Synthesis of new chiral schiff bases from (+)-3-carene and their use in asymmetric oxidation of sulfides catalyzed by metal complexes

Article abstract of DOI:10.1134/S1070428009060037

A number of new chiral Schiff bases were synthesized starting from accessible monoterpene (+)-3-carene, and the products were used as ligands in metal complex-catalyzed oxidation of sulfides to chiral sulfoxides. The optical purity and the sign of optical rotation of chiral sulfoxides were found to strongly depend on the oxidation temperature. Pleiades Publishing, Ltd., 2009.

Full text of DOI:10.1134/S1070428009060037

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2009, Vol. 45, No. 6, pp. 815–824. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © E.A. Koneva, K.P. Volcho, D.V. Korchagina, N.F. Salakhutdinov, A.G. Tolstikov, 2009, published in Zhurnal Organicheskoi
Khimii, 2009, Vol. 45, No. 6, pp. 832–841.
Synthesis of New Chiral Schiff Bases from (+)-3-Carene
and Their Use in Asymmetric Oxidation of Sulfides
Catalyzed by Metal Complexes
E. A. Konevaa, K. P. Volchoa, D. V. Korchaginaa, N. F. Salakhutdinova, and A. G. Tolstikovb
a Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 9, Novosibirsk, 630090 Russia
e-mail: volcho@nioch.nsc.ru
b Boreskov Institute of Catalysis, Siberian Division, Russian Academy of Sciences, Novosibirsk, Russia
Received July 28, 2008
Abstract—A number of new chiral Schiff bases were synthesized starting from accessible monoterpene
(+)-3-carene, and the products were used as ligands in metal complex-catalyzed oxidation of sulfides to chiral
sulfoxides. The optical purity and the sign of optical rotation of chiral sulfoxides were found to strongly depend
on the oxidation temperature.
DOI: 10.1134/S1070428009060037
In the past few decades, asymmetric metal complex
catalysis has become one of the most promising fields
of fine organic synthesis. Variation of metal (Mn, Al,
Co, V, Cr) and chiral ligand made it possible to obtain
indispensable catalysts for asymmetric synthesis [1–4].
Chiral Schiff bases derived from substituted salicyl-
aldehydes are widely used as chiral ligands in metal
complex catalysis [5–8]. These ligands ensured suc-
cessful asymmetric reactions, in particular catalytic
hydrophosphorylation [7], addition of carbon dioxide
to epoxypropane [5], condensation of nitromethane
with aldehydes (nitroaldol reaction) [4], asymmetric
sulfoxidation [2], etc.
The recent interest in asymmetric metal complex-
catalyzed sulfoxidation has been stimulated by wide
application of optically active sulfoxides in asym-
metric synthesis [9–11] and by the fact that a number
of natural compounds contain a chiral sulfoxide group.
Moreover, some sulfoxides with a definite configura-
tion showed high biological activity [12–15]. Taking
into account the above stated, development of effective
procedures for the synthesis of chiral sulfoxides has
attracted strong attention. Among known methods, one
of the most convenient is asymmetric oxidation of pro-
chiral sulfides in the presence of vanadium-containing
metal complex systems [16].
Schiff bases derived from differently substituted sali-
cylaldehydes [17, 18]; in almost all cases, derivatives
of optically active amino acids were used as chiral
auxiliaries [16, 19–21]. We recently showed [22, 23]
that some terpenoids, in particular accessible (+)- and
(–)-α-pinenes (I), can be used as source of chirality in
the synthesis of optically active Schiff bases IIIa–IIIk.
A number of new chiral Schiff bases IIIa–IIIk were
synthesized from various substituted salicylaldehydes
and amino alcohols (+)- and (–)-II which were
prepared from the corresponding optically active
pinenes according to the procedure reported in [24]
(Scheme 1). Schiff bases IIIa–IIIk were successfully
used as ligands in vanadium-catalyzed asymmetric
oxidation of methylsulfanylbenzene [22] (which is
often used as model compound) and heterocyclic
sulfide IV which is precursor of optically active
Omeprazole (V) [25] (Scheme 2). The S enantiomer of
Omeprazole (Esomeprazole) is a highly efficient anti-
ulcer drug [26].
Compound IIIa turned out to be the most effective
ligand in the asymmetric oxidation of methylsulfanyl-
benzene [22], whereas the best results in the synthesis
of optically active Omeprazole (V) were achieved
using Schiff base IIIb [25]. These data demonstrate
that there are no universal ligands equally suitable for
the oxidation of any sulfide and that a broad series of
ligands with different structures should be disposable
As follows from numerous publications on asym-
metric catalysis, the ligand structure was varied using
815

KONEVA et al.
816
Scheme 1.
R1
Me
R2
R3
OH
Me
Me
N
R3
R2
CHO
HO
HO
Me
R1
NH2
Me
IIIa–IIIj
OH
CHO
Me
Me
(+)-I
Me
Me
Me
OH
Me
Me
N
(–)-II
HO
HO
IIIk
Me
Me
Me
R1 = R3 = t-Bu, R2 = H (a); R1 = R2 = R3 = H (b); R1 =
, R2 = H, R3 = Me (c); R1 = R3 = PhC(Me)2, R2 = H (d); R1 =
R2 = H, R3 = NO2 (e); R1 = R3 = NO2, R2 = H (f); R1 = R2 = H, R3 = OMe (g); R1 = OMe, R2 = R3 = H (h); R1 = R3 = H, R2 =
NEt2 (i); R1 = Br, R2 = H, R3 = NO2 (j).
to develop effective procedures for asymmetric oxida-
tion of complex sulfides.
We have synthesized compound XI from (+)-3-car-
ene (VI), following the above procedure [27]. The
reaction of (+)-3-carene (VI) with chlorosulfonyl iso-
cyanate was carried out in diethyl ether at room tem-
perature. After treatment of the reaction mixture with
an aqueous solution of sodium sulfite and recrys-
tallization from hexane, we isolated compound VII in
50% yield. Lactam VII was then treated with di-tert-
butyl dicarbonate in anhydrous tetrahydrofuran in the
presence of a catalytic amount of N,N-dimethylpyri-
din-4-amine (DMAP), and subsequent purification by
column chromatography quantitatively afforded com-
pound VIII which was subjected to methanolysis in
the presence of sodium methoxide; the yield of com-
pound IX was 95%.
The goal of the present study was to synthesize new
chiral Schiff bases on the basis of substituted salicyl-
aldehydes and an accessible optically active mono-
terpene, (+)-3-carene (VI), and examine the efficiency
of the products as ligands in metal complex-catalyzed
asymmetric oxidation of methylsulfanylbenzene.
