A new efficient protocol for the preparation of chiral bisphosphines of the BICP family

Article abstract of DOI:10.1080/10426500490466977

A new procedure for the synthesis of chiral BICP ligands is described. The protocol involves the reaction of sodium diarylphosphide-borane complex with chiral 2,2′-bisbenzenesulfonyl-1,1′-dicyclopentane in toluene, followed by HBF4·OMe₂-mediate

Full text of DOI:10.1080/10426500490466977

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Phosphorus, Sulfur, and Silicon and the Related
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A NEW EFFICIENT PROTOCOL FOR THE PREPARATION OF
CHIRAL BISPHOSPHINES OF THE BICP FAMILY
Daniel G. Genov a
a DSM Pharma Chemicals , Greenville, North Carolina, USA
Published online: 16 Aug 2010.
To cite this article: Daniel G. Genov (2004) A NEW EFFICIENT PROTOCOL FOR THE PREPARATION OF CHIRAL
BISPHOSPHINES OF THE BICP FAMILY, Phosphorus, Sulfur, and Silicon and the Related Elements, 179:10, 1949-1958, DOI:
10.1080/10426500490466977
To link to this article: http://dx.doi.org/10.1080/10426500490466977
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Phosphorus, Sulfur, and Silicon, 179:1949–1958, 2004
ꢀC
Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490466977
A NEW EFFICIENT PROTOCOL FOR THE
PREPARATION OF CHIRAL BISPHOSPHINES
OF THE BICP FAMILY
Daniel G. Genov
DSM Pharma Chemicals, Greenville, North Carolina, USA
(Received January 1, 2004; accepted February 12, 2004)
A new procedure for the synthesis of chiral BICP ligands is de-
scribed. The protocol involves the reaction of sodium diarylphosphide–
borane complex with chiral 2,2ꢁ-bisbenzenesulfonyl-1,1ꢁ-dicyclopentane
in toluene, followed by HBF4·OMe2-mediated BH3 decomplexation.
Keywords: BICP; chiral bisphosphines; phosphine-borane
INTRODUCTION
Chiral phosphorus compounds, especially chelating bisphosphines,
constitute one of the most important classes of ligands utilized
in transition-metal-catalyzed asymmetric reactions.1 The principal
method for the synthesis of such bisphosphines involves the reac-
tion of an appropriate homochiral bissulfonate (bismesylate, bisto-
sylate) with an alkali diarylphosphide.2 As the alkali diarylphos-
phides are very strong bases, usually poor yields are obtained
for bisphosphines prepared via a nucleophilic substitution at an
sp3-carbon atom, due to a competing base-mediated elimination.2
One such bisphosphine is Zhang’s (2R,2ꢁ R)-bis(diphenylphosphino)-
(1R,1ꢁ R)-dicyclopentane ((R,R)-BICP) (1a; Scheme 1), a chiral 1,4-
bisphosphine with four stereogenic carbon centers in the backbone.3
The original preparation of this ligand involved the reaction of the
The author wishes to thank Professor Barry M. Trost (Stanford University) and
Dr. Joe Miller for helpful discussions. Dr. John Dankwardt is acknowledged for carry-
ing out some of the base-screening experiments.
Address correspodence to Daniel G. Genov, Theravance, Inc., 901 Gateway Boulevard,
South San Francisco, CA 94080. E-mail: danielgenov@hotmail.com
1949

