Synthesis of chiral polydentate ligands and the use of their titanium complexes as pre-catalysts for the asymmetric trimethylsilylcyanation of benzaldehyde

Article abstract of DOI:10.1007/s11172-008-0266-6

A number of polydentate ligands based on enantiomerically pure binaphthol have been synthesized. The ligand complexes with titanium isopropoxide were used as catalysts for the asymmetric addition of trimethylsilyl cyanide to benzaldehyde. A fragment with axial chirality is responsible for the configuration of O-trimethylsilyl cyanohydrin product. In the case of the optimum ligand based on (R)-binaphthol and (S)-leucinol, an enantiomeric excess of 86% and quantitative yield were achieved in 4 h.

Full text of DOI:10.1007/s11172-008-0266-6

Russian Chemical Bulletin, International Edition, Vol. 57, No. 9, pp. 1981—1988, September, 2008
1981
Synthesis of chiral polydentate ligands
and the use of their titanium complexes as preꢀcatalysts
for the asymmetric trimethylsilylcyanation of benzaldehyde
Yu. N. Belokon,a D. A. Chusov,a T. V. Skrupskaya,a D. A. Bor'kin,a L. V. Yashkina,a K. A. Lyssenko,a
M. M. Il'in,a T. V. Strelkova,a G. I. Timofeeva,a A. S. Peregudov,a and M. Northb
aA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6356. Eꢀmail: yubel@ineos.ac.ru
bSchool of Natural Sciences and University Research Centre in Catalysis
and Intensified Processing, Bedson Building, University of Newcastle,
Great Britain, Newcastle Upon Tyne
A number of polydentate ligands based on enantiomerically pure binaphthol have been
synthesized. The ligand complexes with titanium isopropoxide were used as catalysts for the
asymmetric addition of trimethylsilyl cyanide to benzaldehyde. A fragment with axial chirality is
responsible for the configuration of Oꢀtrimethylsilyl cyanohydrin product. In the case of
the optimum ligand based on (R)ꢀbinaphthol and (S)ꢀleucinol, an enantiomeric excess of 86%
and quantitative yield were achieved in 4 h.
Key words: asymmetric catalysis, titanium complexes, cyanohydrins, trimethylsilyl cyanide,
benzaldehyde.
The role of asymmetric catalysis is difficult to overestiꢀ
mate. Nowadays, many pharmaceutical drugs are proꢀ
duced using chiral catalysts.1 Despite the fact that the
preparation and application of synthetic asymmetric cataꢀ
lysts is rapidly developing, as never before, only an insigꢀ
nificant portion of synthetic catalytic systems can comꢀ
pete with natural catalysts, enzymes, in activity or enantiꢀ
oselectivity.1 A narrow substrate specificity, limited choice
of solvents and reaction conditions can be considered as
the disadvantages of enzyme catalysis.1 It is obvious that
development of synthetic asymmetric system possessing
the advantages of the enzyme catalysts whilst lacking their
disadvantages seems to be rather promising.
All the ligands were synthesized from (R)ꢀ or (S)ꢀ3,3´ꢀdiꢀ
An important property of enzymes is that both the subꢀ
strate and the reagent are simultaneously activated in their
active center.2 Note that many metalloenzymes contain
two metal ions in their active center.3—5 One of the reasons
of such organization can be the mutual fixation and actiꢀ
vation of two reagents in those centers. Earlier, we have
reported on the development of highly efficient binuclear
titanium(IV) complex obtained from the hexadentate ligand
1 and Ti(OPri)4. The activity of such a binuclear catalyst
considerably exceeds the activity of the mononuclear anaꢀ
log in terms of both TOF and stereodifferentiating ability.6
The present work deals with a search for optimum substitꢀ
uents in ligand 1.
formylꢀ2,2´ꢀdihydroxyꢀ1,1´ꢀbinaphthyl ((Ra)ꢀ2 or (Sa)ꢀ2)
and the corresponding aminoalcohols or (S)ꢀvaline. Each
enantiomer of dialdehyde 2 was obtained from the binaphꢀ
thol 3 enantiomers (Scheme 1).
Aminoalcohols 6—11 were synthesized from the corꢀ
responding aminoacids by reduction (Scheme 2) or by reꢀ
action with the Grignard reagent (Scheme 3).
The condensation of dialdehydes 2 with 2 equiv. of
aminoalcohols 6—11 led to the formation of the bisꢀSchiff
bases 12—21 (Scheme 4).
The catalysts were obtained in situ by mixing the Schiff
base with 2 equiv. of titanium isopropoxide. The molecular
mass of complex 22, obtained by the reaction of Schiff
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1946—1953, September, 2008.
1066ꢀ5285/08/5709ꢀ1981 © 2008 Springer Science+Business Media, Inc.

1982
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
Belokon et al.
Scheme 1
Scheme 4
Reagents: i. 1) NaH/DMF, 2) MOMCl; ii. 1) BuLi/Et2O,
2) DMF; iii. HCl/THF.
Compound
12, 18
R1
Me
R2
H
Compound
15
R1
But
R2
H
Scheme 2
13, 19
14, 20
Bui
Bus
H
H
16, 21
H
17
H
Ph
i. Δ, benzene—ethanol.
case binuclear complex 23 was formed, as was confirmed
by Xꢀray analysis (Fig. 1, Table 1).
Complex 23 crystallized as a solvate with two chloroꢀ
form molecules. The titanium atoms in compound 23 are
hexacoordinated. Their coordination polyhedron can be
described as a distorted octahedron and a degree of distorꢀ
tion in the case of the Ti(1) atom is considerably higher,
namely, the equatorial planes N(1), N(2´), O(1), O(2)
and N(1´), N(2), O(1´), O(2´) are distorted by 0.004 and
0.12 Å, respectively. In addition to the change in degree of disꢀ
tortion of the coordination polyhedron, variation of the bond
distances was also observed for the Ti(1) and Ti(2) atoms.
i. LiAlH4/THF.
R = Me (6), Bui (7), Bus (8), But (9),
(10)
Scheme 3
i. PhMgBr/THF.
base 1 with a 2ꢀfold excess of titanium isopropoxide, was
determined by an ultracentrifugation method (see Experiꢀ
mental). It corresponded to the molecular mass of comꢀ
pound 22, in which there were two fragments of the Schiff
base 1 and four titanium atoms.
