Synthesis of chiral aza crown ethers having exocyclic hydroxy groups and their use in asymmetric reduction of ketones with sodium tetrahydridoborate

Article abstract of DOI:10.1023/B:RUJO.0000003201.57627.ee

New chiral diaza crown ethers with exocyclic hydroxy groups were synthesized by reactions of (2S,3S)-1,4-dibenzyloxy-2,3-bis(2-oxiranylmethoxy) butane with N,N′-dibenzyl-1,2-ethanediamine and (4S,5S)-4,5- bis(benzylaminomethyl)-2,2-dimethyl-1,3-dioxolane. Catalytic debenzylation of the products gave the corresponding derivatives having secondary amino groups. The obtained diaza crown ethers, as well as some known crown ethers, were used as asymmetric catalysts in the reduction of pinacolone and acetophenone with sodium tetrahydridoborate in methylene chloride. Depending on the catalyst structure, the optical yield of the reduction products ranged from 5 to 90%.

Full text of DOI:10.1023/B:RUJO.0000003201.57627.ee

Russian Journal of Organic Chemistry, Vol. 39, No. 7, 2003, pp. 1042 1047. Translated from Zhurnal Organicheskoi Khimii, Vol. 39, No. 7, 2003,
pp. 1107 1112.
Original Russian Text Copyright
2003 by Luk’yanenko, Lobach, Leus.
Synthesis of Chiral Aza Crown Ethers Having
Exocyclic Hydroxy Groups and Their Use in Asymmetric
Reduction of Ketones with Sodium Tetrahydridoborate
N. G. Luk’yanenko, A. V. Lobach, and O. N. Leus
Bogatskii Physicochemical Institute, Ukrainian National Academy of Sciences,
Lyustdorfskaya doroga 86, Odessa, 65080 Ukraine
e-mail: ngl@farlep.net
Received July 29, 2002
Abstract New chiral diaza crown ethers with exocyclic hydroxy groups were synthesized by reactions of
(2S,3S)-1,4-dibenzyloxy-2,3-bis(2-oxiranylmethoxy)butane with N,N -dibenzyl-1,2-ethanediamine and (4S,5S)-
4,5-bis(benzylaminomethyl)-2,2-dimethyl-1,3-dioxolane. Catalytic debenzylation of the products gave the
corresponding derivatives having secondary amino groups. The obtained diaza crown ethers, as well as some
known crown ethers, were used as asymmetric catalysts in the reduction of pinacolone and acetophenone with
sodium tetrahydridoborate in methylene chloride. Depending on the catalyst structure, the optical yield of
the reduction products ranged from 5 to 90%.
One of the simplest procedures for the preparation
of chiral secondary alcohols is asymmetric hydride
reduction of unsymmetrical ketones in the presence
of chiral catalysts. This gave an impetus to extensive
studies on the enantioselectivity of ketone reduction
in two-phase systems involving various chiral phase-
transfer catalysts [1]. Such reactions were studied
most thoroughly in liquid liquid and liquid solid
systems with chiral quaternary ammonium salts and
conformationally rigid 1,1 -binaphthalene derivatives
[1 3]. Only a few examples have been reported on the
use of chiral crown ethers [4, 5] and aza crown ethers
[6, 7] as phase-transfer catalysts. In most cases,
secondary alcoholos were obtained with high chemical
yields (60 100%), but enantiomeric excess was as
a rule small (1 8% [4], 20 48% [7]) or absent [6].
Greater optical yields (25 65%) were achieved only
in the reduction of sterically hindered ketones in the
presence of aminoborane (NH3BH3) complexes with
chiral tetraphenyl-18-crown-6 [5].
In the reduction of ketones with sodium tetra-
hydridoborate in the presence of chiral ligands, pre-
ferential formation of one enantiomer is determined
by the presence of a chiral barrier in the ligand. This
leads to steric and hence energetic nonequivalence of
intermediate complexes formed with participation of
the ligand, reagent, and substrate. Therefore, efficient
enantiodifferentiation requires that the reagent (in our
case, tetrahydridoborate ion) sufferred the effect of
the ligand chiral barrier to the maximum possible
extent.
