Synthesis and structure determination of novel chiral imine-alkoxytitanium complexes

Article abstract of DOI:10.1002/(SICI)1099-0690(199806)1998:6<1063::AID-EJOC1063>3.0.CO;2-W

The imines 4 containing a diphenylcarbinol moiety serve as chiral ligands in novel enantiomerically pure imine-alkoxytitanium(IV) complexes. Depending on the molar ratio of the starting materials, imines 4 and titanium tetraisopropoxide, mono-chelated complexes 5 or bis-chelated complexes 6/7 result. The latter are formed diastereoselectively and the isomers 6 are main or exclusive products. Their (A) configuration is determined by a crystal-structure analysis of 6b. The bis-ligand complexes 6 or mixtures of 6/7, which are found to be remarkably stable, are used as precursors not only for the reactive dihalo complexes 8a/8b but also for the preparation of the mixed chloroisopropoxytitanium complex 8c.

Full text of DOI:10.1002/(SICI)1099-0690(199806)1998:6<1063::AID-EJOC1063>3.0.CO;2-W

FULL PAPER
Synthesis and Structure Determination of Novel Chiral Imine-Alkoxytitanium
Complexes
a
b
a
Ralf Fleischer , Hartmut Wunderlich , and Manfred Braun*
a
b
Institut für Organische Chemie und Makromolekulare Chemie , Institut für Anorganische Chemie und Strukturchemie ,
Universität Düsseldorf,
Universitätsstraße 1, D-40225 Düsseldorf, Germany
Fax: (internat.) ϩ 49(0)211/81-13085
E-mail: braunm@uni-duesseldorf.de
Received December 5, 1997
Keywords: 2-Amino-1,1,2-triphenylethanol / Bridging ligands / Crystal structure / Diastereoselectivity / Titanium
The imines 4 containing a diphenylcarbinol moiety serve as
chiral ligands in novel enantiomerically pure imine-alkoxyti-
tanium(IV) complexes. Depending on the molar ratio of the
starting materials, imines 4 and titanium tetraisopropoxide,
mono-chelated complexes 5 or bis-chelated complexes 6/7
result. The latter are formed diastereoselectively and the iso-
mers 6 are main or exclusive products. Their (A) configura-
tion is determined by a crystal-structure analysis of 6b. The
bis-ligand complexes 6 or mixtures of 6/7, which are found
to be remarkably stable, are used as precursors not only for
the reactive dihalo complexes 8a/8b but also for the prepara-
tion of the mixed chloroisopropoxytitanium complex 8c.
Tuned reactivity and improved selectivity are the out- nesium bromide, the amino alcohol (R)-2 resulted in 66%
standing features of titanium reagents compared to their yield.[
13][14]
The slow addition of salicylaldehyde (3a), 3-
polar organometallic counterparts, mainly lithium and tert-butyl-2-hydroxybenzaldehyde (3b) or the di-tert-butyl-
magnesium compounds. Although discovered less than two substituted homologue 3c to a cooled solution of 2 resulted
[
1]
decades ago, these advantages led to a plethora of novel in the formation of the imines 4a, 4b, and 4c, respectively.
titanium compounds which are used either in a stoichio- In an analogous way 2-hydroxy-1-naphthaldehyde (3d) was
metric way or catalytically and brought about enormous converted into the Schiff base 4d. The condensation of alde-
success in chemo-, diastereo-, and enantioselective trans- hydes with 2-amino alcohols is known to lead in several
[
2]
[15]
formations. The latter rely mainly on various chiral li- cases to 1,3-oxazolidines besides imines.
The former
gands which enable complexation of the titanium. Es- were, however, not found as side products in the prep-
[3]
pecially titanates derived from carbohydrates, tartaric aration of the Schiff bases 4aϪd.
[
4]
[5]
acid, and axially chiral biaryls as well as di- and oligo-
In most cases, chiral titanates used in asymmetric synth-
eses are generated in situ from achiral titanium precursors
[
6]
peptides found wide application in the enantioselective
addition of nucleophiles to carbonyl compounds. More
recently, imine-alkoxytitanium catalysts were used for en-
antioselective trimethylsilylcyanations and diketene ad-
ditions
[
7]
[7]
by ligand-exchange reactions. The aim of this work, how-
ever, was the isolation and structure elucidation or at least
the spectroscopic characterization of titanium complexes
derived from the imines 4aϪd. It was found that the type
of titanium compound formed thereby depended strongly
on the stoichiometric ratio of the titanate used as achiral
precursor and the chiral ligands. Thus, the treatment of ti-
tanium tetraisopropoxide in deuteriochloroform with the
imines 4aϪd in a molar ratio of 1:1 gave solutions of the
unstable chelate complexes 5aϪd besides two equivalents of
[8]
[
8b][9]
to aldehydes. The corresponding Schiff bases
were usually prepared by condensation of salicylaldehyde
derivatives with amino alcohols, preferably valinol, tert-leu-
[
8b]
and 2-amino-1,2-diphenylethanol.[8c] Despite of
cinol,
the success of imine-alkoxytitanium complexes with respect
to chemical and optical yields, only a few details are known
about the structure of these catalysts.[
8a][10]
In this paper, we report for the first time on the synthesis,
the isolation and the structure determination of imine-al-
koxytitanium complexes which are derived from (R)-2-
amino-1,1,2-triphenylethanol (2), both in the crystalline
state and in solution. This chiral auxiliary which is readily
available from (R)-phenylglycine methyl ester hydrochloride
2
-propanol, as shown by NMR spectroscopy. The titanium
complex 5c could also be obtained free of solvent and 2-
propanol, though in this case it decomposed rapidly even
when stored under an inert atmosphere.
When, on the other hand, the starting materials titanium
tetraisopropoxide and imines 4aϪd were mixed in a molar
ratio of 1:2 and stirred in dichloromethane for several
(
1) contains the diarylhydroxymethyl group discovered to
[11]
be crucial in many chiral reagents used by us and others.
hours, TiL -type complexes 6/7 resulted and were isolated.
2
Results and Discussion
One diastereomer was formed predominantly in the cases
When methyl ester hydrochloride 1, accessible from (R)- 4a, 4b, and 4d, and a single isomer arose from the reaction
[
12]
phenylglycine,
was treated with an excess of phenylmag- of 4c with titanium tetraisopropoxide. The diastereomeric
Eur. J. Org. Chem. 1998, 1063Ϫ1070
 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1434Ϫ193X/98/0606Ϫ1063 $ 17.50ϩ.50/0
1063

R. Fleischer, H. Wunderlich, M. Braun
FULL PAPER
ratio of 6/7 in the crude product mixture could be deter-
mined by NMR spectroscopy since the isomers differ signif-
1
13
1
icantly in their H and C spectra. In addition, the H-
NMR spectra of the main products 6aϪd display a charac-
teristic upfield shift of 0.8Ϫ1.4 ppm of either the aromatic
proton signal or the tert-butyl group signal in the ortho po-
sition of the phenol moiety, compared with the imines
4
aϪd, as shown in Table 1. The diastereomers 6aϪd were
Table 1. Yield and selected proton shift in the imines 4; diastere-
easily isolated as enantiomerically pure isomers by column omeric ratio of 6/7; yield, selected proton shift and optical rotation
chromatography or by crystallization. These complexes ex-
of the titanium complexes 6
hibited exceptionally high amounts of optical rotation, es-
4
6/7
[ppm] d.r.
[b]
6
pecially the non-alkyl substituted derivatives 6a and 6d. In
the case of the isomeric mixture 6b/7b the minor dia-
stereomer 7b could also be obtained as pure compound.
The bis-chelated complexes 6 and 7 were found to be stable
at room temperature in the air.
20[c]
yield [%]
δ
H
[a]
yield [%]
δ
H
[a]
[ppm] [α]
D
[b]
a
b
c
81
91
88
93
6.89
83:17
1.38 91:9
68
75
49
78
5.45
929
0.55 296
0.55 287
1021
[
d]
[
e]
[f]
1.39
On the other hand, the decision which geometric ar-
rangement of the ligand atoms had to be assigned to the
main product 6 could not be made based on the NMR data.
Therefore, the structure of the predominant isomer 6b was
determined by a crystal-structure analysis, the result of
d
6.90
87:13
5.52
[
[
a]
Aromatic proton in the ortho position to the phenol moiety. Ϫ
Protons of the tert-butyl group in the ortho position to the
b]
[
c]
[d]
phenol moiety. Ϫ c ϭ 1 in chloroform. Ϫ Optical rotation of
20
the minor diastereomer 7b: [α]
D
ϭ ϩ170 (c ϭ 1 in chloroform).
which is shown in Figure 1. In a distorted octahedron, the Ϫ [ Only a single isomer was detected. Ϫ T ϭ 25°C, c ϭ 0.74.
e]
[f]
central titanium atom is covalently bound to the phenolic
oxygen atom and to the oxygen atom at the tertiary carbon ment of the two ligands, octahedral chirality results and
atom of each ligand. In addition, the nitrogen atoms of the (A) configuration has to be assigned to the complex 6b
both imino groups form coordinative bonds to the titanium according to the literature.[ The obtuse, relatively large
atom with bond lengths of 214.9(5) and 216.0(5) pm, TiϪOϪC angles, which range from 128.5(4) in a five-mem-
respectively. For clarity, only the core of the complex 6b, as bered to 137.7(4)° in a six-membered chelate, indicate a sub-
determined by the X-ray structure analysis, is shown in Fig- stantial π-donation effect of the oxygen lone pairs. As a
ure 2. Obviously, the terdendate ligand 4b is bound to the consequence, the TiϪO bonds are shortened to average val-
central atom in a meridional manner. Due to this arrange- ues of 185.9(4) within the five-membered and of 192.5(4)
16]
1064
Eur. J. Org. Chem. 1998, 1063Ϫ1070

Novel Chiral Imine-Alkoxytitanium Complexes
FULL PAPER
within the six-membered rings compared to the calculated
value of 210 pm.[ The two six-membered rings display
small but nevertheless remarkable torsions in the conju-
gated system, and the titanium atom projects out of these
chelate planes (e. g. torsion angles N1ϪTiϪO1ϪC12 30.7,
N2ϪTiϪO2ϪC22 Ϫ41.2°). The titanium complex 6b is dis-
tinctly monomeric. Both the thermal and the chemical sta-
bility of 6b are easily understood if one takes into account
that the metal atom obtains the favoured hexacoordi-
Figure 2. Inner skeleton of the complex 6b[a]
17]
[
10][18]
nation,
that the periphery is largely shielded by bulky
substituents (aryl and tert-butyl), and that neither bond
lengths nor angles are extraordinary. The structural proper-
ties of 6b are in accordance with the NMR data so that any
dissociation in solution can be excluded. The structures of
the complex 6b as well as of 6a, 6c, and 6d were also con-
firmed by the CI mass spectra which showed the character-
istic titanium isotope pattern of the protonated molecular
ion in each case. The configurations of 6a, 6c, and 6d are
assigned based on the NMR spectra and by analogy with
the complex 6b.