Attempted synthesis of a similar complex from (S)ꢀvaꢀ
line and dialdehyde (Ra)ꢀ2 was unsuccessful. In this case,
it was impossible to incorporate more than one titanium
molecule per binaphthol residue, however, even in this

Precatalysts for addition of Me3SiCN to benzaldehyde Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
1983
Table 2. Reaction of asymmetric addition of trimethylsilyl cyaꢀ
nide to benzaldehydea
Entry
Ligand
Degree of
conversionb
eec
(product configuration)
%
1
2
3
4
5
6
7
8
12
18
16
21
17
13
14
19
20
15
1
94
>99
88
56
17
>99
94
>99
>99
90
>99
>99
>99
>99
>99
68 (R)
58 (S)
44 (R)
18 (S)
27 (R)
86 (R)
83 (R)
37 (S)
40 (S)
81 (R)
86 (R)
38 (R)
5 (R)
The distortions and changes in geometry of the moleꢀ
cule observed are apparently caused by the steric overloꢀ
ading of the molecules. In fact, a shortened contact
C(4)...C(4´) (3.301(1) Å) was observed for the two naphꢀ
thalene rings in the complex, the length of which is conꢀ
siderably less than the sum of the van der Waals radii
for carbon atoms. The geometries of two binaphthol ligands
in compound 23 are close. In particular, the turning angle
of two naphthalene ligands is 107.7 and 106.9°. In addiꢀ
tion to steric factors, effects of crystal packing can also
have an influence on the geometry of the complex. Both
solvate molecules in the crystal form shortened contacts
with the ester groups with the distances O...Cl being
2.924(1)—2.942(1) Å.
Despite the fact that the complex based on valine posꢀ
sessed catalytic activity, its stereodifferentiating ability
turned out to be extremely low. During the standard time
at +4 °C, mandelonitrile was formed in quantitative yield
but in only 5% enantiomeric excess (Table 2, entry 15).
When ligand 12 based on (S)ꢀalaninol and (R)ꢀbinaphꢀ
thol was used, formation of the product with (R)ꢀconfiguꢀ
ration and enantiomeric purity of 68% was observed
(see Table 2, entry 1). In the case of ligand 18 differing
only in configuration of the binaphthol fragment, product
with enantiomeric purity of 58% but having (S)ꢀconfiguꢀ
ration was obtained (see Table 2, entry 2). To sum up, it is
obvious that comparatively small size of the methyl group
in diastereoisomers 12 and 18 has virtually no affect on the
stereodifferentiating ability of the complexes on their basis
with the configuration of the binaphthol fragment being
the major factor determining the sign of asymmetric inꢀ
9
10
11
12d
13e
14
15
13
13
24
23f
28 (S)
5 (R)
a Reaction conditions: 1—6 °C, CH2Cl2, 4 h, 10 mol.% of catalyst.
b Determined by 1H NMR spectroscopy.
c
Determined by GLC on
a
DPꢀTFAꢀγꢀcD column
(32 m × 0.20 mm), the absolute configuration was determined by
comparison of the optical rotation angle of the product with
the literature data.7
d Amount of the catalyst was 5 mol.%.
e Amount of the catalyst was 1 mol.%.
f Isolated complex was used.
duction. An increase in the coordinating ability of the
ligand on going from the Schiff bases 12 and 18 derived
from alaninol to the Schiff bases 16 and 21 derived from
phenylserinol (see Table 2, entries 3 and 4) leads to
a decrease in their catalytic activity and in the enantiomerꢀ
ic excess of (R)ꢀmandelonitrile from 68 to 44%. In this
case, the determining role of the configuration of the ligand
binaphthol fragment for the sign of asymmetric induction
of the catalyst is retained. The complex formed from
(Ra,S,S)ꢀSchiff base 16 leads to the formation of (R)ꢀmanꢀ
delonitrile, whereas the complex formed from (Sa,S,S)ꢀ
isomer, to the (S)ꢀproduct. The titanium complex of the
Schiff base 17 formed from diphenylaminoethanol and
(Ra)ꢀ2 possessed still lower catalytic activity, giving during
the standard time the product with (R)ꢀconfiguration in
17% chemical yield and 27% ee (see Table 2, entry 5). It is
obvious that the introduction of bulky substituents at the
βꢀposition of the aminoalcohol hinders approach of the
substrate and reagent to the reaction center of the catalyst,
the metal ion.
Table 1. Basic bond distances (d) in complex 23
Bond
d/Å
Bond
d/Å
Ti(1)—O(1´)
Ti(1)—O(2´)
Ti(1)—O(4)
Ti(1)—O(5)
Ti(1)—N(1´)
Ti(1)—N(2)
1.860(5)
1.946(5)
1.843(5)
1.926(5)
2.181(6)
2.172(6)
Ti(2)—O(1)
Ti(2)—O(2)
Ti(2)—O(4´)
Ti(2)—O(5´)
Ti(2)—N(1)
Ti(2)—N(2´)
1.854(5)
1.985(6)
1.837(5)
1.908(5)
2.145(6)
2.159(6)
Introduction of more bulky alkyl residues such as isobuꢀ
tyl (leucinol) and secꢀbutyl (isoꢀleucinol) leads to a conꢀ
siderable increase in asymmetric induction by the catalyst
in comparison with alaninol derivatives. Thus, in the case

1984
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
Belokon et al.
