Diastereoselective reductive amination of pyrazolidinyl alkyl ketones

Article abstract of DOI:10.1007/s10593-008-0073-x

Reductive amination of pyrazolidinyl alkyl ketones with sodium triacetoxyborohydride or sodium tripivaloyloxyborohydride takes place diastereoselectively with the formation of aminoalkyl-pyrazolidines of trans structure. The volume of the substituent in t

Full text of DOI:10.1007/s10593-008-0073-x

Chemistry of Heterocyclic Compounds, Vol. 44, No. 5, 2008
DIASTEREOSELECTIVE REDUCTIVE
AMINATION OF PYRAZOLIDINYL
ALKYL KETONES*
L. A. Sviridova1, G. A. Golubeva1, A. N. Tavtorkin2,
Yu. V. Nelyubina2, and K. A. Kochetkov2
Reductive amination of pyrazolidinyl alkyl ketones with sodium triacetoxyborohydride or sodium
tripivaloyloxyborohydride takes place diastereoselectively with the formation of aminoalkyl-
pyrazolidines of trans structure. The volume of the substituent in the borohydrides does not affect the
ratio of stereoisomers.
Keywords: primary and secondary amines, ketones, pyrazolidines, sodium triacetoxyborohydride,
diastereoselective reductive amination.
Reductive amination of ketones concerns a widely applied methods of synthesis of amines [1]. In the
series of reducing agents used [2-4] sodium triacetoxyborohydride is especially convenient, possessing a high
chemoselectivity, which enables the use of a wide circle of amines and carbonyl compounds [5]. However the
synthetic possibilities of this compound and its analogs in stereoselective reduction has been little studied [6-9],
although the use of spatially hindered reducing agents usually permits stereoselectivity to be increased [8, 9].
In the present work we have studied the reductive amination of ketones 1 and 3, existing as racemates of
trans structure [10], using sodium triacetoxyborohydride and sodium tripivaloyloxyborohydride and a series of
primary and secondary amines. On reductive amination of racemic ketones 1 and 3 with a nonchiral amine two
diastereomers are formed and on using a chiral amine four. The yields and ratios of the resulting diastereomers 2
and 4 are given in Table 1.
The results show that the diastereoselectivity of the process of reductive amination of compounds 1 and
3 does not depend on the volume of the substituents in the sodium triacyloxyborohydride in difference to the
data of [8, 9]. Probably the given organic radicals in the reducing agent (methyl in the triacetoxyborohydride
and tert-butyl in the tripivaloyloxyborohydride) are too far removed from the reaction centers and consequently
do not influence the stereochemistry of the process. On using dimethylamine and benzylamine the
stereoselectivity of the reaction did not exceed 3.5:1. Diastereomers 2c were isolated in the pure state by column
chromatography and were characterized by spectral methods. On using (S)-ethylphenylamine only two
_______
* Dedicated to the memory of A. A. Potekhin, renowned teacher, scientist, and editor of journal "Chemistry of
Heterocyclic Compounds"
_________________________________________________________________________________________
1Chemical Faculty, M. V. Lomonosov State Moscow University, Moscow 119899, Russia; e-mail:
2
svirid@org.chem.msu.ru. A. N. Nesmeyanov Institute of Oganoelement Compounds, Russian Academy of
Sciences, Moscow 119991; e-mail: const@ineos.ac.ru. Translated from Khimiya Geterotsiklicheskikh
Soedinenii, No. 5, pp. 691-698, May, 2008. Original article submitted February 15, 2008.
542
0009-3122/08/4405-0542©2008 Springer Science+Business Media, Inc.

diastereomers of 4d of the four possible were formed preferentially in a ratio of 3:2, and the two others were not
detected by spectral methods, which shows the fairly high stereoselectivity of the process. The diastereomer of
4d predominating in the mixture was isolated by crystallization as the hydrochloride.
Me
Me
R
R
R1
[H]
O
N
N
N
Ph
Ph
R2
R1R2NH
N
N
Ac
Ac
2a–c
1a,c
Me
Me
Me
Me
R1
O
[H]
N
N
Ac
N
N
Ac
R1R2NH
R2
N
Ph
Ph
4a,b,d
3a
[H] = NaBH(O2CMe)3, NaBH(O2CCMe3)3; 1 a R = Me; c R = Ph; 2, 4 a R = R1 = R2= Me;
b R = Me, R1 = H, R2 = Bn; c R = Ph, R1 = H, R2 = Bn; 4d R1 = H, R2= CH(Me)Ph
In the 1H NMR spectra of the obtained amines, compared to the initial ketones [10], there was a doublet
or doublet of doublets for the proton of the emerging methine group, the signals of the α-protons were displaced
from 2.5-4.0 to the 1.5-2.0 ppm region, in compounds 2a,b and 4a,b the signals of the methyl group of the
functional substituent (singlet at ~2 ppm) were displaced by ~1 ppm towards high field and split into a doublet.