1950
D. G. Genov
SCHEME 1 Synthesis of (R,R)-BICP and (S,S)-BICP. Reagents and condi-
tions: a) NaOBut/BuLi, Ar2PH(BH3), 2b, toluene, 0◦C to RT, 24 h, 50–51% yield;
b) HBF4xOMe2, CH2Cl2, 0◦C to RT, 24 h, >90% yield.
bismesylate obtained from (1R,1ꢁ R)-dicyclopentane-(2S,2ꢁS)-diol∗ with
lithium diphenylphosphide in tetrahydrofuran (THF).3 This protocol
affords (R,R)-BICP in only 20% yield after a tedious chromatographic
purification. The Rh- and Ru-complexes of BICP provide excellent cat-
alysts for asymmetric hydrogenation reactions.3 Therefore, the devel-
opment of a new, more practical synthesis of the ligand was necessary
in order to enable its application in industrial processes.
In this article we describe a new higher yielding protocol for the
preparation of BICP via the reaction of sodium diphenylphosphide-
borane complex with the chiral bisbenzenesulfonate 2b (Scheme 1).
This procedure allows the large-scale synthesis of BICP (1a) as well as
the preparation of new BICP-type ligands (1b and 1d; Figure 1).
∗One shortcoming for the general use of BICP as a ligand is that its original syn-
thesis involves a hydroboration with Alpine-borane, which is only available as one iso-
mer. We have solved this problem by developing a different synthetic sequence that af-
fords both BICP enantiomers. The route involves an enzymatic kinetic resolution that
gives both (1R, 1ꢁ R)-dicyclopentane-(2S, 2ꢁ S)-diol and (1S, 1ꢁ S)-dicyclopentane-(2R, 2ꢁ R)-
diol. This route will be reported in due course.

Chiral Bisphosphines
1951
FIGURE 1 Chiral bisphosphine ligands of the BICP family.
RESULTS AND DISCUSSION
The great potential of phosphine–borane complexes for the synthesis of
chiral phosphines was first recognized by Imamoto.4 Since then a large
number of ligands have been prepared via phosphine–boranes as syn-
thetic vehicles.5 The alkali anions derived from secondary phosphine–
boranes display sufficient nucleophilicity in substitution reactions, but
they are less basic than their corresponding borane-free counterparts.
Therefore, their application is advantageous in order to avoid unwanted
base-mediated eliminations.5
A few years ago Livinghouse reported a general protocol for the
synthesis of homochiral bisphosphines that entails deprotonation of a
secondary phosphine-borane complex with BunLi in THF at −78◦C, fol-
lowed by the addition of a DMF solution of the homochiral bis p-toluene
sulfonate bistosylate of interest.6 The desired chiral bisphosphine is
then released from its bisborane complex by the tetrafluoroboric acid-
dimethyl ether complex [HBF4·OMe2]–mediated BH3 decomplexation.6
Our attempt to synthesize BICP using this protocol was not success-
ful. The experiments where the bistosylate 2c∗∗ was reacted (Scheme 1)
with LiPPh2-BH3 in THF/DMF produced predominantly the mono
phosphine–borane 4 (Table I, entries 1 and 2). Different solvents were
then explored, and it was found that BICP–bisborane (3a) (Table I)
was formed as the major product only when the reaction was carried
out in toluene (Table I, entries 4–6). Thus, when the bistosylate 2c
was reacted with 3 equivalents of LiPPh2-BH3 in toluene, the corre-
sponding BICP–bisborane (3a) was obtained in 35% yield after col-
umn chromatography. However, this reaction can be carried out only
at low temperature (−78◦C) because at temperatures in the range of
∗∗In the screening experiments shown in Table 1 and discussed throughout the text
(1R, 1ꢁ R, 2S, 2ꢁ S)-2 was used to give (R, R)-BICP.