Crown ethers tend to complex formation with metal
cations. Here, tetrahydridoborate ion resides above the
macroring plane and does not form short contacts with
the macroring [8]. Therefore, it is difficult to expect
efficient enantiodifferentiation, for sodium cation is
in fact replaced by a bulkier crown ether sodium
cation complex, which should not affect appreciably
steric requirements of the reactive species, tetra-
hydridoborate ion. Thus, a necessary condition for
enantioselective reduction is the presence in a crown
ether molecule of additional groups which are capable
of binding tetrahydridoborate ion [2]. Such groups
may by hydroxy and amino [1, 2, 4, 7, 9, 10]. Accord-
ing to most published data, such groups were usually
located in the side chain of a chiral crown ether, so
that they were remote from the macroring to a longer
or shorter distance. As a result, the enantioselectivity
in reduction of ketones was poor.
In order to check out whether the above statement
is true and to search for new catalysts for asymmetric
hydride reduction of carbonyl compounds we syn-
thesized a series of new chiral diaza crown ethers
IV VI in which exocyclic hydroxy groups are
attached directly to the macrocyclic framework. The
resulting compounds were then tested for enantio-
1070-4280/03/3907-1042$25.00 2003 MAIK Nauka/Interperiodica

SYNTHESIS OF CHIRAL AZA CROWN ETHERS
1043
Scheme 1.
IV VI, X, R = PhCH2 (a), H (b).
selectivity in the reduction of some ketones with
sodium tetrahydridoborate. For comparison, we also
examined enantiodifferentiating properties in the same
reactions of chiral podands I and III and previously
described crown ethers VII, VIII, XI, and XII [11]
and aza crown ethers IX, Xa, and Xb [12] (Scheme 1).
The initial chiral compounds for the synthesis of aza
crown ethers IV VI were diol I [13] and diamine III.
Alkylation of diol I with 1-chloro-2,3-epoxypropane
under conditions of phase-transfer catalysis gave
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 7 2003

1044
LUK’YANENKO et al.
Reduction of pinacolone and acetophenone with sodium tetrahydridoborate in methylene chloride in the presence of
chiral ligands I and III XII
Reaction time, h
[ ]2D0, deg
Optical yield,a
%
Predominant enantiomer
3,3-dimethyl- 1-phenyl-
Ligand
no.
pinaco-
lone
aceto-
phenone
3,3-dimethyl- 1-phenyl-
3,3-dimethyl-
2-butanol
1-phenyl-
ethanol
2-butanol
ethanol
2-butanol
ethanol
I
III
68
74
14
8
11
8
57
66
13
6
10
7
0.5
0.8
0.5
6.2
5.4
6.9
6.3
6.5
1.3
2.1
3.2
4.2
4.8
1.5
2.5
2.1
3.0
6.5
10.4
64.9
80.5
70.1
89.6
81.8
84.4
16.9
27.3
41.6
54.5
62.3
19.5
32.5
4.9
7.0
S
R
R
S
R
S
S
R
S
S
R
S
R
S
S
S
S
S
IVa
IVb
Va
Vb
VIa
VIb
VII
VIII
IX
25.3
31.3
27.0
34.7
32.2
34.3
5.1
59.0
73.0
62.9
80.9
75.0
79.9
11.9
17.9
34.0
47.1
55.0
17.0
24.9
10
5
9
4
26
18
20
14
10
20
12
23
16
18
12
9
7.7
S
S
14.6
20.2
23.6
7.3
R
R
S
R
R
R
R
R
R
R
Xa
Xb
XI
17
10
XII
10.7
a
Ratio (in percent) of the specific rotation of the product to the specific rotation of the pure enantiomer; [ ]2D0 values of the pure
enantiomers of 3,3-dimethyl-2-butanol and 1-phenylethanol were assumed to be equal to 7.7 [16] and 42.9 [17], respectively.
diepoxy derivative II which reacted with N,N -diben-
zyl-1,2-ethanediamine or diamine III to afford the
corresponding diaza crown ethers IVa and Va. By
debenzylation of IVa and Va we obtained diaza
crown ethers IVb and Vb having secondary amino
groups. Deacetalization of Va yielded diaza crown
ether VIa, and its subsequent debenzylation afforded
compound VIb.
The catalytic activity and enantiodifferentiating
properties of compounds I and III XII were estimated
in the reduction of pinacolone and acetophenone with
sodium tetrahydridoborate in methylene chloride at
0 C. The amount of the catalyst was 10 mol % with
respect to the substrate. The time necessary for com-
plete conversion of the initial ketone was taken as
a measure of catalytic activity. In all cases, the yields
of 3,3-dimethyl-2-butanol and 1-phenylethanol were
no less than 97% (according to the GLC data). In the
absence of a catalyst, the yield of the alcohols did not
exceed 1%; therefore, the contribution of noncatalytic
process was neglected.