The signals of the remaining protons did not undergo significant changes. In the spectra of compound
Fig. 1. General shape of the predominant diastereomer of aminoethylpyrazolidine 4d
hydrochloride. Some of the hydrogen atoms are not shown for clarity.
543

TABLE 1. Yields and Ratios of Diastereomers of Amines 2, 4
NaBH(O2CMe)3
NaBH(O2CCMe3)3
Initial
amine
Reaction
product
Ketone
Ratio
Ratio
Yield, %
Yield, %
of diastereomers
of diastereomers
1a
Me2NH
BnNH2
BnNH2
Me2NH
BnNH2
RNH2*2
2а
2b
2c
4а
4b
4d
72
65
34
70
67
40
3.5:1
5:4
65
58
3.5:1
1:1
1c
3
6:5
—*
73
—*
2:1
2:1
2.5:1
3:2:0:0
37
2.5:1
—*
—*
_______
* Reaction not performed.
*2 R = (S)-PhCH(Me).
4d hydrochloride the signal of the methyl group of the acetyl substituent (1.31 ppm) was found at a high field
unusual for it, probably due to the anisotropic influence of the aromatic nucleus (see Fig. 1). In the spectrum of
4d base this signal was found in the usual position. In the IR spectra of the amines the absorption band of the
ketone carbonyl group had disappeared and for the benzylamine derivatives 2b,c and 4b an absorption band
appeared for the NH group at 3300-3400 cm-1.
An X-ray crystallographic analysis was carried out for compound 4d hydrochloride and its absolute
configuration was determined (Fig. 1). The diastereomer was identified as 1-acetyl-3S-[2S-(1S-phenyl-
ethylamino)propyl]-5R-methyl-2-phenylpyrazolidine. Bond lengths and valence angles for the heterocycle were
close to those for previously studied pyrazolidine derivatives [11, 12]: N(1)–N(2) 1.424(3), N(1)–C(3) 1.502(4),
N(2)–C(5) 1.493(4), C(3)–C(4) 1.516(4), C(4)–C(5) 1.522(4) Å; C(3)N(1)N(2) 112.2(3), N(1)N(2)C(5)
102.3(2), N(2)C(5)C(4) 102.8(3), C(3)C(4)C(5) 103.9(3)°. The conformation of the heterocycle is a theoretical
envelope with emergence of atom C(5) by 0.601(2) Å from the plane formed by atoms C(3), C(4), N(1), and
N(2). Atoms N(1) and N(2) in their turn are significantly pyramidalized (sums of valence angles were 332.4 and
356.1°) with clearly expressed flattening of the first due to its conjugation with the acetyl fragment. It should be
noted that the C(17) methyl group is located directly above the plane of the phenyl ring C(20)–C(25) with the
distance of the C(17) atom to the center of the ring being 3.56 Å. Although the minimum H···C distances (3.07
and 3.36 Å) significantly exceed the sum of the van der Waals radii and the H···π interaction is not exerted, such
a contact may fully lead to shielding of the methyl group hydrogen atoms in the 1H NMR spectra.
According to analysis of the crystal packing of compound 4d, the cations participate in the formation of
N–H···Cl (N···Cl 3.150(3)-3.174(3) Å) hydrogen bonds of moderate strength, which unite them in chains
directed along the x crystallographic axis. The remaining interionic contacts (C–H···Cl, C–H···O, and C–H···H)
correspond to weak van der Waals interactions.
On the basis of the structure of the initial heterocycle as a racemate of trans structure [10], on condition
that (S)-phenylethylamine interacts with enantiomers 3a nonselectively, but the resulting imine is reduced
stereoselectively [13], then the structure 1-acetyl-3R-[2R-(1S-phenylethylamino)propyl]-5R-methyl-2-phenyl-
pyrazolidine must be assigned to the other (minor) diastereomer of 4d.
