Diastereoselective synthesis of chiral non-racemic 2-substituted 2-boranatophosphino ethanoic acid: A potential intermediate to chiral ligands for asymmetric catalysis

Article abstract of DOI:10.1016/S0957-4166(03)00287-8

Chiral α-amidophosphine boranes 7a-b can be diastereoselectively alkylated, using a phenylglycinol derivative as a chiral inducer, to furnish α-substituted α-amidophosphine boranes 8-12 with up to 99% diastereoisomeric excess. Selective reduction of the amidophosphine boranes afforded optically pure β-boranatophosphine-alcohol 13. The latter one can then be oxidized in boronatophosphine acid 14.

Full text of DOI:10.1016/S0957-4166(03)00287-8

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 14 (2003) 1637–1644
Diastereoselective synthesis of chiral non-racemic 2-substituted
2-boranatophosphino ethanoic acid: a potential intermediate to
chiral ligands for asymmetric catalysis
Jean-Philippe Ebran, Philippe Jubault,* Xavier Pannecoucke* and Jean-Charles Quirion
Laboratoire d’He´te´rochimie Organique associe´ au CNRS, IRCOF, INSA et Universite´ de Rouen, 1 rue Tesnie`re,
76821 Mont Saint-Aignan Cedex, France
Received 20 February 2003; revised 21 March 2003; accepted 1 April 2003
Abstract—Chiral a-amidophosphine boranes 7a–b can be diastereoselectively alkylated, using a phenylglycinol derivative as a
chiral inducer, to furnish a-substituted a-amidophosphine boranes 8–12 with up to 99% diastereoisomeric excess. Selective
reduction of the amidophosphine boranes afforded optically pure b-boranatophosphine-alcohol 13. The latter one can then be
oxidized in boronatophosphine acid 14. © 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
directly associated with the transition metal in the
catalytic species, the creation of a stereogenic center at
the neighboring a-position should enhance facial dis-
crimination and thus lead to an improved level of
enantioselectivity. In previous papers, we described
diastereoselective alkylation12 and diastereoselective
Michael addition13 processes to access chiral a-substi-
tuted b-amidophosphines 1, key intermediates for the
synthesis of chiral ligands via acid 2 (Scheme 1).
During the past three decades, numerous potential chi-
ral ligands1 have been synthesized and some of them
shown to be excellent ligands (for example DIPAMP,2
DIOP,3 BINAP,4 PennPHOS5 and DuPHOS6) and
have been developed for a variety of catalytic reactions.
However, all the phosphorus containing ligands
employed in asymmetric catalysis1 can be classified into
two types depending on the location of the stereogenic
information, which may be found on the phosphorus
atom (DIPAMP) or on a side chain. For the latter case,
the stereogenicity can be carbon centered (VALAP,7
CHIRAPHOS8) or of axial type (BINAP).
From this acid, a broad range of chiral phosphine–
amines 3 were prepared and their application in the
field of enantioselective hydrogen-transfer with ruthe-
nium catalysts was assayed.14 Preliminary experiments
gave very encouraging results with more than 82% ee
when R=Me in the reduction of aromatic ketones.
Following the model of Noyori15 with our ligands, the
phosphorus and the nitrogen atoms would form a
six-membered ring with the metal. In order to complete
our study and investigate the influence of the ring size,
we turned our attention to a general access to chiral
b-aminophosphines. In this paper, we wish to report
the first general synthesis of the chiral non racemic
When the stereogenicity is carbon centered, most of the
ligands in frequent use are derived from amino acids or
from the chiral pool,9 which limits their structural
diversity. To the best of our knowledge, very few of
them were obtained by creation of a stereogenic center.
In those rare examples, their syntheses are based or on
racemic starting materials, and need a resolution10 or
are based on an enantioselective synthesis.11
easily
tunable
2-substituted-2-boranatophosphino
The development of new asymmetric phosphine ligands
is of great interest. Since the phosphorus atom is
ethanoic acid, via the diastereoselective alkylation of
boronato-a-amidophosphines. Indeed, this key interme-
diate should give us access to various types of ligands
(phosphine–amine, phosphine–amide, phosphine–oxa-
zoline, phosphine–aminophosphine, phosphine–phos-
phinite…), after simple transformation and removal of
borane protection (DABCO, 40°C in toluene).12
* Corresponding authors. Tel.: (33) 2 35 52 24 27; fax: (33) 2 35 52 29
59; e-mail: xavier.pannecoucke@univ-rouen.fr
0957-4166/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0957-4166(03)00287-8

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J.-P. Ebran et al. / Tetrahedron: Asymmetry 14 (2003) 1637–1644
Scheme 1.
2. Results and discussion
ing agents (HMPA, LiBr, LiCl) surprisingly increased
the diastereoisomeric excesses (Table 1, entries 2–4).
The conversion rate was always good to excellent after
4 h reaction and the best de (>98%) was obtained using
LiCl and LiBr as additive (Table 1, entry 4). Indeed
lithium salts are well known to accelerate the alkylation
rate which is effectively the case in our study. The role
of LiCl on the diastereoselectivity is less well docu-
mented but Seebach22 has proposed that it may modify
the aggregation state. For N-benzylamide 7b, LiCl also
has a beneficial effect and the de increased to 97%
(Table 1, entry 5). The conversion rate was good, but
needed more than 6 h to be complete. By increasing the
reaction temperature to −20°C, the conversion rate was
99% in less than 2 h, but the de slightly decreased to
93% (Table 1, entry 6). So, to summarize, the standard
conditions selected for this process were: metallation
conditions, 2.5 equiv. of n-butyllithium, 6 equiv. of
LiCl, temperature: −20°C, 2 h, and alkylation condi-
tions 3 equiv. of methyl iodide, temperature: −40°C,
4–6 h.
In the course of our study on the diastereoselective
functionalization of amides using phenylglycinol as a
chiral auxiliary, we described the alkylation of N-pro-
tected amides with de’s higher than 97%.16 Therefore,
to create the asymmetric center a to the phosphorus
atom, we decided to apply this methodology to the
synthesis of chiral boronato-a-substituted a-amido-
phosphines.