In the series of compounds IV XII, the lowest
catalytic activity was observed for crown ethers VII
and XI and aza crown ether IX which contain no
hydroxy groups. The presence of hydroxy groups in
the macroring considerably increases the reaction rate.
In this respect, illustrative are the data for compounds
VII and VIII, IX and Xa, and XI and XII. Aza crown
ethers are more efficient catalysts than nitrogen-free
analogs. Crown ethers IVb, Vb, VIb, and Xb with
secondary amino groups exhibit a higher catalytic
activity than those having tertiary nitrogen atoms
(IVa, Va, VIa, Xa). These data indicate participation
of the hydroxy and amino groups in the reduction
process. As shown previously, successful reduction of
carbonyl compounds with sodium tetrahydridoborate
in aprotic solvents in the presence of crown ethers
requires catalysis by proton-donor compounds (e.g.,
water or alcohols) [14]. Presumably, a similar catalytic
effect is produced by the hydroxy and amino groups
present in the aza crown ether molecule. An alter-
native explanation for the observed acceleration of
the reduction process in the presence of hydroxy or
amino macrocyclic compounds may be change of the
reagent nature as a result of the reaction of crown
ether with tetrahydridoborate ion, which could lead to
trihydroalkoxyborate or trihydroaminoborate ions.
All the examined crown and aza crown ethers
IV XII turned out to be superior to acyclic podands
I and III in the catalytic activity. This means that
cyclic structure is the determining factor in the forma-
tion of soluble complexes with the reagent (see table).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 7 2003

SYNTHESIS OF CHIRAL AZA CROWN ETHERS
1045
It should be emphasized that the relation between
the efficiency of asymmetric induction (optical yield)
and structural parameters of the compounds under
study is almost analogous to the relation observed
for their catalytic activity: (1) asymmetric induction
of cyclic compounds IV XII is considerably greater
than that observed for acyclic compounds I and III;
(2) in the series of cyclic compounds, asymmetric
induction caused by crown ethers VII, VIII, XI, and
XII is considerably less effective than that typical
of aza crown ethers IV VI, IX, and X; (3) the pres-
ence of exocyclic hydroxy groups increases the enan-
tioselectivity of the reaction (cf. VII and VIII; IX and
Xa; XI and XII); (4) aza crown ethers IVa, Va, VIa,
and Xa with tertiary amino groups give rise to a lower
asymmetric induction than those having secondary
amino groups (compounds IVb, Vb, VIb, and Xb;
see table).
It may be seen that the catalytic activity and the
magnitude of asymmetric induction for the examined
compounds is determined by the same or similar
factors. The most probable is formation of alkoxytri-
hydridoborate anions which are fixed in the close
vicinity to the chiral barrier of the macroring or
participation of hydroxy groups at asymmetric centers
of the molecule in hydride ion transfer. Nitrogen
atoms could stabilize the structure of intermediate
complex or transition state [1].
oxide (L 5/40 m, neutral; development with iodine
vapor). Glass columns charged with silica gel
(L 40/100 m) or Al2O3 (L 40/250 m, neutral) were
used for preparative liquid chromatography.
(2S,3S)-1,4-Bis(benzyloxy)-2,3-bis(2,3-epoxy-
propyloxy)butane (II). A solution of 6.0 g (20 mmol)
of (2S,3S)-1,4-bis(benzyloxy)-2,3-butanediol (I) [13]
in 5.9 g (64 mmol) of 1-chloro-2,3-epoxypropane was
added dropwise under vigorous stirring at 45 C to
a mixture of 9.4 g (102 mmol) of 1-chloro-2,3-epoxy-
propane, 4.8 g (120 mmol) of sodium hydroxide, 0.5 g
(28 mmol) of distilled water, and 0.14 g (0.4 mmol)
of tetrabutylammonium hydrogen sulfate. The mixture
was then stirred for 1.5 h at 40 C, cooled, and diluted
with 25 ml of benzene, and the precipitate was filtered
off and washed with benzene (2 5 ml). The filtrate
was combined with the washings and dried over
Na2SO4. The solvent and excess 1-chloro-2,3-epoxy-
propane were distilled off under reduced pressure, and
the residue was subjected to column chromatography
on silica gel (eluent hexane acetone, 3:1) to isolate
5.6 g (68%) of the product as a colorless oily sub-
stance. [ ]2D0 = +3.4 C (c = 2.5, CH3OH). H NMR
1
spectrum, , ppm: 2.59 2.81 m (4H, CH2, ring), 3.51
3.92 m (12H, CH2, CH), 4.55 s (4H, CH2Ph), 7.33 s
(10H, Ph). Found, %: C 69.47; H 7.21. M+ 414.