A synthesis has therefore been developed for the previously unavailable trans diastereomers of
pyrazolidinylalkylamines 2 and 4. Compounds of this type are a promising class of substances displaying high
thrombolytic activity [14].
544

EXPERIMENTAL
1
The IR spectra were obtained on a UR-20 instrument in films. The H NMR spectra were recorded on
Bruker Avance 400 (400 MHz) instruments in CDCl3 at 30°C, the standard was the residual protons of the
solvent, δ 7.26 ppm. Coupling constants were measured with a precision of ±0.1 Hz, and the ratio of
1
diastereomers by the H NMR method. Elemental analysis was carried out on a Carlo Erba EA1108 CHNS-O
CHN microanalyzer. The purity of the obtained compounds was checked by TLC on Silufol plates in the
systems petroleum ether–ethyl acetate, 1:1, and chloroform–methanol, 10:1, with visualization with iodine
vapor and FeCl3 in alcohol solution. Chromatographic purification of the obtained compounds was carried out
by flash chromatography on a dry column of silica gel type L 5/40.
Preparation of Amines (General Method). Glacial acetic acid (125 µl, 2.17 mmol) was added
dropwise to a mixture of methylene chloride (1.5 ml) and sodium borohydride (24 mg, 0.62 mmol). After 30
min treatment in an ultrasound bath, ketone (0.31 mmol) and amine (0.37 mmol) were added, and the mixture
was stirred for several days (check by TLC). For purification the reaction mixture was washed with saturated
potassium carbonate solution (1 ml) and distilled water (2×1 ml). Hexane (1 ml) and a saturated solution of
oxalic acid (2 ml) were added to the residue, the mixture shaken, the organic layer was separated, and the
aqueous layer extracted with a methylene chloride–hexane, 1:1 mixture. Potassium carbonate (1 g) was added to
the aqueous phase and the mixture extracted with a methylene chloride–hexane, 1:1 mixture. The organic
extract was evaporated in vacuum, and the residue separated on a dry column in the system chloroform–
methanol in a gradient from 100:1 to 1:1 (or petroleum ether–ethyl acetate in a gradient from 10:1 to 0:1).
TABLE 2. Crystallographic Data, Main Parameters of the X-Ray
Diffraction Experiment, and Refinement of the Crystal Structure of 4d Salt
Compound
4d
Empirical formula
C27H40ClN3O3
490.07
Mass of formula unit
Color, crystal shape
Crystal size, mm
Temperature, K
Crystal system
Space group
a, Å
Colorless needles
0.15×0.15×0.25
120(2)
Rhombic
P 212121
7.7712(10)
12.442(2)
28.128(5)
2719.8(8)
4 (1)
b, Å
c, Å
V, Å3
Z (Z')
F(000)
1056
Dcalc
,
⋅
g
cm-3
⋅
1.197
Absorption coeff., µ, cm-1
Scanning type
2.26
ω
Range of θ, deg
Number of reflections
measured
3.19-28.00
10382
independent (Rint)
with I>2σ(I)
6390 (Rint = 0.037)
3295
Number of parameters used
R(Fhkl) : R1
258
0.0544
wR2
0.1084
GOF
0.993
Residual electron density, e•Å–3 (dmin/dmax
)
0.269-0.234
545

1-Acetyl-5-(2-dimethylaminopropyl)-3-methyl-2-phenylpyrazolidine (2a). Yield 72%, oil. Two
diastereomers, ratio 3.5:1. IR spectrum, ν, cm-1: 1670 (CO).
1
Predominant isomer. H NMR spectrum, δ, ppm (J, Hz): 0.99 (3H, d, J = 6.6, γ-CH3); 1.21 (3H, d,
J = 7.0, 3-CH3); 1.49 (1H, m, H-4); 1.81 (1H, m, H-α); 1.96, 1.99 (2H, m, H'-α, H'-4); 2.02 (3H, s, CH3CO);
2.17 (6H, s, (CH3)2N); 2.59 (1H, m, H-β); 4.09 (1H, m, H-3); 4.40 (1H, m, H-5); 6.88-6.97 (3H, m, H-o,p); 7.23
(2H, m, H-m).
