Catalytic enantioselective fluorination of β-ketoesters

Article abstract of DOI:10.1002/1521-3773(20001201)39:23<4359::AID-ANIE4359>3.0.CO;2-P

Isolated and crystallized [Ti(TADDOLato)] complexes were used as catalysts for the first catalytic enantioselective (up to 90 % ee) C-F bond-forming reaction, the fluorination of β-ketoesters with the N-fluorotriethylenediammonium salt F-TEDA [Eq. (1)]. T

Full text of DOI:10.1002/1521-3773(20001201)39:23<4359::AID-ANIE4359>3.0.CO;2-P

COMMUNICATIONS
[
0
=
=
C
450
H
456Cd24
N
120
O
66] ´ xH
2
O ´ yDMF =4): Cd=NO
3
)
2
´ 4H
2
O
=48.3 mg,
[13] N. Walker, BASFAG; DIFABS Programm for empirical Absorptions-
korrektur Version9.00, April 1992; N. Walker, D. Stuart; Acta
Crystallogr. Sect. A 1983, 39, 158.
[14] G. M. Sheldrick, SHELXS-97, Program for Crystal Structure Solution,
Universität Göttingen, 1997.
.16 mmol) and 1 ´ HCl =46.0 mg, 0.10 mmol) were dissolved inDMF
10 mL). Water =10 mL) followed by triethylamine =2 mL) in methanol
8 mL) were carefully layered on top. Over a period of two months orange
À3
crystals of 4 grew. Yield: 6.2 mg =0.55 Â 10 mmol, 8.2%); elemental
analysis found =%): C 45.51, H 3.85, N 14.46; calcd =for x ˆ 30, y ˆ 10): C
[15] G. M. Sheldrick, SHELXL-97, Program for Crystal Structure Refine-
ment, Universität Göttingen, 1997.
4
5.82, H 4.66, N 14.48.
[
16] PLATON Program: A. L. Spek, Acta Crystallogr. Sect. A 1990, 46,
Crystallography: Intensity data were collected on an Enraf-Nonius CAD4
diffractometer employing the w-2q scanmethod, the data were corrected
for Lorentz and polarization effects. An empirical absorption correction
C34.
[
13]
was applied for 2 and 4. All structures were solved using direct methods
[
14]
=
SHELXS-97) and refined using a full-matrix least-squares refinement
[
15]
procedure =SHELXL-97).
The data of 4 were corrected using the
ªSQUEEZEº routine in PLATON.[ Crystallographic data =excluding
structure factors) for the structures reported inthis paper have been
deposited with the Cambridge Crystallographic Data Centre as supple-
mentary publication no. CCDC-146818 ± 146821 for 1, 2, 3, an d4,
respectively. Copies of the data canbe obtai en d free of charge on
applicationto CCDC, 12 U ni onRoad, Cambridge CB21EZ, UK =fax:
16]
Catalytic Enantioselective Fluorination of
b-Ketoesters**
Lukas Hintermann and Antonio Togni*
=
‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
Although in nature organofluorine metabolites are ex-
tremely rare, bioactive fluoroorganic compounds are emi-
nently important in medicinal chemistry.[ Therefore, it is not
surprising that research in the field of synthetic organo-
fluorine chemistry is flourishing more than ever.[ Protocols
for the introduction of the fluorine atom into organic
Received: July 7, 2000 [Z15413]
1]
2, 3]
[
[
1] B. F. Abrahams, P. A. Jackson, R. Robson, Angew. Chem. 1998, 110,
801; Angew. Chem. Int. Ed. 1998, 37, 2656; B. F. Abrahams, J. Coleiro,
2
B. F. Hoskins, R. Robson, Chem. Commun. 1996, 603.
[4]
molecules rely upon the use of dozens of different reagents,
2] P. J. Bailey, K. J. Grant, L. A. Mitchell, S. Pace, A. Parkin, S. Parsons, J.
Chem. Soc. Dalton Trans. 2000, 1887, and references therein; P. J.
Bailey, R. O. Gould, C. N. Harmer, S. Pace, D. S. Wright, Chem.
Commun. 1997, 1161, and references therein; P. J. Bailey, A. J. Blake,
M. Kryszczuk, S. Parsons, D. Reed, Chem. Commun. 1995, 1647.
3] G. R. Giesbrecht, A. Shafir, J. Arnold, J. Chem. Soc. Dalton Trans.
[
5, 6]
the most successful of which contain the NÀF fragment.
Methods for the enantioselective fluorination =CÀF bond-
forming reactions) of organic molecules are quite rare, and
catalytic methods are not known. An important breakthrough
occurred when Differding and Lang reported the first
example of enantioselective electrophilic fluorination of a b-
ketoester enolate in up to 70% ee by using an N-fluorosultam
[
1
999, 3601, and references therein; N. Thirupathi, G. P. A. Yap, D. S.