[
a]
Selected bond lengths [pm] and angles [°]: TiϪO1 193.8(4),
TiϪO2 191.2(4), TiϪN1 214.9(5), TiϪN2 216.0(5), TiϪO3
1
83.5(4), TiϪO4 188.2(4), N1ϪC1 128.6(7), N2ϪC2 128.5(7);
O1ϪTiϪN1 80.7(2), O2ϪTiϪN2 80.7(2), N1ϪTiϪO3 74.7(2),
N2ϪTiϪO4 74.7(2), N1ϪTiϪN2 169.5(2), O1ϪTiϪO2 87.8(2),
Figure 1. Crystal structure of the compound 6b·2 CHCl
3
[
19]
(
SHELXTL-PLUS ; 25% probability displacement ellipsoids; hy- O3ϪTiϪO4 93.9(2), TiϪO1ϪC12 137.7(4), TiϪO2ϪC22 135.0(4),
drogen atoms and chloroform molecules omitted for clarity)
TiϪO3ϪC4 132.2(3), TiϪO4ϪC6 128.5(4).
the dichlorotitanate 8a in quantitative yield. This showed
itself to be a highly air- and moisture-sensitive solid but,
nevertheless, was characterized by its NMR and CI mass
spectra. In an analogous way, the difluoro complex 8b was
accessible from 6b by treatment with titanium tetrafluoride.
Remarkably, two fluorine resonances were displayed at δ ϭ
1
40.0 and 201.2 in the 19F-NMR spectrum at room tem-
perature. When the isomeric mixture of 6b/7b was allowed
to react with dichlorotitanium diisopropoxide, the mono-
chlorotitanate 8c resulted diastereoselectively, and only a
single isomer could be detected by NMR spectroscopy. In
addition, the complex 8c showed the characteristic intensity
ϩ
pattern of [MNH4] in its CI mass spectrum. Thus, the
In consequence of theoretical reflections, nine facial dia-
stereomers besides two mer-isomers are conceivable by chel-
highly reactive, Lewis acidic halo complexes 8aϪc are read-
ily available from the novel stable bis-chelated titanates 6/7.
The titanium complexes 8 are expected to be useful cata-
lysts for asymmetric transformations. The corresponding
work, the results of which will be published in future com-
munications, is in progress in our laboratory.
ation of two homochiral terdentate ligands, each of them
[20]
possessing three different functional groups.
Due to the
rigid arrangement in the ligands 4aϪd the formation of one
or more of the fac-isomers seems to be strongly disfavoured.
Presumably, the minor diastereomers 7 are formed as meri-
dional isomers with a (C) configuration.
The stable bis-chelated complex 6b and/or its dia-
stereomer 7b turned out to be suitable, storage-type precur-
This work was supported by the Fonds der Chemischen Industrie,
the Graduiertenförderung and the Dr. Jost-Henkel-Stiftung (grants
to R. F.). We would like to thank Mrs. M. Beuer, Dr. W. Peters,
Mr. G. Broszeit, and Mr. R. Bürgel for recording the spectra. Spe-
sors of the reactive halo complexes 8aϪc. Thus, the ad- cial thanks go to Mrs. K. Kölling for preliminary investigations in
dition of titanium tetrachloride to a solution of 6b/7b gave connection with the X-ray structure analysis and to Dr. U.
Eur. J. Org. Chem. 1998, 1063Ϫ1070
1065

R. Fleischer, H. Wunderlich, M. Braun
FULL PAPER
Matthiesen, who detected the protonated molecular ions of several
titanium complexes.
was added and the mixture was warmed with a heat gun without
stirring. After the start of the reaction, a solution of bromobenzene
(
273 ml, 2.61 mol) in 500 ml of diethyl ether was added through
the dropping funnel within 3 h, in course of that the mixture boiled
gently without external heating. After stirring for an additional 3
h at room temp., the mixture was cooled to 0°C and (R)-1 (58.0 g,
Experimental Section
General: All reactions were carried out under dry, purified argon.
The solvents were dried according to established procedures and
distilled under argon. Diethyl ether and dichloromethane were
withdrawn from the receiving flask, which was closed by a septum,
with syringes or cannulas. Deuteriochloroform was dried with mo-
0
.29 mol) was added in small portions at such a rate that the temp.
did not exceed 5°C. After stirring for 6 h at room temp., the reac-
tion mixture was slowly poured into a steel beaker containing 2 kg
of ice. The mixture was treated with 6  hydrochloric acid (500 ml)
and stirred vigorously. The hydrochloride of (R)-2 formed thereby
as a white precipitate was collected in a suction filter, washed with
diethyl ether and dissolved in a 2  solution of sodium hydroxide
in methanol. The solution was concentrated in a rotary evaporator
and the oily residue was distributed between dichloromethane (2 l)
and water (1 l). The aqueous phase was removed and the organic
layer was washed three times with water (500 ml), dried with
˚
lecular sieves (4 A) and kept over beaten silver. 3-tert-Butyl-2-
[21]
hydroxybenzaldehyde (3b)
and dichlorotitanium diisopropox-
[
22]
ide
were prepared according to literature procedures. Of the
commercially available reagents, solids were employed without
further purification and liquids were distilled prior to use. For gen-
eral remarks concerning reactions under inert atmosphere, see
[
23]
ref.
Ϫ M.p. (uncorrected): Büchi B-510 and B-540; Reichert
Thermovar. Ϫ Specific rotations: Perkin-Elmer 341. Ϫ IR: Bruker
Vector 22 and Perkin-Elmer 1420. Ϫ NMR: Bruker DRX 500 and
Varian VXR 300; unless stated otherwise, CDCl
TMS as internal standard. Ϫ EI-MS: Varian MAT 311A. Ϫ FAB-
MS: Varian MAT 8200. Ϫ CI-MS: Finnigan MAT Incos 50. Ϫ
TLC: Precoated silica gel 60 F254 aluminium plates (Merck). Ϫ
CC: Silica gel 60, mesh size 0.04Ϫ0.063 mm (Merck). Ϫ Elemental
analyses: Mikroanalytisches Laboratorium Beller (Göttingen) and
Institut für Pharmazeutische Chemie (Universität Düsseldorf).
MgSO , and concentrated. The white solid residue thus obtained
4
was recrystallized from toluene (75 ml) to give 54.9 g (66%) of (R)-
3
solutions and
2
(
(ref.
[13]
49%); m.p. 130.5Ϫ132°C (ref.
[14]
131Ϫ133°C); R
ϭ ϩ235 (c ϭ 1 in chloroform).
Ϫ IR (KBr): ν˜ ϭ 3400 cm , 3100, 3080, 3040, 1600, 1580, 1500,
f
ϭ 0.15
20
n-hexane/ethyl acetate, 5:1); [α]
D
Ϫ1
1
1
450, 1180, 920, 750, 740, 705. Ϫ H NMR (300 MHz): δ ϭ 1.56
(
br. s, 2 H, NH ), 4.70 (br. s, 1 H, OH), 4.97 (s, 1 H, 2-H),
2
6
.97Ϫ7.40 (m, 13 H, aromatic H), 7.71Ϫ7.74 (m, 2 H, aromatic H).