Minor isomer. 1H NMR spectrum, δ, ppm (J, Hz): 0.94 (3H, d, J = 6.4, γ-CH3); 1.18 (1H, m, H-α); 1.21
(3H, d, J = 7.0, 3-CH3); 1.80 (1H, m, H'-α); 1.99 (1H, m, H-4); 2.02 (3H, s, CH3CO); 2.20 (6H, s, (CH3)2N)];
2.24 (1H, m, H'-4); 2.59 (1H, m, H-β); 4.09 (1H, m, H-3); 4.40 (1H, m, H-5); 6.88-6.97 (3H, m, H-o,p); 7.23
(2H, m, H-m). Found, %: C 69.79; H 9.54; N 13.71. C17H27N3O. Calculated, %: C 70.55; H 9.40; N 14.52.
1-Acetyl-5-(2-benzylaminopropyl)-3-methyl-2-phenylpyrazolidine (2b). Yield 65%, oil, two
diastereomers, 5 : 4. IR spectrum, ν, cm-1: 1670 (CO), 3330 (NH).
1
Predominant isomer. H NMR spectrum, δ, ppm (J, Hz): 1.16 (3H, d, J = 6.2, γ-CH3); 1.22 (3H, d,
J = 6.7, 3-CH3); 1.31 (1H, m, H-α); 1.75, 1.83 (2H, m, H-4, H'-α); 2.04 (3H, s, CH3CO); 2.04 (1H, m, H'-4);
2.77 (1H, m, H-β); 3.66 (1H, d, J = 12.0, CH2Ph); 3.84 (1H, d, J = 12.0, CH'2Ph); 4.07 (1H, m, H-3); 4.58 (1H,
m, H-5); 6.92-6.98 (3H, m, H-o,p, C6H5); 7.22-7.42 (7H, m, CH2C6H5, H-m, N-C6H5).
1
Minor isomer. H NMR spectrum, δ, ppm (J, Hz): 1.09 (3H, d, J = 6.4, γ-CH3); 1.22 (3H, d, J = 6.6,
3-CH3); 1.54 (1H, m, H-α); 1.75, 1.83 (2H, m, H-4, H'-α); 1.96 (1H, ddd, J = 12.4, J = 7.7, J = 2.3, H'-4); 2.07
(3H, s, CH3CO); 2.84 (1H, q, J = 6.3, H-β); 3.71 (1H, d, J = 12.6, CH2Ph); 3.82 (1H, d, J = 12.4, CH'2Ph); 4.12
(1H, m, H-3); 4.58 (1H, m, H-5); 6.92-6.98 (3H, m, H-o,p, N-C6H5); 7.22-7.42 (7H, m, CH2C6H5, H-m, N–C6H5).
Elemental analysis was carried out on the phenylthiocarbamoyl derivative. Found, %: C 72.09; H 7.14; N 11.21.
C29H34N4OS. Calculated, %: C 71.57; H 7.04; N 11.51.
1-Acetyl-5-(2-benzylamino-2-phenylethyl)-3-methyl-2-phenylpyrazolidine (2c). Ratio of diastere-
omers, 6:5.
1
Predominant isomer. Yield 19%, oil. IR spectrum, ν, cm-1: 1665 (CO), 3325 (NH). H NMR spectrum,
δ, ppm (J, Hz): 1.19 (3H, d, J = 6.8, 3-CH3); 1.81 (2H, m, H-α, H'-α); 1.90, 1.98 (2H, m, H-4, H'-4); 2.09 (3H,
s, CH3CO); 2.30 (1H, br. s, NH); 3.54 (1H, d, J = 12.4, CH2Ph); 3.58 (1H, d, J = 12.4 CH'2Ph); 3.79 (1H, dd,
J = 8.7, J = 5.0, H-β); 4.09 (1H, m, H-3); 4.52 (1H, m, H-5); 6.90-7.40 (15H, Ar).
Minor isomer. Yield 15%, oil. IR spectrum, ν, cm-1: 1665 (CO), 3325 (NH). 1H NMR spectrum, δ, ppm
(J, Hz): 1.18 (3H, d, J = 6.7, 3-CH3); 1.58 (2H, m, H-α, H-4); 1.60 (1H, m, H'-4); 1.78 (1H, s, NH); 2.04 (3H, s,
CH3CO); 2.44 (1H, m, H'-α); 3.47 (2H, m, CH2Ph); 3.62 (1H, m, H-β); 3.98 (1H, m, H-3); 4.55 (1H, m, H-5);
6.9-7.4 (15H, Ar). Elemental analysis was carried out on the phenylthiocarbamoyl derivative. Found, %:
C 72.09; H 7.14; N 11.21. C34H35N4OS. Calculated, %: C 74.56; H 6.44; N 10.23.