The starting a-amidophosphines 7 were synthesized in
five steps from chlorodiphenylphosphine (Scheme 2):
this was protected as its borane derivative and reduced
with
lithium
aluminum
hydride
to
afford
hydrogenophosphine borane 4 in 95% yield.17 Conden-
sation of 4 with ethyl chloroacetate, followed by sapon-
ification yielded the acid 6 in 82% yield. Finally the
amides 7a,b were obtained by reaction of the acyl
chloride of 6 with the corresponding N-protected
phenylglycinol18 under standard conditions. For N-ben-
zylated phenylglycinol, we observed ester formation as
a side reaction, even if intramolecular O“N acyl trans-
fer is predominant and N-acyl form is strongly favored
under basic conditions.19
We then turned our attention to the influence of the
chiral auxiliary. First, pseudoephedrine, which is
known to be an efficient chiral inductor,19 was tested,
but as already observed in our group,12 introduction of
a substituent a to the oxygen atom of the aminoalcohol
decreased the diastereoselectivity. When (S)-4-benzyl-2-
oxazolidinone auxiliary of Evans23 was used as the
chiral auxiliary, no alkylated product could be
observed, whatever the conditions.
In a first attempt, compound 7a20 was subjected to the
conditions already optimized for the diastereoselective
alkylation of amide enolates21 (i.e. formation of the
enolate with s-BuLi at −20°C and at concentrations
above 0.085 mmol mL−1, followed by the addition of
the electrophile at −78°C) but using this procedure, no
alkylated product was observed. Different temperatures
for the addition of the electrophile were then tried. The
reaction occurred only at −40°C, yielding compound 8a
in 80% de (Table 1, entry 1).
Next, we decided to investigate the influence of the
base, the temperature and the presence of additives in
the methylation reaction. We only tried lithiated bases,
as the lithium ion proved to be the best counter ion for
the chemioselectivity (C- or O-alkylation) and
diastereoselectivity (formation of the alcoholate is
required).21 The best results for the alkylation step were
obtained at −40°C using n-BuLi as base instead of
s-BuLi. Lower temperatures gave no alkylation product
and higher temperatures, lower de’s. Addition of chelat-
Scheme 2.

J.-P. Ebran et al. / Tetrahedron: Asymmetry 14 (2003) 1637–1644
Table 1. Influence of the additive on the diastereoselective alkylation
1639
Entry
R
Additive
Conversion ratea (%)
Dea (%)
Product
1
2
3
4
5
6
Me
Me
Me
Me
Bn
/
98
93
87
96
90
99
80
97
>98
>98
97
8a
8a
8a
8a
8b
8b
HMPA
LiBr
LiCl
LiCl
LiClb
Bn
93
a Determined by HPLC.
b Addition of MeI at −20°C.
To evaluate the scope of the reaction, a range of
electrophiles have been assayed in this reaction using
7a,b (chiral vector: N-methyl and N-benzylphenylgly-
cinol respectively) as substrates; the formation of prod-
ucts 8–12 is summarized in Table 2. The electrophilic
substitutions proceeded in good yields and in low to
excellent diastereoselectivities depending on the size and
of the reactivity of the electrophile.
dropped from 91 to 20% with allyl and metallyliodide
as electrophiles, respectively. Concerning the nature of
the group on the nitrogen atom, N-Me afforded slightly
better diastereoisomeric excesses than N-benzyl confirm-
ing the results already obtained in amide alkylation16
(Table 2, entries 1, 8). It is also to be noted that benzyl
protection on nitrogen atom increased the proportion
of O-alkylation, especially when benzyl bromide was
used as electrophile. Indeed in the latter case, only the
dialkylated product could be observed. Nevertheless at
that stage, whatever the substituents are, the
diastereoisomers can be easily separated by simple
chromatography on silica gel, affording optically pure
a-substituted-a-amidophosphine borane.
The results depicted in Table 2 clearly indicate the
dramatic influence of the electrophile on diastereoiso-
meric excesses. Two factors seem to be crucial for the
diastereoselectivity: the reactivity and the steric hin-
drance of the electrophile. Indeed using iodide instead
of bromide allowed the reaction to take place at lower
temperature and so a better de was observed (Table 2,
entries 2, 3, 6 and 7). The same result was obtained
with the reactive methyliodide, where the substitution
can occur at −40°C and so the de can reach more than
98% (Table 2, entry 1). Steric hindrance also plays an
important role as shown in entries 5 and 7 where the de
X-Ray analysis24 of the major diastereoisomer of 11 has
allowed unambiguous assignment of the (S)-configura-
tion to the newly created stereogenic center (Fig. 1).
To explain the diastereoselectivity, a model including a
chelating intermediate has been proposed (Scheme 3).21
Table 2. Influence of the electrophile
Entry
R
EX
Conversion ratea (%)
Yielda (%)
t (°C)
Time (h)
Deb (%)
Product
1
2
3
4
5
6
7
8
Me
Me
Me
Me
Me
Me
Me
Bn
MeI
BnBr
BnI
BrCH2CO2t-Bu
CH2ꢀCHCH2I
CH2ꢀC(CH3)CH2Br
CH2ꢀC(CH3)CH2I
MeI
95
100
71
77
100
55
90
60
55
55
87
32
51
80
−40
rt
4
24
5
24
2
48
5
6
>98
38
45
77
91
15
20
>98
8a
9
9
10
11
12
12
8b
0
rt
0
rt
0
−40
62
90
a Isolated yield.
b Determined by HPLC.

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J.-P. Ebran et al. / Tetrahedron: Asymmetry 14 (2003) 1637–1644
Figure 1. X-Ray structure of the major diastereoisomer of 11.
alcohol 13 with lithium amide borane complex,19 fol-
lowed by an oxidation at room temperature with
chromic acid afforded pure acid 14 ([h]2D0=+39.0) with-
out epimerization as confirmed by chiral HPLC studies.