General Procedure for the Synthesis of the Imines 4aϪd: A two-
Methyl (R)-2-Aminophenylacetate Hydrochloride (1): A three-
necked flask was equipped with a reflux condenser, a stopper, and
a fritted gas-dispersion tube, which allowed the introduction of hy-
drochloric acid gas via a three-way stopcock. The gas was passed
through two gas-washing bottles and the reflux condenser was
closed with a three-way cock, which was not only connected to a
combined argon/vacuum line but also to a bubble gage filled with
silicon oil. The flask was charged with (R)-2-aminophenylacetic
acid (phenylglycine) (50.2 g, 0.33 mol), and the air in the flask was
replaced by argon. Absolute methanol (250 ml) was poured into
the flask while a vigorous stream of argon was maintained. The
suspension thus formed was cooled to 0°C and subsequently satu-
rated with gaseous hydrogen chloride. In the course of this, the
mixture was allowed to reach room temp. and a clear colourless
solution formed. The solution was refluxed for 3 h and kept at
room temp. overnight. Thereby, a white precipitate formed which
was washed with diethyl ether and recrystallized from methanol/
diethyl ether (1:1). The crystals were subsequently washed with di-
ethyl ether and dried at 50°C in vacuo (oil pump). Concentration
of the mother liquors in the recrystallization described above gave
another crop of 1 which was treated in the same way. Total yield:
necked pear-shaped flask was charged with 15.75 mmol of the alde-
hyde 3, connected to the combined argon/vacuum line and closed
with a septum. The air in the flask was replaced by argon, and
absolute methanol (50 ml) was added by syringe. In a second,
round-bottom three-necked flask, equipped with a magnetic stirrer,
a connection to the combined argon/vacuum line, and two septa, a
2 4
mixture of (R)-2 (4.34 g, 15.0 mmol), Na SO (4.30 g, 30.3 mmol),
absolute methanol (40 ml) and dichloromethane (40 ml) was stirred
under argon and cooled to Ϫ20°C. The solution of the aldehyde 3
was added slowly through a cannula whereby the flask containing
the amino alcohol 2 was slightly evacuated. Immediately, the mix-
ture turned bright yellow. During the addition, the temp. as moni-
tored by a thermocouple, introduced through the septum, was not
allowed to exceed Ϫ18°C. After treating the mixture under the re-
action conditions given below, the mixture was filtered at 0°C. (In
the case of 4d, the mixture was diluted with 100 ml of dichloro-
methane prior to filtration.) Thereupon, the filtrate was concen-
trated in vacuo at 0°C. In the cases of 4a, 4b, and 4d the solid
residue was treated with n-pentane (40 ml) and stirred vigorously
for 30 min. The solid thus formed was filtered in a sintered glass
frit, washed with 40 ml of n-pentane and dried at 40°C for 5 h in
vacuo (oil pump). Crude 4c was submitted to CC.
[
12c]
[12b]
5
(
8.0 g (87%) (ref.
33%, ref.
70Ϫ85%); m.p. 220.5Ϫ221°C
ref.[
12c]
222Ϫ223°C); [α]
20
ϭ Ϫ115 (c ϭ 1 in water) {ref.
[12c]
:
D
24
ϭ Ϫ119 (c ϭ 1.09 in water)}. Ϫ IR (KBr): ν˜ ϭ 3000 cmϪ1,
[α]
D
According to this procedure, the following were obtained:
1
2940, 1735, 1560, 1500, 1420, 1380, 1240, 1050, 710. Ϫ H NMR
(
R)-2-{[(2-Hydroxy-1,2,2-triphenylethyl)imino]methyl}phenol
4a): Light yellow solid, prepared in 81% yield by stirring at Ϫ18°C
for 18 h; m.p. 125Ϫ126°C; R ϭ 0.4 (n-hexane/ethyl acetate, 5:1);
2 4
(300 MHz, D O, [D ]sodium trimethylsilylpropionate): δ ϭ 3.82
(
(
s, 3 H, CH ), 5.34 (s, 1 H, 2-H), 7.49Ϫ7.57 (m, 5 H, aromatic H).
3
f
2
5
Ϫ1
(
R)-2-Amino-1,1,2-triphenylethanol (2): A four-necked flask was [α]
equipped with an overhead stirrer, a jacketed coil condenser con- 3100, 3080, 1635, 1590, 1500, 1455, 1280, 1060, 765, 705. Ϫ H
nected to the combined argon/vacuum line, a pressure-equalizing NMR (300 MHz): δ ϭ 2.93 [s, 1 H, Ph C(OH)], 5.49 [s, 1 H,
D
ϭ ϩ207 (c ϭ 1 in chloroform). Ϫ IR (KBr): ν˜ ϭ 3580 cm
,
1
2
dropping funnel closed by a septum, and a stopper. The flask was
charged with magnesium cuttings (63.7 g, 2.62 mol), and the air
PhCH(N)], 6.81 (t, J3-H,4-H ϭ J4-H,5-H ϭ 7.6 Hz, 1 H, 4-H), 6.89
(d, J5-H,6-H ϭ 8.2 Hz, 1 H, 6-H), 7.06Ϫ7.35 (m, 15 H, aromatic H),
was replaced by argon. Absolute diethyl ether (100 ml) was added 7.58Ϫ7.61 (m, 2 H, aromatic H), 8.32 (s, 1 H, NCHAr), 12.82 (s,
1
3
through the dropping funnel and the stopper was removed for the
addition of crystalline iodine (approx. 0.05 g). The flask was closed
immediately and the mixture was stirred until the brownish color
disappeared. Thereafter, neat bromobenzene (7.9 ml, 0.075 mol)
1 H, ArOH). Ϫ C NMR (75 MHz): δ ϭ 78.8 [PhCH(N)], 80.5
[Ph C(OH)], 116.9 (C-6), 118.7 (C-4), 118.8 (C-2), 126.4Ϫ129.7
2
[aromatic C (Ph)], 131.8, 132.7 (C-3, C-5), 138.2, 143.7, 144.7 [aro-
matic ipso-C (Ph)], 160.6 (C-1), 167.3 (NCHAr). Ϫ EI-MS (70 eV);
1066
Eur. J. Org. Chem. 1998, 1063Ϫ1070

Novel Chiral Imine-Alkoxytitanium Complexes
FULL PAPER
ϩ
ϩ
ϩ
ϩ
2 2
m/z (%): 393 (1) [M ], 212 (16), 211 (100) [M Ϫ Ph CO], 260 (70)
CO], 210 (27) 444 (26) [M ϩ 1], 262 (35), 261 (100) [M Ϫ Ph
ϩ
ϩ
[M
Ϫ Ph
07 (8) [hydroxytropylium cation], 106 (26), 105 (53) [PhCO and/ [Ph
)], 91 (27) [C ], 77 (27), 51 (9). Ϫ C27
393.5): calcd. C 82.42, H 5.89, N 3.56; found C 82.24, H 5.98, cation], 106 (41), 105 (80) [PhCO and/or PhC(NH
N 3.55. [C ], 77 (75), 51 (18). Ϫ C31 (443.5): calcd. C 83.94, H
2
C(OH)], 194 (4) [211 Ϫ OH], 183 (21), 182 (25) [Ph
2
CO], [M Ϫ Ph
CO], 167 (24) [Ph
(CH )(OH)], 136 (21), 115 (17), 107 (21) [hydroxytropylium
)], 91 (34)
2
C(OH)], 244 (11) [261 Ϫ OH], 183 (28), 182 (15)
1
2
2
CH], 165 (21) fluorenyl cation], 157 (20)
or PhC(NH
2
7
H
7
H
23NO
2
[C10H
6
2
(
2
7
H
7
H25NO
2
5
.69, N 3.16; found C 83.58, H 5.83, N 3.23.
(
R)-2-(1,1-Dimethylethyl)-6-{[(2-hydroxy-1,2,2-triphenylethyl)-
General Procedure for the Preparation of NMR Samples of 5aϪd:
imino]methyl}phenol (4b): Light yellow solid, prepared in 91% yield
Under argon, the corresponding imine 4 (0.34 mmol) was dissolved
in 2.5 ml of deuteriochloroform in a 10-ml flask. Freshly distilled
titanium tetraisopropoxide (0.1 ml, 0.34 mmol) was added by syr-
inge, and the mixture was stirred for 12 h at room temp. A part of
this solution (0.7 ml) was transferred into an argon-filled NMR
tube. In all cases no signals arising from the corresponding imine
by stirring at Ϫ18 to 0°C for 18 h; m.p. 124.5Ϫ126.5°C; R
f
ϭ 0.6
ϭ ϩ193 (c ϭ 1 in chloroform).
Ϫ IR (KBr): ν˜ ϭ 3450 cm , 3060, 3040, 2960, 1615, 1600, 1495,
25
(
n-hexane/ethyl acetate, 6:1); [α]
D
Ϫ1
1
1
[
6
450, 1435, 1265, 1145, 750, 700. Ϫ H NMR (300 MHz): δ ϭ 1.38
s, 9 H, C(CH ], 3.04 [s, 1 H, Ph C(OH)], 5.44 [s, 1 H, PhCH(N)],
.74 (t, J3-H,4-H ϭ J4-H,5-H ϭ 7.7 Hz, 1 H, 4-H), 6.97 (dd, J ϭ 7.7
3
)
3
2
4
could be detected and the diastereomeric mixture of 6/7 was only
Hz, J3-H,5-H ϭ 1.6 Hz, 1 H, 3-H or 5-H), 7.08Ϫ7.33 (m, 14 H,
aromatic H), 7.59Ϫ7.61 (m, 2 H, aromatic H), 8.35 (s, 1 H,
obtained as byproduct in small amounts besides unreacted titanium
tetraisopropoxide (usually < 4%; in the case of 5d 39%). After the
removal of the solvent under reduced pressure (oil pump), 5c was
kept in vacuo for 1 h, after which the complex was free of solvent
and 2-propanol and could also be characterized spectroscopically.
13
NCHAr), 13.24 (s, 1 H, ArOH). Ϫ C NMR (75 MHz): δ ϭ 29.2
C(CH ], 34.8 [C(CH ], 79.2 [PhCH(N)], 80.4 [Ph C(OH)],
17.9 (C-4), 118.6 (C-6), 126.4Ϫ130.1 [aromatic C (Ph), C-3, C-5],
[
)
3 3
3
)
3
2
1
1
1
37.2, 138.5, 143.7, 144.7 [aromatic ipso C (Ph), C-2], 160.0 (C-1),
ϩ
67.9 (NCHAr). Ϫ EI-MS (70 eV); m/z (%): 450 (1) [M ϩ 1], 268
The following NMR data were obtained:
ϩ
ϩ
(
20), 267 (100) [M Ϫ Ph
26), 182 (12) [Ph CO], 163 (2) [(C
07 (12) [hydroxytropylium cation], 106 (63), 105 (46) [PhCO and/
2
CO], 266 (23) [M Ϫ Ph
2
C(OH)], 183
(
R)-{2-{[(2-Hydroxy-1,2,2-triphenylethyl)imino]methyl}-
(
1
2
4 9
H
)-hydroxytropylium cation],
phenolato(2Ϫ)-N,O,OЈ}titanium Bis-1-methylethoxide (5a·2 iPr-
1
OH): H NMR (500 MHz): δ ϭ 1.13 [d, J ϭ 6.0 Hz, 6 H,
or PhC(NH
C H31NO
31 2
2
)], 91 (25) [C
(449.6): calcd. C 82.82, H 6.95, N 3.12; found C 82.69,
H 6.89, N 3.07.