C(31)
C(30)
C(31´)
C(32)
C(22)
C(20)
C(27)
C(28)
C(22´)
O(6)
C(30´)
C(23)
C(21)
C(21´)
N(2)
C(29)
C(27´)
C(23´)
C(28´)
C(19)
C(20´)
C(32´)
O(6´)
C(24´)
O(5)
O(2´)
C(19´)
N(2´)
C(24)
C(18)
C(26)
C(26´)
C(29´)
C(25´)
C(25)
O(4)
Ti(1)
C(18´)
C(17´)
C(1´)
Ti(2)
O(5´)
C(17)
O(3´)
O(1´)
C(13´)
O(4´)
O(2)
C(1)
C(2´)
C(9)
O(1)
C(2)
C(15´)
C(14´)
C(12´)
C(13)
C(9´)
C(10)
N(1´)
O(3)
C(14)
C(3´)
C(10´)
C(3´)
C(11´)
C(8´)
C(8)
N(1)
C(5´)
C(4)
C(12)
C(15)
C(11)
C(4´)
C(16´)
C(7)
C(16)
C(7´)
C(6´)
C(6)
Fig. 1. General view of complex 23.
of ligands 13 and 14, the reaction product possessed an
enantiomeric purity of 86 and 83% ee, respectively, with
predominance of the product with (R)ꢀconfiguration
(see Table 2, entries 6 and 7) as compared to 68% ee for
the catalyst containing an alaninol residue (see Table 2,
entry 1). At the same time, for ligands 19 and 20 deꢀ
rived from (S)ꢀbinaphthol, a decrease in enantioselectivity
of the process in comparison with the alaninol derivaꢀ
tives was observed. The enantiomeric excess of (S)ꢀmanꢀ
delonitrile decreased from 58% ee (see Table 2, entry 2)
to 37% ee (entry 8) and 40% ee (entry 9), however, even in
these cases it was higher than for the valinol derivative 24
(entry 14).
Further increase in the size of the alkyl group to
tertꢀbutyl led to a decrease in the (R)ꢀmandelonitrile ee to 81%
(see Table 2, entry 10). As can be seen from Table 2, the
complexes derived from ligands 1 and 13, giving the prodꢀ
ucts in quantitative yield and enantioselectivity of 86%,
possess the highest catalytic activity and stereodifferentiꢀ
ating ability among the catalysts presented (see Table 2,
entries 6 and 11). For the optimum catalyst derived from
ligand 13, experiments with lower amounts of the catalyst,
viz., 5 and 1 mol.%, respectively, have been carried out.
It turned out that the catalyst did not lose its activity, but a
sharp decrease in its stereodifferentiating ability, from 86
to 38 and 5%, respectively, occurred (see Table 2, entries
12 and 13). This suggests that the real catalytic species
possessing high asymmetric inducing ability is similar in
its structure to tetranuclear species 22. When the concenꢀ
tration of the preꢀcatalyst decreases, a dissociation of the
tetranuclear species to the corresponding dititanium comꢀ
plexes takes place, which possess high catalytic activity,
but have low stereodifferentiating ability.
Resulting conclusion, it was shown that the introducꢀ
tion of bulky substituents at the αꢀposition of the aminoalꢀ
cohol fragment causes a considerable decrease in the yield
of the reaction products. An exchange of the aminoalcohol
fragment for an aminoacid one leads to virtually entire loss

Precatalysts for addition of Me3SiCN to benzaldehyde Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
1985
Synthesis of dialdehydes (general procedure).8 (R)ꢀ3,3´ꢀDiꢀ
formylꢀ2,2´ꢀbis(methoxymethoxy)ꢀ1,1´ꢀbinaphthyl ((R)ꢀ5).
Compound (R)ꢀ4 (13.4 mmol) and anhydrous tetramethylethylꢀ
enediamine (8 mL, 53 mmol) were dissolved in anhydrous ether
(350 mL) under argon. The reaction mixture was cooled to 0 °C.
A solution of butyllithium (1.6 M, 33 mL, 52.8 mmol) in hexane
was added dropwise to the cold solution under argon over 10 min,
the reaction mixture was stirred for 1 h at 0 °C. Then, anhydrous
dimethylformamide (5 mL, 65 mmol) was added followed by
additional stirring for 2 h at ~20 °C. After that, the reaction
mixture was acidified to pH 5 by addition of 1 M aq. HCl. The
organic layer was separated. The product was extracted from the
water phase with ethyl acetate (3×100 mL), the combined organꢀ
ic fractions were washed with saturated aq. NaHCO3, brine, and
dried with Na2SO4. The yellow oil obtained after evaporation
of the solvent was purified by column chromatography (hexꢀ
ane—ethyl acetate, 4 : 1). The yield was 4.1 g (72%), Rf 0.17.
1H NMR (CDCl3), δ: 2.87 (s, 6 H, Me); 4.69 (d, 2 H, CH2,
J = 6.6 Hz); 4.73 (d, 2 H, CH2, J = 6.3 Hz); 7.22 (d, 2 H, Ar,
J = 8.7 Hz); 7.42 (ddd, 2 H, Ar, J = 0.9 Hz, J = 7.5 Hz, J = 8.1 Hz);
7.52 (ddd, 2 H, Ar, J = 0.9 Hz, J = 6.9 Hz, J = 7.8 Hz); 8.08 (d, 2 H,
Ar, J = 8.1 Hz); 8.62 (s, 2 H, Ar); 10.55 (s, 2 H, CHO). 13C NMR
(CDCl3), δ: 57.0, 100.6, 125.9, 126.1, 126.3, 128.8, 129.6, 130.1,
130.3, 132.29, 136.7, 154.0, 190.6.
of enantiomeric purity of the product. It was found that
the optimum ligands are 1 and 13, in these cases a 86%
enantiomeric excess and quantitative yield of the product
can be reached in 4 h. Catalysts with other ligands possess
lower stereodifferentiating ability.
Experimental
1
H and 13C NMR spectra were recorded on a Bruker Avance
600 (600 MHz) and Bruker Avance 300 (300 and 75.5 MHz,
respectively) spectrometers, chemical shifts were determined relꢀ
ative to the residual signal of undeuterated solvent. IR spectra
were recorded on a URꢀ20 spectrometer in KВr pellets.
Optical rotations were determined on a Perkin—Elmer 241
polarimeter in a 5ꢀcm incubatable cuvette at 25 °C. For all the
compounds, the solvent and concentration (g per 100 mL of the
solvent) are given.
Enantiomeric analysis of cyanohydrin trimethylsilyl ethers
obtained was performed on a gas chromatograph (model 3700ꢀ00)
using a DPꢀTFAꢀγꢀcD chiral stationary phase (32 m × 0.20 mm).
A racemic sample of each compound was used as the standard.
Enantiomeric analysis of dialdehydes (Ra)ꢀ2 and (Sa)ꢀ2 was
performed by HPLC using a Kromasil chiral stationary
phase (0.46 cm × 25 cm, eluent: hexane—isopropanol, 100 : 4,
1 mL min–1, UV detector, λ = 254 nm), tR(R) = 22.8 min,
tR(S) = 20.8 min.