To conclude, we have developed a new and general
method to introduce, with good to excellent
diastereoselectivity, a substituent a to the phosphorus
atom of a phosphine. After reduction of the amido-
phosphine borane, we obtained enantiomerically pure
b-boranatophosphine alcohol 13 which can be oxidized
in boronatophosphine acid 14. To the best of our
knowledge, this result constitutes the first stereoselec-
tive synthesis of such compounds. Phosphine deriva-
tives 13 and 14 can be considered as sources of
potential chiral ligands and as useful intermediates for
the preparation of chiral catalysts. Their synthesis is
currently being investigated.
Scheme 3.
Indeed Evans has proved that enolates generally adopt
a Z configuration,25 and it is also well accepted that
A1,3 allylic strain favors intermediate Z-1 compared to
Z-2.26 An approach of the electrophile from the topside
of the enolate Z-1 (anti to the NꢁLi bond) is in
agreement with the observed configuration of the newly
created stereogenic center.
3. Experimental
3.1. General
As a final step, we studied the removal of the chiral
auxiliary as previously depicted.21 Unfortunately, what-
ever the conditions were, acid or basic, removal of the
chiral auxiliary always led to complete epimerization of
the stereogenic center a to the phosphorus atom
(Scheme 4). Indeed amide cleavage under acidic or
basic conditions needs high temperature, which is not
compatible with a stereogenic center a to phosphine
and to CꢀO functional groups.27,28 To circumvent this
epimerization, the enantiomerically pure acid 14 was
prepared by a two-step procedure: reduction to the
Optical rotations were measured using a sodium lamp
at ambient temperature and are reported as follows:
[h]l (c g/100 mL) with the units of degree g cm−3. IR
spectra were recorded using KBr pellets or NaCl plates,
and only partial data are reported. NMR spectra were
recorded on a Bruker DX 300 spectrometer operating
at 300 MHz for proton, 75.4 MHz for carbon and
121.5 MHz for phosphorus. This probe is equipped
with pulsed-field (z) gradients. Chemical shifts (l) are
expressed in ppm relative to TMS for 1H and 13C nuclei
and to H3PO4 for 31P nuclei. Data are reported as
follows: chemical shift, multiplicity (s=singlet, d=dou-
blet, t=triplet, q=quartet, br=broad, m=multiplet),
coupling constants (Hz), integration.
Solvents were purified by conventional methods prior
to use. TLC was performed on Merck 60F-250 silica gel
plates and column chromatography over silica gel SI 60
(230–240 mesh). Mp’s were taken on a Kofler appara-
tus and were uncorrected. Elemental analyses were
carried out on a Carlo Erba EA 1100 analyzer.
Scheme 4.

J.-P. Ebran et al. / Tetrahedron: Asymmetry 14 (2003) 1637–1644
1641
3.2. 2-Boranatodiphenylphosphino ethyl acetate 5
solution of (R)-N-alkylated phenylglycinol (4.42 mmol)
and triethylamine (447.2 mg, 4.42 mmol) in THF (20
mL). After 2 h at rt, water (5 mL) was added. The
product mixture was extracted by ethyl acetate (3×20
mL) and the organic layer was dried over magnesium
sulfate. Purification of the product by flash column
chromatography eluting with cyclohexane: EtOAc
50:50 afforded the pure amide (7a: 63%, 7b: 31%) as
white powders.
To an ice-cooled solution of sodium hydride (1.60 g,
65.5 mmol) in THF (30 mL) was added via cannula a
solution of diphenylphosphine–borane 4 (5.00 g, 25.0
mmol) and ethyl chloroacetate (3.98 g, 32.5 mmol) in
THF (50 mL). The solution was stirred at rt for 2 h,
then excess hydride was quenched by the careful addi-
tion of 1N aqueous hydrochloric acid solution (20 mL).
The mixture was extracted with ethyl acetate (3×30 mL)
and the combined organic extracts were dried over
magnesium sulfate and concentrated. Purification of the
residue by flash column chromatography (cyclohexane/
EtOAc, 80:20) afforded ester 5 as a colorless oil (6.17 g,
86%): Rf=0.40 (cyclohexane/EtOAc 70:30). 31P NMR
(121.5 MHz, CDCl3): l 17.79 (d, J=57.6 Hz). 1H
NMR (300 MHz, CDCl3): l 0.50–1.42 (br, 3H), 1.04 (t,
J=7.2 Hz, 3H), 3.22 (d, J=10.7 Hz, 2H), 3.97 (d,
J=7.2 Hz, 2H), 7.43–7.53 (m, 6H), 7.70–7.77 (m, 4H).
13C NMR (75 MHz, CDCl3): l 13.8, 33.9 (d, J=29.3
Hz), 61.5, 128.0 (d, J=55.7 Hz), 128.8 (d, J=10.3 Hz),
131.6 (d, J=2.9 Hz), 132.5 (d, J=9.8 Hz), 166.8 (d,
J=4.0 Hz). IR (neat): 2983, 2388, 1732, 1266, 1116,
1061, 738, 693 cm−1. Anal. calcd for C16H20BO2P: C,
67.17; H, 7.05. Found: C, 66.87; H, 6.68.