Richeson, Chem. Commun. 1999, 2483, and references therein.
3
Å
[
4] 0.10  0.10  0.10 mm , triclinic, P1, a ˆ 8.905=2), b ˆ 9.807=2), c ˆ
1
1
2
3.086=3) Š,
a ˆ 88.10=3),
b ˆ 78.50=3),
g ˆ 83.89=3)8,
Vˆ
[7]
derived from camphor. This strategy, requiring the inter-
3
À3
113.5=4) Š ,
1
calcd ˆ 1.378 gcm
,
2qmax ˆ 1208, l ˆ 1.54178 Š, Tˆ
mediate generation of the enolate from an activated methyl-
ene compound, has been further developed more recently.[
Another impetus in this field came also from the discovery
and commerical availability of new NÀF reagents, such as
93 K, 3774 measured reflections, 3278 independent reflections
8±13]
À1
=
R
int ˆ 0.0359), m ˆ 1.856 mm , 340 parameters, R
1
ˆ 0.0678, wR2 ˆ
À3
0
.1880, max. residual electronde ns ity 0.354 eŠ
.
3
Å
[
5] 0.33  0.14  0.03 mm , triclinic, P1, a ˆ 12.848=1), b ˆ 13.0504=6), c ˆ
1
2
2
5.158=2) Š, a ˆ 92.667=7), b ˆ 102.81=1), g ˆ 110.512=6)8, Vˆ
1
-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane
3
À3
299.6=5) Š ,
1
calcd ˆ 1.644 gcm
,
2qmax ˆ 1208, l ˆ 1.54178 Š, Tˆ
bis{tetrafluoroborate} =F-TEDA; also called Selectfluor, see
93 K, 7858 measured reflections, 6818 independent reflections
[
14, 15]
À1
Scheme 1; TEDA ˆ triethylenediamine).
However, the
=
R
int ˆ 0.0568), m ˆ 11.343 mm
, min./max. transmission factors
ˆ 0.0669, wR2 ˆ 0.1424, max. residual
0
.141/0.698, 591 parameters, R
1
total absence of an efficient catalytic reaction for stereo-
selective fluorination prompted us to embark in a study aimed
at developing such a reaction. Recent reports had indicated
À3
electronde ns ity 1.219 eŠ
.
3
Å
[
6] 0.54  0.46  0.34 mm , trigonal =hexagonal settings), R3, a ˆ
3
À3
1
2
2
6.310=2), c ˆ 21.552=3) Š, Vˆ 4965=1) Š ,
1
calcd ˆ 1.610 gcm
,
q
max ˆ 54.98, l ˆ 0.71073 Š, Tˆ 140 K, 3173 measured reflections,
537 independent reflections =Rint ˆ 0.0273), numerical absorption
À1
correction, m ˆ 2.296 mm , min./max. transmission factors 0.314/
0
.490, 181 parameters,
R
1
ˆ 0.0391, wR2 ˆ 0.1204, max. residual
À3
electronde ns ity 1.141 eŠ
.
[
[
7] I. M. Müller, R. Robson, unpublished results.
8] K. N. Zelenin, A. G. Saminskaya, O. B. Kuznetsova, Zh. Obshch.
Khim. 1996, 66, 141.
Scheme 1. The catalytic fluorination of 1a with F-TEDA.
3
Å
[
9] 0.46  0.43  0.34 mm , trigonal =hexagonal settings), R3, a ˆ
3
À3
3
2
1
3.838=7), c ˆ 46.23=1) Š, Vˆ 45845=18) Š ,
1
calcd ˆ 1.227 gcm
,
q
max ˆ 1008, l ˆ 1.54178 Š, Tˆ 130 K, 11987 measured reflections,
À1
[*] Prof. Dr. A. Togni, L. Hintermann
0394 independent reflections =Rint ˆ 0.1104), m ˆ 7.051 mm , min./
Laboratory of Inorganic Chemistry
Swiss Federal Institute of Technology, ETH Zentrum
max. transmission factors 0.120/0.264, 473 parameters, R
1
ˆ 0.1064,
À3
wR2 ˆ 0.3105, max. residual electronde ns ity 0.385 eŠ
.
8
092 Zürich =Switzerland)
[
[
[
10] For recent reviews, see A. Müller, C. Serain, Acc. Chem. Res. 2000, 33,
; A. Müller, P. Kögerler, Coord. Chem. Rev. 1999, 182, 3.
Fax : =‡41)1-632-1090
2
E-mail: togni@inorg.chem.ethz.ch
11] O. D. Fox, M. G. B. Drew, P. D. Beer, Angew. Chem. 2000, 112, 140;
Angew. Chem. Int. Ed. 2000, 39, 136.
