Stereoselective reactions of chiral amines with racemic chlorophosphines

Article abstract of DOI:10.1080/10426500490459650

Racemic chlorophosphines react stereoselectively with chiral l-phenylethylamines or amino acid esters to give diastereomerically enriched aminophosphines 3, which were isolated as diastereomerically pure crystalline borane complexes. Oxidation, thionation, the reaction with methyl iodide provide optically active derivatives of aminophosphines. (R,S)- and (S,S)-stereomers of phosphinic acid amides were separated by crystallization and a flash-chromatography. The stereochemical properties of phosphorus acid amides were investigated. The mechanism of asymmetric induction at the trivalent phosphorus atom was rationalized.

Full text of DOI:10.1080/10426500490459650

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STEREOSELECTIVE REACTIONS OF CHIRAL AMINES WITH
RACEMIC CHLOROPHOSPHINES
Evgenyi V. Gryshkun a , Natalia V. Andrushko a & Oleg I. Kolodiazhnyi a
a National Academy of Sciences of Ukraine , Kiev, Ukraine
Published online: 16 Aug 2010.
To cite this article: Evgenyi V. Gryshkun , Natalia V. Andrushko & Oleg I. Kolodiazhnyi (2004) STEREOSELECTIVE REACTIONS
OF CHIRAL AMINES WITH RACEMIC CHLOROPHOSPHINES, Phosphorus, Sulfur, and Silicon and the Related Elements, 179:6,
1027-1046, DOI: 10.1080/10426500490459650
To link to this article: http://dx.doi.org/10.1080/10426500490459650
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Phosphorus, Sulfur, and Silicon, 179:1027–1046, 2004
ꢀC
Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490459650
STEREOSELECTIVE REACTIONS OF CHIRAL
AMINES WITH RACEMIC CHLOROPHOSPHINES
Evgenyi V. Gryshkun, Natalia V. Andrushko,
and Oleg I. Kolodiazhnyi
National Academy of Sciences of Ukraine, Kiev, Ukraine
(Received July 16, 2003; accepted September 30, 2003)
Racemic chlorophosphines react stereoselectively with chiral l-pheny-
lethylamines or amino acid esters to give diastereomerically enriched
aminophosphines 3, which were isolated as diastereomerically pure
crystalline borane complexes. Oxidation, thionation, the reaction with
methyl iodide provide optically active derivatives of aminophosphines.
(R,S)- and (S,S)-stereomers of phosphinic acid amides were separated
by crystallization and a flash-chromatography. The stereochemical
properties of phosphorus acid amides were investigated. The mecha-
nism of asymmetric induction at the trivalent phosphorus atom was
rationalized.
Keywords: Asymmetric induction; chiral aminophosphines; stereose-
lectivity
Chiral trivalent organophosphorus compounds having a stereogenic
phosphorus center are important subjects of investigation due to the
widespread use of these compounds as ligands for transition metal
catalysis.1,2 The numerous patented chiral phosphines and aminophos-
phines are proof of the interest in such catalytic reactions from the
industrial world.3,4 Therefore the preparation of enantiomerically pure
organophosphorus compounds is an important and challenging area of
contemporary synthetic organic chemistry.
Earlier we described the asymmetric synthesis of chiral organophos-
phorus compounds by the reaction of chiral secondary alcohols1,5–10
with chlorophosphines, resulting in the formation of optically active
phosphinites. In general case it is possibly to suggest that reactions
of chiral chlorophosphines with chiral nucleophiles will proceed with
Financial support of this work from the State Foundation of Basic Research of the
Ukraine (Project 03.07/00047) is gratefully acknowledged.
Address correspondence to Oleg I. Kolodiazhnyi, Institute of Bioorganic Chemistry
and Petrochemistry, National Academy of Sciences of Ukraine, Murmanskaya Street, 1,
Kiev, Ukraine. E-mail: oikol123@bpci.kiev.ua
1027

1028
E. V. Gryshkun et al.
HNu∗ = chiral nucleophile, B = base
asymmetric induction at the phosphorus atom. Therefore we have ex-
amined the reaction of the chlorophosphines with chiral amines result-
ing in the formation of diastereomerically enriched aminophosphines.
The present reaction provides an easy access to optically active
aminophosphines, used as precursor compounds in the synthesis of chi-
ral organophosphorus compounds. Moreover, this reaction is convenient
for studies of the mechanism and stereochemistry of nucleophilic sub-
stitution at trivalent phosphorus.
RESULTS AND DISCUSSION
The reaction of optically active amines 2 with racemic chlorophosphines
1 in the presence of triethylamine, or other organic base, proceeds with
asymmetric induction at the phosphorus atom to give diastereomeri-
cally enriched aminophosphines 3. The stereoselective substitution of
chlorine at phosphorus by an amino group is achieved by reaction of
two equivalents of optically active 1-phenylethylamine or amino acid
esters 2 with one equivalent of chlorophosphine 1 or by reaction with
an equimolar mixture of chiral amines and the triethylamine. The reac-
tion proceeds in hexane, diethyl ether, THF, benzene or toluene to give
N-substituted aminophosphines 3 in good yield (Scheme 1).
SCHEME 1