1952
D. G. Genov
TABLE I Selected Experiments Carried Out to Develop Conditions for the
Synthesis of BICP
Bis/Monoa
(3a/4)
Base
2
Equiv. Base
Solvent
T (◦C)
1
2
3
4b
5
6
7
8
9
BunLi
2c
2a
2a
2c
2a
2a
2a
2a
2a
2a
2a
2b
2b
2b
2b
2b
2d
2b
2b
2b
2b
2b
2b
2b
2.2
2.2
2.2
2.4
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.4
4.5
2.4
3
4
3
3
3
3
3
3
4.5
3
THF/DMF
THF/DMF
THF
−78 to rt
−78 to rt
−78 to rt
−78 to rt
0 to rt
rt
Mono
Mono
3/1
BunLi
BunLi
BunLi
PhMe
Bis (35%)c
Mono
1/8
BunLi
MTBE
Dioxane
MeOH
THF/PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe/DMF
THF/DMF
PhMe
PhMe
PhMe
BunLi
KOH
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
0 to rt
Mono
NR
Mono
Mono
1/3
1/2
9/1
3/1
PriMgCl
KOBut
10
LiOBut
11
12
13
14
15
16
17
18
19
20
21
22
23
23
NaOBut
NaOBut
NaOBut
BunLi/NaOBut
BunLi/NaOBut
BunLi/NaOBut
BunLi/NaOBut
BunLi/NaOBut
BunLi/NaOBut
BunLi/KOBut
NaN(SiMe3)2
NaOMe
>10/1 (50%)d
>10/1
>10/1
Mono
Mono
Mono
1/1
Mono
NR
1/8
NaH
NaOtC5H11
PhMe
PhMe
aThe ratio was determined by HPLC.
bThe same conditions were used for performing the reaction with the 2a, 2b, and 2d.
cIsolated yield by column chromatography.
dIsolated yield by crystallization from heptane.
−20◦C to rt, LiPPh2-BH3 forms a viscous, sticky material in toluene
that prevents efficient stirring of the reaction mixture. This makes
the reaction inapplicable for scaleup. Therefore, we carried out exper-
iments using other bases (Table I, entries 7–23). These experiments
revealed that, unlike LiPPh2-BH3, NaPPh2-BH3 or KPPh2-BH3 form

Chiral Bisphosphines
1953
solid suspensions in toluene at the temperature range between −20◦C
and rt without creating a problem for stirring. Of the bases examined,
only ButONa/BunLi† gave BICP–bisborane (3a) as the major product
in acceptable yields. An excess of 3 equivalents of the base and the
secondary phosphine–borane was necessary to maximize the yield of
BICP-bisborane. Higher excesses (Table I, entries 14–16) did not im-
prove the yield. Under the best conditions found, ButONa (3 equiv.)
was suspended in dry toluene at 0◦C and BunLi (1.6 M in hexanes;
3 equiv.) was added. After stirring for 20 min at this temperature, a
toluene solution of the chiral bisbenzenesulfonate 2b was added at
0◦C; the mixture was stirred at this temperature for 30 min and then
at rt for 24 h. In this way, both enantiomers of BICP–bisborane (3a;
Scheme 1) were obtained in 50–51% yield after crystallization from
heptane. The reaction was carried out at up to 50 g scale. Similar yields
were obtained when bistosylate 2c or bis(p-chlorobenzene)sulfonate
2d were used instead of bisbenzenesulfonate 2b. These substrates
are, however, significantly less soluble in toluene than the bisbenzene-
sulfonate and therefore are less applicable for a large-scale prepara-
tion. A lower yield in the reaction was obtained using 2a as a sub-
strate. Interestingly, when ButOK/BunLi (3 equivalents) was used as
a base instead of ButONa/BunLi, monophosphine–borane 4 (Table I,
entry 20) was obtained with very little formation of BICP–bisborane
(3a).
The BH3 decomplexation was easily carried out with HBF4·OMe2
using the standard conditions developed by Livinghouse to give (R,R)-
BICP or (S,S)-BICP (Scheme 1) in >90% yield.
The new procedure also allowed the preparation of new ligands of
the BICP family (1b, 1d; Figure 1) and the known bisphosphine 1c in
yields similar to those obtained for the parent ligand BICP. Ligands 1b
and 1d are not accessible by the original Zhang protocol.
In summary, a new procedure for the synthesis of BICP has been
developed. The procedure involves the reaction in toluene of bisben-
zenesulfonate 2b with NaPPh2 (BH3), derived from the secondary
phosphine–borane and ButONa/BunLi, followed by the decomplexa-
tion of the resulting chiral BICP–bisborane with HBF4·OMe2. Using
this procedure, new ligands from the BICP family were obtained. In
addition, the new protocol allows the synthesis of the BICP ligands on
large scale.#
†For the application of ButONa/BunLi in organic synthesis see Schlosser [7].
#Both (R, R)-BICP and (S, S)-BICP were prepared using the new protocol and are now
commercially available in research quantities from Strem.