3.5. 2-(Boranatodiphenylphosphino)-N-(2-hydroxy-1-
(R)-phenylethyl)-N-methylacetamide 7a
Rf=0.32 (cyclohexane/EtOAc, 5:5). mp <50°C. [h]2D0=
−76.7 (c 1.1, CHCl3). 31P NMR (121.5 MHz, CDCl3): l
1
17.24 (d, J=41.2 Hz). H NMR (83:17 rotamer ratio,
asterisk denotes minor rotamer peaks, 300 MHz,
CDCl3): l 0.50–1.30 (br, 3H), 2.20 (s, 1H), 2.57 (s, 3H),
2.59* (s, 3H), 3.32 (dd, J=1.8, 9.5 Hz, 2H), 3.77–3.86
(m, 2H), 4.97* (dd, J=4.6, 8.9 Hz, 1H), 5.55 (dd,
J=4.5, 8.2 Hz, 1H), 6.94–6.96 (m, 2H), 7.06–7.13 (m,
3H), 7.24–7.29 (m, 6H), 7.59–7.64 (m, 4H). 13C NMR
(75 MHz, CDCl3): l 32.6 (d, J=30.5 Hz), 32.9, 58.7,
62.7, 126.9, 128.2, 128.2, 129.0, 129.1 (d, J=10.3 Hz),
131.9 (d, J=2.3 Hz), 132.9 (d, J=9.9 Hz), 136.8, 168.1
(d, J=2.9 Hz). IR (neat): 3402, 3059, 2939, 2387, 1628,
1437, 1108, 1062, 752, 698 cm−1. MS (IC, 25 eV) m/z:
400.5 [M−BH3+Na]+. Anal. calcd for C23H27BNO2P: C,
70.61; H, 6.96; N, 3.58. Found: C, 70.34; H, 7.19; N,
3.53. HPLC Kromasil C 18, 1 mL/min, MeOH/H2O
7/3, t=11.30 min.
3.3. 2-Boranatodiphenylphosphino ethanoic acid 6
Potassium hydroxide (216.0 mg, 3.80 mmol) dissolved
in a mixture of water (250 mL) and ethanol (1 mL) was
added dropwise at 0°C to the ester 5 (1.00 g, 3.50
mmol). The mixture was stirred for 2 h at rt, and the
ethanol was evaporated under reduced pressure. The
collected oil was dissolved in water (3 mL), washed
with diethyl ether (3×5 mL). The aqueous layer was
first acidified until pH 1, with hydrochloric acid 1 M,
saturated with sodium chloride, and extracted with
dichloromethane (3×10 mL). The organic layer was
dried (MgSO4) and evaporated under reduced pressure
affording carboxylic acid 6 (0.9 g) in 99% yield as a
white powder: mp 141°C; 31P NMR (121.5 MHz,
3.6. 2-(Boranatodiphenylphosphino)-N-benzyl-N-(2-
hydroxy-1-(R)-phenylethyl) acetamide 7b
Rf=0.45 (cyclohexane/EtOAc, 5:5). mp <50°C. [h]2D0=
−44.9 (c 1.0, CHCl3). 31P NMR (121.5 MHz, CDCl3): l
1
17.66. H NMR (82:18 rotamer ratio, asterisk denotes
minor rotamer peaks, 300 MHz, CDCl3): l 0.20–1.40
(br, 3H), 3.32 (d, J=11.3 Hz, 2H), 3.50–3.98 (m, 4H),
4.42 (s, 2H), 5.21* (dd, J=5.1, 7.4 Hz, 1H), 5.45 (dd,
J=5.1, 7.9 Hz, 1H), 7.00–7.19 (m, 10H), 7.37–7.43 (m,
5H), 7.65–7.71 (m, 5H). 13C NMR (75 MHz, CDCl3): l
33.5 (d, J=30.5 Hz), 49.0, 62.0, 63.3, 126.4, 127.9,
128.1 (d, J=54.0 Hz), 128.4, 128.9, 129.1, 129.2, 129.3,
131.9 (d, J=2.3 Hz), 132.9 (d, J=9.8 Hz), 136.7, 137.3,
168.9 (d, J=2.9 Hz). IR (neat): 3422, 2383, 1637, 1437,
1061, 736, 698 cm−1. MS (IC, 25 eV) m/z: 476.4 [M−
BH3+Na]+. Anal. calcd for C29H31BNO2P: C, 74.53; H,
6.69; N, 3.00. Found: C, 74.42; H, 6.76; N, 2.96. HPLC
Kromasil C 18, 1 mL/min, MeOH/H2O 8/2, t=8.53
min.
1
CDCl3): l 17.77 (d, J=48.2 Hz). H NMR (300 MHz,
CDCl3): l 0.20–1.60 (br, 3H), 3.11 (d, J=6.6 Hz, 2H),
7.21–7.32 (m, 6H), 7.44–7.52 (m, 4H). 13C NMR (75
MHz, CDCl3): l 34.1 (d, J=28.2 Hz), 127.9 (d, J=56.3
Hz), 129.3 (d, J=10.9 Hz), 132.1 (d, J=2.3 Hz), 132.8
(d, J=9.8 Hz), 172.4. IR (neat): 2978, 2663, 2570, 2402,
2361, 1703, 1436, 1303, 1141, 1103, 1060, 739, 692
cm−1. Anal. calcd for C14H16BO2P: C, 65.16; H, 6.25.
Found: C, 65.19; H, 6.48.
3.4. General procedure for the coupling reaction
between N-alkylated amino alcohols and 6
3.7. General procedure for the alkylation of phosphine–
amide boranes 7
To
a
stirred ice-cooled solution of 2-boranato-
diphenylphosphino ethanoic acid 6 (880.0 mg, 3.40
mmol) in dichloromethane (18 mL) was added drop-
wise oxalyl chloride (863.0 mg, 6.80 mmol) under
argon. The mixture was stirred at rt for 4 h. Removal
of solvent and excess of oxalyl chloride under reduced
pressure afforded alcoyl chloride in quantitative yield as
a red oil. A solution of alcoyl chloride in THF (20 mL)
was added via cannula over 10 min to an ice-cooled
All the alkylation reactions were realized under argon
with a flame-dried flask. The amide and the lithium
chloride (6 equiv.) were weighted and dried under
reduced pressure in the presence of silica gel for 12 h.