Chiral Amines with Racemic Chlorophosphines
1029
FIGURE 1 31P NMR spectrum of crude reaction mixture of the N-(1-pheny-
lethyl)amino-tert-butylphenylphosphine 3a.
Aminophosphines 3a–d are colorless liquids, configurationally sta-
ble at room temperature. They can be distilled under vacuum, without
any decomposition or racemization. Compounds 3a–d are hydrolytically
stable, but are easily oxidized by oxygen, therefore all manipulations
with these compounds have to be performed in an inert atmosphere.
According to 31P NMR spectra, the compounds 3 contain an asym-
metric phosphorus atom, and are obtained as a mixture of two diastere-
omers. The (Rp,S)- and (Sp,S)-diastereomers of compounds 3 are easily
observed by NMR spectroscopy and high performance liquid chromatog-
raphy (HPLC) (Figure 1).
The stereoselectivity of the reaction of the chlorophosphines with
chiral amines depends to a great degree on the reaction conditions,
especially on the nature of organic bases, solvents, and temperature.
The effect of the reaction conditions on the stereoselectivity of the re-
action of t-butylphenylchlorophosphine with 1-methylbenzylamine is
shown in Table I. The analysis of these data allowed us to optimize

1030
E. V. Gryshkun et al.
TABLE I Stereoselectivity of the Reaction of t-Bu(Ph)PCl with
(S)-NH2CH(Me)Ph
Ratio of 1:2:
Base (mole ratio)
Entry
Solvent
Base
Et3N
Temp.
dra
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Benzene
Benzene
Benzene
Benzene
Benzene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Benzene
Toluene
Toluene
Toluene
Ether
20◦C
20
20
20
20
70
20
0
1:1:1
1:1:2
1:1:10
1:2:1
1:1:1
1:1:1
1:1:1
1:1:1
1:1:1
2:1:1
4:1:1
1:1:4
1:1:1
1:1:1
1:1:1
1:1:1
1:1:1
1:1:1
1:1:1
1:1:1
1:1:1
8:92
13:87
21:79
17.5:82.5
20.5:79.5
16:84
16:84
20:80
26:74
15:85
14:86
18:82
25:75
17.5:82.5
42:58
12:88
19:81
20:80
38:62
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
DABCO
PEA
DBU
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
−20
20
20
20
20
20
20
20
Ether
Hexane
THF
Ether
Benzene
−20
20
20
20
20
36:64
75:25
aThe diastereomeric ratio was obtained by the 31P NMR method as average value of
2–3 measurements; PEA = 1-methylbenzylamine; DBU = diazabicycloundecene,
DABCO = diazabicyclooctane.
the reaction conditions, ensuring the highest stereoselectivity. The re-
action should be carried out at 20◦C, with a very slow addition rate of
1-methylbenzylamine and triethylamine in benzene solution to a so-
lution of the chlorophosphine in benzene. Then, the mixture should
be allowed to stand for 8–12 h at room temperature to complete the
reaction.
Special interest attaches to the question of asymmetric induc-
tion at trivalent phosphorus in the reaction of chlorophosphines with
chiral amines in the presence of organic bases. Literature data on
this question are insufficient though the mechanism and stereochem-
istry of nucleophilic substitution at pentavalent phosphorus were
investigated.1,4,11–17
Examples of asymmetric induction in reactions of chlorides of triva-
lent phosphorus with alcohols and amines were described earlier. For
example Mislow obtained menthyl esters of phosphinic acids in low
stereochemical yield by reaction of chlorophosphines with menthol in

Chiral Amines with Racemic Chlorophosphines
1031
the presence of pyridine.12 In our previous work we have observed a high
degree of asymmetric induction in the reaction of chlorophosphines with
1,2:5,6-diisopropylidene glucofuranose, together with some other opti-
cally active secondary alcohols in the presence of triethylamine which
proceeded under kinetic control.1,5−7
The stereochemistry of the reaction compounds of trivalent phospho-
rus with nucleophiles was investigated insufficiently, while the mech-
anism and stereochemistry of the reaction of chlorophosphines with
nucleophiles in the presence of tertiary organic bases was not studied.
Basically, asymmetric induction at trivalent phosphorus can be ex-
plained, as follows: (a) by the SN2P mechanism of nucleophilic substi-
tution or (b) by a mechanism involving the formation of trigonal bipyra-
midal intermediates arising from attack of the nucleophile at an apical
position, and the leaving group, departing from an apical position. The
leaving group must depart before ligand reorganization (Berry pseu-
dorotation or turnstile mechanism) can operate.
The first mechanism of SN2P substitution, shown in Scheme 2, is
typical for reactions proceeding under kinetic control. Chiral (S)-1-
methylbenzylamine reacts with (S)-chlorophosphine faster than with
(R)-chlorophosphine to give, preferentially, the (RP, S)−diastereomer
of the aminophosphine 3. It is well known that chiral chlorophosphines
are configurationally labile compounds existing as an equilibrium
racemic mixture of (R)- and (S)-enantiomers.4,11,17 For example, tert-
butylphenylchlorophosphine, prepared by Omelanczuk,17b lost readily
its optical activity even in the polarimeter cell. Wild and coworkers17c
reported that isopropylphenylchlorophosphine in palladium (II) com-
plex can be resolved; however liberation of epimeric chlorophosphines
from the complex led to complete racemization of the free phosphine
within 5 min. Lambert described mechanisms of the pyramidal atomic
inversion in chlorophosphines.17d
SCHEME 2
The first mechanism explains the formation of (R,S)-aminopho-
sphine as the diastereomer of the lowest energy of formation, as proved
by MOPAC calculations. MOPAC calculations of the free energy of the