7 7 4 9
H ], 77 (27), 57 (16) [C H ], 51 (7). Ϫ
OCH(CH
J ϭ 6.0 Hz, 3 H, OCH(CH
3
)
2
], 1.20 [d, J ϭ 6.0 Hz, 12 H, HOCH(CH
)(CH )], 1.34 [d, J ϭ 6.0 Hz, 3 H,
)], 4.01 [m, 2 H, HOCH(CH ], 4.68 [sept, J ϭ
], 4.89 [sept, J ϭ 6.0 Hz, 1 H,
], 5.98 [s, 1 H, PhCH(N)], 6.75Ϫ7.40 (m, 17 H, aro-
3 2
) ], 1.30 [d,
3
3
OCH(CH
3
)(CH
3
3 2
)
(
R)-2,4-Bis-(1,1-dimethylethyl)-6-{[(2-hydroxy-1,2,2-triphenyl- 6.0 Hz, 1 H, OCH(CH
3
)
2
ethyl)imino]methyl}phenol (4c): Yellow solid, prepared by stirring
at Ϫ18°C for 72 h and isolated by CC in 88% yield (n-hexane/ethyl
OCH(CH
3
)
2
matic H), 7.73Ϫ7.75 (m, 2 H, aromatic H), 8.48 (s, 1 H, NCHAr).
20
13
acetate, 10:1); m.p. 129.5Ϫ130.5°C; R
f
ϭ 0.5; [α]
D
ϭ ϩ187 (c ϭ
Ϫ
C NMR (125 MHz): δ ϭ 25.4 [HOCH(CH
3
)
2
], 25.8, 25.9
], 78.6, 79.2 [OCH(CH ], 87.5
C(OTi)], 118.1, 119.0 (C-4, C-6), 121.0 (C-2),
125.7Ϫ129.3 [aromatic C (Ph)], 133.2, 135.7 (C-3, C-5), 140.2,
C(OH)], 5.46 [s, 146.0, 148.3 [aromatic ipso-C (Ph)], 164.3 (C-1), 166.3 (NCHAr).
.5 in chloroform). Ϫ IR (KBr): ν˜ ϭ 3450 cmϪ1, 3060, 3040, 2960, [OCH(CH
625, 1600, 1480, 1450, 1390, 1360, 1250, 1170, 750, 700. Ϫ H [PhCH(N)], 90.6 [Ph
)
], 64.4 [HOCH(CH
)
3 2
0
1
3
2
3 2
)
1
2
NMR (300 MHz): δ ϭ 1.25 [s, 9 H, C(CH
3
)
3
bound to C-4], 1.39
[
s, 9 H, C(CH
3
)
3
bound to C-2], 3.06 [s, 1 H, Ph
2
1
7
H, PhCH(N)], 6.96 (d, J3-H,5-H ϭ 2.4 Hz, 1 H, 3-H or 5-H),
.06Ϫ7.35 (m, 14 H, aromatic H), 7.58Ϫ7.61 (m, 2 H, aromatic
(
R)-{2-(1,1-Dimethylethyl)-6-{[(2-hydroxy-1,2,2-triphenyl-
ethyl)imino]methyl}phenolato(2Ϫ)-N,O,OЈ}titanium Bis-1-methyl-
ethoxide (5b·2 iPrOH): H NMR (500 MHz): δ ϭ 1.06 [d, J ϭ 6.0
13
H), 8.40 (s, 1 H, NCHAr), 13.00 (s, 1 H, ArOH). Ϫ C NMR
75 MHz): δ ϭ 29.4, 31.4 [C(CH ], 34.1, 35.0 [C(CH ], 79.0
PhCH(N)], 80.4 [Ph C(OH)], 117.9 (C-6), 126.4Ϫ129.6 [aromatic
1
(
[
)
3 3
3 3
)
Hz, 3 H, OCH(CH
HOCH(CH ], 1.23 [d, J ϭ 6.0 Hz, 3 H, OCH(CH
.31Ϫ1.32 [m, 6 H, OCH(CH ], 1.45 [s, 9 H, C(CH ], 4.01 [m,
H, HOCH(CH ], 4.72 [m, 1 H, OCH(CH ], 4.88 [m, 1 H,
], 5.95 [s, 1 H, PhCH(N)], 6.69Ϫ7.42 (m, 16 H, aro-
matic H), 7.67Ϫ7.68 (m, 2 H, aromatic H), 8.46 (s, 1 H, NCHAr).
3
)(CH
3
)], 1.20 [d, J ϭ 6.0 Hz, 12 H,
2
)
)(CH )],
3
2
3
3
C (Ph), C-3, C-5], 136.6, 138.8, 140.2, 143.9, 145.0 [aromatic ipso-
C (Ph), C-2, C-4], 157.7 (C-1), 168.5 (NCHAr). Ϫ FAB-MS (NBA);
1
2
3
)
2
3 3
)
3
)
2
3 2
)
ϩ
ϩ
m/z (%): 506 (6) [M ϩ 1], 324 (24), 323 (100) [M Ϫ Ph
2
CO], 322
], 203 (11), 183 (22)
CH], 106 (17), 105 (41) [PhCO and/or
], 77 (19), 57 (42) [C ], 51 (5), 41 (20)
(505.7): calcd. C 82.72, H 7.96, N 2.84;
found C 83.05, H 7.74, N 2.72.
3 2
OCH(CH )
ϩ
(
55) [M Ϫ Ph
Ph C(OH)], 167 (12) [Ph
PhC(NH )], 91 (26) [C
]. Ϫ C35
2 4 9
C(OH)], 266 (6) [323 Ϫ C H
[
2
2
13
Ϫ
C NMR (125 MHz): δ ϭ 25.4 [HOCH(CH
6.06, 26.12 [OCH(CH ], 29.5 [C(CH ], 35.0 [C(CH
HOCH(CH ], 78.1, 78.9 [OCH(CH ], 86.8 [PhCH(N)], 90.7
Ph C(OTi)], 117.4 (C-4), 121.4 (C-6), 125.6Ϫ129.4 [aromatic C
Ph)], 131.6, 132.4 (C-3, C-5), 139.0, 140.4, 146.6, 149.0 [aromatic
3 2
) ], 25.0, 26.0,
2
7
H
7
4 9
H
2
[
[
)
3 2
)
3 3
)
], 64.4
3
3
[C
3
H
5
H39NO
2
3
)
2
3 2
)
2
(
(
R)-1-{[(2-Hydroxy-1,2,2-triphenylethyl)imino]methyl}-2-naph-
thol (4d): Yellowish brown solid, prepared in 93% yield by stirring
at Ϫ18 to 0°C for 18 h; m.p. 124Ϫ126°C; R ϭ 0.1 (n-hexane/ethyl
ϭ ϩ 203 (c ϭ 1 in chloroform). Ϫ IR (KBr):
ν˜ ϭ 3420 cm , 3060, 3035, 1625, 1545, 1495, 1450, 1355, 750, 700.
ipso-C (Ph), C-2], 163.7 (C-1), 166.8 (NCHAr).
f
(R)-{2,4-Bis-(1,1-dimethylethyl)-6-{[(2-hydroxy-1,2,2-triphen-
ylethyl)imino]methyl}phenolato(2Ϫ)-N,O,OЈ}titanium
methylethoxide (5c): H NMR (300 MHz): δ ϭ 1.07 [d, J ϭ 6.1 Hz,
25
acetate, 5:1); [α]
D
Bis-1-
Ϫ1
1
1
Ϫ H NMR (500 MHz): δ ϭ 3.38 [s, 1 H, Ph
PhCH(N)], 6.90 (d, J3-H,4-H ϭ 9.5 Hz, 1 H, 3-H), 7.10Ϫ7.35 (m, 15 OCH(CH
H, aromatic H), 7.58 (d, J5-H,6-H ϭ 7.6 Hz, 1 H, 5-H), 7.63Ϫ7.67 J ϭ 6.1 Hz, 3 H, OCH(CH
m, 4 H, aromatic H), 8.80 (s, 1 H, NCHAr), 14.81 (s, 1 H, ArOH). OCH(CH )(CH )], 1.47 [s, 9 H, C(CH
C(OH)], J ϭ 6.1 Hz, 1 H, OCH(CH ], 4.90 [sept, J ϭ 6.1 Hz, 1 H,
], 5.96 [s, 1 H, PhCH(N)], 6.90Ϫ7.51 (m, 15 H, aro-
matic H), 7.68Ϫ7.70 (m, 2 H, aromatic H), 8.50 (s, 1 H, NCHAr).