Gyónfalvi et al. [27] described a procedure for the
synthesis of (+)-amino alcohol XI from (+)-3-carene
(VI). In the first step, optically active monoterpene
reacted with chlorosulfonyl isocyanate to give β-lac-
tam VII (Scheme 3). Acid hydrolysis of compound
VII was impossible because of its low stability in acid
medium. Therefore, the NH group was activated via
introduction of tert-butoxycarbonyl group. The subse-
quent methanolysis of Boc-protected lactam VIII,
hydrolysis of IX, and reduction of ester X gave amino
alcohol XI [27].
We tried to reproduce the procedure reported in
[27] for removal of tert-butoxycarbonyl protecting
group from compound IX. However, the reaction of IX
with trifluoroacetic acid in methylene chloride at room
temperature was accompanied by strong tarring. We
Scheme 2.
MeO
MeO
O
Me
OMe
Me
OMe
N
N
[O]
S
S
N
H
N
H
Me
Me
N
N
IV
(S)-V
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 6 2009

SYNTHESIS OF NEW CHIRAL SCHIFF BASES FROM (+)-3-CARENE
817
Scheme 3.
Boc
Me
H
Me
Me
N
N
O
O
(1) ClSO2NCO
(2) Na2SO3–H2O
Boc2O, DMAP
Me
Me
Me
Me
VI
Me
Me
VII
VIII
Boc
Me
O
O
Me NH2
Me
NH
NH2
CF3COOH
LiAlH4
MeOH, MeONa
OMe
OMe
OH
Me
Me
Me
Me
Me
Me
IX
X
XI
succeeded in minimizing tar formation by lowering the
temperature to 0°C; by column chromatography we
isolated 57% of compound X. Reduction of the latter
with lithium tetrahydridoaluminate gave amino alcohol
XI in 68% yield.
were precipitated from diethyl ether with hexane, and
2-hydroxy-3,5-dinitrobenzaldehyde derivative XIId
was recrystallized from diethyl ether.
We previously found that, unlike all other alde-
hydes, 2-hydroxy-3,5-dinitrobenzaldehyde reacted
with amino alcohol (–)-II to give a mixture of tricyclic
compound XIII as the major product and expected
Schiff base IIIf (Scheme 5); the ratio XIII:IIIf was
1:0.6 at 28°C [22]. However, the product obtained
from (+)-3-carene (VI) and the same aldehyde had the
structure of Schiff base XIId, whereas compound XIIe
derived from 2-hydroxy-5-methoxybenzaldehyde con-
tained an appreciable amount (~23% at 28°C) of tri-
cyclic structure XIV (Scheme 6). According to the
1H NMR data, closure of oxazine ring occurred to
some extent (up to 10%) in the synthesis of Schiff
bases XIIc and XIIf; compounds XIIa and XIIb were
formed only as open-chain isomers.
By condensation of amino alcohol XI with sub-
stituted salicylaldehydes we synthesized new chiral
Schiff bases XIIa–XIIg (Scheme 4). The reaction rate
and method for purification of the product strongly
depended on the initial aldehyde. Schiff bases XIIb–
XIIf and XIIg were synthesized by stirring a mixture
of the reactants in anhydrous methanol at room tem-
perature for 2.5 to 24 h, while the reaction of amino
alcohol XI with 3,5-di-tert-butyl-2-hydroxybenzalde-
hyde required heating under reflux over a period of
7 days to obtain Schiff base XIIa. Compounds XIIa
and XIIb were purified by column chromatography on
silica gel, chiral Schiff bases XIIc and XIIe–XIIg
Scheme 4.
17
18
R2
19 22
17 16
16
R1
CHO
15
R1
21
18
15 20
OH
OH
Me
13
14
14
NH2
13
OH
12
OH
OH
R2
CHO
N
N
Me
8 Me
11
Me
3
6
OH
OH
2
1
4
5
Me
Me
9Me
7
Me
Me10
XIIg
XIIa–XIIf
XI
R1 = R2 = t-Bu (a), H (b), O2N (d); R1 = H, R2 = O2N (c), MeO (e); R1 = MeO, R2 = H (f).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 6 2009

KONEVA et al.
818
Scheme 5.
O2N
O2N
Me
NO2
OH
NO2
NO2
NH2
Me
OH
OH
OH
+
HN
O
Me
Me
N
Me
O2N
CHO
OH
Me
Me
Me
Me
(–)-II
IIIf
XIII
Scheme 6.
Me
Me
Me
Me
Me
NH
OMe
Me
OMe
N
O
HO
XIIe
HO
HO
XIV
We can conclude that Schiff bases derived from
amino alcohol of the pinane series and their 3-carene-
based analogs display radically different relations be-
tween electronic effects of substituents in the benzene
ring and the ability to form tricyclic oxazine structure.
Closure of oxazine ring in compounds IIIa–IIIk
requires the presence of two strongly acceptor groups,
while the formation of cyclic structure from Schiff
bases XIIa–XIIg is favored by donor substituents in
the benzene ring.
Both lowering the temperature to 0°C and heating to
30°C (Table 1; run nos. 2, 3) resulted in reduced
enantioselectivity. Replacement of methylene chloride
as solvent by chloroform led to almost complete loss
of enantioselectivity.
It should be emphasized that the reaction tempera-
ture affects not only ee value but also configuration
of the major stereoisomer. Analogous temperature de-
pendence of enantiomeric excess was observed previ-
ously in asymmetric oxidation of aryl methyl sulfides
in the presence of various metal complex systems, in
particular in the oxidation of 4-methylsulfanyltoluene
with Ti(OPr-i)4–(+)-diethyl tartrate–H2O–t-BuOOH
[28] and of methylsulfanylbenzene (XV) in the pres-
ence of vanadium complex with ligand IIIa [22]. In
these cases, both reduction and rise in temperature
relative to some optimal value impaired the optical
purity.
New chiral Schiff bases XIIa–XIIg derived from
accessible optically active (+)-3-carene (VI) were
tested as ligands in vanadium-catalyzed asymmetric
oxidation of methylsulfanylbenzene (XV). The oxida-
tion conditions were optimized using Schiff base XIIb
as model ligand. Under the optimal conditions en-
suring the best enantioselectivity in the asymmetric
oxidation of XV (Scheme 7) in the presence of Schiff
bases derived from α-pinene (I) (room temperature,
solvent methylene chloride, oxidant 70% hydrogen
peroxide) [22] we obtained sulfoxide XVI with
an ee (enantiomeric excess) value of 20% (Table 1).