1954
D. G. Genov
EXPERIMENTAL
All experiments were performed under an argon atmosphere.
Diphenylphosphine–borane complex and BunLi (1.6 M in hexanes)
were purchased from Aldrich (Milwaukee, WI, USA). ButONa
was purchased from Strem (Newburyport, MA, USA). Anhy-
drous solvents were used in all reactions. Bis(4-methoxyphe-
nyl)phosphine-borane, bis(3,5-dimethylphenyl)phosphine-borane, and
bis(4-methoxy-3,5-dimethylphenyl)phosphine-borane were prepared
by known methods.8 Chiral bissulfonates 2 were synthesized by re-
acting the corresponding diol with RSO2Cl (2.1 equiv.) in THF in the
presence of 3 equivalents of N-methylimidazole. Bissulfonates 2 were
obtained in quantitative yields and used without purification. The enan-
tiopurities of the bisphosphines were determined by chiral high perfor-
mance liquid chromatography (HPLC) analysis.‡
(2R,2ꢀR)-Bis(diphenylphosphino)-(1R,1ꢀR)-
dicyclopentane, Bisborane Complex (3a)3
NaOBut (12.84 g, 0.134 mol) was suspended in dry toluene (100 ml). The
mixture was cooled to 0◦C and BuLi (1.6 M in hexane, 0.134 mol) was
added via syringe. The yellow suspension was stirred at 0◦C for 20 min.
Diphenylphosphine-borane complex (26.73 g, 0.134 mol, 3 equiv.) was
dissolved in 90 ml dry toluene, and the solution was added to the
base (NaOBut/BuLi) at 0◦C. The mixture was stirred for 20 min at
0◦C (the color of the suspension turns white) and bisbenzenesulfonate
2b (20.00 g, 0.0445 mol) in toluene (200 ml) was added. The mixture
was stirred at 0◦C for 1 h and then at room temperature for 24 h. The
progress of the reaction was followed by 31P NMR and HPLC. The mix-
ture was washed with cold brine (300 ml). The water phase was back-
extracted with CH2Cl2 (3 × 150 ml). The combined organic fractions
were dried over Na2SO4. The solution was concentrated on a rotary
evaporator to about 50 ml and dichloromethane (200 ml) was added.
The solution was concentrated to about 50 ml and filtered through a
plug of silica gel (100 g, washed after that with ∼700 ml CH2Cl2). The
solution was concentrated to about 50 ml and heptane (400 ml) was
added. The mixture was concentrated to ∼200 ml (white solid forms),
stirred at 0◦C for 1 h and filtered to give pure (R, R)-BICP-bisborane
‡
The enantiopurity of each enantiomer of 1a (>99% ee) was determined by chiral
HPLC analysis (Chiralcel OD 250 × 4.6 mm column, 5% EtOH in hexane as an eluent,
flow rate 1 ml/min, column temperature 30◦C) of the corresponding bisphosphine oxides.
The phosphine oxides were obtained by treating each of (R, R)-BICP and (S, S)-BICP with
3% H2O2 in toluene at 65◦C and quenching the reaction with cold aqueous Na2S2O3.