2
C(OH)], 5.57 [s, 1 H,
3
H, OCH(CH
)(CH )], 1.26 [s, 9 H, C(CH
)(CH
3
)(CH
3
)], 1.22 [d,
J
ϭ
6.1 Hz,
3
H,
3
3
3
)
3
bound to C-4], 1.32 [d,
3
3
)], 1.33 [d, J ϭ 6.1 Hz, 3 H,
bound to C-2], 4.74 [sept,
(
Ϫ
3
3
3 3
)
13
C NMR (75 MHz): δ ϭ 75.4 [PhCH(N)], 80.6 [Ph
2
3 2
)
1
(
07.6 (C-1), 118.3, 122.9 (C-6, C-8), 123.1 (C-3), 126.4 [aromatic C OCH(CH
Ph)], 126.6 (C-10), 126.8Ϫ129.5 [aromatic C (Ph), C-7], 129.1 (C-
), 133.3 (C-9), 136.5 (C-4), 137.5, 143.6, 144.0 [aromatic ipso-C
3 2
)
1
3
5
(
Ϫ
3 3
C NMR (75 MHz): δ ϭ 26.0 [OCH(CH )(CH )], 26.1
Ph)], 159.6 (NCHAr), 171.9 (C-2).[ Ϫ FAB-MS (NBA); m/z (%): [OCH(CH
24]
)
], 26.2 [OCH(CH )(CH )], 29.6, 31.3 [C(CH
)
3 3
], 34.1,
3
2
3
3
Eur. J. Org. Chem. 1998, 1063Ϫ1070
1067

R. Fleischer, H. Wunderlich, M. Braun
FULL PAPER
35.2 [C(CH
3 3
) ], 77.9, 78.7 [OCH(CH
)
], 86.9 [PhCH(N)], 90.6 anol and chloroform (1:1). When half of the solvent had evaporated
3 2
[
Ph
2
C(OTi)], 120.5 (C-6), 125.6Ϫ130.6 [aromatic C (Ph), C-3, C-5], at room temp., yellow crystals formed which were suitable for a
38.2, 139.6, 140.6, 146.7, 149.1 [aromatic ipso-C (Ph), C-2, C-4], crystal-structure analysis. M.p. 283Ϫ284°C; R
ϭ 0.8 (chloroform/
ϭ ϩ296 (c ϭ 1 in chloroform). Ϫ IR (KBr):
ν˜ ϭ 3060 cm , 3020, 2955, 2865, 1615, 1550, 1420, 1390, 1300,
1
1
f
2
0
61.9 (C-1), 167.2 (NCHAr).
R)-{1-{[(2-Hydroxy-1,2,2-triphenylethyl)imino]methyl}-2-
naphtholato(2Ϫ)-N,O,OЈ}titanium Bis-1-methylethoxide (5d·2 iPr-
n-hexane, 2:1); [α]
D
Ϫ1
(
1
1
200, 1045, 910, 875, 755, 705. Ϫ H NMR (500 MHz): δ ϭ 0.55
[s, 18 H, C(CH ], 6.48 [d, J ϭ 1.3 Hz, 2 H, PhCH(NCHAr)], 6.63
t, J3-H,4-H ϭ J4-H,5-H ϭ 7.6 Hz, 2 H, 4-H), 6.95Ϫ7.13 (m, 22 H,
aromatic H), 7.51Ϫ7.60 (m, 12 H, aromatic H), 8.42 [d, J ϭ 1.3
1
3 3
)
OH): Ϫ H NMR (500 MHz): δ ϭ 1.06 [m, 6 H, OCH(CH
.19 [d, J ϭ 5.7 Hz, 12 H, HOCH(CH ], 1.36 [d, J ϭ 5.7 Hz, 3
H, OCH(CH )(CH )], 1.40 [d, J ϭ 5.7 Hz, 3 H, OCH(CH )(CH )],
.99 [sept, J ϭ 5.7 Hz, 2 H, HOCH(CH ], 4.55 [m, J ϭ 5.7 Hz,
H, OCH(CH ], 4.95 [m, J ϭ 5.7 Hz, 1 H, OCH(CH ], 6.13
3 2
) ],
(
1
3 2
)
3
3
3
3
1
3
Hz, 2 H, PhCH(NCHAr)]. Ϫ C NMR (75 MHz): δ ϭ 28.5
C(CH ], 31.2 [C(CH ], 89.0 [PhCH(N)], 93.1 [Ph C(OTi)],
17.0 (C-4), 121.8 (C-6), 125.7Ϫ130.4 [aromatic C (Ph)], 131.8,
32.2 (C-3, C-5), 137.6, 140.4, 147.2, 148.2 [aromatic ipso-C (Ph),
); m/z (%): 943
)(NH )], 200 (30)
C(OH)], 123 (6) [PhCO(NH )]. Ϫ EI-
3
1
3 2
)
[
3
)
3
)
3 3
2
)
3 2
3 2
)
1
1
[
s, 1 H, PhCH(N)], 6.90Ϫ7.98 (m, 21 H, aromatic H), 9.36 (s, 1
H, NCHAr).
C-2], 164.4 (C-1), 164.6 (NCHAr). Ϫ CI-MS (NH
3
General Procedure for the Synthesis of the Bis-Chelated Com-
plexes 6aϪd: A two-necked flask, equipped with a magnetic stirrer,
a reflux condenser with a connection to the combined argon/vac-
uum line, and a septum, was charged with 2.05 mmol of the corre-
sponding imine 4. The air in the flask was replaced by argon, and
absolute dichloromethane (6 ml) was added. Freshly distilled ti-
tanium tetraisopropoxide (0.3 ml, 1.02 mmol) was injected, and
the solution was treated according to the reaction conditions given
below. The solvent was removed in a rotary evaporator and the
solid residue was either submitted to crystallization (6c) or to CC
ϩ
(
[
100) [M
Ph CO(NH
MS (70 eV); m/z (%): 760 (46) [M Ϫ Ph
ϩ
1], 217 (38) [Ph
2
CO(NH
3
4
2
4
)], 183 (4) [Ph
2
4
ϩ
ϩ
2
CO], 578 (65) [M Ϫ 2
CO; z ϭ 2], 183 (6), 182 (29)
CO], 165 (10) fluorenyl cation], 106 (9), 105 (100) [PhCO and/
or PhC(NH )], 91 (20) [C ], 77 (64), 64 (34), 57 (56) [C ], 51
30), 43 (30) [C ]. Ϫ C62 Ti (943.0): calcd. C 78.95, H
.20, N 2.97; found C 78.64, H 6.24, N 2.99. Ϫ Intensity pattern
ϩ
(
Ph
2 2
CO)], 380 (21) [M Ϫ Ph
[Ph
2
2
7
H
7
4 9
H
(
6
3
H
7
58 2 4
H N O
ϩ
of [M ϩ 1]; m/z (calcd., found [%]): 947 (3.2, 4), 946 (12.2, 12),
45 (35.3, 34), 944 (74.3, 73), 943 (100.0, 100), 942 (16.5, 19), 941
9.8, 11).
9
(
(
6a, 6b, and 6d), both methods resulting in the isolation of the
enantiomerically pure main products 6. For the isolation of the
pure diastereomeric mixtures of 6/7, an alternative procedure to
CC can be followed: The residue was suspended in 10 ml of meth-
anol (6b, 6d) or n-hexane (6a) and stirred vigorously for 30 min.
Thereupon, the solid was collected in a glass frit, washed with 10
ml of the suspension agent used before and dried at 40°C in vacuo
for 6 h.
[
OC-6-22Ј-(A),(R),(R)]-Bis-{2,4-bis-(1,1-dimethylethyl)-6-
{
[(2-hydroxy-1,2,2-triphenylethyl)imino]methyl}phenolato(2Ϫ)-
N,O,OЈ}titanium (6c): Bright yellow crystals, prepared in 49% yield
by heating to reflux for 4 h and crystallization in methanol/chloro-
form (2:1); m.p. 279.5Ϫ281°C; [α]
form). Ϫ IR (KBr): ν˜ ϭ 3060 cm , 3025, 2960, 2870, 1620, 1540,
310, 1255, 1175, 1030, 850, 760, 700. Ϫ H NMR (500 MHz): δ ϭ
.55 [s, 18 H, C(CH bound to C-2], 1.24 [s, 18 H , C(CH
2
5
D
ϭ ϩ287 (c ϭ 0.74 in chloro-
Ϫ1
1
1
0
According to this procedure, the following were obtained:
3
)
3
3 3
)
[
OC-6-22Ј-(A),(R),(R)]-Bis-{2-{[(2-hydroxy-1,2,2-triphen- bound to C-4], 6.45 [s, 2 H, PhCH(N)], 6.94Ϫ6.99 (m, 12 H, aro-
ylethyl)imino]methyl}phenolato(2Ϫ)-N,O,OЈ}titanium (6a): Bright matic H), 7.05 [d, J3-H,5-H ϭ 2.5 Hz, 2 H, 3-H or 5-H), 7.10Ϫ7.12
yellow solid, prepared in 68% yield by stirring 12 h at room temp.; (m, 6 H, aromatic H), 7.22 (d, J3-H,5-H ϭ 2.5 Hz, 2 H, 3-H or 5-
2
0
m.p. 239Ϫ241°C; R
f
ϭ 0.6 (chloroform/n-hexane, 3.5:1); [α]
D
ϭ
H), 7.50Ϫ7.60 (m, 12 H, aromatic H), 8.42 (s, 2 H, NCHAr). Ϫ
Ϫ1
13
ϩ929 (c ϭ 1 in chloroform). Ϫ IR (KBr): ν˜ ϭ 3060 cm , 3035,
620, 1545, 1445, 1390, 1310, 1260, 1040, 910, 805, 755, 700. Ϫ H [C(CH ], 88.9 [PhCH(N)], 93.0 [Ph C(OTi)], 121.1 (C-6),
3 3
C NMR (125 MHz): δ ϭ 28.7, 31.4 [C(CH ) ], 34.0, 34.4
1
1
3
)
3
2
NMR (500 MHz): δ ϭ 5.45 (d, J5-H,6-H ϭ 8.8 Hz, 2 H, 6-H), 6.38
125.6Ϫ127.1 [aromatic C (Ph)], 127.4 (C-3 or C-5), 127.9Ϫ128.1
[s, 2 H, PhCH(N)], 6.59 (t, J3-H,4-H ϭ J4-H,5-H ϭ 7.6 Hz, 2 H, 4-
[aromatic C (Ph)], 130.3 (C-3 or C-5), 130.5 [aromatic C (Ph)],
H), 6.92Ϫ7.10 (m, 20 H, aromatic H), 7.16 (d, J3-H,4-H ϭ 7.6 Hz, 136.8, 139.1, 140.6, 147.4, 148.4 [aromatic ipso-C (Ph), C-2, C-4],
H, 3-H), 7.19Ϫ7.46 (m, 4 H, aromatic H), 7.98Ϫ7.99 (m, 4 H,
162.7 (C-1), 164.8 (NCHAr). Ϫ CI-MS (NH ); m/z (%): 1055 (48)
)], 200 (100) [Ph CO(NH )],
C(OH)], 123 (17) [PhCO(NH )], 106 (20) [PhCHO].