To a stirred, cooled (−78°C) solution of the amide and
the lithium chloride in THF ([7]=0.085 mmol mL−1)
was slowly added a solution of n-butyllithium (1.6 M in

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J.-P. Ebran et al. / Tetrahedron: Asymmetry 14 (2003) 1637–1644
hexanes, 2.5 equiv.). The suspension was warmed to
−20°C during 2 h. The electrophile (3 equiv.) was added
to the reaction mixture at −40°C. The solution was
stirred at temperature from −40 to rt depending on the
electrophile during 4 to 24 h and quenched by the
addition of saturated aqueous ammonium chloride
solution. The mixture was partitioned between satu-
rated aqueous ammonium chloride solution and ethyl
acetate, and the aqueous layer was separated and
extracted with ethyl acetate. The combined organic
extracts were dried over magnesium sulfate and concen-
trated to afford yellow oil. Purification of the residue
by flash chromatography (cyclohexane/ethyl acetate)
affords amide.
(m, 1H), 6.85–7.46 (m, 25H), 7.71–7.77 (m, 5H). 13C
NMR (75 MHz, CDCl3): l 14.9 (d, J=2.9 Hz), 37.0 (d,
J=29.9 Hz), 49.7, 50.7*, 61.4, 62.3*, 63.0, 63.2*, 126.3,
126.7*, 127.1 (d, J=56.9 Hz), 127.8, 128.0 (d, J=58.6
Hz), 128.5, 128.8, 128.9, 129.0*, 129.1, 129.2*, 129.4,
129.4*, 131.8 (d, J=2.3 Hz), 131.9 (d, J=2.3 Hz), 133.8
(d, J=9.2 Hz), 134.2 (d, J=9.8 Hz), 137.3, 137.7,
173.1. IR (neat): 3401, 3060, 2932, 2383, 1640, 1436,
1353, 1064, 740, 698 cm−1. MS (IC, 25 eV) m/z: 489.9
[M−BH3+Na]+. Anal. calcd for C30H33BNO2P: C,
74.85; H, 6.91; N, 2.91. Found: C, 74.62; H, 6.80; N,
3.02. HPLC Kromasil C 18, 1 mL/min, MeOH/H2O
8/2, t=9.42 min (for a mixture of diastereoisomers, (S)
t1=9.42 min; (R) t2=16.37 min).
3.8. 2-(S)-(Boranatodiphenylphosphino)-N-(2-hydroxy-1-
(R)-phenylethyl)-N-methylpropionamide 8a
3.10. 2-(Boranatodiphenylphosphino)-N-(2-hydroxy-1-
(R)-phenylethyl)-N-methyl-3-phenylpropionamide 9
Amide 7a (300.0 mg, 0.767 mmol) was alkylated by
iodo methane (326.6 mg, 2.3 mmol) at −40°C. Purifica-
tion by flash chromatography (40% of ethyl acetate in
cyclohexane) gave 240 mg of white powder of the title
compound (77%) and 60 mg of diastereoisomers mix-
ture. Rf=0.51 (cyclohexane/EtOAc, 5:5). mp 64°C.
[h]D20=−63.8 (c 1.34, CHCl3). 31P NMR (121.5 MHz,
Amide 7a (300.0 mg, 0.767 mmol) was alkylated by
benzyliodide (501.2 mg, 2.3 mmol) at 0°C. Purification
by flash chromatography (30% of ethyl acetate in cyclo-
hexane) gave 203.0 mg (55%) of white powder of the
diastereoisomeric mixture (72.5% of 2S, 27.5% of 2R).
Rf=0.57 (cyclohexane/EtOAc, 5:5). 31P NMR (121.5
1
MHz, CDCl3): l 23.90 (br). H NMR (75:25 rotamer
1
CDCl3): l 25.90 (br). H NMR (86:14 rotamer ratio,
ratio, asterisk denotes minor rotamer peaks, 300 MHz,
CDCl3): l 0.70–1.60 (br, 3H), 1.85 (s, 1H), 2.19* (s,
3H), 2.30 (s, 3H), 3.16 (m, 2H), 3.78 (m, 2H), 4.02 (m,
1H), 4.44* (m, 1H), 5.68 (m, 1H), 6.71 (m, 3H), 7.20
(m, 8H), 7.56 (m, 4H,), 7.86 (m, 3H), 8.27 (m, 2H). 13C
NMR (75 MHz, CDCl3): l 32.2, 32.8*, 36.0, 36.4*, 44.3
(d, J=27.0 Hz), 45.2* (d, J=27.6 Hz), 58.3, 59.7*,
61.7, 61.9*, 126.6 (d, J=51.2 Hz), 127.2, 127.3 (d,
J=49.4 Hz), 127.4*, 127.9, 128.2, 128.7, 129.0, 129.1,
132.0 (d, J=2.9 Hz), 132.1 (d, J=2.3 Hz), 133.5* (d,
J=9.8 Hz), 133.9 (d, J=9.2 Hz), 134.3 (d, J=9.8 Hz),
134.9* (d, J=9.8 Hz), 139.0, 139.2, 170.8 (d, J=2.3
Hz), 171.2* (d, J=2.3 Hz). IR (neat): 3430, 3060, 2927,
2383, 1632, 1481, 1438, 1107, 1063, 742, 700 cm−1. MS
(IC, 25 eV) m/z: 489.9 [M−BH3+Na]+. Anal. calcd for
C30H33BNO2P: C, 74.85; H, 6.91; N, 2.91. Found: C,
74.73; H, 7.25; N, 2.98. HPLC Kromasil C 18, 1
mL/min, MeOH/H2O 73/27, 72.5% (S) t1=24.46 min;
27.5% (R) t2=27.32 min.