Figure shows the relation between the optical purity
of sulfoxide XVI and reaction temperature in the
oxidation catalyzed by VO(acac)2–IIIa–H2O2 [22] and
VO(acac)2–XIIb–H2O2. Analogous relation was re-
Scheme 7.
O
S
O
O
SMe
S
[O], VO(acac)2, XIIb
Me
Me
+
XV
(S)-XVI
XVII
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 6 2009

SYNTHESIS OF NEW CHIRAL SCHIFF BASES FROM (+)-3-CARENE
819
Table 1. Asymmetric oxidation of methylsulafanylbenzene (XV) in the presence of Schiff base XIIb
Yield,b %
XVII
Reaction Temperature,
time, h
Conversion,
%
XVI,c
ee, %
Run no.
Oxidanta
Solvent
oC
XVI
1
2
3
4
70% H2O2
70% H2O2
70% H2O2
70% H2O2
1.5
3.0
1.0
2.0
20
00
30
20
CH2Cl2
CH2Cl2
CH2Cl2
CHCl3
100
100
100
068
80
85
91
90
20
15
09
10
20 (S)
11 (R)
05 (R)
03 (S)
a
b
c
Molar ratio VO(acac)2–XIIb–XV–H2O2 1:1.5:106:132.
Calculated on the reacted sulfide XV (according to the 1H NMR data).
1
The optical purity of sulfoxide XVI was determined by H NMR spectroscopy using (R)-(-)-3,5-dinitro-N-(1-phenylethyl)benzamide
as chiral shift reagent. The absolute configuration was determined by comparing the sign of optical rotation of the product with
published data.
ported in [28]; presumably, the presence of a maxi-
mum on the curve given therein results from change of
the oxidation mechanism.
α-pinene (I), introduction of two nitro groups resulted
in reversal of configuration of the major stereoisomer
(Table 2, run no. 3).
Change of the sign of optical rotation of the product
was observed only in the presence of Schiff base XIIb
as ligand. This dependence may be interpreted assum-
ing that the oxidation process involves two concurrent
pathways. One of these leads to preferential formation
of the R isomer, and its enantioselectivity only slightly
depends on the temperature. By contrast, enantioselec-
tivity of the second process which leads to the S isomer
strongly depends on the temperature. The final result is
determined by relative contributions of the above proc-
esses, and it may show strong temperature dependence:
the corresponding curve has a clearly defined maxi-
mum. Such assumption makes it possible to rational-
ize, at least partially, moderate enantioselectivity in the
oxidation of sulfide XV.
The newly synthesized Schiff base ligands are
characterized by considerably different steric hin-
drances created by substituents in the vicinity of the
active center, as well as by different electronic factors,
which makes them promising for searching optimal
conditions for asymmetric oxidation of complex
sulfides.
EXPERIMENTAL
1
The H and 13C NMR spectra were recorded on
Bruker DRX-500 and AM-400 spectrometers (500.13
1
and 400.13 MHz for H and 125.76 and 100.61 MHz
for 13C, respectively) from solutions in CDCl3–CCl4
(~1:1, by volume) or acetone-d6. The chemical shifts
were measured relative to the solvent signals (CHCl3,
δ 7.24 ppm; CDCl3, δC 76.90 ppm; acetone-d5,
δ 2.04 ppm; acetone-d6, δC 29.8 ppm). The product
With a view to elucidate the effect of the nature and
size of substituents in the aromatic ring of the ligand,
oxidation of compound XV was performed in the pres-
ence of Schiff bases XIIa and XIIc–XIIg under the
conditions indicated in Table 1, run no. 1. Introduction
of tert-butyl groups into the ortho and para positions
with respect to the hydroxy group (compound XIIa)
considerably reduced the optical purity of sulfoxide
XVI (to 9%). Lower ee value was also obtained with
the use of 2-hydroxynaphthyl derivative XIIg (Table 2,
run no. 6). The oxidation in the presence of Schiff
bases containing both electron-withdrawing (nitro
group in the para position; Table 2, run no. 2) and
electron-donating groups in the aromatic ring (me-
thoxy group in the para or ortho position; Table 2, run
nos. 4, 5) gave almost racemic sulfoxide XVI. The cor-
responding ee values (1–2%) approach the experimen-
tal error. As in the oxidation with ligands based on
1
structure was determined by analysis of the H NMR
40 ee, %
1
2
20
10
T, °C
–30
–20
–10
10
20
40
–10
–20
Plots of the optical purity of methyl phenyl sulfoxide XVI
versus temperature in the oxidation of methylsulfanylben-
zene with the catalytic systems (1) VO(acac)2–IIIa–H2O2
[22] and (2) VO(acac)2–XIIb–H2O2.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 6 2009

KONEVA et al.
820
Table 2. Asymmetric oxidation of methylsulfanylbenzene (XV) in the presence of compounds XIIa and XIIc–XIIg
as ligandsa
Yield,b %
Run no. Compound no. Reaction time, h
Conversion, %
ee,c %
XVI
XVII
1
2
3
4
5
6
XIIa
XIIc
XIId
XIIe
XIIf
XIIg
3.0
1.5
2.5
1.0
1.0
1.5
078
100
099
100
100
100
96
81
88
82
83
86
04
19
12
18
17
14
9 (S)
1 (S)
6 (R)
0 (S)
1 (S)
4 (S)
a
b
c
Molar ratio VO(acac)2–ligand–XV–H2O2 1:1.5:106:132; temperature 20°C; solvent methylene chloride, 5 ml.
Calculated on the reacted sulfide XV (according to the 1H NMR data).
1
The optical purity of sulfoxide XVI was determined by H NMR spectroscopy using (R)-(-)-3,5-dinitro-N-(1-phenylethyl)benzamide
as chiral shift reagent. The absolute configuration was determined by comparing the sign of optical rotation of the product with
published data.