Chiral Bisphosphines
1955
1
(3a) as a white solid (11.9 g, 50% yield). H NMR (CDCl3) δ 7.80–7.30
(m, 20H), 2.55–1.35 (m, 16H); 31P NMR (CDCl3) δ 17.68; 13C NMR
(CDCl3) δ 133.43 (d, JPC = 8.5 Hz), 132.25 (d, JPC = 8.5 Hz), 132.08
(d, JPC = 50.0 Hz), 130.67 (d, JPC = 2.1 Hz), 130.57 (d, JPC = 2.1 Hz),
129.71 (d, JPC = 56.5 Hz), 128.39 (d, JPC = 9.4 Hz), 128.29 (d, JPC = 9.1
Hz), 46.28 (m), 36.26 (d, JPC = 30.6 Hz), 31.35, 29.69, 22.68.
(2S,2ꢀS)-Bis(diphenylphosphino)-(1S,1ꢀS)-
dicyclopentane, Bisborane Complex (3a)
Diphenylphosphine–borane complex (59.95 g, 0.3 mol) and (1S,1ꢁS,2R,
2ꢁ R)-2b (45.00 g, 0.1 mol) were reacted as above to give after crystalliza-
tion from heptane bisboronato-(S,S)-BICP (3a) as a white solid (27.2 g,
51%). Spectroscopic data the same as for the (R,R)-enantiomer.
(2R,2ꢀR)-Bis[di(4-methoxyphenyl)phosphino]-(1R,1ꢀR)-
dicyclopentane, Bisborane Complex
Bis(4-methoxyphenyl)phosphine-borane complex (4.20 g, 0.0162 mol)
and (1R,1ꢁ R,2S,2ꢁS)-2b (2.44 g, 5.41 × 10−3 mol) were reacted as
above to give, after purification by column chromatography (elut-
ing with 30/70 hexane/CH2Cl2 first and then 10/90 hexane/CH2Cl2)
and crystallization from heptane, 1.90
g
of (2R,2ꢁ R)-bis[di(4-
methoxyphenyl)phosphino]-(1R,1ꢁ R)-dicyclopentane, bisborane com-
1
plex as a white solid (53%). H NMR (CDCl3) δ 7.65–6.88 (m, 16H),
3.93 (s, 6H), 3.81 (s, 6H), 2.48–1.41 (m, 16H); 31P NMR (CDCl3)
δ 14.70; 13C NMR (CDCl3) δ 161.63 (d, JPC = 2.3 Hz), 161.51 (d,
JPC = 2.3 Hz), 135.20 (d, JPC = 9.8 Hz), 133.96 (d, JPC = 9.2 Hz),
123.49 (d, JPC = 54.8 Hz), 121.06 (d, JPC = 61.7 Hz), 114.14 (d,
JPC = 10.4 Hz), 113.92 (d, JPC = 10.1 Hz), 55.53, 55.26, 46.49, 36.69
(d, JPC = 32.5 Hz), 31.50, 29.84, 22.68. HRMS calcd. for C38H50B2P2O4:
654.3384; Found 654.3411.
(2R,2ꢀR)-Bis[di(3,5-dimethylphenyl)phosphino]-(1R,1ꢀR)-
dicyclopentane, Bisborane Complex3
Bis(3,5-dimethylphenyl)phosphine-borane complex (3.93 g, 0.0153 mol)
and (1R,1ꢁ R,2S,2ꢁS)-2b (2.30 g, 5.11 × 10−3 mol) were reacted as
above to give, after crystallization from heptane, bisboranato-(2R,2ꢁ R)-
bis[di(3,5-dimethylphenyl)-phosphino]-(1R,1ꢁ R)-dicyclopentane as
a
1
white solid (1.76 g, 56%). H NMR (CDCl3) δ 7.36–7.03 (m, 12H), 2.41
(s, 12H), 2.31 (s, 12H), 2.54–1.25 (m,16H); 31P NMR (CDCl3) δ 17.05;
13C NMR (CDCl3) δ 137.93–129.30 (Ph), 46.33 (m), 35.44 (d, JPC
30.9 Hz), 29.75, 22.95, 21.45, 21.25.
=