1032
E. V. Gryshkun et al.
FIGURE 2 Thermodynamically stable conformation B.
diastereomers show that in the case of (S)-1-methylbenzylamine and
t-Bu(Ph)PCl the reaction results in the formation of the most thermody-
namically stable conformation B leading to the diastereomer (RP,S)-3a
(Figure 2).
However, the first mechanism does not explain the important role
of the tertiary base that follows from experimental studies. Therefore,
we suggest that the second mechanism shown in Scheme 3 is more
probable. This mechanism includes the formation of a pentacoordinate
transition state, pseudorotation and an exchange of ligands at pentaco-
ordinate phosphorus as a result of which the thermodynamically most
stable diastereomer is formed. The stability of the intermediate 3, the
apicophilicity of ligands, and also the asymmetric induction under the
effect of the optically active 1-methylbenzylamine determine the stere-
ochemical outcome of the reaction.
SCHEME 3
The analysis of the results of various factors describing the influence
on the stereochemical outcome of the reaction of tert-butylphenylchloro-
phosphine with 1-methylbenzylamine in the presence of organic bases
presented in Table I leads to the following conclusions:

Chiral Amines with Racemic Chlorophosphines
1033
1) the stereoselectivity of the reaction depends on the nature of the sol-
vent, decreasing in the sequence, THF > hexane > toluene > benzene
> diethyl ether;
2) the stereoselectivity of the reaction depends on the nature of the
organic bases, increasing strength and concentration of organic bases
reduces the stereoselectivity, thus Et3N > DABCO > DBU;
3) an increase of the amount of chlorophosphine increases the stere-
oselectivity, while an increase of the amount of methylbenzylamine
reduces the stereoselectivity;
4) a decrease of the reaction temperature reduces the stereoselectivity;
5) (S)-1-methylbenzylamine generates the (R)-configuration at phos-
phorus while, in contrast, (R)-1-methylbenzylamine gives rise to the
(S)-configuration.
In the overwhelming majority of cases SN2 nucleophilic substitution
at chiral tricoordinate trivalent phosphorus results in the inversion of
configuration that assumes the formation of a pentacoordinate anionic
species (SN2 type), containing attacking and leaving groups in apical
positions.
The results obtained show a significant role of the tertiary organic
base in the process of nucleophilic substitution at trivalent phospho-
rus. Thus, the reaction of chlorophosphine with the sodium derivative
of 1-methylbenzylamine proceeds with low stereoselectivity to give the
diastereomers (R, S)-3a and (S, S)-3a in the ratio 2:1, unlike the reac-
tion of chlorophosphine with 1-methylbenzylamine in the presence of
triethylamine:
1 + (S)-LiNHCH(Me)Ph → (R,S)-3a + (S, S)-3a.
The depending of the stereoselectivity on the temperature shows that
the reaction is not kinetically controlled because in case of kinetically
controlled reactions the decreasing of the temperature raises the stere-
oselectivity.
It is possible to suggest the formation of complexes of phosphorus
chlorides with organic base of type C, having an ammonium structure.18
Complexes of this type are formed, in particular, with chlorides of car-
boxylic acids and also phosgene with pyridine or triethylamine.18a,b The
role and influence of these complexes on kinetics and mechanism of nu-
cleophilic substitution reactions at the carbonyl sp2-carbon atom have
been investigated.18a
Complex C reacts with amine to give the intermediate D. Pseudoro-
ꢀ
ꢁ
tation of the latter, C
E, and subsequent deprotonation determine
the diastereomeric ratio of reaction product 3.

1034
E. V. Gryshkun et al.
We have observed the formation of the complex having proba-
bly the structure of the type C by 31P NMR during the reaction
of tert-butylphenylchlorophosphine with DBU. Mixing of tert-buty-
lphenylchlorophosphine with DBU in diethyl ether at low temperature
led to the formation of a colorless, salt-like product precipitating
from the solution as a voluminous solid (Scheme 4). The formation
of the adduct was followed by 31P NMR. The δ(31P) value of tert-
butylphenylchlorophosphine (108 ppm) changed to lower field
(165.86 ppm). In one spectrum both signals were seen, δP 108 ppm, and
165.86 ppm, when an equimolar quantity of DBU was added. Further
treatment of the reaction mixture with 1-methylphenylamine furnished
the aminophosphine 3a.
SCHEME 4
The effect of various factors on the stereochemical course of the re-
action suggests an equilibrium competition between the formation of
a pentacoordinate intermediate and its deprotonation. Therefore, an
increase of the strength and concentration of the organic bases results
in deprotonation before an equilibrium is established. This explains
the decrease in stereoselectivity at low temperature (Entries 9 and 17;
Table I). A decrease in temperature slows down the ligand pseudorota-
tion, therefore the pentacoordinate intermediate is deprotonated before
equilibrium is attained. It is quite possible that some degree of asym-
metric induction is achieved in the first step of the reaction during
the nucleophilic attack of the amine on the chlorophosphine, because a
small but distinct increase of asymmetric induction is observed when
the amount of chlorophosphine in the reaction mixture increases (En-
tries 1–3, 9–11; Table I).
Diastereomeric mixtures of the aminophosphine 3 were obtained and
then purified via their borane complexes.17–20 The diastereomerically
pure phosphine-borane complex 4 was prepared in one step from the
aminophosphine 3 and the borane-tetrahydrofuran complex. The reac-
tion of aminophosphines 3 with borane proceeded readily in tetrahydro-
furan to give, in almost quantitative yield, stable crystalline complexes
4. The complexes 4 were then additionally purified by crystallization
1
from hexane. The H and 31P NMR investigation of the borane com-
plexes 4 indicated the formation of only one diastereomer.
The structure and stereochemical purity of the borane complexes
1
was confirmed by H, 13C NMR, and 31P spectroscopy. The δP value of
the borane complex is observed at +70 ppm as a broad doublet, due to