1
spectra using H–1H double resonance technique,
Compound VII, 3.040 g (17 mmol), was dissolved
JMOD 13C NMR spectra, off-resonance 13C NMR
in 25 ml of anhydrous tetrahydrofuran, 0.5 ml of tri-
ethylamine, 7.270 g (33 mmol) of di-tert-butyl di-
carbonate, and a catalytic amount of N,N-dimethyl-
pyridin-4-amine were added, and the mixture was
diluted with 25 ml of anhydrous THF, stirred for 0.5 h,
and heated for 3 h under reflux. The solvent was
distilled off, and the residue was purified by column
chromatography on silica gel using hexane–ethyl
acetate (0 to 100% of the latter, gradient elution) to
isolate 1.823 g of initial compound VII (conversion
62%) and 1.953 g of tert-butyl (1R,3R,5S,7S)-4,4,7-tri-
methyl-9-oxo-8-azatricyclo[5.2.0.03,5]nonane-8-car-
boxylate (VIII) (quantitative yield calculated on the
spectra, and two-dimensional H–13C correlation spec-
1
1
tra (direct coupling constants, C–H COSY, JCH
=
135 Hz). The high-resolution mass spectra were ob-
tained on a Finnigan MAT-8200 instrument. The spe-
cific optical rotations [α]580 and [α]589 were measured
on Polamat A and PolAAr 3005 polarimeters, respec-
tively.
The purity of the initial compounds and reaction
products was checked by GLC on a Varian Model
3700 gas chromatograph equipped with a flame ioniza-
tion detector (ZB-5 quartz capillary column, 30000×
0.25 mm; carrier gas helium, inlet pressure 1 atm).
1
reacted compound VII). The H NMR spectrum of
{(1R,3R,4S,6S)-4-Amino-4,7,7-trimethylbicyclo-
[4.1.0]heptan-3-yl}methanol (XI). 3-Carene (VI,
VIII coincided with that reported in [27].
22
580
Compound VIII, 2.508 g (9 mmol), was dissolved
in 10 ml of anhydrous methanol, a catalytic amount of
sodium methoxide was added under stirring, and the
mixture was stirred for 3 h. The solvent was distilled
off, and the residue was treated with water and ex-
tracted with chloroform. The extract was dried over
MgSO4 and evaporated to isolate 2.664 g (95%) of
methyl (1R,3R,4S,6S)-4-(tert-butoxycarbonylamino)-
4,7,7-trimethylbicyclo[4.1.0]heptane-3-carboxylate
89%; [α]
= +10.14°, c = 2.5, CHCl3), 6.420 g
(47 mmol), was dissolved in 50 ml of anhydrous di-
ethyl ether, 5.3 ml (61 mmol) of chlorosulfonyl iso-
cyanate was added dropwise under stirring and cooling
with an ice bath, and additional 50 ml of anhydrous
diethyl ether was added. The cooling bath was re-
moved, and the mixture was stirred for 24 h. A solution
of 10 g of Na2SO3 in 132 ml of water was added, and
the mixture was adjusted to pH ~7–8 by adding 20%
aqueous sodium hydroxide and stirred for 3 h. The
organic phase was separated, and the aqueous phase
was extracted with diethyl ether. The extracts were
combined with the organic phase and dried over
MgSO4, the solvent was distilled off, and the residue
was recrystallized from hexane. We thus isolated
4.223 g (50%) of (1R,3R,5S,7S)-4,4,7-trimethyl-8-aza-
1
(IX) whose H NMR spectrum coincided with that re-
ported in [27].
A solution of 0.430 g (1.4 mmol) of compound IX
in 20 ml of methylene chloride was cooled in an ice
bath, 1.1 ml of trifluoroacetic acid was added, and the
mixture was stirred for 3 h on cooling, neutralized with
a saturated aqueous solution of sodium hydrogen car-
bonate, and extracted with methylene chloride (2×
65 ml). The extract was dried over MgSO4 and evap-
tricyclo[5.2.0.03,5]nonan-9-one (VII) whose H NMR
spectrum coincided with that reported in [27].
1
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 6 2009

SYNTHESIS OF NEW CHIRAL SCHIFF BASES FROM (+)-3-CARENE
821
orated, and the residue was purified by column chro-
matography on silica gel (gradient elution with
hexane–ethyl acetate, 0 to 100% of the latter) to isolate
0.170 g (57%) of methyl (1R,3R,4S,6S)-4-amino-
4,7,7-trimethylbicyclo[4.1.0]heptane-3-carboxylate
(XIIb). A solution of 0.034 g (0.28 mmol) of 2-hy-
droxybenzaldehyde in 5 ml of anhydrous methanol
was added dropwise under stirring to a solution of
0.053 g (0.29 mmol) of compound XI in 4 ml of an-
hydrous methanol, and the mixture was stirred for 6 h.
When the reaction was complete (TLC, hexane–ethyl
acetate, 3:4), the solvent was distilled off, and the
1
(X) whose H NMR spectrum coincided with that
reported in [27].
product was purified as described above for compound
A solution of 0.170 g (0.81 mmol) of compound X
in 3 ml of tetrahydrofuran was added dropwise under
stirring to a suspension of 0.064 g (1.7 mmol) of
LiAlH4 in 4 ml of anhydrous THF on cooling with
an ice bath. The cooling bath was removed, the
mixture was stirred for 3.5 h and cooled again, and
water was added dropwise under stirring and cooling
until hydrogen no longer evolved. The precipitate was
22
XIIa. Yield 0.042 g (53%), [α] = +52.6° (c = 0.6,
580
1
CHCl3). H NMR spectrum (CDCl3–CCl4), δ, ppm:
1.00 s and 1.02 s (C9H3, C10H3), 1.32 s (C8H3), 0.69–
0.90 m (1-H, 6-H), 1.35–1.41 m (2-H), 1.52–1.71 m
2
(4-H, 5-H), 1.80 d.d (5′-H, J = 15, J5′, 4 = 7 Hz),
2
1.97 d.d (2′-H, J = 15, J2′,1 = 9 Hz), 3.33 d.d (11-H,
2J = 11, J11,4 = 5.5 Hz), 3.60 d.d (11′-H, J = 11, J11′,4
=
=
2
1
5.5 Hz), 6.78 d.d.d (17-H, J17,16 = J17,18 = 7.5, J17,15
filtered off. Yield of XI 0.100 g (68%); its H NMR
1.2 Hz), 6.86 br.d (15-H, J15,16 = 8 Hz), 7.21 d.d (18-H,
J18,17 = 7.5, J18,16 = 2 Hz), 7.24 d.d.d (16-H, J16,15 = 8,
J16,17 = 7.5, J16,18 = 2 Hz), 8.36 s (12-H). 13C NMR
spectrum (CDCl3–CCl4), δC, ppm: 17.80 d (C1), 35.45 t
(C2), 59.05 s (C3), 45.09 d (C4), 21.20 t (C5), 19.03 d
(C6), 17.55 s (C7), 24.49 q (C8), 15.35 q (C9), 28.83 q
(C10), 64.66 t (C11), 161.17 d (C12), 118.73 s (C13),
162.67 s (C14), 117.65 d (C15), 132.29 d (C16), 117.75 s
(C17), 131.42 s (C18). Found: m/z 287.19030 [M]+.