Elemental analysis was performed in the Elemental Analysis
Laboratory of A. N. Nesmeyanov Institute of Organoelement
Compounds of the Russian Academy of Sciences, prior to which
the substances were heated in vacuo using a waterꢀjet pump to 78 °C.
Commercial reagents (Aldrich or Acros) were used. Benzalꢀ
dehyde and trimethylsilyl cyanide were distilled under argon at
atmospheric pressure.
(S)ꢀ3,3´ꢀDiformylꢀ2,2´ꢀbis(methoxymethoxy)ꢀ1,1´ꢀbinaphꢀ
thyl ((S)ꢀ5) was obtained similarly from compound (S)ꢀ4 (5.0 g,
13.4 mmol). The yield was 4.0 g (69%), Rf 0.17. 1H NMR specꢀ
trum of compound (S)ꢀ5 is similar to that of compound (R)ꢀ5.
Removal of methoxymethyl protection.9 (R)ꢀ3,3´ꢀDiformylꢀ2,2´ꢀ
dihydroxyꢀ1,1´ꢀbinaphthyl ((Ra)ꢀ2). Compound (R)ꢀ5 (4.76 mmol)
was dissolved in THF (40 mL) and cooled in an iceꢀwater bath.
Then, HCl (12 M, 17 mL) was added over 5 min with stirring and the
iceꢀwater bath was removed. Formation of yellow precipitate
was observed and the stirring was continued for 3 h at ~20 °C. Then,
the product was extracted with ethyl acetate (7×40 mL). The
organic phase was washed with water, saturated aq. NaHCO3, and
brine and dried with anhydrous Na2SO4. The solvent was evapoꢀ
rated on a rotary evaporator at reduced pressure to obtain the
product as a yellow powder. The yield was 1.56 g (96%), m.p.
Introduction of methoxymethyl protection. (R)ꢀ2,2´ꢀBisꢀ
(methoxymethoxy)ꢀ1,1´ꢀbinaphthyl ((R)ꢀ4).
A solution of
(R)ꢀ2,2´ꢀbinaphthol (4.87 g, 17 mmol) in DMF (50 mL) was
added in small portions over 5 min to a stirred suspension of
sodium hydride (2.88 g, 120 mmol) in DMF (50 mL) cooled in
an iceꢀwater bath. The reaction mixture was stirred under coolꢀ
ing for 30 min, then, methoxymethyl chloride (6 mL) was added
in one portion. After 5 min, the iceꢀwater bath was removed and
additional portion of methoxymethyl chloride (0.8 mL) was added
followed by stirring for 3 h at ~20 °C. Then, the reaction mixture
was poured into water (400 mL) and extracted with ether
(300 mL). The combined organic fractions were washed with
water (4 times), saturated aqueous Na2CO3, and dried with anꢀ
hydrous Na2SO4. The solvent was evaporated on a rotary evapoꢀ
rator at reduced pressure. The yellowish solid substance left was
recrystallized from ethyl acetate to obtain the product (5.37 g,
84%) as white crystals, m.p. 99 °C. 1H NMR (CDCl3), δ: 3.15
(s, 6 H, Me); 4.99, 5.10 (both d, 2 H each, 2 CH2, J = 6.7 Hz);
7.14—7.28 (m, 4 H, Ar); 7.36 (t, 2 H, Ar, J = 7.3 Hz); 7.59 (d, 2 H,
Ar, J = 9.0 Hz); 7.88 (d, 2 H, Ar, J = 8.1 Hz); 7.96 (d, 2 H, Ar,
J = 9.0 Hz). 13C NMR (CDCl3), δ: 55.8, 95.1, 117.2, 121.2,
124.0, 125.5, 126.3, 127.8, 129.4, 129.8, 134.0, 152.6.
25
20
285 °C, [α]D +249.5 (c 0.8, CH2Cl2) (cf. Ref. 9: [α]D –254
(c 0.3, CH2Cl2) for (S)ꢀenantiomer). 1H NMR (CDCl3), δ:
7.11—7.15 (m, 2 H); 7.32—7.36 (m, 4 H); 7.93—7.97 (m, 2 H);
8.31 (s, 2 H); 10.13 (s, 2 H, OH); 10.53 (s, 2 H, CHO), ee 98.8%.
(S)ꢀ3,3´ꢀDiformylꢀ2,2´ꢀdihydroxyꢀ1,1´ꢀbinaphthyl ((Sa)ꢀ2)
was obtained similarly using compound (S)ꢀ5. The yield was
1.5 g (95%), [α]D25 –267 (c 0.5, CH2Cl2) (cf. Ref. 8: [α]D20 –254
(c 0.3, CH2Cl2)), ee 100%. 1H NMR spectrum of compound
(Sa)ꢀ2 is similar to that of compound (R)ꢀ2.
Synthesis of aminoalcohols.10 Aminoacid (0.085 mol) was
carefully added in 20 portions to a suspension of lithium alumiꢀ
num hydride (5 g, 0.131 mol) in anhydrous THF (100 mL) under
argon at ~20 °C. The reaction mixture was refluxed for 16 h,
cooled to ~20 °C, and poured into diethyl (or methyl tertꢀbutyl)
ether (100 mL). Further, water (15 mL), 15% aq. sodium hyꢀ
droxide (15 mL), and water (45 mL) were sequentially added to
the ethereal fraction. The solution was filtered, the precipitate
was washed with ether (2×50 mL). The organic layers were comꢀ
bined and dried with anhydrous sodium sulfate. Pure aminoalcoꢀ
hol was obtained by distillation in vacuo.
(S)ꢀ2,2´ꢀBis(methoxymethoxy)ꢀ1,1´ꢀbinaphthyl ((S)ꢀ4) was
obtained similarly from (S)ꢀ2,2´ꢀbinaphthol (4.87 g, 17 mmol),
1
the yield was 5.3 g (83%), white crystals. H NMR spectrum of
25
compound (S)ꢀ4 is similar to that of compound (R)ꢀ4; [α]D
(S)ꢀAlaninol (6). The yield was 2 g (89%), [α]D25 +36.6 (c 2,
CHCl3) (cf. Ref. 11: [α]D25 +36.2 (c 2, CHCl3)), b.p. 59—61 °C
–64.4 (c 1, THF).