Chiral Amines with Racemic Chlorophosphines
1035
FIGURE 3 The 31P NMR spectra of the borane complex 4a.
9
1
spin-spin coupling, 31P-{ B} (Figure 3). The H and 13C spectra show
the signals of all hydrogen and carbon atoms in the molecule, without
any doubling caused through the presence of diastereomers.
Borane complexes of aminophosphines 4 are useful initial com-
pounds for preparation of stereochemically pure chiral reagents
(Scheme 5).
The treatment of 4 with diethylamine furnished the initial amino-
phosphine 2 in 100% stereochemical purity. The BH3-part of the
phosphine-borane complex was removed on treatment with a large ex-
cess of an amine such as diethylamine. This reaction has been proved
to proceed in a stereospecific manner with retention of configuration.9
SCHEME 5

1036
E. V. Gryshkun et al.
The identity of the purified (RP,S)-diastereomer 3a, and the major
diastereomer of the initial diastereomeric mixture of the aminophos-
phine (RP,S)-3a and (SP,S)-3a was confirmed by 31P NMR spectra of
the mixture of these two products. The reaction proceeds slowly, and is
completed only on heating of the complex in a solution of diethylamine
at 50◦C over a period of 16 h.
The oxidation of compounds 4 with hydrogen peroxide in a diox-
ane proceeds stereospecifically and gives aminophosphine oxides 5 with
very good yields and purity. The treatment of 4 with diethylamine and
sulfur in a toluene gives aminophosphine sulfides 5 with very good
yields and 100% stereochemical purity.
At the same time the analogous reaction of diastereomeric mixtures
of aminophosphines 3 provide the compounds 5 and 6 as diastere-
omeric mixtures (Scheme 6). The (SP,S)- and (RP,S)-diastereomers of
the aminophosphine oxides 5 are easily identified through their 31P
NMR spectra and HPLC.
SCHEME 6
The major (SP S)-aminophosphine oxides have a longer retention
time than the (RP,S)-isomers presented to a smaller proportion. No sig-
nificant difference between the diastereomeric ratio of the compounds,
as estimated by 31P NMR and HPLC, was noted. The diastereomers of
compound 5 were separated by flash-chromatography. A 50 cm column
filled with silica gel was used; a mixture of isopropanol-hexane in a 92:8
ratio served as an eluent. The chromatographic fractions were analyzed
by HPLC. Under these conditions we were able to completely separate

Chiral Amines with Racemic Chlorophosphines
1037
TABLE II Diastereomeric Pairs of Aminophosphine Derivatives 5,6
20
Compd.
Formule
Mp
[α]D
δP
(S,S)-5a
171–172◦C
−82.5 (ethanol)
41.32
42.86
46.91
(R,S)-5a
(+)-5c
142–144
140–141
−125.5 (ethanol)
+6
(−)-5c
128
106–06
Oil
−68.2
−66
—
46.90
78.10
80.74
80.82
(S,S)-6a
(R,S)-6a
(+)-6c
62–62.5
+81
(−)-6c
Oil
—
81.4
the diastereomers and obtain them in a pure state. Some physical and
chemical data of the diastereomerically pure compounds 5,6 are shown
in the Table II.
The subsequent recrystallization allowed us to obtain the diastere-
omers of compound 4 with ca ∼100% stereochemical purity. The purity
of these compounds was confirmed by 31P and 1H NMR spectroscopy.
The signals of the tert-butyl and methyl groups (of MeOCO) were ob-
served in the spectra without any doubling, confirming the high purity
of the compounds.
The synthesis of the 1-phenylethylamide of tert-butylphenylphosphi-
nic acid as a mixture of diastereomers was described.21 However, this
compound was not purified, its diastereomers were not separated and
the stereochemical properties were not studied. Therefore, the physical
and chemical data of 1-phenylethylamino-tert-butylphenylphosphine

1038
E. V. Gryshkun et al.
oxide described in Kolodiazhnyi24 differ strongly from those of the stere-
omerically pure compound 4, prepared in the present work.
Since the 1-phenylethylamine used in the synthesis had the (S)-
configuration, the configuration at phosphorus in this major diastere-
omer 5 is S. Accordingly, the other (minor) diastereomer must have the
(S ,RP)-configuration.
C
The thionation of the diastereomeric mixture of 3 proceeds
with change of the diastereomeric ratio to give, mainly the (S,S)-
diastereomer 6. The diastereomers of the phosphine sulfide 6 were ob-
served through HPLC and NMR spectroscopy. The pure major diastere-
omer 5 was isolated by crystallization from hexane as a colorless stable
solid (needles) in ∼100% diastereoisomeric purity. The minor diastere-
omer of (R,S)-(−)-5 was isolated as a colorless viscous liquid containing
about 20% of (R,S)-diastereomer which could not be separated either
by crystallization or by column chromatography. The aminophophines
3 are easily alkylated by methyl iodide with formation of the phospho-
nium salts 7.
The absolute configuration of the compounds was established by
chemical methods. The amino group of the compound (SP,S)-(+)-5b
was replaced by a methoxy group at the reflux in methanol containing
sulfuric acid for 5 h. In result the methyl ether (R)-(−)-phenyl(mesityl)-
phosphinic acids (ee 75%) which has been earlier described15 is formed.
The sign of optical rotation allows us to define a configuration of phos-
phorus atom in the initial amide which, obviously, should beSP because
SN2 replacement proceeds with the inversion of the configuration.11 The
given reactions proceed stereospecifically according to the SN2 mecha-
nism with the inversion of the configuration at the phosphorus atom.11
The compound (RP,S)-(+)-3a was hydrolyzed by formic acid with the
formation of (S)-(−)-tert-butylphenylphosphine oxide, which has been
earlier described.22,23 The (S)-configuration of the hydrolysis product
was confirmed by its negative optical rotation.24
The compound (SP,S)-(−)-5a is stable to hydrolysis and is not hy-
drolyzed even at reflux during 48 h in aqueous dioxane, containing
sulfuric acid. It was not possible to effect the methanolysis of (SP,S)-
(−)-5a. The compound was unchanged during 48 h reflux in methanol,
containing 5% of sulfuric acid.
EXPERIMENTAL
Melting points are uncorrected. The NMR spectra were recorded on a
Varian VXR-300 spectrometer at 300 (1H), 60 (13C) and 126.16 MHz
(31P). 1H and 13C chemical shifts are given in δ (ppm), relative to Me4Si