C18H25NO2. Calculated: M 287.18852.
spectrum coincided with that reported in [27].
2,4-Di-tert-butyl-6-[(1S,3S,4R,6R)-4-hydroxy-
methyl-3,7,7-trimethylbicyclo[4.1.0]heptan-3-yl-
iminomethyl]phenol (XIIa). A solution of 0.098 g
(0.42 mmol) of 3,5-di-tert-butyl-2-hydroxybenzalde-
hyde in 3 ml of anhydrous methanol was filtered and
added dropwise under stirring to a solution of 0.073 g
(0.40 mmol) of compound XI in 5 ml of anhydrous
methanol, and the mixture was heated for 7 days under
reflux. When the reaction was complete (TLC, hex-
ane–ethyl acetate, 3:4), the solvent was distilled off,
and the residue was purified by column chromatog-
raphy on silica gel [gradient elution with hexane (con-
taining 1% of triethylamine)–chloroform, 0 to 100%
2-[(1S,3S,4R,6R)-4-Hydroxymethyl-3,7,7-tri-
methylbicyclo[4.1.0]heptan-3-yliminomethyl]-4-
nitrophenol (XIIc). A solution of 0.047 g (0.28 mmol)
of 2-hydroxy-5-nitrobenzaldehyde in 5 ml of anhy-
drous methanol was added dropwise under stirring to
a solution of 0.057 g (0.31 mmol) of amino alcohol XI
in 4 ml of anhydrous methanol, and the mixture was
stirred for 2.5 h. When the reaction was complete
(TLC, hexane–ethyl acetate, 3:4), the solvent was dis-
tilled off, and the product was purified by reprecip-
of the latter]. Yield 0.079 g (49%), orange crystals,
22
mp 155–161°C, [α]
= +1.5° (c = 1.9, MeOH).
580
1H NMR spectrum (CDCl3–CCl4), δ, ppm: 0.69 m
(1-H), 0.72 m (6-H), 1.02 s (C9H3, C10H3), 1.03 s
(C8H3), 1.32 s and 1.45 s (t-Bu), 1.37 m (2-H), 1.43 m
2
(4-H), 1.63 d.d.d (5-H, J = 15.0, J5,4 = 12.5, J5,6
7.0 Hz), 1.85 d.d (5′-H, J = 15.0, J5′,4 = 6.5 Hz),
2.07 d.d (2′-H, J = 15.0, J2′,1 = 9.0 Hz), 3.42 d.d
(11-H, J = 10.5, J11,4 = 6.0 Hz), 3.78 d.d (11′-H, J =
10.5, J11′,4 = 5.5 Hz), 7.12 d (18-H, J18,16 = 2.5 Hz),
=
2
itation from diethyl ether with hexane. Yield 0.097 g
2
22
580
(96%), yellow crystals, mp 162–164°C, [α]
=
2
2
1
+116.7° (c = 0.08, CHCl3). H NMR spectrum
(CDCl3–CCl4), δ, ppm: 0.77 d.d.d (1-H, J1,2′ = 9.4,
J1,6 = 9.1, J1,2 = 5.1 Hz), 0.83 d.d (6-H, J6,1 = 9.1,
J6, 5′ = 7.6 Hz), 0.96 s (C9H3), 1.01 s (C10H3),
1.33 d.d.d.d (4-H, J4,5′ = 12.5, J4,5 = 6.7, J4,11 = 4.4,
J4,11′ = 4.0 Hz), 1.38 d.d (2-H, J = 15.4, J2,1 = 5.1 Hz),
13
7.37 d (16-H, J16,18 = 2.5 Hz), 8.46 s (12-H). C NMR
spectrum (CDCl3–CCl4), δC, ppm: 17.87 d (C1), 34.39 t
(C2), 58.83 s (C3), 45.09 d (C4), 21.23 t (C5), 18.95 d
(C6), 17.29 s (C7), 25.43 q (C8), 15.19 q (C9), 28.80 q
(C10), 64.90 t (C11), 162.43 d (C12), 117.96 s (C13),
158.48 s (C14), 136.70 s and 139.39 s (C15, C17),
126.47 d (C16), 125.88 d (C18), 34.97 s (C19, C20), 29.32 q
and 31.43 q (CH3, t-Bu). Found: m/z 399.31316
[M]+. C26H41NO2. Calculated: M 399.31371.
2
1.48 s (C8H3), 1.69 d.d (5-H, J = 15.3, J5,4 = 6.7 Hz),
2
1.83 d.d.d (5′-H, J = 15.3, J5′,4 = 12.5, J5′,6 = 7.6 Hz),
2
2.21 d.d (2′-H, J = 15.4, J2′,1 = 9.4 Hz), 3.48 d.d
2
(11-H, J = 11.2, J11,4 = 4.4 Hz), 3.62 d.d (11′-H,
2J = 11.2, J11′,4 = 4.0 Hz), 6.57 d (15-H, J15,16
=
2-[(1S,3S,4R,6R)-4-Hydroxymethyl-3,7,7-tri-
methylbicyclo[4.1.0]heptan-3-yliminomethyl]phenol
9.7 Hz), 7.97 d.d (16-H, J16,15 = 9.7, J16,18 = 2.9 Hz),
8.21 d (18-H, J18, 16 = 2.9 Hz), 8.29 br.s (12-H),
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 6 2009

KONEVA et al.
822
22
1
14.96 br.s (OH). 13C NMR spectrum (CDCl3–CCl4),
δC, ppm: 17.24 d (C1), 34.20 t (C2), 59.59 s (C3),
43.73 d (C4), 20.22 t (C5), 18.80 d (C6), 18.06 s (C7),
24.35 q (C8), 15.00 q (C9), 28.64 q (C10), 62.82 t (C11),
162.52 d (C12), 113.71 s (C13), 177.86 s (C14), 122.71 d
(C15), 131.99 d (C16), 135.02 s (C17), 129.63 d (C18).
titative, [α] = +73.9° (c = 0.5, CHCl3). H NMR
580
spectrum (CDCl3–CCl4), δ, ppm: 0.71 d.d.d (1-H,
J1,6 = J1,2′ = 9.4, J1,2 = 4.8 Hz), 0.77 d.d (6-H, J6,1
=
9.4, J6,5 = 7.8 Hz), 1.01 s (C9H3), 1.02 s (C10H3), 1.31 s
(C8H3), 1.36 d.d (2-H, J = 15.0, J2,1 = 4.8 Hz), 1.41 m
2
2
(4-H), 1.59 d.d.d (5-H, J = 14.7, J5,4 = 11.9, J5,6
7.8 Hz), 1.81 d.d (5′-H, J = 14.7, J5′,4 = 6.7 Hz),
1.96 d.d (2′-H, J = 15.0, J2′,1 = 9.4 Hz), 3.33 d.d
=
1
2
The H NMR spectrum of XIIc indicated the presence
2
of a small amount (~6%) of cyclic tautomer (analogous
to XIV); it contained a singlet at δ 5.43 ppm assignable
to 12-H in the cyclic structure. Found: m/z 332.1724
[M]+. C18H24N2O4. Calculated: M 332.17306.