C24H30O6. Calculated, %: C 69.55; H 7.29. M 414.49.
N-Benzyl[(4S,5S)-5-benzylaminomethyl-2,2-di-
methyl-1,3-dioxolan-4-yl]methanamine (III). Di-
ethyl (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-dicar-
boxylate [15], 5.0 g (20 mmol), and benzylamine,
4.5 g (42 mmol), were added to a solution of 0.05 g
(2.2 mmol) of metallic sodium in 20 ml of anhydrous
methanol. The mixture was stirred for 3 h at room
temperature and was left overnight. The mixture was
then evaporated by half, and the precipitate was fil-
tered off. An equal volume of anhydrous diethyl ether
was added to the filtrate, and the precipitate was
filtered off and recrystallized from 8 ml of anhydrous
methanol to obtain 6.5 g (87%) of N,N -dibenzyl-
(4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbox-
Some of the examined diaza crown ethers having
exocyclic hydroxy groups, e.g., compounds IVb, Vb,
VIa, and VIb, showed a strong asymmetric induction
in the reduction of ketones with sodium tetrahydrido-
borate; therefore, they are promising as catalysts for
asymmetric synthesis of alcohols.
EXPERIMENTAL
1
The H NMR spectra were recorded on a Bruker
AM-250 spectrometer (250 MHz) using CDCl3 as
solvent and HMDS as internal reference. The mole-
cular weights were determined from the mass spectra
which were obtained on Varian MAT-112 and MKh-
1321 instruments with direct sample admission into
the ion source (electron impact, 20 70 eV). The
optical rotations ([ ]2D0) were measured on a Perkin
Elmer 241MC polarimeter. GLC analysis was per-
formed on a Chrom-5 chromatograph equipped with
a flame-ionization detector; glass column, 1200
3 mm; stationary phase 5% of SE-30 on Inerton AW-
DMCS (0.100 0.125 mm); carrier gas helium. Thin-
layer chromatography was performed on Silufol plates
(development with a solution of ninhydrin in diethyl
ether) and glass plates with a fixed layer of aluminum
amide. Colorless crystals, mp 167 168 C. [ ]D20
=
1
+6.7 (c = 1.0, CH3OH). H NMR spectrum, , ppm:
1.32 s (6H, CH3), 3.96 t (4H, CH2Ph), 4.20 4.42 m
(2H, CH), 7.11 7.43 m (12H, NH, Ph). Found, %:
C 68.34; H 6.45; N 7.71. M+ 368. C21H24N2O4.
Calculated, %: C 68.46; H 6.57; N 7.60. M 368.43.
A 6.2-g (17-mmol) amount of N,N -dibenzyl-
(4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbox-
amide was added in small portions under vigorous
stirring in an argon atmosphere to a suspension of
1.4 g (37 mmol) of lithium aluminum hydride in
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 7 2003

1046
LUK’YANENKO et al.
25 ml of anhydrous THF. The mixture was stirred for
4 h, heated for 4 h under reflux, and left overnight.
It was then cooled with ice, 1.4 ml of ice water was
added, the precipitate was filtered off and was shaken
with THF (2 10 ml), and the suspension was filtered.
The filtrates were combined and dried over NaOH,
the solvent was distilled off under reduced pressure,
and the residue was subjected to column chromatog-
raphy on silica gel (eluent chloroform methanol,
10:1) to isolate 4.2 g (73%) of compound III as
a colorless oily substance. [ ]2D0 = +12.6 (c = 2.5,
oxolo[4,5-j][1,4,8,13]dioxadiazacyclohexadecane-
7,14-diol (Va) was synthesized as described above for
diaza crown ether IVa from 3.8 g (9.2 mmol) of com-
pound II and 3.1 g (9.2 mmol) of diamine III in
a mixture of 46 ml of THF and 46 ml of ethanol.