Chiral Amines with Racemic Chlorophosphines
1039
as internal standard. 31P NMR spectra were recorded relative to 85%
H3PO4 as an external standard. All manipulations were carried out in
an argon atmosphere. The following solvents were distilled in an inert
atmosphere: diethyl ether, hexane, heptane, benzene, CCl4 (over P4O10),
methanol, triethylamine (over sodium), ethyl acetate (over CaCl2).
HPLC separations were carried out on the instruments Milichrom-
1A (Russia) and LKB (Sweden) with Ultrapack TSK ODS 120 T 5 um
250 × 4.6 mm column (65–75% aqueous methanol as eluent); Silasorb
DEA column 120 × 2 mm (hexane-isopropanol mixture in a 95:5 ratio
as eluent); Silasorb C18 120 × 2 mm column (50% aqueous acetonitrile
as eluent); UV detector, λ 260 nm.
Column chromatography was performed using silica gel 60 (Fluka).
Optical rotations of the compounds were determined on a Perkin-
Elmer Model 241 spectropolarimeter. Solvents were purified by stan-
dard methods. Optically active reagents, (−)-(S)- and (+)-(R)-1-
phenylethylamines, were obtained from Fluka, and were used without
special purification.
N-(1-Phenylethyl)amino-tert-butylphenylphosphine (3a)
To a solution of 4.5 g (0.025 mmol) of tert.-butylphenylchlorophosphine
in 10 ml of benzene was added slowly with stirring over 3 h a solu-
tion of 0.025 mol of (S)-N-(1-methylbenzyl)amine and 0.026 mmol of
triethylamine in 10 ml of benzene. The solution was stirred for 2–3 h
at room temperature. Then, the reaction mixture was allowed to stand
at room temperature overnight. The precipitate of triethylamine hy-
drochloride was filtered off and washed with 50 ml of diethyl ether.
The filtrate was evaporated under reduced pressure; the residue was
distilled in vacuo. The product was obtained as a colorless liquid. The
reaction was performed under different conditions. Depending on the
nature of the tertiary base and the solvent different ratios of diastere-
omers were obtained (see Table I).
b.p. 140◦C (0.01 mmHg). Yield: 80%.
Anal. Calcd for C18H24NP: N 4.91; P 10.85. Found: N 4.85; P 10.91.
1H NMR, δ, ppm, (CDCl3): 0.77 d [3 JHP 5.0, (CH)3C]; 0.81 d [3 JHP 7.0,
(CH)3Cꢁ]; 1.60 m (CH); 1.45 d [3 JHH 14.0, (CH3)]; 1.51 d [3 JHH 14.0,
ꢁ
(CH3 )]; 3.54 m (NH); 7.10–7.33 m (C6H5). 31P NMR (CDCl3), δP: 49.9;
47.24.
N-(1-Phenylethyl)amino-phenymesitylphosphine (3b)
The product was prepared analogously to compound 3a. Yield 85%.
The product was prepared in spectroscopically pure state and used

1040
E. V. Gryshkun et al.
for further conversions without special purification. 31P NMR, δ, ppm
(CDCl3), δP: 29.75; 29.23.
N-(l-carbomethoxy-3-methyl)butylamino-tert-
butylphenylphosphine (3c)
To a solution of 9 g (0.05 mmol) of tert-butyl-phenylchlorophosphine
and 10 g (0.1 mmol) of triethylamine in 100 ml of benzene cooled in
an ice-bath was added with stirring 7.2 g (0.05 mmol) of L-Leucine
methyl ester. The solution was stirred for 30 min at room temperature
and then the reaction mixture was left overnight. The precipitate of
triethylamine hydrochloride was filtered off and washed with 100 ml of
ether. The filtrate was evaporated and the residue was distilled under
reduced pressure.
Yield 10.85 g (70%), b.p. 148–150◦C (0.04 mm Hg). Colorless oil.
Anal. Calcd. for C17H28NO2P: P 10.01. Found: P 9.81.
1H NMR, δ, ppm; J, Hz (CDCl3): δH: 0.78 m [(CH3)C]; 0.85 d [J HH 10
(CH3)3C]; 0.87 d [JHH 10.0 (CH3)3Cꢁ]; 1.52 m (CH2); 1.82, spt (CH);
2.21 dd (JHH 11.0, JHP 11.0, NH); 3.34 s (CH3O); 3.66 s (CH3O); 3.60
m (CHN); 7.26 m; 7.86 m (C6H5). 31P NMR, δ, ppm; (CDCl3): δP: 56.98.
N-(l-carbomethoxy-2-methyl)propylamino-tert-
butylphenylphosphine (3d)
The product was prepared analogously to compound 3a. Yield 80%, b.p.
120–125◦C (0 04 mm Hg). Colorless oil. 1H NMR, δ, ppm, J, Hz, (CDCl3):
δH 0.8 dd [(CH3)2C], 0 9 d [JHH 10 (CH3)3C], 1 52 m (CH2); 1.9, spt (CH),
3 2 m (NH), 3 15 s (CH3O); 3 8 m (CHN), 7 26 m; 7 86; m (C6Hs). 31P
NMR, δ, ppm; (CDCl3): δP 56.96; 57.69.
Borane Complex of the (SP)-N-(1-phenylethyl)
amino-tert-butylphenylphosphine (4a)
To an (S,S)+(R,S)-diastereomeric mixture of N-(1-phenylethyl)amino-
tert-butyl-phenylphosphine 3a (0.1 mmol) in 5 ml THF a solution of
0.12 mmol of borane in THF was added dropwise with stirring. Then,
the reaction mixture was allowed to stand at room temperature. After
6 h the solvent was removed in vacuo and the crystalline complex 3 was
obtained in satisfactory purity for further synthetic applications. Com-
plex 3 could be purified additionally by recrystallization from hexane or
by filtration through a short column over silica gel with hexane-ethyl
acetate as eluent.