2
3
1
3
ϩ
aromatic H), 8.64 (s, 2 H, NCHAr). Ϫ C NMR (75 MHz): δ ϭ [M ϩ 1], 217 (32) [Ph
7.0 [PhCH(N)], 92.9 [Ph
C(OTi)], 117.0 (C-4), 118.5 (C-6), 120.0 183 (23) [Ph
C-2), 125.5Ϫ129.6 [aromatic C (Ph)], 133.0 (C-3), 134.8 (C-5), Ϫ EI-MS (70 eV); m/z (%): 873 (100) [MH Ϫ Ph
2
CO(NH
3
)(NH
4
2
4
8
(
1
2
2
4
ϩ
2
CO], 691 (71)
CO; z ϭ 2], 182 (12)
)], 83 (62), 77 (21), 57
ϩ
ϩ
41.7, 146.8, 146.9 [aromatic ipso-C (Ph)], 164.3 (C-1), 166.3
[MH Ϫ 2 (Ph
2
CO)], 436.5 (38) [MH Ϫ Ph
2
ϩ
(NCHAr). Ϫ CI-MS (NH
3
); m/z (%): 831 (100) [M ϩ 1], 217 (51) [Ph
2
C(OH)], (30) [C
ϩ
CO], 105 (39) [PhCO and/or PhC(NH
2
ϩ
[Ph
2
CO(NH
23 (14) [PhCO(NH
3
)(NH
4
)], 200 (43) [Ph
2
CO(NH
4
)], 183 (5) [Ph
2
4
H
9
74 2 4
]. Ϫ C70H N O Ti (1055.2). Ϫ Intensity pattern of [M
ϩ 1]; m/z (calcd., found [%]): 1059 (4.4, 4), 1058 (15.5, 13), 1057
], (41.6, 37), 1056 (82.2, 75), 1055 (100.0, 100), 1054 (17.2, 15), 1053
1
4
)]. Ϫ EI-MS (70 eV); m/z (%): 648 (47) [M
ϩ
Ϫ Ph
24 (11) [M Ϫ Ph
Ph CO], 165 (15) fluorenyl cation], 106 (9), 105 (63) [PhCO and/or
PhC(NH
3 (100) [C
2
CO], 466 (69) [M Ϫ 2 (Ph
2
CO)], 375 (23) [466 Ϫ C
7
H
7
ϩ
3
[
2
CO; z ϭ 2], 256 (40), 183 (10), 182 (39) (9.7, 9).
2
[
OC-6-22Ј-(A),(R),(R)]-Bis-{1-{[(2-hydroxy-1,2,2-
triphenylethyl)imino]methyl}-2-naphtholato(2Ϫ)-N,O,OЈ}titanium
6d): Bright yellow solid, prepared in 78% yield by heating to reflux
2
)], 91 (11) [C
]. Ϫ C54
7
H
H
7
], 77 (29), 57 (98) [C
4 9
H ], 51 (12), 44 (83),
4
3
H
7
42
N
O
2 4
Ti (830.8): calcd. C 78.05, H 5.10,
(
ϩ
N 3.37; found C 77.78, H 5.23, N 3.63. Ϫ Intensity pattern of [M
ϩ 1]; m/z (calcd., found [%]): 835 (2.3, 3), 834 (9.5, 10), 833 (29.5,
3
f
for 4 h; m.p. 200.5Ϫ202°C; R ϭ 0.6 (chloroform/n-hexane, 2:1),
20
ϭ 1021 (c ϭ 1 in chloroform). Ϫ IR (KBr): ν˜ ϭ 3070 cmϪ1
[α]
D
,
0), 832 (66.2, 68), 831 (100.0, 100), 830 (15.9, 17), 829 (10.0, 11).
3
030, 1620, 1605, 1540, 1455, 1400, 1360, 1340, 1195, 1045, 825,
OC-6-22Ј-(A),(R),(R)]-Bis-{2-(1,1-dimethylethyl)-6-{[(2- 750, 700. Ϫ H NMR (300 MHz): δ ϭ 5.52 (d, J3-H,4-H ϭ 9.1 Hz,
1
[
hydroxy-1,2,2-triphenylethyl)imino]methyl}phenolato(2Ϫ)-
N,O,OЈ}titanium (6b): Bright yellow solid, prepared in 75% yield
2 H, 3-H), 6.44 [s, 2 H, PhCH(N)], 6.84Ϫ7.49 (m, 36 H, aromatic
1
3
H), 7.96Ϫ8.00 (m, 4 H, aromatic H), 9.48 (s, 2 H, NCHAr). Ϫ
C
by stirring 12 h at room temp. In order to obtain a crystalline NMR (75 MHz): δ ϭ 88.0 [PhCH(N)], 93.2 [Ph
2
C(OTi)], 110.6 (C-
product, a sample was dissolved in the minimum amount of meth-
068
1), 119.0 (C-6 or C-8), 121.9 (C-3), 122.9 (C-6 or C-8), 125.6Ϫ129.6
1
Eur. J. Org. Chem. 1998, 1063Ϫ1070

Novel Chiral Imine-Alkoxytitanium Complexes
FULL PAPER
[
aromatic C (Ph), C-5, C-7], 127.3 (C-10), 133.2 (C-9), 135.7 (C-4), mmol) was dissolved in absolute acetonitrile (1 ml) under argon.[25]
1
42.0, 146.9, 147.0 [aromatic ipso-C (Ph)], 160.8 (NCHAr), 165.9
The latter solution was added dropwise by syringe to the solution
); m/z (%): 931 (100) [M ϩ 1], 217 (41) of 6b at room temp. After stirring for 12 h, the solvent was removed
)], 200 (91) [Ph CO(NH )], 183 (19) under reduced pressure and the solid, yellow residue was exposed
C(OH)], 123 (26) [PhCO(NH )]. Ϫ FAB-MS (NBA); m/z (%): to oil pump vacuum for 1 h at room temp. Yield: 105 mg (99%).
[
24]
ϩ
(C-2).
Ϫ CI-MS (NH
3
[
[
Ph
Ph
2
CO(NH )(NH
3
4
2
4
2
4
ϩ
ϩ
ϩ
1
931 (7) [M ϩ 1], 853 (2) [M Ϫ Ph], 748 (29) [M Ϫ Ph
2
CO],
CO)], 492 (14), 462 C(CH
PhCNH], 359 (29), 207 (50), 157 (49) H), 7.31Ϫ7.37 (m, 3 H, aromatic H), 7.47 (dd, J ϭ 7.5 Hz,
)(OH)], 106 (26), 105 (33) [PhCO and/or PhC(NH )],
], 77 (100), 51 (45). Ϫ C62 Ti (930.9). Ϫ Inten-
Ϫ
3
H NMR {500 MHz, [D ]acetonitrile}: δ ϭ 1.34 [s, 9 H,
ϩ
ϩ
6
71 (13) [M Ϫ Ph
3
CO], 566 (65) [M Ϫ 2 (Ph
2
3 3
)
], 6.54 [s, 1 H, PhCH(N)], 6.84Ϫ7.20 (m, 10 H, aromatic
(
15) [566
(CH
1 (56) [C
Ϫ
[C
10
H
6
2
2
J
3-H,5-H ϭ 1.7 Hz, 1 H, 3-H or 5-H), 7.57Ϫ7.69 (m, 4 H, aromatic
1
3
9
7
H
7
H
46
N
O
2 4
H), 8.82 (s,
1
H, NCHAr).
ϭ 29.6 [C(CH
12.1, 17), 933 (35.2, 38), 932 (74.2, 72), 931 (100.0, 100), 930 (16.5, [PhCH(N)], 94.0 [Ph
Ϫ
C
NMR {125 MHz,
ϩ
sity pattern of [M ϩ 1]; m/z (calcd., found [%]): 935 (3.2, 5), 934
(
[D
3
]acetonitrile}:
δ
)
3 3
], 35.4 [C(CH ], 85.8
3 3
)
2
C(OTi)], 120.2 (C-4), 123.1 (C-6),
126.5Ϫ130.8 [aromatic C (Ph)], 133.4, 133.8 (C-3, C-5), 138.0,
40.9, 147.0, 148.2 [aromatic ipso-C (Ph), C-2], 162.4 (C-1), 167.8
1
8), 929 (9.8, 10).
1
Minor Diastereomer [OC-6-22Ј-(C),(R),(R)]-Bis-{2-(1,1-dimeth-
19
(
3
NCHAr). Ϫ F NMR {470 MHz, [D ]acetonitrile}: δ ϭ 140.0 (s,
ylethyl)-6-{[(2-hydroxy-1,2,2-triphenylethyl)imino]methyl}-
phenolato(2Ϫ)-N,O,OЈ}titanium (7b): Dec.p. 272Ϫ273°C; R ϭ 0.4
ϭ ϩ170 (c ϭ 1 in chloroform).