asterisk denotes minor rotamer peaks, 300 MHz,
CDCl3): l 0.50–1.80 (br, 3H), 1.47 (dd, J=6.9, 14.8 Hz,
3H), 1.93 (s, 1H), 2.62* (s, 3H), 2.76 (s, 3H), 3.85 (m,
1H), 3.96 (m, 2H), 5.06* (dd, J=4.6, 9.2 Hz, 1H), 5.83
(dd, J=5.1, 7.4 Hz, 1H), 7.27 (m, 4H, Ha), 7.50 (m,
6H), 7.78 (m, 3H), 8.06 (m, 2H).). 13C NMR (75 MHz,
CDCl3): l 14.7 (d, J=2.3 Hz), 32.3, 36.3 (d, J=31.0
Hz), 58.4, 61.7, 126.6 (d, J=56.3 Hz), 127.3 (d, J=40.8
Hz), 128.1, 128.2, 128.9 (d, J=9.8 Hz), 129.1, 129.2 (d,
J=8.6 Hz), 131.8 (d, J=2.3 Hz), 132.0 (d, J=2.3 Hz),
133.7 (d, J=9.2 Hz), 134.3 (d, J=9.2 Hz), 137.2, 172.5
(d, J=2.9 Hz). IR (neat): 3402, 3059, 2928, 2380, 1627,
1437, 1401, 1063, 742, 698 cm−1. MS (IC, 25 eV) m/z:
414.0 [M−BH3+Na]+. Anal. calcd for C24H29BNO2P: C,
71.13; H, 7.21; N, 3.46. Found: C, 70.76; H, 7.58; N,
3.48. HPLC Kromasil C 18, 1 mL/min, MeOH/H2O
7/3, t=12.35 min (for a mixture of diastereoisomers,
(S) t1=12.35 min; (R) t2=18.15 min).
3.9. 2-(S)-(Boranatodiphenylphosphino)-N-benzyl-N-(2-
hydroxy-1-(R)-phenylethyl) propionamide 8b
3.11. t-Butyl 3-(boranatodiphenylphosphino)-3-N-(2-
hydroxy-1-(R)-phenylethyl)-N-methyl carboxamide
propanoate 10
Amide 7b (200.0 mg, 0.428 mmol) was alkylated by
iodomethane (182.2 mg, 1.28 mmol) at −40°C. Purifica-
tion by flash chromatography (30% of ethyl acetate in
cyclohexane) gave 165 mg of white powder of the title
compound (80%).
Amide 7a (200.0 mg, 0.511 mmol) was alkylated by
t-butyl bromoacetate (299.1 mg, 1.53 mmol) at rt for 24
h. Purification by flash chromatography (10% of ethyl
acetate in cyclohexane) gave 141.0 mg (55%) of white
powder of the diastereoisomeric mixture (88.5% of 2S,
11.5% of 2R). Rf=0.42 (cyclohexane/EtOAc, 7:3). 31P
Rf=0.65 (cyclohexane/EtOAc, 5:5). mp 67°C. [h]2D0=
−62.6 (c 1.07, CHCl3). 31P NMR (121.5 MHz, CDCl3):
1
NMR (121.5 MHz, CDCl3): l 22.68 (br). H NMR (1:1
1
l 26.34 (d, J=42.3 Hz). H NMR (77:23 rotamer ratio,
rotamer ratio, asterisk denotes minor rotamer peaks,
300 MHz, CDCl3): l 0.60–1.90 (br, 3H), 1.40 (s, 9H),
1.46* (s, 9H), 1.64 (s, 1H), 2.60 (m, 1H), 2.70 (s, 3H),
3.08 (m, 1H), 3.95 (m, 2H), 4.17 (m, 1H), 5.71 (m, 1H),
6.96 (m, 2H), 7.26 (m, 3H), 7.40 (m, 3H), 7.51 (m, 3H),
7.80 (m, 2H), 8.14 (m, 2H). 13C NMR (75 MHz,
CDCl3): l 28.4, 28.5*, 33.5, 36.9 (d, J=29.3 Hz), 56.1,
asterisk denotes minor rotamer peaks, 300 MHz,
CDCl3): l 0.25–1.75 (br, 3H), 1.17 (dd, J=6.9, 14.3 Hz,
3H), 1.28* (dd, J=6.9, 15.1 Hz, 3H), 2.55 (s, 1H), 3.63
(m, 1H), 3.85* (d, J=15.1 Hz, 1H), 4.06 (m, 2H), 4.40
(d, J=17.7 Hz, 1H), 4.65 (d, J=17.7 Hz, 1H), 5.09* (d,
J=15.1 Hz, 1H), 5.56* (dd, J=4.9, 9.0 Hz, 1H), 5.66

J.-P. Ebran et al. / Tetrahedron: Asymmetry 14 (2003) 1637–1644
1643
68.9, 69.9*, 81.1, 81.2*, 126.2 (d, J=54.6 Hz), 127.3 (d,
J=52.3 Hz), 127.6, 128.4, 128.7 (d, J=12.1 Hz), 129.0,
129.2 (d, J=10.3 Hz), 131.9 (d, J=1.7 Hz), 133.1 (d,
J=2.3 Hz), 133.7 (d, J=9.2 Hz), 134.7 (d, J=9.2 Hz),
137.2, 170.6 (d, J=4.6 Hz), 170.4. IR (neat): 3443,
3278, 2929, 2388, 1726, 1634, 1140, 1063, 742, 699
cm−1. MS (IC, 25 eV) m/z: 514.1 [M−BH3+Na]+. Anal.
calcd for C29H37BNO4P: C, 68.92; H, 7.38; N, 2.77.
Found: C, 68.82; H, 7.09; N, 2.61. HPLC Kromasil C
18, 1 mL/min, MeOH/H2O 8/2, 88.5% (S) t1=34.17
min; 11.5% (R) t2=36.95 min.
Hz), 126.7 (d, J=55.2 Hz), 126.9* (d, J=53.4 Hz),
127.5 (d, J=53.4 Hz), 128.0*, 128.0, 128.3*, 128.3,
128.8, 128.9*, 129.1* (d, J=10.9 Hz), 129.2 (d, J=10.3
Hz), 131.8* (d, J=2.3 Hz), 132.0, 133.6* (d, J=9.2
Hz), 133.9 (d, J=9.2 Hz), 134.1 (d, J=9.2 Hz), 134.6*
(d, J=9.2 Hz), 136.4*, 137.1, 142.6 (d, J=10.2 Hz),
143.0* (d, J=12.1 Hz), 171.0 (d, J=2.3 Hz), 171.7* (d,
J=3.4 Hz). MS (IC, 25 eV) m/z: 453.8 [M−BH3+Na]+.