Chiral Amines with Racemic Chlorophosphines
1041
20
m.p.140–141◦C (hexane). Yield: 80%; [α]D = +24.5 (c 1, CH2Cl2).
Anal. Calcd. for C18H27BNP: P 10.35. Found: P 10.46.
1H NMR, δ, ppm; J, Hz (CDCl3): 0.2-2, m (BH3); 1.01 d [3 JHP 14.16,
(CH3)3C]; 1.50 d [3 J HH 6.72, (CH3)]; 2.07 br.d [2 JHP16.0, (NH)]; 4.45
m (CHN); 7.10–7.40 m (C6H5). 13C NMR, δ, ppm (CDCl3): 24.57 d
[2 J 2.76, (CH3)3C]; 25.57 d [3 J 5.20 (CH3)CHN]; 30.69 d [1 J
CP
CP
CP
43.40, (CH3)3C]; 52.47 d [2 JCP 2.01, (CHN)]; 126.10 s; 126.94 s; 127.58
d JCP 9.50; 130.37 d J 2.50; 130.75 d J 46.80; 131.94 d JCP 9.40
CP
CP
(C6H5).31P NMR, δ, ppm (CDCl3): 69.76 br, d [1 J 90 Hz].
BP
Borane Complex of the N-(l-Carbomethoxy-3-methyl)-
butylamino-tert-butyl-phenylphosphine (4c)
The product was prepared analogously to compound 4a.
20
Yield: 75%; m.p. 93◦C (hexane). [α]D = +91 (c 1, hexane).
1H NMR, δ, ppm; J, Hz (CDCl3): 0.2–2, m (BH3); 0.83 d 3 JHH 6.6, 0.86,
d3 JHH 6.6 [(CH3)2C]; 0.98 d [3 JHP 14.3, (CH3)3C]; 1.492 t [3 JHH 6.6,
(CH2)]; 2.6 br.d [2 JHP 10.0, (NH)]; 3.4 s (OCH3); 3.98 m (NHCH) 7.20–
7.60 m (C6H5). 31P NMR, δ, ppm; (CDCl3): 71.5 br. d [1 J 90 Hz].
BP
Decomplexation of Borane Complex (4a).(SP,S)-N-
(1-Phenylethyl)amino-tert-butyl-phenylphosphine (3a)
A solution of 3 g (0.01 mmol) of complex 4a in 10 ml of degassed diethy-
lamine was kept under argon at +50◦C for 16 h. Then, excess diethy-
lamine was removed in vacuo to leave the optically pure aminophos-
phine 3a. The 31P NMR spectrum showed only one signal, due to
the (SR)-diastereomer (confirmed by mixed testing with an authentic
diastereomer).
Yield: 50%. bp. 160–161◦C (0.02 mm Hg). [α]D +120 (0.3, toluene).
20
1H NMR, δ, ppm; J, Hz (CDCl3): 0.81 d [3 JHP 7.0, CH3C]; 1.60 m (NH);
1.45 d [3 JHH 14.0, (CH3)3C]; 3.54 m (CHN); 7.10–7.33 m (C6H5). 31
NMR, δ, ppm; (CDCl3): 49.00.
P
N-(1-Phenylethyl)amino-tert-butylphenylphosphine
Oxide (5a)
(a) To a solution of the borane complex 4a in dioxane an equimolar
quantity of hydrogen peroxide was added with cooling. After the tem-
perature was raised to room temperature, the reaction mixture was
allowed to stand for 6 h. The solvent was evaporated, and the residue
was obtained as a solid to which heptane was added, and which was left