Ϫ IR (KBr): ν˜ ϭ 3060 cm , 3020, 2955, 2865, 1620, 1555, 1420,
ϩ
1
F), 201.2 (s, 1 F). Ϫ CI-MS (NH
3
); m/z (%): 568 (82) [M
ϩ
f
ϩ
ϩ
NH
74 (4), 259 (8), 217 (95) [Ph
Ph CO(NH )], 183 (14) [Ph C(OH)], 136 (14), 123 (9)
PhCO(NH )], 111 (48). Ϫ C31 NO Ti (533.5). Ϫ Intensity
]; m/z (calcd., found [%]): 554 (3.8, 3), 553
15.8, 12), 552 (42.3, 57), 551 (100.0, 100), 550 (13.8, 14), 549
3
ϩ NH
4
], 551 (70) [M ϩ NH
4
], 534 (20) [M ϩ 1], 462 (17),
CO(NH )(NH )], 200 (100)
20
(chloroform/n-hexane, 2:1); [α]
D
2
[
[
2
3
4
Ϫ1
2
4
2
1
1390, 1300, 1200, 1005, 875, 755, 705. Ϫ H NMR (500 MHz): δ ϭ
1.14 [s, 18 H, C(CH ], 6.67 [d, J ϭ 1.9 Hz, 2 H, PhCH(NCHAr)],
6.68 (t, J3-H,4-H ϭ J4-H,5-H ϭ 7.6 Hz, 2 H, 4-H), 6.70Ϫ6.74 (m, 4
4
H
29
F
2
2
)
3 3
ϩ
pattern of [M ϩ NH
4
(
(
H, aromatic H), 7.00Ϫ7.23 (m, 24 H, aromatic H), 7.33Ϫ7.34 (m,
H, aromatic H), 7.37 (dd, J ϭ 7.6 Hz, J3-H,5-H ϭ 1.9 Hz, 2 H, 3-
10.4, 13).
4
13
(R)-Chloro-{2-(1,1-dimethylethyl)-6-{[(2-hydroxy-1,2,2-tri-
H or 5-H), 8.00 [d, J ϭ 1.9 Hz, 2 H, PhCH(NCHAr)]. Ϫ C NMR
75 MHz): δ ϭ 29.8 [C(CH ], 35.0 [C(CH ], 85.8 [PhCH(N)],
4.8 [Ph C(OTi)], 117.3 (C-4), 121.7 (C-6), 126.4Ϫ132.1 [aromatic
phenylethyl)imino]methyl}phenolato(2Ϫ)-N,O,OЈ}titanium
1-
(
9
3
)
3
3 3
)
Methylethoxide (8c): The synthesis was effected by analogy with
the preparation of the dichlorotitanium complex 8a. In place of
titanium tetrachloride, the diastereomeric mixture of 6b/7b (94.3
mg, 0.1 mmol) was treated with a 0.1  solution of dichloroti-
tanium diisopropoxide (1.1 ml, 0.11 mmol) in dichloromethane.
Thereafter, the light-orange-coloured mixture was allowed to reach
room temp. within 6 h. After the removal of the solvent, the residue
was dried in vacuo for 1 h to give solid, orange 8c in 67% yield
2
C (Ph)], 132.2, 132.3 (C-3, C-5), 136.1, 137.8, 145.6, 147.9 [aromatic
ipso-C (Ph), C-2], 161.7 (NCHAr), 164.0 (C-1).
(
R)-Dichloro-{2-(1,1-dimethylethyl)-6-{[(2-hydroxy-1,2,2-tri-
phenylethyl)imino]methyl}phenolato(2Ϫ)-N,O,OЈ}titanium (8a): A
solution of the titanium complex 6b and/or 7b (107.5 mg, 0.114
mmol) in 3 ml of absolute dichloromethane was stirred under argon
at Ϫ78°C. A 0.23  solution of titanium tetrachloride (0.5 ml,
(
byproducts: 25% dichlorotitanium complex 8a, unreacted 6b/7b).
0
.114 mmol) in dichloromethane, also prepared under argon, was
1
Ϫ
H NMR (500 MHz): δ ϭ 1.10 [d, J ϭ 5.7 Hz, 3 H,
OCH(CH )(CH )], 1.20 [d, J ϭ 5.7 Hz, 3 H, OCH(CH )(CH )],
.46 [s, 9 H, C(CH ], 4.86 [sept, J ϭ 5.7 Hz, 1 H, OCH(CH ],
.10 [s, 1 H, PhCH(N)], 6.85Ϫ7.83 (m, 18 H, aromatic H), 8.58 (s,
added slowly by syringe at such a rate that the temp. did not exceed
Ϫ70°C. The deeply orange-coloured mixture formed immediately
was allowed to reach room temp. within 2 h. Subsequently, the
solvent was removed in vacuo and the residue was exposed to oil-
pump vacuum for 30 min to give quantitatively 122 mg solid, or-
ange 8a which had to be stored under argon. Ϫ IR (KBr): ν˜ ϭ
3
8
3
3
3
3
1
6
1
5
2
3
)
3
3 2
)
ϩ
H, NCHAr). Ϫ CI-MS (NH
3
); m/z (%): 607 (3) [M ϩ NH
90 (12) [M ϩ 1], 274 (9), 257 (4), 217 (48) [Ph CO(NH )(NH
00 (100) [Ph CO(NH )], 183 (36) [Ph C(OH)], 123 (8)
)], 111 (56), 105 (12) [PhCO]. Ϫ C34 36ClNO Ti
590.0). Ϫ Intensity pattern of [M ϩ 1]; m/z (calcd., found [%]):
4
],
)],
ϩ
2
3
4
2
4
2
Ϫ1
080 cm , 3055, 3015, 2955, 1600, 1555, 1445, 1420, 1391, 1000,
[PhCO(NH
4
H
3
1
85, 755, 710, 700. Ϫ H NMR (500 MHz): δ ϭ 1.54 [s, 9 H,
ϩ
(
3 3
C(CH ) ], 6.49 [s, 1 H, PhCH(N)], 6.98Ϫ7.38 (m, 15 H, aromatic
5
4
95 (1.5, 2), 594 (6.2, 6), 593 (18.4, 16), 592 (48.3, 43), 591 (48.2,
2), 590 (100.0, 100), 589 (13.6, 10), 588 (10.0, 9).
H), 7.65 (d, J ϭ 7.6 Hz, 1 H, 3-H or 5-H), 7.76Ϫ7.77 (m, 2 H,
aromatic H), 8.70 (s, 1 H, NCHAr). Ϫ 13C NMR (125 MHz): δ ϭ
Crystal-Structure Analysis of 6b·2 CHCl
64 6 2 4
H60Cl N O Ti (1181.7), F(000) ϭ 1228, lattice parameters from
:[26] Ϫ Crystal data:
3
2
1
1
3 3 3 3 2
9.8 [C(CH ) ], 35.2 [C(CH ) ], 90.3 [PhCH(N)], 97.8 [Ph C(OTi)],
22.0 (C-4), 122.7 (C-6), 126.4Ϫ129.3 [aromatic C (Ph)], 132.2,
35.0 (C-3, C-5), 138.4, 138.6, 143.2, 145.6 [aromatic ipso-C (Ph),
C
3
1
2 reflections (20° < 2Θ < 24°): a ϭ 1316.7(4), b ϭ 1863.0(4), c ϭ
3
358.1(3) pm, β ϭ 115.78(4)°, V ϭ 2.9999(13) nm , Z ϭ 2, dcalcd.
ϭ
C-2], 163.3 (C-1), 167.4 (NCHAr). Ϫ CI-MS (NH
3
); m/z (%): 583
], 566 (2) [M ϩ 1], 432 (9), 274 (17), 256 (5),
CO(NH )(NH )], 200 (100) [Ph CO(NH )], 183 (45)
C(OH)], 123 (5) [PhCO(NH )], 111 (23). Ϫ C31 NO Ti
566.4). Ϫ Intensity pattern of [M ϩ NH ]; m/z (calcd., found
Ϫ3
ϩ
ϩ
1.308, dfound ϭ 1.311 gcm , monoclinic, P2
lection: Siemens P2 /P3 diffractometer, Mo-K
1
(no. 4). Ϫ Data col-
(λ ϭ 71.073 pm),
(
2
[
(
8) [M ϩ NH
17 (52) [Ph
Ph
4
1
α
2
3
4
2
4
graphite monochromator, crystal size 0.60 ϫ 0.40 ϫ 0.30 mm, T ഠ
300 K, ω/2Θ scan, 4° Յ 2Θ Յ 53°, indices 0 Յ h Յ 16; 0 Յ k Յ
2
4
H
29Cl
2
2
ϩ
4
2
3; Ϫ17 Յ l Յ 15, reflections: 6663 collected, 6405 independent
[%]): 588 (6.5, 7), 587 (20.0, 20), 586 (30.6, 30), 585 (76.7, 78), 584
Ϫ1
(
R
int ϭ 0.04), 3510 observed (I > 2σ
I
), µ ϭ 0.46 mm , absorption
(48.0, 51), 583 (100.0, 100), 582 (13.0, 14), 581 (9.7, 12).
correction not applied. Ϫ Structural analysis and refinement: The
(
R)-Difluoro-{2-(1,1-dimethylethyl)-6-{[(2-hydroxy-1,2,2-tri- measured density (by flotation) pointed to the addition of two mol-
phenylethyl)imino]methyl}phenolato(2Ϫ)-N,O,OЈ}titanium (8b): A ecules of CHCl per complex, which was confirmed by the crystal
0-ml flask, equipped with a magnetic stirrer and a connection to structure. However, the strong decrease of the intensities in depen-
the combined argon/vacuum line, was charged with 6b (94.3 mg, dence of Θ together with the low percentage of observed reflections
3
1
0.1 mmol) and closed with a septum. The air in the flask was re-
indicated a disorder within the structure mainly caused by the sol-
placed by argon, and absolute dichloromethane (3 ml) was injected
vent. The structure was solved by automatic interpretation of the
by syringe. In a second flask, titanium tetrafluoride (13.6 mg, 0.11 Patterson function[ localizing the central octahedron. The com-
19]
Eur. J. Org. Chem. 1998, 1063Ϫ1070
1069

R. Fleischer, H. Wunderlich, M. Braun
FULL PAPER
[
10]
T. Aoyama, S. Ohba, Y. Saito, C. Sasaki, M. Kojima, J. Fujita,
K. Nakajima, Acta Crystallogr. 1988, C44, 1309Ϫ1311; C. Sa-
saki, K. Nakajima, M. Kojima, J. Fujita, Bull. Chem. Soc. Jpn.
plex was completed in the usual way and at a later stage the two
molecules of the solvent had to be added. During the final refine-
ment by full-matrix least squares on F ,
placement parameters and fixed H atoms, a twofold disorder of the
Cl atoms with restraints to their geometry had to be introduced.