1986
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
Belokon et al.
(5 Torr) (cf. Ref. 12: b.p. 59—60 °C (5 Torr)). 1H NMR (CDCl3),
δ: 1.03 (d, 3 H, Me, J = 6.45 Hz); 2.14 (br.s, 3 H, NH2,
OH); 2.92—3.01 (m, 1 H, CH(Me)); 3.21 (dd, 1 H, CH(CH2),
J = 7.7 Hz, J = 10.7 Hz); 3.51 (dd, 1 H, CH(CH2), J = 3.5 Hz,
J = 10.2 Hz).
solvent 87%), m.p. 136—138 °C, [α]D –38.1 (c 1.05, CHCl3).
Found (%): C, 75.04; H, 6.39; N, 5.19. C28H28N2O4•0.5C6H6.
Calculated (%): C, 75.13; H, 6.30; N, 5.65. 1H NMR (CDCl3),
δ: 1.22 (d, 6 H, J = 5.97 Hz); 1.87 (br.s, 2 H); 3.64 (m, 6 H); 7.18
(m, 2 H); 7.28—7.32 (m, 4 H); 7.87—7.90 (m, 2 H); 7.98, 8.69
(both s, 2 H each); 13.25 (br.s, 2 H). 13C NMR (CDCl3), δ: 18.2,
66.9, 116.6, 120.9, 123.5, 124.7, 127.6, 128.5, 128.9, 133.6, 135.3,
154.6, 165.3. IR, ν/cm–1: 3369, 2926, 1632, 1254, 1042.
25
(S)ꢀLeucinol (7). The yield was 2.98 g (85%), [α]D25 +4.3 (c 0.9,
25
EtOH) (cf. Ref. 13: [α]D +4.2 (c 0.9, EtOH)), b.p. 92—94 °C
(5 Torr) (cf. Ref. 14: b.p. 73—74 °C (1.4 Torr)). 1H NMR
(CDCl3), δ: 0.9, 0.93 (both d, 3 H each, Me, J = 6.66 Hz); 1.18
(t, 2 H, CH2, J = 6.99 Hz); 1.63—1.74 (m, 1 H, CH(Me)); 1.87
(br.s, 3 H, NH2, OH); 2.86—2.94 (m, 1 H, CHNH2); 3.21 (dd, 1 H,
CH(CH2O), J = 8.06 Hz, J = 10.42 Hz); 3.56 (dd, 1 H,
CH(CH2O), J = 3.88 Hz, J = 10.43 Hz).
(S)ꢀ1ꢀ{2ꢀHydroxyꢀ3ꢀ[((S)ꢀ2ꢀhydroxyꢀ1ꢀmethylethyl)imino]ꢀ
methylꢀ1ꢀnaphthyl}ꢀ3ꢀ[((S)ꢀ2ꢀhydroxyꢀ1ꢀmethylethyl)imino]ꢀ
methylꢀ2ꢀnaphthol (18). The yield was 1.1 g (97%, without residꢀ
ual solvent 90%), m.p. 128—130 °C, [α]D –4.7 (c 1, CHCl3).
Found (%): C, 67.07; H, 5.84; N, 5.40. C28H28N2O4•0.65CH2Cl2.
Calculated (%): C, 67.24; H, 5.77; N, 5.47. H NMR spectrum
of compound 18 is similar to that of compound 12. IR, ν/cm–1
25
1
(2S,3S)ꢀ2ꢀAminoꢀ3ꢀmethylpentanꢀ1ꢀol (8). The yield was
25
20
2.9 g (84%), [α]D +3.8 (c 1, EtOH) (cf. Ref. 15: [α]D +3.5
(c 1, EtOH)), b.p. 88—90 °C (5 Torr) (cf. Ref. 16: b.p. 111—115 °C
(20 Torr)). 1H NMR (CDCl3), δ: 0.79—0.86 (m, 6 H); 1.01—1.14,
1.26—1.35, 1.39—1.47 (all m, 1 H each); 2.57—2.63 (m, 4 H);
3.25 (dd, 1 H, J = 8.67 Hz, J = 10.59 Hz); 3.57 (dd, 1 H, J = 3.6 Hz,
J = 10.65 Hz).
:
3361, 2940, 1632, 1253, 1041.
(R)ꢀ1ꢀ{2ꢀHydroxyꢀ3ꢀ([(1S,2S)ꢀ1ꢀ(hydroxymethyl)ꢀ2ꢀmeꢀ
thylbutyl]iminomethyl)ꢀ1ꢀnaphthyl}ꢀ3ꢀ([(1S,2S)ꢀ1ꢀ(hydroxymeꢀ
thyl)ꢀ2ꢀmethylbutyl]iminomethyl)ꢀ2ꢀnaphthol (14). The yield was
1.27 g (94%, without residual solvent 84%), m.p. 108—110 °C,
25
25
(S)ꢀtertꢀLeucinol (9). The yield was 2.46 g (70%), [α]D
[α]D –146.7 (c 0.55, CHCl3). Found (%): C, 69.88; H, 6.85;
+36.5 (c 1.5, EtOH) (cf. Ref. 17: [α]D25 +37 (c 1.5, EtOH)), b.p.
87—89 °C (5 Torr) (cf. Ref. 18: b.p. 65—70 °C (1.3 Torr)).
1H NMR (CDCl3), δ: 0.89 (s, 9 H, 3 Me); 1.71 (br.s, 3 H, NH2,
OH); 2.50 (dd, 1 H, J = 3.9 Hz, J = 10.2 Hz); 3.19 (t, 1 H,
J = 10.2 Hz); 3.69 (dd, 1 H, J = 3.9 Hz, J = 10.2 Hz).
N, 4.55. C34H40N2O4•0.65CH2Cl2. Calculated (%): C, 69.84;
H, 6.99; N, 4.70. 1H NMR (CDCl3), δ: 0.83 (t, 6 H, J = 7.37 Hz);
0.91 (d, 6 H, J = 6.8 Hz); 1.11 (m, 2 H); 1.47 (br.s, 2 H); 1.64
(m, 4 H); 3.2 (m, 2 H); 3.75 (m, 4 H); 7.17 (m, 2 H); 7.29 (m, 4 H);
7.88 (m, 2 H); 7.99, 8.64 (both s, 2 H each); 13.18 (br.s, 2 H).