Anal. calcd for C27H33BNO2P: C, 72.82; H, 7.47; N,
3.15. Found: C, 72.49; H, 7.54; N, 3.11. HPLC Kro-
masil C 18, 1 mL/min, MeOH/H2O 75/25, 60% (S)
t1=11.75 min; 40% (R) t2=13.12 min).
3.12. 2-(S)-(Boranatodiphenylphosphino)-N-(2-hydroxy-
1-(R)-phenylethyl)-N-methylpent-4-enamide 11
3.14. 2-(S)-Boranatodiphenylphosphino propan-1-ol 13
Amide 7a (200.0 mg, 0.511 mmol) was alkylated by
3-iodopropene (257.5 mg, 1.53 mmol) at 0°C for 2 h.
Purification by flash chromatography (40% of ethyl
acetate in cyclohexane) furnished amide 11 as a mixture
of diastereomers (95.5% of 2S, 5.5% of 2R) (193 mg,
87%). A single recrystallization from mixture of 30% of
ethyl acetate in cyclohexane yielded enantiomerically
pure (2S)-11. Rf=0.57 (cyclohexane/ethyl acetate, 5:5).
Mp 146°C. [h]2D0=−58.5 (c 1.3, CHCl3). 31P NMR
(121.5 MHz, CDCl3): l 23.85 (d, J=16.5 Hz). 1H
NMR (300 MHz, CDCl3): l 0.50–1.70 (br, 3H), 2.54
(m, 1H), 2.73 (s, 3H), 2.74 (m, 1H), 3.84 (m, 1H), 3.94
(m, 2H), 5.09 (m, 2H), 5.71 (m, 1H), 5.86 (m, 1H), 7.29
(m, 4H), 7.56 (m, 6H), 7.81 (m, 3H), 8.07 (m, 2H). 13C
NMR (75 MHz, CDCl3): l 32.5, 34.4, 41.4 (d, J=27.6
Hz), 58.6, 61.7, 118.4, 126.6 (d, J=55.7 Hz), 127.4 (d,
J=54.0 Hz), 128.1, 128.2, 128.9 (d, J=10.3 Hz), 129.0,
129.4 (d, J=10.3 Hz), 132.0 (d, J=2.3 Hz), 132.1 (d,
J=2.3 Hz), 133.6 (d, J=9.2 Hz), 134.0 (d, J=9.8 Hz),
134.2 (d, J=9.2 Hz), 135.0 (d, J=12.0 Hz), 137.2, 171.1
(d, J=2.9 Hz). IR (neat): 3500, 3062, 2981, 2921, 2380,
1625, 1478, 1440, 1402, 1108, 1059, 742, 697 cm−1. MS
(IC, 25 eV) m/z: 439.9 [M−BH3+Na]+. Anal. calcd for
C26H31BNO2P: C, 72.40; H, 7.24; N, 3.25. Found: C,
72.52; H, 7.54; N, 3.22. HPLC Kromasil C 18, 1
mL/min, MeOH/H2O 8/2, t=6.99 min(for a mixture of
diastereoisomers, (S) t1=6.99 min; (R) t2=9.09 min).
To a solution of borane–ammonia complex (90%, 84
mg, 2.45 mmol, 5 equiv.) in THF (2 mL) at 0°C was
added a solution of n-butyllithium in hexanes (1.6 M,
1.25 mL, 2.0 mmol, 4 equiv.). The resulting solution
was stirred at 0°C for 15 min and then warmed to rt.
After 15 min, the suspension was cooled to 0°C. A
solution of amide 8a (200.0 mg, 0.49 mmol) in THF (2
mL) was added dropwise and the reaction mixture was
held at that temperature for 4 h. The excess hydride
was quenched by the careful addition of 2N aqueous
hydrochloric acid solution (2 mL). The mixture was
stirred for 1 h at 0°C and then extracted with ethyl
acetate (3×5 mL). The combined organic extracts were
washed sequentially with 2N aqueous sodium hydrox-
ide solution (3 mL) and brine (3 mL). The extracts were
dried over magnesium sulfate and concentrated. Purifi-
cation by preparative TLC on silica gel (40% of ethyl
acetate in cyclohexane) afforded the alcohol as white
crystals, mp=66°C (112.6 mg, 89%). Rf=0.47 (cyclo-
hexane/EtOAc, 5:5). [h]2D0=−32.5 (c 0.75, CHCl3). 31P
NMR (121.5 MHz, CDCl3): l 20.35 (d, J=39.2 Hz).
1H NMR (300 MHz, CDCl3): l 0.40–1.80 (br, 3H), 1.18
(dd, J=7.2, 15.6 Hz, 3H), 2.83 (m, 1H), 3.78 (m, 2H),
7.46 (m, 6H), 7.70–7.82 (br, 4H). 13C NMR (75 MHz,
CDCl3): 12.3, 32.1 (d, J=35.1 Hz), 63.7 (d, J=6.3 Hz),
128.1 (d, J=55.2 Hz), 129.1 (d, J=9.7 Hz), 129.2 (d,
J=9.2 Hz), 131.7, 132.7 (d, J=8.6 Hz), 133.0 (d, J=8.6
Hz). IR (neat): 4053, 3390, 3058, 2636, 2361, 1436,
1106, 1065, 1028, 738, 694. MS (IC, 25 eV) m/z: 245.1
[M−BH3+H]+. Anal. calcd for C15H20BOP: C, 69.80; H,
7.81. Found: C, 69.76; H, 7.83. HPLC Daicel Chiracel
OJ, 1 mL/min, 10% 2-PrOH/heptane, t=17.6 min (for
a mixture of enantiomers, (S) t1=17.6 min; (R) t2=
21.0 min).