12] S. Weiss, H. Krommer =SKW Trostberg AG, Germany) DE-B 83-
[**] This work was supported by Solvias AG, Basel, Switzerland. We thank
D. Broggini and M. Wörle, ETH Zürich, for the X-ray crystallographic
3
341645 [Chem. Abstr. 1986, 104, 206730].
study of compounds [=R)-3a=DME)] and [=R)-3b=NCMe)
2
].
Angew. Chem. Int. Ed. 2000, 39, No. 23 ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1433-7851/00/3923-4359 $ 17.50+.50/0
4359

COMMUNICATIONS
that NÀF reagents were capable of fluorinating unactivated
ketones in the a-position in refluxing acetonitrile, whereas
activated ketones, notably b-ketoesters and b-diketones, were
already fluorinated at room temperature.[ As these reac-
tions proceed via the enol form of the substrate, we reasoned
that substochiometric amounts of a Lewis acid might accel-
erate the reaction by catalyzing the enolization process.[
Thus, we started a systematic study with model compound 1a
16]
17]
=
Scheme 1), a monosubstituted b-ketoester, and found that it
does not react with a saturated solution of F-TEDA in
acetonitrile at room temperature, in accordance with its low
1
enol content =<0.5% inCD CN by H NMR spectroscopy).
3
However, the additionof a range of Lewis acids [
18, 19]
=5 mol%
level) effectively catalyzed the reaction=Table 1).
Table 1. Qualitative ordering of catalytic activity of several Lewis acids for
[
a]
the reactionshowninScheme 1.
Very fast
<1 h)
Fast
=<1 d)
Slow
=ꢀ2 w)
Very slow or
no reaction
Figure 1. Structures of the complexes [R-3a=DME)] and [R-3b=NCMe)
ORTEP views; hydrogenatoms are omitted for clarity). Selected bond
lengths [Š] and angles [8]: [R-3a=DME)]: Ti-O=1) 1.752=5), Ti-O=2)
.765=5), Ti-O=5) 2.224=5), Ti-O=6) 2.164=6), Ti-Cl=1) 2.337=2), Ti-Cl=2)
.342=3), O=1)-Ti-O=2) 98.6=2), O=1)-Ti-O=5) 90.9=2), O=2)-Ti-O=6) 96.8=2),
O=5)-Ti-O=6) 73.7=2), Cl=1)-Ti-Cl=2) 164.97=10); [R-3b=NCMe) ]: Ti-O=1)
.780=3), Ti-O=2) 1.773=3), Ti-N=1) 2.283=4), Ti-N=2) 2.264=4), Ti-Cl=1)
.3343=13), Ti-Cl=2) 2.3622=13), O=1)-Ti-O=2) 97.18=12), O=1)-Ti-N=1)
0.74=13), O=2)-Ti-N=2) 88.86=13), N=1)-Ti-N=2) 83.24=14), Cl=1)-Ti-Cl=2)
62.11=5).
2
]
=
=
=
>2 w)
TiCl
AlCl
4
[CpTiCl
[TiCl
3
]
[Cp
HBF
BF
Me
2
Ti=OTf)
2
]
[Cp TiCl ]
2
2
1
2
3
2
=diolato)]
4
HCl
ZnCl
Cu=ClO
Cp Zr=OTf)
TiF
TaCl
Yb=OTf)
3
2
2
3
SiOTf
4 2
)
1
2
9
1
[
2
2
]
4
5
3
[
a] OTf ˆ trifluoromethanesulfonate.
different b-ketoesters are presented in Table 2. We so far
restricted this reactionto substrates beari gn an a-methyl
It is evident that titanium-based Lewis acids constitute the
group, thus leading to products having a quaternary stereo-
genic center. The reactions have been typically conducted at
room temperature ina closed vessel and with a slight excess of
a saturated F-TEDA solutioninacetonitrile =this proved to be
more reactive than, e.g., N-fluorobenzenesulfonimide or N-
fluoropyridinium tetrafluoroborate). Products were isolated
most potent catalysts, with TiCl4 driving the reaction to
completion in less than 1 h at room temperature. Since many
chiral, enantiopure Lewis acidic Ti complexes are known, we
were inthe comfortable situationof bei ng able to screena
large number of known catalysts[ for the enantioselective
version of this reaction. We found that with 5 mol% of in situ
20]
inanalytically pure form after columnchromatography, inall
[21]
[25]
prepared [TiCl =R,R-TADDOLato)] ==R)-3a) as catalyst, a
cases inyields between80% a nd more than95%.
It is
2
quite fast reactionof racemic b-ketoester 1a with F-TEDA
took place =quantitative conversion in less than 5 h), yielding
the fluoro-b-ketoester 2a ingood yield a nd with 28% ee.
apparent from Table 2 that the steric bulk of the catalyst is
important with regard to the stereoselectivity. Thus, the better
enantioselectivities for all substrates under study were
obtained by using catalysts 3b, bearing 1-naphthyl groups.
