C = 6.4 Hz, CH3), 12.1 (d, JP,C = 42 Hz,
CH2), 31.5 (d, JP,C = 6 Hz, CH2), 43.04 (d, JP,C = 43 Hz, PCHPh),
=
6.9 Hz), 122.33 (d, JP,C = 12 Hz), 127.57 (t, JP,C = 6, JP,C = 2.3 Hz),
128.35 (d, JP,C = 2.3 Hz), 128.4 (s), 128.5 (d, JP,C = 3.2 Hz),129.40
(d, JP,C = 3 Hz), 131.61 (d, JP,C = 4.5 Hz), 133.49 (d, JP,C = 5.5 Hz),
133.80 (d, JP,C = 6.5 Hz), 137.54 (d, JP,C = 2 Hz), 161.14 (d, JP,C
=
1.8 Hz) ppm. HRMS (ES): calcd. for C24H26OP 361.1716; found
361.1716.
Supporting Information (see footnote on the first page of this arti-
cle): Spectroscopic data for all compounds.
128.5 (d, JP,C = 2.7 Hz), 128.7 (d, JP,C = 5 Hz), 129.5 (d, JP,C
=
2.2 Hz), 132.3 (d, JP,C = 5 Hz, Cq) ppm. 19F NMR (235 MHz,
CDCl3): δ = –78.23 (s) ppm. HRMS (ES): calcd. for C20H26P
297.1762; found 297.17627.
Acknowledgments
(2S,5S)-(–)-1-Ethyl-1-butyl-2,5-diphenylphospholanium Trifuorometh-
anesulfonate (10): [α]2D0 = –3.3 (c = 0.700, CHCl3). 1H NMR
(250 MHz, CDCl3): δ = 0.61–0.79 (m, 6 H), 1.06–1.23 (m, 4 H),
1.75–1.92 (m, 4 H), 2.13–2.37 (m, 2 H), 2.48–2.56 (m, 4 H,
PCHPhCH2), 4.33–4.40 (m, 2 H, PCHPh), 7.19–7.44 (m, 10 H)
ppm. 31P NMR (101.2 MHz, CDCl3): δ = 48.22 ppm. 13C NMR
(62.9 MHz, CDCl3): δ = 5.17 (d, JP,C = 6 Hz, CH3), 12.66 (d, JP,C
= 43 Hz, PCH2), 13.11 (s, CH3), 17.9 (d, JP,C = 41 Hz, P,CH2),
22.85 (d, JP,C = 5.5 Hz, CH2), 23.7 (d, JP,C = 14.5 Hz, CH2), 31.39
We wish to thank the Agence Universitaire de la Francophonie,
the Romanian Ministry of Education, and the French Ministry of
Education and Research (MENESR) for financial support.
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(d, JP,C = 5 Hz, CH2), 31.56 (d, JP,C = 5.5 Hz, CH2), 43.04 (d, JP,C
=
43 Hz, PCHPh), 128.53 (d, JP,C = 2.7 Hz), 128.67 (d, JP,C = 2.7 Hz),
128.74 (d, JP,C = 2.7 Hz), 129.52 (sl), 132.42 (d, JP,C = 5 Hz, Cq),
132.62 (d, JP,C = 5 Hz, Cq) ppm. 19F NMR (235 MHz, CDCl3): δ =
–78.17 ppm. (s). HRMS (ES): calcd. for C22H30P 325.2080; found
325.20841.
(2S,5S)-(–)-1-Ethyl-1-octyl-2,5-diphenylphospholanium Trifuorometh-
anesulfonate (11): [α]2D0 = –4.6 (c = 0.735, CHCl3). 1H NMR
(250 MHz, CDCl3): δ = 0.73–0.87 (m, 6 H), 1.10–1.23 (m, 12 H),
1.87–2.01 (m, 2 H), 2.21–2.44 (m, 2 H), 2.55–2.63 (m, 4 H,
PCHPhCH2), 4.39–4.41 (m, 2 H, PCHPh), 7.30–7.47 (m, 10 H)
ppm. 31P NMR (101.2 MHz, CDCl3): δ = 46.23 ppm. 13C NMR
(62.9 MHz, CDCl3): δ = 5.19 (d, JP,C = 6.5 Hz, CH3), 12.70 (d, JP,C
= 43 Hz, PCH2), 14.00 (s, CH2), 18.31 (d, JP,C = 40 Hz, CH2), 20.99
(d, JP,C = 6 Hz, CH2), 22.51 (s, CH2), 28.69 (d, JP,C = 2.7 Hz, CH2),
29.70 (s, CH2), 30.53 (s, CH2), 31.50 (s, CH2), 31.53 (s, CH2), 43.30
(d, JP,C = 7.5 Hz, PCHPh), 43.30 (d, JP,C = 7.5 Hz, PCHPh) 128.55
(d, JP,C = 2.7 Hz), 128.65 (d, JP,C = 2.2 Hz), 128.73 (d, JP,C
2.2 Hz), 129.58 (s), 132.35 (dd, JP,C = 5 Hz, Cq), 132.60 (dd, JP,C
=
=
5 Hz, Cq) ppm. 19F NMR (235 MHz, CDCl3): δ = –78.17 ppm. (s).
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Eur. J. Org. Chem. 2008, 2439–2445
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