1042
E. V. Gryshkun et al.
to crystallize. Then the crystalline product was filtered off to provide
the pure diastereomer (Sp,S)-5a.
20
(Sp,S)-diastereomer. m.p. 171–172◦C (heptane). Yield 80%. [α]D
-
82.5 (c 0.5, ethanol).
(b) To a solution of the aminophosphine 3a in dioxane an equimolar
quantity of hydrogen peroxide was added with cooling. After the tem-
perature was raised to room temperature, the reaction mixture was
allowed to stand for 0.5 h. The solvent was evaporated, and the residue
was obtained as a viscous liquid to which hexane was added, and which
was left to crystallize. The next day the crystalline product was filtered
off and was recrystallized from ethyl acetate. The mother liquor was
evaporated. The residue, enriched in the minor diastereomer, was sep-
arated by column chromatography (SiO2; 92: 8 hexane-isopropanol as
eluent).
(Sp,S)-diastereomer. m.p.171–172◦C (from ethyl acetate). Yield 75%.
[α]D20-82.5 (c 0.5, ethanol).
Anal. Calcd. for C18H24NOP. N 4.65; P 10.28. Found: %: N 4.67; P 10.42.
1H NMR, δ, ppm; J, Hz (CDCl3): δH 1.01, d JHH 14.8 [(CH3)3C]; 1.33 d,
JHP 7.0 (CH3); 2.80 br (NH); 4.44 br JHH 8 (CH); 7.19–7.4 m; 7.87 m
(C6H5). 31P NMR, δ, ppm; (CDCl3): δP 41.32.
(Rp,S)-diastereomer. M.p. 142–144◦C (heptane). [α]D −125.5 (c 0.5,
ethanol). Yield 5%.
Anal. Calcd. for C18H24NOP: N 4.65; P 10.28. Found: N 4.65; P 10.32.
1H NMR, δ, ppm; J, Hz (CDCl3): δH 1.04 d JHP 14.4 [(CH3)3C]; 1.48 d
JHH 7.4 (CH3C); 2.76 dd J 7 (NH); 4.17 m (CH); 7.13–7.57 (C6H5).
31P NMR, δ, ppm; (CDCl3): δP 42.86.
(S,SP)-1-Phenylethylamino-mesitylphenylphosphine
Oxide (5b)
The product was prepared analogously to compound 5a.
20
Yield 50%. [α]D +10 (c 1, ethanol), m.p. 157◦C (ethyl acetate). 1H NMR
(CDCl3), δ, ppm (J, Hz): 1.67 d, (3H, PhCHMe, JHH 7); 2.29 c (3H,
4-Me); 2.38 s (6H, 2- ;4-Me), 3.00 m (1H, NH,JHH 9.0, J 9.0); 4.5
PH
m (1H, PhCHMe); 6.9 d (2H, 3-,5-H, J 4.0); 7.2–7.4 m (5H, C6H5);
PH
7.35 m (5H, C6H5). 31P NMR, δ, ppm; (CDCl3): δP 28.0.14
N-(l-Carbomethoxy-3-methyl)butylamino-tert-
butylphenylphosphine Oxide (5c)
The product was prepared analogously to compound 5a. The col-
umn chromatography (silica gel L 100/160) of crude product using

Chiral Amines with Racemic Chlorophosphines
1043
hexane-isopropanol (95:5) as eluent yielded two fractions of two di-
astereoisomers in the following order:
(+)-Diastereomer. Yield 0.3 g (10%), m.p. 140–141.5◦C (heptane), color-
20
less needles, [α]D + 6◦ (c = 2.5, C2H5OH).
Anal. calcd. for C17H28NO3P: N 4.30; P 9.52. Found N 4.38; P 9.61.
1H NMR, δ, ppm; J, Hz (CDCl3): δH: 0.70 d [JHH 6.5, (CH3)2C]; 0.79
d [J HH 6.5, (CH3)2C]; 1.10 d [J HH 15.0, (CH3)3C]; 1.47 m (JHH 6.3,
CHO; 1.64 m (CH); 3.24 dd (J HH 11, JHP 11, NH); 3.71 s (CH3O); 3.8
m (CHN); 7.46 m; 7.79 m (C6H5). 31P NMR, δ, ppm; (CDCl3): δP 46.91.
(−)-Diastereomer. Yield 2.0 g (61%), m.p. 128˚C (hexane), colorless pris-
20
matic crystals, [α]D −68.42◦ (c = 1, C2H5OH). IR (liquid, ν,cm−1):
1180 (P O); 1720 (C O); 3400 (NH).
Anal. calcd. for C17H28NO3P: N 4.30; P 9.52. Found N 4.35; P 9.58.
1H NMR, δ, ppm; J, Hz (CDCl3): δH: 0.87 d [JHH 6.3, (CH3)2C]; 0.89 d
[JHH 6.3, (CH3)2Cꢁ]; 1.09 d [JHH 15.0, (CH3)3C]; 1.58 m (CH,); 1.806
spt (CH); 3.19 dd (JHH 11, JHP 11, NH); 3.558 s (CH3O); 3.79 m
(CHN); 7.247 m; 7.696 m (C6H5). 31P NMR, δ, ppm; (CDCl3): δP 46.9.
Alcoholysis of (+)-(SP,S)-N-(1-Phenylethyl)amino
(phenyl)mesitylphosphine Oxide (5b)
The mixture of 18.2 mmol (+)-(SP,S)-N-(1-phenylethyl)amino(phenyl)-
mesitylphosphine oxide (5b) ethanol and 1.6 ml of 98% sulfuric acid
was refluxed for 5 h. The reaction mixture was cooled, and 200 ml of
chloroform was added. The mixture was washed with 10% solution of
sodium bicarbonate (3 × 50 ml) and water (2 × 50 ml). The organic part
was treated with magnesium sulfate and concentrated under vacuum.
The residue was purified by flesh-chromatography. The methyl (R)-(−)-
methyl-(2,4,6-trimethylmethyl)phosphinate was obtained as a colorless
liquid.
20
Yield 4.0 g (80%); [α]D -20 (c 1, ethanol).15
1H NMR, δ, ppm; J, Hz (CDCl3): 2.3 c (3H, 4-CH3), 2.50 d (6 H, 2-,
6-CH3, J 1.2), 3.70 d (3 H, OCH3, J 11.1), 6.90 d (2 H, 3-, 5-H,
PH
PH
J
4.2), 7.5 m (3 H, C6H5), 7.60 m (2 H, C6H5); 31P NMR, δ, ppm;
PH
(CDCl3): δP 37.0 ppm.
1-Phenylethylamino-tert-butylphenylphosphine
Sulphide (6a)
(a) A solution of the borane complex 4a in diethylamine was kept under
argon at +50◦C for 16 h. Then, excess diethylamine was removed in
vacuo, the rest was dissolved in benzene and an equimolar quantity of