2
2
(11-H, J = 10.8, J11,4 = 5.9 Hz), 3.61 d.d (11′-H, J =
10.8, J11′,4 = 5.7 Hz), 3.76 s (OCH3), 6.74 d (18-H,
J18,16 = 3.0 Hz), 6.82 d (15-H, J15,16 = 8.9 Hz), 6.86 d.d
(16-H, J16,15 = 8.9, J16,18 = 3.0 Hz), 8.34 s (12-H).
13C NMR spectrum (CDCl3–CCl4), δC, ppm: 17.89 d
(C1), 35.50 t (C2), 59.20 s (C3), 45.25 d (C4), 21.26 t
(C5), 19.09 d (C6), 17.53 s (C7), 24.56 q (C8), 15.35 q
(C9), 28.85 q (C10), 64.85 t (C11), 160.82 d (C12),
118.49 s (C13), 156.01 s (C14), 118.01 d (C15), 119.37 d
(C16), 151.74 s (C17), 114.78 d (C18), 55.76 q (C19).
2-[(1S,3S,4R,6R)-4-Hydroxymethyl-3,7,7-trimeth-
ylbicyclo[4.1.0]heptan-3-yliminomethyl]-4,6-dini-
trophenol (XIId). A solution of 0.065 g (0.31 mmol)
of 3,5-dinitrosalicylaldehyde in 5 ml of anhydrous
methanol was added dropwise under stirring to a solu-
tion of 0.063 g (0.34 mmol) of compound XI in 4 ml
of anhydrous methanol, and the mixture was stirred for
4.5 h. When the reaction was complete (TLC, hexane–
ethyl acetate, 3:4), the solvent was distilled off, and
the product was recrystallized from diethyl ether. Yield
0.073 g (62%), orange crystals, mp 255–260°C,
1
Tautomer XIV. H NMR spectrum (CDCl3–CCl4),
δ, ppm: 0.52 d.d.d (1-H, J1,2′ = 9.5, J1,6 = 9.2, J1,2
5.0 Hz), 0.68 d.d.d (6-H, J6,1 = 9.2, J6,5′ = 8.8, J6,5
=
=
1.2 Hz), 0.86 s (C9H3), 0.99 s (C10H3), 1.14 d.d (2-H,
22
580
1
2J = 15.4, J2, 1 = 5.0 Hz), 1.36 s (C8H3), 1.64 d.d.d
[α] = +27.1° (c = 0.14, CHCl3). H NMR spectrum
2
(acetone-d6), δ, ppm: 0.85–0.93 m (1-H, 6-H), 1.03 s
(5-H, J = 15.3, J5, 4 = 8.5, J5, 6 = 1.2 Hz), 1.90 d.d
(2′-H, J = 15.4, J2′,1 = 9.5 Hz), 2.27 d.d.d (5′-H, J =
15.3, J5′,6 = 8.8, J5′,4 = 8.8 Hz), 3.61 s (OCH3), 4.21 d.d
(C9H3, C10H3), 1.50 d.d.d.d (4-H, J4,5′ = 12.5, J4,5 = 6.8,
2
2
2
J4,11′ = 4.0, J4,11 = 3.8 Hz), 1.54 d.d (2-H, J = 15.5,
2
2
J2,1 = 4.8 Hz), 1.63 s (C8H3), 1.80 d.d (5-H, J = 15.4,
(11-H, J = 11.5, J11,4 = 2.1 Hz), 5.42 s (12-H), 6.71 d
2
J5,4 = 6.8 Hz), 2.00 d.d.d (5′-H, J = 15.4, J5′,4 = 12.5,
(18-H, J = 3.0 Hz); signals from the other protons were
overlapped by those of the major isomer. 13C NMR
spectrum (CDCl3–CCl4), δC, ppm: 15.13 d (C1), 33.97 t
(C2), 48.53 s (C3), 34.44 d (C4), 18.58 t (C5), 17.74 d
(C6), 17.15 s (C7), 24.76 q (C8), 15.41 q (C9), 28.13 q
(C10), 67.94 t (C11), 80.59 d (C12), 125.00 s (C13),
152.73 s (C14), 115.29 and 117.04 d (C15, C16), 149.10 s
(C17), 111.16 d (C18), 55.65 q (C19). Found: m/z
317.1981 [M]+. C19H27NO3. Calculated: M 317.19855.
2
J5′,6 = 7.6 Hz), 2.45 d.d (2′-H, J = 15.5, J2′,1 = 9.4 Hz),
2
3.54 d.d (11-H, J = 11.3, J11,4 = 3.8 Hz), 3.78 d.d
2
(11′-H, J = 11.2, J11′,4 = 4.0 Hz), 8.67 d (18-H, J18,16
=
3.2 Hz), 8.72 d (16-H, J16,18 = 3.2 Hz), 8.94 br.s (12-H),
14.59 br.s (OH). 13C NMR spectrum (acetone-d6), δC,
ppm: 17.80 d (C1), 34.02 t (C2), 61.38 s (C3), 43.87 d
(C4), 20.46 t (C5), 19.47 d (C6), 18.67 s (C7), 24.03 q
(C8), 15.19 q (C9), 28.92 q (C10), 62.87 t (C11), 165.66
d (C12), 118.35 s (C13), 171.11 s (C14), 131.05 s (C15),
127.54 d (C16), 142.09 s (C17), 137.52 d (C18). Found:
m/z 377.1578 [M]+. C18H23N3O6. Calculated:
M 377.1581.