1-Acetyl-3-(2-dimethylaminopropyl)-5-methyl-2-phenylpyrazolidine (4a). Yield 70%, oil, two
diastereomers, ratio 2:1. IR spectrum, ν, cm-1: 1670 (C=O).
1
Predominant isomer. H NMR spectrum, δ, ppm (J, Hz): 1.07 (3H, d, J = 6.2, γ-CH3); 1.22 (1H, m,
H-α); 1.40 (3H, d, J = 6.4, 5-CH3); 1.78 (2H, m, H-4, H'-α); 2.00 (1H, ddd, J = 12.3, J = 7.8, J = 0.9, H'-4); 2.02
(3H, s, CH3CO); 2.23 (6H, s, (CH3)2N); 2.74 (1H, m, H-β); 4.02 (1H, m, H-3); 4.38 (1H, m, H-5); 6.86-7.27
(5H, m, C6H5).
Minor isomer. 1H NMR spectrum, δ, ppm (J, Hz): 0.88 (3H, d, J = 6.6, γ-CH3); 1.28 (1H, m, H-α); 1.40
(3H, d, J = 6.4, 5-CH3); 1.78 (1H, m, H-4); 1.81 (1H, ddd, J = 12.6, J = 8.7, J = 0.7, H'-α); 1.93 (1H, ddd,
J = 12.6, J = 8.0, J = 0.7, H'-4); 1.99 (3H, s, MeCO); 2.26 (6H, s, (CH3)2N); 2.88 (1H, m, H-β); 4.25 (1H, m,
H-5); 4.38 (1H, m, H-3); 6.91 (1H, m, H-p); 7.07 (2H, m, H-o); 7.25 (2H, m, H-m). Found, %: C 70.06; H 9.44;
N 14.35. C17H27N3O. Calculated, %: C 70.55; H 9.40; N 14.52.
1-Acetyl-3-(2-benzylaminopropyl)-5-methyl-2-phenylpyrazolidine (4b). Yield 67%, oil, two
distereomers, 2.5:1. IR spectrum, ν, cm-1: 1670 (amide), 3330 (NH).
546

1
Predominant isomer. H NMR spectrum, δ, ppm (J, Hz): 1.25 (3H, d, J = 6.1, γ-CH3); 1.30 (1H, m,
H-α); 1.39 (3H, d, J = 6.4, 5-CH3); 1.68 (1H, m, H'-α); 1.76 (1H, m, H-4); 1.96 (1H, m, H'-4); 1.92 (3H, s,
CH3CO); 2.89 (1H, m, H-β); 3.72 (1H, d, J = 13.1, CH2Ph); 3.85 (1H, d, J = 13.1, CH'2Ph); 4.07 (1H, m, H-3);
4.37 (1H, m, H-5); 6.87 (1H, t, J = 7.2, H-p, N–C6H5); 6.98 (2H, d, J = 8.1, H-o, N–C6H5); 7.12-7.41 (7H, m,
CH2C6H5, H-m, N-C6H5).
Minor isomer. 1H NMR spectrum, δ, ppm (J, Hz): 1.19 (3H, d, J = 6.3, γ-CH3); 1.37 (1H, m, α-H); 1.39
(3H, d, J = 6.2, 5-CH3); 1.51 (1H, m, H'-α); 1.81 (1H, ddd, J = 12.6, J = 8.7, J = 7.2, H'-α); 1.92 (1H, dd,
J = 12.4, J = 7.8, H'-4); 2.00 (3H, s, CH3CO); 2.96 (1H, m, H-β); 3.75 (1H, d, J = 12.6, CH2Ph); 4.03 (1H, d,
J = 12.7, CH'2C6H5); 4.36 (2H, m, H-3,5); 6.87 (1H, t, J = 7.15, H-p, N–C6H5); 6.98 (2H, d, J = 8.1, H-o, N–C6H5);
7.12-7.41 (7H, m, CH2C6H5, H-m, N–C6H5). Elemental analysis was carried out on the phenylthiocarbamoyl
derivative. Found, %: C 71.64; H 7.09; N 11.41. C29H34N4OS. Calculated, %: C 71.57; H 7.04; N 11.51.
1-Acetyl-5-methyl-3-[2-(1-phenylethylamino)propyl]-2-phenylpyrazolidine (4d). Yield was 40%,
oil, two diastereomers, ratio 3:2. IR spectrum, ν, cm-1: 1660 (C=O), 3320 (NH).