1956
D. G. Genov
(2S,2ꢀS)-Bis[di(4-methoxy-3,5-dimethylphenyl)-
phosphino]-(1S,1ꢀS)-dicyclopentane, Bisborane Complex
Bis(4-methoxy-3,5-dimethylphenyl)phosphine-borane complex (6.00 g,
0.019 mol) and (1S,1ꢁS,2R,2ꢁ R)-2b (2.86 g, 6.35 × 10−3 mol) were re-
acted as above to give, after purification by column chromatography
(eluting with 50/50 hexane/CH2Cl2 first and then 30/70 hexane/CH2Cl2)
and crystallization from heptane, 2.70
g
of (2S,2ꢁS)-bis[di(4-
methoxy-3,5-dimethylphenyl)phosphino]-(1S,1ꢁS)-dicyclopentane, bis-
borane complex as a white solid (55%). 1H NMR (CDCl3) δ 7.39 (d,
J
= 10.1 Hz, 4H, Ar), 7.13 (d, J = 9.8 Hz, 4H, Ar), 3.78 (s, 6H,
PH
PH
OCH3), 3.72 (s, 6H, OCH3), 2.46 (s, 12H, CH3), 2.24 (s, 12H, CH3), 2.48–
1.27 (m, 16H, CH2, CH); 13P NMR (CDCl3) δ 15.05; 13C NMR (CDCl3)
δ 159.16, 134.04 (d, JPC = 9.2 Hz), 132.73 (d, JPC = 8.6 Hz), 131.43 (d,
JPC = 10.7 Hz), 131.01 (d, JPC = 10.4 Hz), 127.26 (d, JPC = 50.9 Hz),
124.62 (d, JPC = 58.9 Hz), 59.68, 59.55, 46.3 (m), 35.70 (d, JPC = 31.4
Hz), 31.22, 29.49, 23.01, 16.36, 16.17. HRMS calcd. for C46H66B2P2O4:
766.4638; Found: 766.4695.
(2R,2ꢀR)-Bis(diphenylphosphino)-(1R,1ꢀR)-dicyclopentane
((R,R)-BICP) (1a)3
(R, R)-BICP-bisborane (3a) (10.45 g, 0.0196 mol) was dissolved in
CH2Cl2 (60 ml), the solution was cooled to 0◦C and tetrafluoroboric acid-
dimethyl ether complex (HBF4·OMe2) (13.10 g, 0.098 mol, 5 equiv.) was
added via syringe. The mixture was stirred at 0◦C for 30 min and at
room temperature for 24 h. The progress of the reaction was followed by
31P NMR. It was then diluted with CH2Cl2 (60 ml) and treated with 2M
NaOH (150 ml) (∼30 equiv.) at 0◦C. After 10 min stirring at 0◦C, the
two phases were separated and the water phase was back-extracted
with CH2Cl2. The combined organic fractions were washed with wa-
ter (100 ml) and dried over Na2SO4. The solution was concentrated to
about 20 ml, and methanol (400 ml) was added. The solution was con-
centrated to ∼150 ml, and the white solid was filtered (stable in air)
and washed with MeOH (20 ml) to give 7.58 g pure BICP (77%). Af-
ter concentration of the methanol filtrate to dryness and washing the
solid with 20 ml cold heptane, an additional 1.78 g of BICP was isolated
(94% combined yield). [α]D20 = −44.5 (c 0.58, CHCl3); 1H NMR (CDCl3)
δ 7.43–7.21 (m, 20H), 2.49–1.37 (m, 16H); 31P NMR (CDCl3) δ − 14.52;
13C NMR (CDCl3) δ 139.46–127.97 (Ph), 45.88 (dd, JPC = 12.3 Hz,
12.3 Hz), 40.34 (d, JPC = 14.4 Hz), 30.87 (dd, JPC = 6.4 Hz, 4.0 Hz),
23.77 (d, JPC = 5.8 Hz).