Yield 4.9 g (71%). Colorless oily substance. [ ]D20
=
+19.6 (c = 1.0, CH3OH). 1H NMR spectrum, , ppm:
1.25 s (6H, CH3), 2.32 2.85 m (8H, NCH2), 3.24
4.10 m (20H, OCH2, OCH, NCH2Ph), OH), 4.40 s
(4H, OCH2Ph), 7.10 7.32 m (20H, Ph). Found, %:
C 71.42; H 7.89; N 3.65. M+ 754. C45H58N2O8. Cal-
culated, %: C 71.59; H 7.74; N 3.71. M 754.95.
1
CH3OH). H NMR spectrum, , ppm: 1.30 s (6H,
CH3), 2.72 2.90 m (4H, NCH2), 3.21 br.s (2H, NH),
3.90 t (4H, CH2Ph), 4.10 4.22 m (2H, CH), 7.09 s
(10H, Ph). Found, %: C 74.21; H 8.20; N 8.16.
M+ 340. C21H28N2O2. Calculated, %: C 74.08;
H 8.29; N 8.23. M 340.46.
(3aS,10S,11S,17aS)-10,11-Bis(hydroxymethyl)-
2,2-dimethylperhydro[1,3]dioxolo[4,5-j][1,4,8,13]di-
oxadiazacyclohexadecane-7,14-diol (Vb) was syn-
thesized as described above for diaza crown ether IVb
by hydrogenation of 0.9 g (1.2 mmol) of compound
Va in 10 ml of anhydrous methanol in the presence of
150 mg of 10% Pd/C. Yield 461 mg (98%). Colorless
oily substance. [ ]2D0 = +11.7 (c = 1.0, CH3OH).
1H NMR spectrum, , ppm: 1.28 s (6H, CH3), 2.20
2.92 m (10H, NCH2, NH), 3.15 3.96 m (18H, OCH2,
OCH, OH). Found, %: C 51.59; H 8.52; N 7.18.
M+ 394. C17H34N2O8. Calculated, %: C 51.76;
H 8.69; N 7.10. M 394.46.
(2S,3S)-8,11-Dibenzyl-2,3-bis(benzyloxymethyl)-
1,4-dioxa-8,11-diazacyclotetradecane-6,13-diol
(IVa). A solution of 1.8 g (4.3 mmol) of compound
II and 1.0 g (4.3 mmol) of N,N -dibenzyl-1,2-ethane-
diamine in a mixture of 22 ml of THF and 22 ml of
ethanol was heated for 8 h under reflux. The solvents
were distilled off under reduced pressure, and the
residue was subjected to column chromatography on
neutral Al2O3 (eluent chloroform benzene 2-prop-
anol methanol, 8:3:0.3:0.3) to isolate 1.9 g (68%)
of compound IVa as a colorless oily substance.
(2S,3S,10S,11S)-8,13-Dibenzyl-2,3-bis(benzyl-
oxymethyl)-1,4-dioxa-8,13-diazacyclohexadecane-
6,10,11,15-tetraol (VIa). Methanol and acetone were
slowly distilled off (over a period of 3 h) from a solu-
tion of 3.0 g (4 mmol) of acetal Va in a mixture
of 4.5 ml of 2 N hydrochloric acid and 20 ml of
methanol. The mixture was cooled, 3.8 ml of a 20%
aqueous solution of sodium hydrogen carbonate was
added, and the mixture was throroughly stirred and
extracted with benzene (5 10 ml). The extract was
dried over Na2SO4, and the solvent was distilled off
under reduced pressure to obtain almost pure com-
pound VIa as a colorless oily substance. Yield 2.5 g
1
[ ]2D0 = +12.2 (c = 1.0, CH3OH). H NMR spectrum,
, ppm: 2.18 2.82 m (8H, NCH2), 3.08 3.85 m (18H,
OCH2, OCH, NCH2Ph, OH), 4.36 s (4H, OCH2Ph),
7.03 7.29 m (20H, Ph). Found, %: C 73.25; H 7.59;
N 4.20. M + 654. C40H50N2O6. Calculated, %:
C 73.37; H 7.70; N 4.28. M 654.84.
(2S,3S)-2,3-Bis(hydroxymethyl)-1,4-dioxa-8,11-
diazacyclotetradecane-6,13-diol (IVb). A stream of
hydrogen was passed over a period of 2 h through
a suspension of 225 mg of 10% Pd/C in 15 ml of
anhydrous methanol. Crown ether IVa, 1.2 g
(1.8 mmol), was then added, and the mixture was
stirred for 16 h in a stream of hydrogen. The catalyst
was filtered and washed with methanol (2 5 ml),
and the solvent (methanol and toluene formed in the
reaction) was distilled off under reduced pressure.