13C NMR (CDCl3), δ: 11.3, 15.7, 25.5, 36.9, 63.9, 116.6, 120.9,
123.4, 124.8, 125.02, 127.6, 128.6, 133.6, 135.3, 154.8, 166.03.
IR, ν/cm–1: 3405, 2945, 1633, 1255, 1045.
(R)ꢀ1ꢀ{2ꢀHydroxyꢀ3ꢀ([(1S,2S)ꢀ1ꢀ(hydroxymethyl)ꢀ2ꢀmeꢀ
thylbutyl]iminomethyl)ꢀ1ꢀnaphthyl}ꢀ3ꢀ([(1S,2S)ꢀ1ꢀ(hydroxymeꢀ
thyl)ꢀ2ꢀmethylbutyl]iminomethyl)ꢀ2ꢀnaphthol (20). The yield was
1.26 g (93%, without residual solvent 80%), m.p. 110—112 °C,
(1S,2S)ꢀ2ꢀAminoꢀ1ꢀphenylpropaneꢀ1,3ꢀdiol (10). The yield
22
was 1.44 g (90%), [α]D25 +26.2 (c 10, MeOH) (cf. Ref. 19: [α]D
+26.6 (c 10, MeOH)), m.p. 115—117 °C. 1H NMR (CDCl3), δ:
1.99 (br.s, 4 H); 3.00 (q, 1 H, J = 5.41 Hz, J = 10.04 Hz); 3.55
(dd, 1 H, J = 5.98 Hz, J = 10.79 Hz); 3.65 (dd, 1 H, J = 4.22 Hz,
J = 10.73 Hz); 4.65 (d, 1 H, J = 5.2 Hz); 7.29—7.32 (m, 1 H);
7.33—7.37 (m, 4 H). Aminoacid (S)ꢀphenylserine used as the
starting compound for the synthesis of aminoalcohol 9 was obꢀ
tained according to the procedure described earlier.20
25
[α]D –156.6 (c 0.76, CHCl3). Found (%): C, 68.09; H, 7.06;
N, 4.48. C34H40N2O4•0.88CH2Cl2. Calculated (%): C, 68.07;
H, 6.84; N, 4.55. 1H NMR spectrum of compound 20 is similar
to that of compound 24. IR, ν/cm–1: 3400, 2951, 1633, 1255, 1045.
(R)ꢀ1ꢀ{2ꢀHydroxyꢀ3ꢀ([(S)ꢀ1ꢀhydroxymethylꢀ2,2ꢀdimethylꢀ
propyl]iminomethyl)ꢀ1ꢀnaphthyl}ꢀ3ꢀ([(S)ꢀ1ꢀhydroxymethylꢀ2,2ꢀ
dimethylpropyl]iminomethyl)ꢀ2ꢀnaphthol (15). Purification was
performed by column chromatography on Sephadex LHꢀ20
(dichloromethane—pyridine, 10 : 1). The yield was 1.27 g (94%,
without residual solvent 68%), m.p. 160—162 °C, [α]D25 –122.2
(c 0.55, CHCl3). Found (%): C, 66.77; H, 7.01; N, 5.79.
C34H40N2O4•1.2CH2Cl2•Py. Calculated (%): C, 66.90; H, 6.62;
Synthesis of 2ꢀaminoꢀ1,1ꢀdiphenylethanol (11). Glycine ethꢀ
yl ester hydrochloride (1.4 g, 10 mmol) was slowly added to
a solution of PhMgBr (1.0 mol L–1, 60 mL, 60.0 mmol) in anhyꢀ
drous THF (100 mL). The solution was stirred for 3 h at 40 °C
and cooled to ~20 °C followed by addition of water (20 mL). The
reaction mixture was diluted with ether (100 mL) and washed
with brine. The water layer was extracted twice with diethyl
ether—THF (3 : 2). The combined organic phases were washed
with brine and dried with Na2SO4. After the solvent was evapoꢀ
rated on a rotary evaporator at reduced pressure, the residue was
recrystallized three times from diethyl ether and purified by colꢀ
umn chromatography (SiO2; CHCl3—MeOH, 8 : 2) to obtain
the product (1.1 g, 52%) as white crystals, m.p. 112—114 °C
(cf. Ref. 21: m.p. 110 °C). 1H NMR (CDCl3), δ: 2.80—3.20 (br.s,
3 H, NH2, OH); 3.38 (s, 2 H, CH2); 7.20—7.50 (m, 10 H, Ar).
Synthesis of the Schiff bases (general procedure). Dialdehyde
(2.5 mmol) was added to a solution of aminoalcohol (5 mmol) in
benzene (5 mL) and ethanol (5 mL). The reaction mixture was
refluxed for 10 h with a Dean—Stark trap. The solvent was evapꢀ
orated on a rotary evaporator at reduced pressure, the residue
was purified by column chromatography on Sephadex LHꢀ20
(dichloromethane). The Schiff bases were obtained as solid redꢀ
dish orange compounds.
1
N, 5.82. H NMR (CDCl3), δ: 0.91 (s, 18 H); 2.17 (br.s, 2 H);
3.00 (dd, 2 H, J = 2.27 Hz, J = 9.12 Hz); 3.67 (t, 2 H, J = 9.5 Hz);
3.69 (dd, 2 H, J = 2.2 Hz, J = 11.04 Hz); 7.14 (m, 2 H); 7.30
(m, 4 H); 7.87 (m, 2 H); 7.97, 8.63 (both s, 2 H each); 13.12 (br.s,
2 H). 13C NMR (CDCl3), δ: 27.1, 33.2, 62.1, 116.6, 120.8,
123.35, 125.03, 127.6, 128.1, 128.9, 133.6, 135.3, 154.7, 166.2.
IR, ν/cm–1: 2961, 3434, 1633, 1254, 1042.
(R)ꢀ1ꢀ{2ꢀHydroxyꢀ3ꢀ([(S)ꢀ1ꢀhydroxymethylꢀ2ꢀmethylbuꢀ
tyl]iminomethyl)ꢀ1ꢀnaphthyl}ꢀ3ꢀ([(S)ꢀ1ꢀhydroxymethylꢀ2ꢀmeꢀ
thylbutyl]iminomethyl)ꢀ2ꢀnaphthol (13). The yield was 1.3 g
25
(96%, without residual solvent 84%), m.p. 130—132 °C, [α]D
–135.3 (c 0.55, CHCl3). Found (%): C, 68.69; H, 6.9; N, 4.3.