Chiral Bisphosphines
1957
(2S,2ꢀS)-Bis(diphenylphosphino)-(1S,1ꢀS)-dicyclopentane
((S,S)-BICP) (1a)
(S,S)-BICP-bisborane (3a) (22.7 g, 0.0425 mol) and HBF4·OMe2 (56.8 g,
0.425 mol) were reacted as above to give after crystallization from
methanol 19.2 g (90%) (S,S)-BICP as a white solid. [α]2D0 = +46.7
(c 0.82, CHCl3). The spectroscopic data are the same as for (R, R)-BICP.
HRMS calcd. for C34H36P2: 506.2292; Found: 506.2294.
(2R,2ꢀR)-Bis[di(4-methoxyphenyl)phosphino]-
(1R,1ꢀR)-dicyclopentane (1b)
(2R,2ꢁ R)-Bis[di(4-methoxyphenyl)phosphino]-(1R,1ꢁ R)-dicyclopentane,
bisborane complex (1.82 g, 2.78 × 10−3 mol) was dissolved in CH2Cl2
(30 ml) and treated with HBF4·OMe2 (3.72 g, 0.028 mol) as described
above. The workup and purification were carried out as described
for BICP. In this way, 1.32 g of pure 1b (76%) was isolated. After
concentration of the methanol filtrate to dryness an additional 0.33 g
of bisphosphine was isolated (95% combined yield). [α]2D0 = −63.6
(c 0.145, CHCl3); 1H NMR (CDCl3) δ 7.38–6.74 (m, 12 H), 3.84 (s,
6H), 3.75 (s, 6H), 2.40–1.34(m, 16H); 31P NMR (CDCl3) δ −19.01; 13C
NMR (CDCl3) δ 159.90, 159.81, 135.27 (d, JPC = 15.0 Hz), 134.99 (d,
JPC = 13.5 Hz), 130.59 (d, JPC = 10.1 Hz), 130.28 (d, JPC = 10.1 Hz),
113.82 (d, JPC = 8.2 Hz), 113.70 (d, JPC = 8.9 Hz), 55.15, 55.05,
45.95 (dd, JPC = 12.2 Hz, 12.2 Hz), 40.67 (d, JPC = 13.0 Hz), 30.91
(dd, JPC = 4.1 Hz, 4.8 Hz), 23.60 (d, JPC = 5.1 Hz). HRMS calcd. for
C38H44P2O4: 626.2715; Found: 626.2688.
(2R,2ꢀR)-Bis[di(3,5-dimethylphenyl)phosphino]-(1R,1ꢀR)-
dicyclopentane (1c)3
Bisboranato-(2R,2ꢁ R)-bis[di(3,5-dimethylphenyl)-phosphino]-(1R,1ꢁ R)-
dicyclopentane (1.23 g, 1.91 × 10−3 mol) was dissolved in CH2Cl2
(30 ml) and treated with HBF4·OMe2 (2.55 g, 0.019 mol) as described
above. The workup and purification were carried out as described
for BICP. In this way 0.91 g pure 1c (77%) was isolated. After con-
centration of the methanol filtrate to dryness an additional 0.19 g of
1
bisphosphine was isolated (93% combined yield). H NMR (CDCl3) δ
7.17–6.88 (m, 12H), 2.34 (s, 12H), 2.18 (s, 12H), 2.40–1.23 (m, 16H);
31P NMR (CDCl3) δ − 16.63; 13C NMR (CDCl3) δ 139.77–130.04 (Ph),
47.36 (dd, JPC = 11.0 Hz, 11.0 Hz), 39.14 (d, JPC = 13.7 Hz), 30.82 (m),
22.41, 21.43, 21.28.

1958
D. G. Genov
(2S,2ꢀS)-Bis[di(4-methoxy-3,5-dimethylphenyl)-
phosphino]-(1S,1ꢀS)-dicyclopentane (1d)
(2S,2ꢁS)-Bis[di(4-methoxy-3,5-dimethylphenyl)phosphino]-(1S,1ꢁS)- di-
cyclopentane, bisborane complex (2.53 g, 3.3 × 10−3 mol) was dissolved
in CH2Cl2 (30 ml) and treated with HBF4 · OMe2 (4.43 g, 0.033 mol)
as described above. The workup and purification were carried out as
described for BICP. In this way, 1.79 g of pure 1d (74%) was isolated.
After concentration of the methanol filtrate to dryness, an additional
0.43 g of bisphosphine was isolated (91% combined yield). [α]2D0 = +102
1
(c 0.205, CHCl3); H NMR (CDCl3) δ 7.24 (d, J = 8.1 Hz, 4H, Ar),
PH
6.98 (d, J = 7.7 Hz, 4H), 3.73 (s, 6H), 3.68 (s, 6H), 2.26 (s, 12H),
PH
2.24 (s, 12H), 2.39–1.19 (m, 16H); 31P NMR (CDCl3) δ − 18.84; 13C
NMR (CDCl3) δ 157.66, 157.41, 135.08 (d, JPC = 21.7 Hz), 134.34 (d,
JPC = 21.7 Hz), 134.50, 133.37, 130.49 (d, JPC = 8.7 Hz), 130.21 (d,
JPC = 8.7 Hz), 59.61, 59.54, 47.26 (dd, JPC = 11.4 and 11.1 Hz), 39.74
(d, JPC = 13.1 Hz), 30.47 (d, JPC = 6.9 Hz), 22.29, 16.24, 16.10. HRMS
calcd. for C46H60P2O4: 738.3967; Found: 738.3945.
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