The refinement of 751 parameters converged at wR2 ϭ 0.128 (6400
reflections) and R1 ϭ 0.055 (3510 observed reflections). The de-
scription of the disorder by split positions (one chloroform mol-
ecule 0.64:0.36, the other 0.50:0.50) remains unsatisfactory with re-
2
[27]
using anisotropic dis-
1
991, 64, 1318Ϫ1324.
[
[
11]
M. Braun, Angew. Chem. 1996, 108, 565Ϫ568; Angew. Chem.
Int. Ed. Engl. 1996, 35, 519Ϫ522.
12] [12a]
[12b]
A. Kossel, Ber. Dtsch. Chem. Ges. 1891, 24, 4145Ϫ4156. Ϫ
H. Reihlen, L. Knöpfle, Justus Liebigs Ann. Chem. 1936,
[12c]
5
23, 199Ϫ210. Ϫ
W. Klyne, P. M. Scopes, R. N. Thomas,
H. Dahn, Helv. Chim. Acta 1975, 54, 2420Ϫ2430.
A. McKenzie, A. C. Richardson, J. Chem. Soc. 1923, 123,
79Ϫ91.
[
[
13]
14]
2
Ϫ4
spect to values of Ueq up to 0.28 (pm ϫ 10 ). The residual elec-
tron density ranged from Ϫ0.39 to 0.45·10 epm
For efficient asymmetric reductions of ketones and α,β-unsatu-
rated ketones catalyzed by the B-methyl-oxazaborolidine de-
rived from (R)-2, see: R. Berenguer, J. Garcia, J. Vilarrasa,
Tetrahedron: Asymmetry 1994, 5, 165Ϫ168; J. Bach, R. Be-
renguer, J. Farr a` s, J. Garcia, J. Meseguer, J. Vilarrasa, ibid. 1995,
Ϫ6
Ϫ3
.
[
[
1]
2]
M. T. Reetz in Topics in Current Chemistry (Ed.: F. L. Boschke),
Springer, Berlin, 1982, vol. 106, pp. 1Ϫ54; B. Weidmann, D.
Seebach, Angew. Chem. 1983, 95, 12Ϫ26; Angew. Chem. Int. Ed.
Engl. 1983, 22, 31Ϫ45.
6
, 2683Ϫ2686.
[
[
15]
16]
K. Higashiyama, H. Inoue, H. Takahashi, Tetrahedron Lett.
1992, 33, 235Ϫ238; A. D. Gupta, B. Singh, V. K. Singh, Ind. J.
Chem. 1994, 33B, 931Ϫ933.
D. Seebach, B. Weidmann, L. Widler in Modern Synthetic
Methods (Ed.: R. Scheffold), Salle, Frankfurt, 1983, vol. 3, pp.
M. F. Brown, B. R. Cook, T. E. Sloan, Inorg. Chem. 1975, 14,
217Ϫ353; D. Seebach, A. K. Beck, M. Schiess, L. Widler, A.
1
273Ϫ1278; G. J. Leigh, Nomenclature of Inorganic Chemistry:
Wonnacott, Pure Appl. Chem. 1983, 55, 1807Ϫ1822; M. T.
Reetz, ibid. 1985, 57, 1781Ϫ1788; M. T. Reetz, Organotitanium
Reagents in Organic Synthesis, Springer, Berlin, 1986; D. Hoppe
in Methoden Org. Chem. (Houben-Weyl) 4th ed. 1952 Ϫ, vol.
E 21b, pp. 1551Ϫ1583.
Recommendations 1990, 1st ed., Blackwell, Oxford, 1990.
J. C. Huffman, K. G. Moloy, J. A. Marsella, K. G. Caulton, J.
Am. Chem. Soc. 1980, 102, 3009Ϫ3014.
[
[
17]
18]
F. E. Hahn, S. Rupprecht, K. H. Moock, J. Chem. Soc., Chem.
Commun. 1991, 224Ϫ225; B. A. Borgias, S. R. Cooper, Y. B.
Koh, K. N. Raymond, Inorg. Chem. 1984, 23, 1009Ϫ1016; G.
D. Smith, C. N. Caughlan, J. A. Campbell, idid. 1972, 11,
[
3]
M. Riediker, R. O. Duthaler, Angew. Chem. 1989, 101,
4
88Ϫ490; Angew. Chem. Int. Ed. Engl. 1989, 28, 494Ϫ495; M.
Riediker, A. Hafner, U. Piantini, G. Rihs, A. Togni, Angew.
Chem. 1989, 101, 493Ϫ495; Angew. Chem. Int. Ed. Engl. 1989,
2
989Ϫ2993.
[
[
[
[
19]
20]
21]
22]
SHELXTL-PLUS Release 4.21/V, Siemens Analytical X-ray In-
struments Inc., Madison, WI, U.S.A., 1990.
28, 499Ϫ500; A. Hafner, R. O. Duthaler in Encyclopedia of Re-
agents for Organic Synthesis (Ed.: L. A. Paquette), Wiley,
Chichester, 1995, pp. 1104Ϫ1106 and references given therein.
R. Dahinden, A. K. Beck, D. Seebach in Encyclopedia of Re-
agents for Organic Synthesis (Ed.: L. A. Paquette), Wiley,
Chichester, 1995, pp. 2167Ϫ2170; A. Hafner, R. O. Duthaler,
ibid. 1995, pp. 1106Ϫ1108.
Four out of five geometric fac-isomers are chiral octahedrons
thus forming pairs of diastereomers.
[
[
4]
5]
M. Hayashi, H. Kaneda, N. Oguni, Tetrahedron: Asymmetry
1995, 6, 2511Ϫ2516.
K. Narasaka, I. Yamamoto, Tetrahedron 1992, 48, 5743Ϫ5754.
R. Devant, U. Mahler, M. Braun, Chem. Ber. 1988, 121,
397Ϫ406.
[23]
K. Mikami, S. Matsukawa, J. Am. Chem. Soc. 1994, 116,
4
077Ϫ4080; K. Mikami in Encyclopedia of Reagents for Organic
[
[
[
24]
25]
26]
Synthesis (Ed.: L. A. Paquette), Wiley, Chichester 1995, pp.
Assignments of the carbon atoms C-1 to C-10 are based on the
calcd. increments for 2-hydroxy-1-naphthaldehyde (3d), see: H.
4
3
03Ϫ406; R. A. Singer, E. M. Carreira, Tetrahedron Lett. 1997,
8, 927Ϫ930.
1
3
O. Kalinowski, S. Berger, S. Braun, C-NMR-Spektroskopie,
1st ed., Thieme, Stuttgart, 1984.
[
6]
A. Mori, H. Nitta, M. Kudo, S. Inoue, Tetrahedron Lett. 1991,
32, 4333Ϫ4336; H. Nitta, D. Yu, M. Kudo, A. Mori, S. Inoue,
Titanium tetrafluoride is insoluble in common aprotic solvents;
however, its solubility is moderate in acetonitrile, see: D. R.
Gauthier, E. M. Carreira, Angew. Chem. 1996, 108, 2521Ϫ2522;
Angew. Chem. Int. Ed. Engl. 1996, 35, 2363Ϫ2365.
Crystallographic data (excluding structure factors) for the struc-
ture reported in this paper have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary publi-
cation no. CCDC-100872. Copies of the data can be obtained
free of charge on application to CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK [fax: (internat.) ϩ 44(1223)/336Ϫ033,
e-mail: deposit@ccdc.cam.ac.uk].
J. Am. Chem. Soc. 1992, 114, 7969Ϫ7975; B. M. Cole, K. D.
Shimizu, C. A. Krueger, J. P. A. Harrity, M. L. Snapper, A. H.
Hoveyda, Angew. Chem. 1996, 108, 1776Ϫ1779; Angew. Chem.
Int. Ed. Engl. 1996, 35, 1668Ϫ1671.
[
[
7]
R. O. Duthaler, A. Hafner, Chem. Rev. 1992, 92, 807Ϫ832.
8] [8a]
M. Hayashi, Y. Miyamoto, T. Inoue, N. Oguni, J. Org.
[
8b]
Chem. 1993, 58, 1515Ϫ1522. Ϫ
M. Hayashi, T. Inoue, Y.
[8c]
Miyamoto, N. Oguni, Tetrahedron 1994, 50, 4385Ϫ4398. Ϫ
Y. Jiang, X. Zhou, W. Hu, Z. Li, A. Mi, Tetrahedron: Asym-
metry 1995, 6, 2915Ϫ2916.
[
9]
[27]
M. Hayashi, T. Inoue, N. Oguni, J. Chem. Soc., Chem. Com-
mun. 1994, 341Ϫ342; E. J. Corey, D. Barnes-Seeman, T. W. Lee,
Tetrahedron Lett. 1997, 38, 4351Ϫ4354.
G. M. Sheldrick, SHELXL-93, University of Göttingen, Ger-
many, 1993.
[97296]
1070
Eur. J. Org. Chem. 1998, 1063Ϫ1070