Predominant (3S,2S,1S,5R)-diastereomer was isolated as the hydrochloride, recrystallized from ethyl
1
acetate; mp 195-200oC (decomp.). H NMR spectrum, δ, ppm (J, Hz), free base: 1.13 (3H, d, J = 6.4, γ-CH3);
1.22 (1H, m, H-α); 1.27 (3H, d, J = 6.3, CH3CHPh); 1.39 (3H, d, J = 6.4, 5-CH3); 1.73, 1.79 (2H, m, H'-α, H-4);
1.85 (3H, s, CH3CO); 2.00 (1H, dd, J = 12.4, J = 7.6, H'-4); 2.81 (1H, m, H-β); 3.85 (1H, q, J = 6.6, MeCHPh); 4.06
(1H, m, H-3), 4.37 (1H, m, H-5); 6.90-6.97 (3H, m, H-o,p, N–C6H5), 7.20-7.40 (7H, m, CHC6H5, H-m, N–C6H5);
hydrochloride (CDCl3): 1.32 (3H, s, CH3CO); 1.41 (3H, d, J = 6.4, 5-CH3); 1.80 (1H, m, H-4); 1.85 (3H, d, J = 6.6,
γ-CH3); 1.90 (3H, d, J = 6.6, CH3CHPh); 1.96 (2H, m, H-α, H'-α); 2.05 (1H, dd, J = 12.7, J = 7.72, H'-4); 3.16
(1H, m, H-β); 4.00 (1H, m, MeCHPh); 4.33 (2H, m, H-3,5); 6.86-7.64 (10H, m, CHC6H5, N–C6H5); 9.93 (1H,
m, N–H); 10.23 (1H, m, N–H').
1
Minor diastereomer. H NMR spectrum, δ, ppm (J, Hz): 1.08 (3H, d, J = 6.4, γ-CH3); 1.22 (1H, m,
H-α); 1.36 (3H, d, J = 6.4, CH3CHPh); 1.43 (3H, d, J = 6.6, 5-CH3); 1.73, 1.79 (2H, m, H'-α, H-4); 2.00 (1H, m,
H'-4); 2.03 (3H, s, CH3CO); 2.93 (1H, m, H-β); 4.15 (1H, q, J = 6.5, MeCHPh); 4.22 (2H, m, H-3,5); 6.90-6.97
(3H, m, H-o,p, N–C6H5); 7.20-7.40 (7H, m, CHC6H5, H-m, N–C6H5). Found, %: C 68.67; H 8.24; N 10.31.
C23H31N3O·HCl. Calculated, %: C 68.72; H 8.02; N 10.45.
X-Ray Structural Investigation of a Crystal of Salt 4d grown in absolute ethyl acetate was carried
out on a SMART 1000 CCD 3-circle diffractometer (MoKα radiation, graphite monochromator, ω-scanning) at
120 K. The structure was solved by the direct method and refined on F2hkl by least squares in an anisotropic full
matrix approximation. The hydrogen atoms of the NH2 group were located from Fourier electron density
difference syntheses and refined in an isotropic approximation. The positions of H on C atoms were calculated
geometrically and were refined in an isotropic approximation according to the rider model with parameters
Uiso(Hi) = 1.2Ueq(Ci), for methyl groups Uiso(Hii) = 1.5 Ueq(Cii), where U(Ci) and U(Cii) are the equivalent
thermal parameters for the carbon atoms to which the appropriate H atoms are linked. Analysis of the Fourier
difference syntheses showed the presence of residual peaks of electron density with height reaching 3.86 e/Å3
and corresponding to randomized solvent (probably ethyl acetate used in the synthesis). Since refining the
randomization did not lead to realistic geometric parameters, the contribution of the solvent to structural
amplitudes was calculated with the aid of the SQUEEZE procedure [15]. On calculating the mass of the formula
unit, F(000), and the density, the presence of one molecule of ethyl acetate for one cation was taken into
consideration in the composition. The main crystallographic data and the refinement parameters are given in
Table 2. All the calculations were carried out with the SHELXTL PLUS set of programs [15]. The complete
crystallographic information has been deposited in the Cambridge Structural Data Bank (deposit No. CCDC
678483)
The work was carried out with the financial support of the Branch of Chemistry and Material Science of
the Russian Academy of Sciences (program No. 10, project "Directed Synthesis of Chiral Biogenic Amines
Containing an Azolidine Ring").
547

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