2-[(1S,3S,4R,6R)-4-Hydroxymethyl-3,7,7-trimeth-
ylbicyclo[4.1.0]heptan-3-yliminomethyl]-6-methox-
yphenol (XIIf). A solution of 0.044 g (0.29 mmol) of
2-hydroxy-3-methoxybenzaldehyde in 5 ml of anhy-
drous methanol was added dropwise under stirring to
a solution of 0.059 g (0.32 mmol) of compound XI in
4 ml of anhydrous methanol, and the mixture was
stirred for 24 h. When the reaction was complete
(TLC, hexane–ethyl acetate, 3:4), the solvent was dis-
tilled off, and the product was purified by reprecip-
2-[(1S,3S,4R,6R)-4-Hydroxymethyl-3,7,7-trimeth-
ylbicyclo[4.1.0]heptan-3-yliminomethyl]-4-methox-
yphenol (XIIe). A solution of 0.042 g (0.28 mmol) of
2-hydroxy-5-methoxybenzaldehyde in 5 ml of anhy-
drous methanol was added dropwise under stirring to
a solution of 0.057 g (0.31 mmol) of compound XI in
4 ml of anhydrous methanol, and the mixture was
stirred for 24 h. When the reaction was complete
(TLC, hexane–ethyl acetate, 3:4), the solvent was dis-
tilled off, and the product was purified by reprecip-
itation from diethyl ether with hexane. Yield quan-
itation from diethyl ether with hexane. Yield quanti-
tative, yellow crystals, mp 133–135°C, [α] = +55.7°
(c = 0.13, CHCl3). H NMR spectrum (CDCl3–CCl4),
δ, ppm: 0.72 d.d.d (1-H, J1,2′ = 10.0, J1,6 = 9.5, J1,2
22
580
1
=
5.0 Hz), 0.87 d.d (6-H, J6,1 = 9.5, J6,5 = 8.80 Hz), 0.98 s
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 6 2009

SYNTHESIS OF NEW CHIRAL SCHIFF BASES FROM (+)-3-CARENE
823
(C9H3), 1.00 s (C10H3), 1.34 s (C8H3), 1.35 d.d (2-H,
2J = 15.0, J2,1 = 5.0 Hz), 1.38 m (4-H), 1.63 d.d.d (5-H,
2J = 14.8, J5,4 = 11.8, J5,6 = 8.0 Hz), 1.77 d.d (5′-H,
Asymmetric oxidation of methylsulfanylbenzene
(XV). A mixture of 2 mg (8 μmol) of VO(acac)2 and
12 μmol of the corresponding ligand in 2 ml of anhy-
drous solvent was stirred until it became homogeneous
(~20 min), a solution of 0.105 g (847 μmol) of sulfide
XV in 3 ml of the same solvent was added, and the
mixture was cooled if necessary. The corresponding
oxidant, 1060 μmol, was then added, and the progress
of the reaction was monitored by GLC. When the reac-
tion was complete, 10 ml of distilled water was added
to the mixture, the organic layer was separated, and the
aqueous phase was extracted with appropriate solvent
(2×5 ml). The extracts were combined with the or-
ganic phase, washed with water (2×10 ml), and dried
over MgSO4, the drying agent was filtered off, and the
solvent was distilled off on a rotary evaporator. The
substrate conversion and product ratio were deter-
2
2J = 14.8, J5′,4 = 6.9 Hz), 1.96 d.d (2′-H, J = 15.0,
2
J2′,1 = 10.0 Hz), 3.32 d.d (11-H, J = 10.8, J11,4
=
2
5.5 Hz), 3.56 d.d (11′-H, J = 10.8, J11′,4 = 5.9 Hz),
3.86 s (OCH3), 6.64 t (17-H, J = 7.9 Hz), 6.78–6.82 m
(16-H, 18-H), 8.27 s (12-H). 13C NMR spectrum
(CDCl3–CCl4), δC, ppm: 17.59 d (C1), 35.61 t (C2),
58.79 s (C3), 45.00 d (C4), 20.98 t (C5), 18.86 d (C6),
17.59 s (C7), 24.26 q (C8), 15.33 q (C9), 28.65 q (C10),
64.56 t (C11), 161.02 d (C12), 117.80 s (C13), 149.38 s
(C14), 155.75 s (C15), 113.23 d C16), 116.27 d (C17),
1
123.15 d (C18), 55.72 q (C19). The H NMR spectrum
of XIIf also contained a singlet at δ 5.42 ppm, which
may be assigned (by analogy with compound XIV) to
12-H of the cyclic tautomer (~9%). Found: m/z
317.1987 [M]+. C19H27NO3. Calculated: M 317.19855.
1
mined by H NMR spectroscopy. The enantiomeric
1
1-[(1S,3S,4R,6R)-4-Hydroxymethyl-3,7,7-trimeth-
ylbicyclo[4.1.0]heptan-3-yliminomethyl]naphtha-
len-2-ol (XIIg). A solution of 0.046 g (0.27 mmol) of
2-hydroxy-1-naphthaldehyde in 5 ml of anhydrous
methanol was added dropwise under stirring to a solu-
tion of 0.056 g (0.31 mmol) of amino alcohol XI in
4 ml of anhydrous methanol, and the mixture was
stirred for 3.5 h. When the reaction was complete
(TLC, hexane–ethyl acetate, 3:4), the solvent was dis-
tilled off, and the product was purified by reprecip-
excess was determined from the H NMR spectrum
(CCl4–CDCl3) recorded in the presence of an equal
amount of (R)-(–)-3,5-dinitro-N-(1-phenylethyl)ben-
zamide.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 06-03-32052).
REFERENCES
itation from diethyl ether with hexane. Yield 0.041 g
1. Handbook of Chiral Chemicals, Ager, D., Ed., Boca
22
(45%), green–yellow crystals, mp 172–175°C, [α]
=
580
Raton: Taylor & Francis, 2006, 2nd ed.
+157.9° (c = 0.4, CHCl3). 1H NMR spectrum (CDCl3–
2. Tolstikov, A.G., Tolstikov, G.A., Ivshina, I.B., Grish-
ko, V.V., Tolstikova, O.V., Glushkov, V.A., Khlebni-
kov, T.B., Salakhutdinov, N.F., and Volcho, K.P., Sovre-
mennye problemy asimmetricheskogo sinteza (Current
Problems in Asymmetric Synthesis), Yekaterinburg:
Ural. Otd. Ross. Akad. Nauk, 2003.