C34H40N2O4•0.8CH2Cl2. Calculated (%): C, 68.67; H, 6.89;
N, 4.60. 1H NMR (CDCl3), δ: 0.88 (dd, 12 H, J = 5.32 Hz,
J = 6.04 Hz); 1.26—1.33 (m, 2 H); 1.46—1.52 (m, 4 H); 2.06
(br.s, 2 H); 3.47 (m, 2 H); 3.58—3.64 (m, 4 H); 7.18 (m, 2 H);
(R)ꢀ1ꢀ{2ꢀHydroxyꢀ3ꢀ[((S)ꢀ2ꢀhydroxyꢀ1ꢀmethylethyl)imino]ꢀ
methylꢀ1ꢀnaphthyl}ꢀ3ꢀ[((S)ꢀ2ꢀhydroxyꢀ1ꢀmethylethyl)imino]ꢀ
methylꢀ2ꢀnaphthol (12). The yield was 1 g (95%, without residual

Precatalysts for addition of Me3SiCN to benzaldehyde Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
1987
7.30 (m, 4 H); 7.87 (m, 2 H); 7.99, 8.67 (both s, 2 H each); 13.21
(br.s, 2 H). 13C NMR (CDCl3), δ: 21.5, 23.5, 24.3, 40.8, 66.4,
70.1, 116.6, 120.8, 123.5, 124.8, 127.6, 128.5, 128.9, 133.7, 154.6,
165.8. IR, ν/cm–1: 2196, 3400, 1632, 1255, 1063.
romethane). Complex 23 was obtained as a red powder. The
complex was recrystallized from chloroform. The yield was
30 mg (15% with subtraction of two solvate chloroform molecules).
Catalytic asymmetric addition of trimethylsilyl cyanide to benꢀ
zaldehyde (general procedure). Titanium(IV) isopropoxide (28 μL,
94 μmol) was added to a solution of a ligand (47 μmol) in dichlorꢀ
omethane (1 mL) under argon. The color of the solution changed
instantly from orange to reddish brown. The reaction mixture
was stirred for 2 h at ~20 °C followed by addition of freshly
distilled benzaldehyde (48 μL, 471 μmol). The solution was
cooled to +1 °C followed by addition of trimethylsilyl cyanide
(100 μL, 750 μmol). The reaction mixture was stirred for 4 h at
4 °C and purified by column chromatography on SiO2 (eluent,
hexane—ethyl acetate, 5 : 1). The product was analyzed by
1H NMR spectroscopy. The spectra obtained agreed with analoꢀ
gous spectra described earlier.22 The chemical yield was calcuꢀ
lated from the correlation of signals for the product and for
the starting aldehyde. The enantiomeric composition was deterꢀ
mined using gas chromatography on a DPꢀTFAꢀγꢀcD column
(32 m × 0.20 mm), the absolute configuration was determined by
comparison of the optical rotation angle of the product obtained
with the data in Ref. 7.
(S)ꢀ1ꢀ{2ꢀHydroxyꢀ3ꢀ([(S)ꢀ1ꢀhydroxymethylꢀ2ꢀmethylbutyl]ꢀ
iminomethyl)ꢀ1ꢀnaphthyl}ꢀ3ꢀ([(S)ꢀ1ꢀhydroxymethylꢀ2ꢀmethylꢀ
butyl]iminomethyl)ꢀ2ꢀnaphthol (19). The yield was 1.31 g (97%),
25
m.p. 126—128 °C, [α]D –143.2 (c 0.9, CHCl3). Found (%):
C, 75.24; H, 7.65; N, 4.95. C34H40N2O4. Calculated (%):
C, 75.53; H, 7.46; N, 5.18. 1H NMR spectrum of compound 19
is similar to that of compound 13. IR, ν/cm–1: 3050, 3400, 1632,
1256, 1060.
(R)ꢀ3ꢀ[(2ꢀHydroxyꢀ2,2ꢀdiphenylethyl)imino]methylꢀ1ꢀ{2ꢀ
hydroxyꢀ3ꢀ[(2ꢀhydroxyꢀ2,2ꢀdiphenylethyl)imino]methylꢀ1ꢀnaphꢀ
thyl}ꢀ2ꢀnaphthol (17). The yield was 1.7 g (93%, without residual
25
solvent 73%), m.p. 112—114 °C, [α]D +11.3 (c 0.7, CHCl3).
Found (%): C, 71.57; H, 5.42; N, 3.10. C50H40N2O4•1.5CH2Cl2.
1
Calculated (%): C, 71.90; H, 5.04; N, 3.26. H NMR (CDCl3),
δ: 2.77 (br.s, 2 H); 4.38 (q, 4 H, J = 12.98 Hz); 7.09 (d, 2 H,
J = 6.96 Hz); 7.19—7.30 (m, 16 H); 7.42—7.45 (m, 12 H);
7.83—7.86 (m, 2 H); 7.92, 8.64 (both s, 2 H each); 12.21 (br.s,
2 H). IR, ν/cm–1: 2922, 3451, 1631, 1254, 1057.
(R)ꢀ2ꢀ{(3ꢀHydroxyꢀ4ꢀ[2ꢀhydroxyꢀ3ꢀ([2ꢀhydroxyꢀ1ꢀ(hydrꢀ
oxymethyl)ꢀ2ꢀ(S)ꢀphenylethyl]iminomethyl)ꢀ1ꢀnaphthyl]ꢀ2ꢀnaꢀ
phthylmethylidene)amino}ꢀ1ꢀ(S)ꢀphenylꢀ1,3ꢀpropanediol (16).