1044
E. V. Gryshkun et al.
sulfur was added. The reaction mixture was allowed to stand for 6 h.
The residue was diluted with hexane and left to crystallize. Next day
a crystalline product was filtered off, and was recrystallized from ethyl
acetate to provide the pure diastereomer (SP,S)-6a.
(SP,S)-Diastereomer. Yield 70%, m.p. 105–106◦C (hexane). [α]D20-66
(c = 2.5, ethanol).
(b) To a solution of the aminophosphine 3a in benzene cooled to 0
to +5◦C was added a 10% excess of sulfur, dissolved in benzene. The
temperature was raised to room temperature, and the reaction mixture
was allowed to stand for 1 h. The residue was obtained as a viscous
liquid which was diluted with hexane and left to crystallize. Next day
a crystalline product was filtered off, and was recrystallized from ethyl
acetate. The mother liquor was evaporated and then chromatographed
on a silica gel column, using a mixture of hexane-isopropanol (92 : 8
ratio) as eluent.
(SP,S)-Diastereomer. Yield 50%, m.p. 105–106◦C (hexane). [α]D20-66
(c = 2.5, ethanol).
1H NMR, δ, ppm; J, Hz (CDCl3): δH 1.15, d JHP 16.2 [(CH3)3C]; 1.5 d
JHH 6, 6 (CH3); 2.3 br (NH); 4.4 dq JHH 6.6 JHP 8 (CHN); 7.2 m; 7.93
m (C6H5). 31P NMR, δ, ppm; (CDCl3): δP 78.10.
(RP,S)-Diastereomer. Yield 8%. Anal. calcd. for C18H24NPS: N 4.41; P
9.76. Found: N 4.45; P 9.62.
1H NMR, δ, ppm; J, Hz (CDCl3): δH: 0.98 d [JHP 16.6 (CH3)3C]; 1.21 d
[JHH 6.0 CH3]; 2.21 m (NH); 4.41 dd.[JHH 6.0, JHP 6.0 (CH); 7.2 m;
7.93 m (C6H5). 31P NMR, δ, ppm; (CDCl3): δP 80.74.
N-(l-Carbomethoxy-l-methyl)butylamid-tert-
butylphenylphosphine Sulphide (6c)
To a solution of 3.1 g (0.01 mmol) of aminophosphine 3c in 5 ml of
benzene was added 0.5 g (0.0155 mmol) of sulfur. The reaction mixture
was allowed to stand for 12 h at room temperature, then the solvent was
evaporated and the residue dissolved in hexane. The excess of sulfur
was filtered off and the hexane was evaporated. The 31P NMR spectrum
indicated that the product was a 75:25 mixture of diastereomers. The
crude product was then chromatographed over a column of a silica gel L
100/160 with hexane-ethylacetate (3:1) as eluent yielding two fractions
of two diastereomers. The first fraction after the evaporation of a solvent
was dissolved in hexane and kept in a refrigerator for 48 h at −20◦C. A
colorless crystalline solid of the major diastereomer was separated and
dried in vacuum.

Chiral Amines with Racemic Chlorophosphines
1045
20
Yield 2.0 (59%), m.p. 62–62.5◦C, [α]D +8.1 (C = 1, CH3OH).
1H NMR, δ, ppm; J, Hz (CDCl3): δH: 0.83 d [J HH 6.3 (CH3)2C]; 0.92 d
[J HH 6.3 (CH3)2Cꢁ]; 1.08 d [J HH 16.8, (CH3)3C]; 1.61 m (CH,); 1.70
spt (CH); 3.0 dd (J HH 11.0, J HP 11.0, NH); 3.48 s (CH3O); 4.12 m
(CHN); 7.37 m; 7.78 m (C6H5). 31P NMR, δ, ppm; (CDCl3): δP: 80.82.
The minor diastereomer was obtained as colorless oil, containing trace
of the first diastereoisomer: Yield 0.4 g (12%).
Anal. Calcd. for the C17H28NO2PS: N 4.10; P 9.07; S 9.37. Found N 4.12;
P 9.29; S 9.55.
1H NMR, δ, ppm; J, Hz (CDCl3): δH: 0.69 d [/ HH 6.3, (CH3)2C]; 0.76 d
[J HH 6.3 (CH3)2Cꢁꢁ]; 1.09 d [J HH 17.0, (CH3)3C]; 1.45 m (CH,); 1.70
spt (CH); 3.01 dd (J HH 11. J HP 11, NH); 3.48 s (CH3O); 4.12 m (CHN);
7.37 m; 7.92 m (C6H,). 31P NMR, δ, ppm; (CDCl3): δP: 81.4.
(RP,S)-(1-Phenylethyl)amino-tert-butyl-
phenyl-methylphosphonium Iodide (7)
To a solution of (1-phenylethyl)amino-tert-butyl-phenylphosphine 3a
(2.8 g; 0.01 mmol) in toluene (10 ml) excess methyl iodide (1.8 g;
0.0125 mmol) was added, and the reaction mixture was allowed to stand
overnight. After 20 h the precipitate was separated and purified by crys-
tallization.
20
Yield: 84%, m.p. 220–221◦C; [α]D -57.3 (c 2.5, C2H5OH).
Anal. Calcd. for C19H27INP: N 3.28; P 7.25. Found: N 3.29; P 7.45.
1H NMR, δ, ppm; J, Hz (CDCl3): δH: 1.21 d (CH3)3C, JHH 16); 1.51d
J 6.5 (CH3); 2.45 d J 11.5 (CH3P); 4.11 br (CH); 6.14 br (NH), 7.30
(C6H5). 31P NMR, δ, ppm; (CDCl3): δP 55.8.
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