CCl4), δ, ppm: 0.83 d.d.d (1-H, J1,2′ = J1,6 = 9.6, J1,2
5.0 Hz), 0.95 d.d.d (6-H, J6,1 = 9.6, J6,5′ = 7.0, J6,5
=
=
1.8 Hz), 0.99 s (C9H3), 1.05 s (C10H3), 1.38 d.d (2-H,
2J = 15.0, J2,1 = 5.0 Hz), 1.38 m (4-H), 1.51 s (C8H3),
2
1.70–1.84 m (2H, 5-H), 2.17 d.d (2′-H, J = 15.0,
J2′,1 = 9.6 Hz), 3.49 d.d (11-H, 2J = 10.8, J11,4 = 5.0 Hz),
3. Pavlov, V.A., Tetrahedron, 2008, vol. 64, p. 1147.
4. Baleizao, C. and Garcia, H., Chem. Rev., 2006, vol. 106,
2
3.60 d.d (11′-H, J = 10.8, J11′,4 = 5.6 Hz), 6.82 d
p. 3987.
(15-H, J15,16 = 9.4 Hz), 7.14 d.d.d (18-H, J18,17 = 7.8,
J18,19 = 7.0, J18,20 = 1.0 Hz), 7.34 d.d.d (19-H, J19,20
8.2, J19,18 = 7.0, J19,17 = 1.4 Hz), 7.52 d.d (17-H,
J17,18 = 7.8, J17,19 = 1.4 Hz), 7.59 d (16-H, J16,15
=
5. Berkessel, A. and Brandenburg, M., Org. Lett., 2006,
vol. 8, p. 4401.
=
6. Ternois, J., Guillen, F., Plaquevent, J.-C., and
Coquerel, G., Tetrahedron: Asymmetry, 2007, vol. 18,
p. 2959.
9.4 Hz), 7.74 br.d (20-H, J20,19 = 8.2 Hz), 8.72 br.s
13
(12-H), 14.72 br.s (OH). C NMR spectrum (CDCl3–
CCl4), δC, ppm: 17.29 d (C1), 35.14 t (C2), 57.11 s (C3),
44.44 d (C4), 20.51 t (C5), 18.77 d (C6), 17.99 s (C7),
24.74 q (C8), 15.24 q (C9), 28.66 q (C10), 63.84 t (C11),
153.49 d (C12), 106.07 s (C13), 178.84 s (C14), 126.13 d
(C15), 137.63 d (C16), 129.25 d (C17), 122.24 d (C18),
127.83 d (C19), 117.21 d (C20), 134.40 s (C21), 125.84 s
(C22). Found: m/z 337.2034 [M]+. C22H27NO2. Calcu-
lated: M 337.2036.
7. Saito, B., Egami, H., and Katsuki, T., J. Am. Chem. Soc.,
2007, vol. 129, p. 1978.
8. Kowalczyk, R., Sidorowicz, L., and Skarzewski, J.,
Tetrahedron: Asymmetry, 2007, vol. 18, p. 2581.
9. Carreno, M.C., Chem. Rev., 1995, vol. 95, p. 1717.
10. Posner, G.H., The Chemistry of Sulphones and Sulphox-
ides, Patai, S., Rappoport, Z., and Stirling, C.J.M., Eds.,
Chichester: Wiley, 1988, p. 55.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 6 2009

KONEVA et al.
824
11. Mikolajczyk, M., Drabowicz, J., and Kielbasiński, P.,
Chiral Sulfur Reagents: Applications in Asymmetric and
Stereoselective Synthesis, Boca Raton: CRC, 1997.
21. Jeong, Y.-C., Huang, Y.D., Choi, S., and Ahn, K.-H.,
Tetrahedron: Asymmetry, 2005, vol. 16, p. 3497.
22. Koneva, E.A., Volcho, K.P., and Korchagina, D.V., Izv.
Ross. Akad. Nauk, Ser. Khim., 2008, p. 105.
12. Yunusov, S.Yu., Alkaloids, Tashkent: FAN, 1981, p. 212.
13. Takaishi, Y., Murakami, Y., Uda, M., Ohashi, T., Hama-
mura, N., Kido, M., and Kadota, S., Phytochemistry,
1997, vol. 45, p. 997.
14. Hogan, P.J., Hopes, P.A., Moss, W.O., Robinson, G.E.,
and Patel, I., Org. Process Res. Dev., 2002, vol. 6,
p. 225.
23. Khomenko, T.M., Salomatina, O.V., Kurbakova, S.Yu.,
Il’ina, I.V., Volcho, K.P., Komarova, N.I., Korchagi-
na, D.V., Salakhutdinov, N.F., and Tolstikov, A.G., Russ.
J. Org. Chem., 2006, vol. 42, p. 1653.
24. Szakonyi, Z., Martinek, T., Hetenyi, A., and Fülöp, F.,
Tetrahedron: Asymmetry, 2000, vol. 11, p. 4571.
15. Cotton, H., Elebring, T., Larsson, M., Li, L., Soren-
sen, H., and von Unge, S., Tetrahedron: Asymmetry,
2000, vol. 11, p. 3819.
25. Klimova, E.A., Volcho, K.P., Korchagina, D.V., Koma-
rova, N.I., Kochnev, A.I., Salakhutdinov, N.F., and Tol-
stikov, A.G., Abstracts of Papers, Vserossiiskaya nauch-
naya konferentsiya “Sovremennye problemy organiche-
skoi khimii” (All-Russian Scientific Conf. “Current
Problems in Organic Chemistry”), Novosibirsk, 2007.
16. Volcho, K.P., Salakhutdinov, N.F., and Tolstikov, A.G.,
Russ. J. Org. Chem., 2003, vol. 39, p. 1537.
17. Zeng, Q., Wang, H., Weng, W., and Lin, W., New J.
Chem., 2005, vol. 29, p. 1125.
26. Lindberg, P., Brändström, A., Wallmark, B., Matt-
sson, H., Rikner, L., and Hoffman, K.-J., Med. Res.
Rev., 1990, vol. 10, p. 1.
18. Barbarini, A., Maggi, R., Muratori, M., and Sartori, G.,
Tetrahedron: Asymmetry, 2004, vol. 15, p. 2473.
27. Gyónfalvi, S., Szakonyi, Z., and Fülöp, F., Tetrahedron:
Asymmetry, 2003, vol. 14, p. 3965.
19. Gluszynska, A., Krajewska, K., and Rozwadowska, M.,
Pol. J. Chem., 2003, vol. 77, p. 1703.
28. Pitchen, P., Dunach, T., Desmukh, N.N., and Ka-
20. Jeong, Y.-C., Choi, S., Hwang, Y.D., and Ahn, K.-H.,
Tetrahedron Lett., 2004, vol. 45, p. 9249.
gan, H.B., J. Am. Chem. Soc., 1984, vol. 106, p. 8188.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 6 2009