Measurement of molecular mass of complex 22 in dichloꢀ
romethane. The molecular characteristics of titanium complex 9
were studied by the sedimentation equilibrium method in
an analytical ultracentrifuge (MOMꢀ3180). The molecular mass
Mw for two samples was determined from the sedimentation
data using the method of established equilibrium for concenꢀ
trations of 0.5—1.0 g dL–1 (with the use of Fillpot—Swenson
optics, the rotor temperature was 25 0.1 °C, the rotational
velocity of the rotor was 50000 rpm). The apparent molecular
mass for the finite concentrations was calculated by the following
formula
25
The yield was 1.5 g (94%, without residual solvent 76%), [α]D
+93.8 (c 0.55, CHCl3), m.p. 144—146 °C. Found (%): C, 68.75;
H, 5.68; N, 3.98. C40H36N2O4•1.3CH2Cl2. Calculated (%):
C, 68.98; H, 5.41; N, 3.90. 1H NMR (CDCl3), δ: 2.77 (br.s, 4 H);
3.54 (m, 6 H); 4.8 (d, 2 H, J = 6.57 Hz); 7.16 (m, 2 H);
7.28—7.32 (m, 14 H); 7.86 (m, 2 H); 7.93, 8.69 (both s, 2 H
each); 13.01 (br.s, 2 H). 13C NMR (CDCl3), δ: 63.0, 74.2, 116.6,
120.7, 123.5, 124.97, 126.6, 127.5, 127.8, 128.3, 129.1, 133.9, 135.3,
140.8, 154.6, 167.9. IR, ν/cm–1: 3030, 2922, 1632, 1254, 1027.
(S)ꢀ2ꢀ{(3ꢀHydroxyꢀ4ꢀ[2ꢀhydroxyꢀ3ꢀ([2ꢀhydroxyꢀ1ꢀ(hydrꢀ
oxymethyl)ꢀ2ꢀ(S)ꢀphenylethyl]iminomethyl)ꢀ1ꢀnaphthyl]ꢀ2ꢀnaꢀ
phthylmethylidene)amino}ꢀ1ꢀ(S)ꢀphenylꢀ1,3ꢀpropanediol (21).
2
Mwapp = {RT/[(1 – Vρ )ω ]}[(dc/dx)/(cx)],
0
where R is the universal gas constant, T is the absolute temperaꢀ
25
The yield was 1.55 g (97%, without residual solvent 79%), [α]D
ture (К), V is the partial specific volume of the substance, ρ is
0
+252.2 (c 0.7, CHCl3), m.p. 144—146 °C. Found (%): C, 70.07;
H, 5.99; N, 4.08. C40H36N2O4•1.1CH2Cl2. Calculated (%):
C, 70.30; H, 5.48; N, 3.99. 1H NMR spectrum of compound 21
is similar to that of compound 16. IR, ν/cm–1: 3030, 2922, 1632,
1254, 1027.
the solvent density (dichloromethane) (g dL–1), ω is the angular
velocity of the rotor rotation, c is the concentration of the subꢀ
stance in solution, x is the distance from the axis of rotation (cm).
app
The true value of Mw was found by extrapolation of 1/Mw
(determined for the finite concentrations) to the infinite dilution
Complex 22. Titanium(IV) isopropoxide (11.4 μL, 39.0 μmol)
was added to a solution of ligand 1 (10.0 mg, 19.5 μmol) in
dichloromethaneꢀd2 (0.5 mL). In the 1H NMR spectrum, many
weak signals for other complexes are present in addition to the
(C → 0). The specific partial volume (V = 0.337 cm3 g–1) and the
solvent density (ρ = 1.3113 g cm–3 at 25 °C) necessary for the
0
calculation of molecular mass from the sedimentation data were
determined pyknometrically. The pyknometer was calibrated
with respect to mercury. The value Mw = 1430 5%.
1
signals for the major product. H NMR (CD2Cl2), δ: 0.87, 1.01
(both d, 6 H each, J = 6.7 Hz); 1.22—1.30 (br.d, 12 H, J = 4.2 Hz);
2.45 (m, 2 H); 3.47 (dd, 2 H, J = 4.2 Hz, J = 9.9 Hz); 3.60—3.80,
4.40—4.48 (both m, 2 H each); 4.58 (dd, 2 H, J = 4.2 Hz,
J = 9.9 Hz); 7.00—7.40 (m, 6 H); 7.80—8.00 (m, 2 H); 8.08, 8.59
(both s, 2 H each).
Complex 23. Dialdehyde (Ra)ꢀ2 (50.0 mg, 0.146 mmol) was
added to a solution of (S)ꢀvaline (34.0 mg, 0.292 mmol) in benꢀ
zene (5 mL) and isopropanol (5 mL). The reaction mixture was
refluxed for 1 h with a Dean—Stark trap followed by addition of
titanium(IV) isopropoxide (86 μL, 0.292 mmol) and refluxing with
a Dean—Stark trap for another 10 h. The solvent was evaporated
on a rotary evaporator at reduced pressure, the residue was puriꢀ
fied by column chromatography on Sephadex LHꢀ20 (dichloꢀ
Xꢀray study. Crystals 23 (C66H58Cl6N4O12Ti2) at 100 K are
monoclinic, a = 10.0376(12) Å, b = 18.579(2) Å, c = 17.159(2) Å,
β = 90.307(4)°, V = 3199.9(7) Å3, dcalc = 1.461 g cm–3, space
group P21, Z = 4. Intensities of 17701 reflections were measured
on a Bruker Smart APEX II CCD automatic difractometer at 100 K
(MoꢀКα irradiation, graphite monochromator, ωꢀscanning,
2θ
= 54°) and 9358 observed reflections were used in further
max
calculations. The structure was decoded by the direct method
and refined by the fullꢀmatrix least squares method in anisoꢀ
tropicꢀisotropic approximation on F2. The hydrogen atoms
were localized from the differential syntheses of electron densiꢀ
ty and refined by riding model. The final divergence factors
wR2 = 0.1677, GOF = 0.958 on reflections (R1 = 0.0605 was

1988
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
Belokon et al.
calculated on 4752 reflections with I > 2σ(I)) were calculated
13. S. Narasimhan, S. Madhavan, P. K. Ganeshwar, Synth. Comꢀ
mun., 1996, 26, 703.
using the SHELXTL PLUS program package.23
14. E. Segel, J. Am. Chem. Soc., 1952, 74, 1096.
15. M. J. McKennon, A. I. Meyers, K. Drauz, M. Schwarm,
J. Org. Chem., 1993, 58, 3568.
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Received June 2, 2008;
in revised form July 3, 2008