Diaza crown ether IVb was isolated as a colorless
oily substance. Yield 523 mg (97%). [ ]2D0 = +7.3
(88%). [ ]2D0 = +13.4 (c = 1.0, CH3OH). H NMR
1
spectrum, , ppm: 2.24 2.88 m (8H, NCH2), 3.28
4.03 m (22H, OCH2, OCH, NCH2Ph, OH), 4.37 s
(4H, OCH2Ph), 7.08 7.27 m (20H, Ph). Found, %:
C 70.68; H 7.74; N 3.79. M+ 714. C42H54N2O8. Cal-
culated, %: C 70.56; H 7.61; N 3.92. M 714.89.
(2S,3S,10S,11S)-2,3-Bis(hydroxymethyl)-1,4-di-
oxa-8,13-diazacyclohexadecane-6,10,11,15-tetraol
(VIb) was synthesized as described above for diaza
crown ether IVb by hydrogenation of 1.7 g
(2.4 mmol) of compound VIa in 15 ml of anhydrous
methanol in the presence of 300 mg of 10% Pd/C.
1
(c = 1.0, CH3OH). H NMR spectrum, , ppm: 2.25
2.98 m (10H, NCH2, NH), 3.18 3.90 m (16H, CH2,
OCH, OH). Found, %: C 49.15; H 8.79; N 9.43.
M+ 294. C12H26N2O6. Calculated, %: C 48.97;
H 8.90; N 9.52. M 294.34.
(3aS,10S,11S,17aS)-5,16-Dibenzyl-10,11-bis-
(benzyloxymethyl)-2,2-dimethylperhydro[1,3]di-
Yield 809 mg (96%). Colorless oily substance. [ ]D20
=
+22.5 (c = 1.0, CH3OH). 1H NMR spectrum, , ppm:
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 7 2003

SYNTHESIS OF CHIRAL AZA CROWN ETHERS
1047
2.15 2.79 m (10H, NCH2, NH), 3.10 3.97 m (20H,
OCH2, OCH, OH). Found, %: C 47.34; H 8.41;
N 7.99. M + 354. C14H30N2O8. Calculated, %:
C 47.45; H 8.53; N 7.90. M 354.40.
5. Atwood, B.L., Shahriari-Zavareh, H., Stoddart, J.F.,
and Williams, D.J., J. Chem. Soc., Chem. Commun.,
1984, p. 1461.
6. Horner, L. and Gerhard, J., Justus Liebigs Ann.
Chem., 1978, no. 5, p. 710.
Asymmetric reduction. A mixture of 0.5 mmol
of appropriate ligand and 0.38 g (10 mmol) of sodium
tetrahydridoborate in 50 ml of methylene chloride was
cooled to 0 C under stirring, and a solution of 0.5 g
(5 mmol) of pinacolone or 0.6 g (5 mmol) of aceto-
phenone in 5 ml of methylene chloride was added.
The mixture was stirred at 0 C until the initial ketone
disappeared completely (GLC), unreacted sodium
tetrahydridoborate was filtered off and washed with
methylene chloride (2 5 ml), and the filtrate was
combined with the washings, washed with water until
neutral reaction, and dried over Na2SO4. The solvent
was distilled off under atmospheric pressure, and
the residue was subjected to column chromatography
on silica gel using pentane diethyl ether (5:2) as
eluent to isolate enantiomeric alcohol mixture; its
specific rotation [ ]D20 was measured (see table).
7. Zhdanov, Yu.A., Alekseev, Yu.E., Korol’, E.L.,
Sudareva, T.P., and Alekseeva, V.G., Russ. J. Gen.
Chem., 1993, vol. 63, p. 1045.
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Bulychev, B.M., and Gusev, A.I., Dokl. Akad. Nauk
SSSR, 1985, vol. 285, p. 129.
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J. Chem. Soc., Chem. Commun., 1983, p. 469.
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bach, D., Chem. Ber., 1980, vol. 113, p. 1619.
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Nazarova, N.Yu., and Karpenko, L.P., Zh. Org.
Khim., 1988, vol. 24, p. 324.
12. Luk’yanenko, N.G., Lobach, A.V., Nazarova, N.Yu.,
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 7 2003