3.13. 2-(Boranatodiphenylphosphino)-N-(2-hydroxy-1-
(R)-phenylethyl)-N-methyl-4-metylpent-4-enamide 12
Amide 7a (300.0 mg, 0.767 mmol) was alkylated by
3-iodo-2-methylpropene (418.4 mg, 2.3 mmol) at rt for
48 h. Purification by flash chromatography (40% of
ethyl acetate in cyclohexane) furnished amide 12 as a
mixture of diastereomers (60% of 2S, 40% of 2R): white
crystalline solid (189 mg, 55%). Rf=0.41 (cyclohexane/
EtOAc, 5:5). 31P NMR (121.5 MHz, CDCl3): l 24.55
3.15. 2-(S)-Boranatodiphenylphosphino propanoic acid
14
1
(br). H NMR (66:34 rotamer ratio, asterisk denotes
Jones’ reagent (3.60 M, 0.330 mL, 1.16 mmol) was
added dropwise to a stirred solution of the alcohol 14
(150 mg, 0.58 mmol) in acetone (15 mL) at 0–5°C.
After 1 h, 2-propanol was added to destroy excess
oxidant. Water (5 mL) was added, and acetone was
removed under reduced pressure. The product was
extracted with EtOAc (3×15 mL). The organic layer
was washed with brine, dried, and evaporated to a
residue, which was purified by flash column chromatog-
raphy (cyclohexane–ethyl acetate–acetic acid, 70:30:0.5;
minor rotamer peaks, 300 MHz, CDCl3): l 0.50–1.70
(br, 3H), 2.02 (s, 3H), 2.04*(s, 3H), 2.40 (m, 1H), 2.67
(s, 3H), 2.78 (m, 1H), 3.96 (br, 3H), 4.77 (m, 2H),
5.63*(m, 1H), 5.81 (m, 1H), 6.81 (m, 1H), 7.18–7.54 (br,
12H), 7.75–7.83 (br, 2H), 8.04–8.21 (br, 2H). 13C NMR
(66:34 rotamer ratio, asterisk denotes minor rotamer
peaks, 75 MHz, CDCl3): l 22.6*, 22.7 32.4, 32.8*, 37.8,
38.3*, 40.2 (d, J=27.6 Hz), 41.0* (d, J=28.2 Hz), 58.6,
59.8*, 61.6, 61.9*, 113.3, 113.6*, 126.4* (d, J=55.2

1644
J.-P. Ebran et al. / Tetrahedron: Asymmetry 14 (2003) 1637–1644
v/v) to give acid 13 as a white powder (123.3 mg, 78%).
Rf=0.24 (cyclohexane–ethyl acetate–acetic acid,
70:30:0.5; v/v). mp 116°C. [h]2D0=+39.0 (c 1, CHCl3).
10. (a) Minami, T.; Okada, Y.; Otaguro, T.; Tawaraya, S.;
Furuichi, T.; Okauchi, T. Tetrahedron: Asymmetry 1995,
6, 2469; (b) Gilbertson, S. C.; Chang, C.-W. T. J. Org.
Chem. 1998, 63, 8424.
1
31P NMR (121.5 MHz, CDCl3): l 26.41 (br). H NMR
(300 MHz, CDCl3): l 0.60–1.60 (br, 3H), 1.36 (dd,
J=7.2, 15.9 Hz, 3H), 3.60 (m, 1H), 7.47 (m, 6H), 7.77
(m, 4H). 13C NMR (75 MHz, CDCl3): l 12.7, 37.7 (d,
J=27.0 Hz), 126.6 (d, J=53.5 Hz), 127.8 (d, J=56.9
Hz), 129.0 (d, J=9.8 Hz), 129.1 (d, J=9.8 Hz), 131.8,
132.1, 133.0 (d, J=9.2 Hz), 133.6 (d, J=9.8 Hz), 175.9.
IR (neat): 3059, 2939, 2363, 1707, 1438, 1108, 1069,
737, 688. MS (negative FAB) m/z: 271 [M−H−BH3]−.
Anal. calcd for C15H18BO2P: C, 66.72; H, 6.67. Found:
C, 67.06; H, 6.76. HPLC Daicel Chiracel OJ, 1 mL/
min, 10% 2-PrOH/heptane+0.5% formic acid, t=14.93
min (for a mixture of enantiomers, (S) t1=14.93 min;
(R) t2=21.57 min).
11. Kobayashi, S.; Shiraish, N.; Lam, W. W.-L.; Manabe, K.
Tetrahedron Lett. 2001, 42, 7303.
12. Le´autey, M.; Castelot-Deliencourt, G.; Jubault, P.; Pan-
necoucke, X.; Quirion, J.-C. J. Org. Chem. 2001, 66,
5566.
13. Le´autey, M.; Castelot-Deliencourt, G.; Jubault, P.; Pan-
necoucke, X.; Quirion, J.-C. Tetrahedron Lett. 2002, 43,
9237.
14. Le´autey, M.; Ebran, J.-P.; Jubault, P.; Pannecoucke, X.;
Quirion, J.-C. Eur. J. Org. Chem., submitted.
15. Noyori, R.; Yamakawa, M.; Hashiguchi, S. J. Org.
Chem. 2001, 66, 7931–7944.
16. Micouin, L.; Schanen, V.; Riche, C.; Chiaroni, A.;
Quirion, J.-C.; Husson, H.-P. Tetrahedron Lett. 1994, 35,
7223.
Acknowledgements
17. Imamoto, T.; Oshiki, T.; Onozawa, T.; Kusumoto, T.;
Sato, K. J. Am. Chem. Soc. 1990, 112, 5244.
18. (R)-N-Methyl-2-amino-2-phenylethanol was prepared in
two steps: protection of the amine as ethyl carbamate and
then reduction with LiAlH4. (R)-N-Benzyl-2-amino-2-
phenylethanol was synthesized following the method
described by Husson et al.: Blanchet, J.; Bonin, M.;
Chiaroni, A.; Micouin, L.; Riche, C.; Husson, H.-P.
Tetrahedron Lett. 1999, 40, 2935.
This work is part of the RINCOF/PUNCHORGA
program, and we thank the Conseil Re´gional de Haute-
Normandie for their financial support as well The
Ministe`re de la Recherche (Grant to J.-P.E.).
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