Also the nature of the ester group clearly influences
enantioselectivity; the best results have been obtained with
the substituted benzyl ester of substrate 2 f =90% ee; using the
insitu prepared catalyst a maximum of 85% ee was obtained).
This level of stereoselectivity compares favorably with the
highest enantioselectivity obtained by using chiral enantio-
pure fluorinating agents.
Notably, [TiCl =TADDOLato)] catalysts have beenexten-
2
[22]
sively used by Seebach and others but these were typically
prepared in situ and not used in isolated form. We found that
the two prototypical catalysts =R)-3a and =R)-3b,[ that have
beenmai nl y exploited for this study as catalysts, may be
isolated inhigh yields =85 ± 90%) as air-stable highly crystal-
line materials as dimethoxyethane =DME) or acetonitrile
adducts, respectively, in the latter case with a varying number
of acetonitrile molecules per titanium. Furthermore, these
isolated materials gave more reliable results thanthe corre-
sponding forms generated in situ, in terms of both reprodu-
cibility and enantioselectivity of catalytic experiments =see
below). Compound [=R)-3a=DME)] and the bis=acetonitrile)
23]
The fluorination of cholesteryl ester 2g using [CpTiCl ] as
3
catalyst gave a diastereoisomeric product ratio of 55:45. This
poor selectivity was gradually improved inthe reactiosn
catalyzed by the complexes =R)-3a =60:40), =R)-3b =80:20),
and =S)-3b =16:84), indicating that for this doubly stereo-
differentiating reaction both the sense and the extent of
asymmetric induction are dominated by the catalyst.
adduct [=R)-3b=NCMe) ] were characterized by X-ray crys-
2
tallography[ and ORTEP views of the octahedral complexes
24]
are showninFigure 1.
The results obtained by using the isolated forms of =R)-3a
or =R)-3b as catalyst precursors for the fluorination of
We assume that the interaction of the b-ketoester with the
catalyst triggers an enolization reaction, and that the coordi-
nated enol or enolate is the reactive form of the substrate,
4360
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1433-7851/00/3923-4360 $ 17.50+.50/0
Angew. Chem. Int. Ed. 2000, 39, No. 23

COMMUNICATIONS
2
Table 2. Selected results of catalytic enantioselective fluorination reactions using isolated [TiCl =TADDOLato)] complexes.
[a]2
[ ee [%]]
0=2)[a]
d= F)=2)
19
[b]
HPLC analysis[c]
1
2
=R ˆ H) =racemic)
=R ˆ F)
Selectivity
=Reactiontime)
D
cat. ˆ =R)-3a
cat. ˆ =R)-3b
2
8% ee =S)
62% ee
=40 min)
‡ 53.8 =c ˆ 0.545)
À 152.3
OB
0.5
96/4
13.5/16.0
=4 h)
[61.7]
5
9% ee
82% ee
=1 d)
‡ 19.0 =c ˆ 1.83)
À 152.5
OJ
1
95/5
14.1/18.9
=1 d)
[56]
5
8% ee
81% ee
=20 min)
‡ 38.2 =c ˆ 1.02)
À 159.5
À 159.5
OJ
0.25
70/30
36.1/39.4
=2 h)
[81.2]
48% ee
71% ee
=<7 min)
‡ 32.5 =c ˆ 0.905)
OJ
1
96/4
11.7/15.3
=15 min)
[70.8]
5
1% ee
68% ee
=<15 min)
‡ 19.6 =c ˆ 1.14)
À 157.4
À 159.2
OJ
1
96/4
24.0/27.7
=
<15 min)
[68.8]
55% ee
90% ee
=<15 min)
‡ 24.1 =c ˆ 1.11)
OD-H
0.3
99.8/0.2
27.8/29.8
=1 h)
[85.6]
[
d]
n.d.[e]
[f]
d.r. ˆ 60:40
d.r. ˆ 80:20
À 157.3
±
±
[
a] Measured inMeOH at room temperature ona sample of given ee [value insquare brackets]. [b] Measured inCDCl
3
, relative to CFCl
3
. [c] Daicel
À1
Chiralcel 25 cm columntype; solvent mixture: hexane/ iPrOH =v/v); flow rate inmLmin . Retention times =HPLC) in min of minor/major enantiomer =UV
detectionat l ˆ 210 nm and 254 nm). [d] =S)-3b: d.r. ˆ 16:84. [e] Not determined. [f] The difference of the shifts between the two diastereomers is Dd ˆ 0.01.
susceptible to external electrophilic attack by the fluorinating
agent. Thus, the role of the Lewis acid consists in activating
the nucleophile and not, as it is more common in reactions
involving carbonyl compounds, in enhancing the electrophi-
licity of the coordinated carbonyl group. We are currently
exploring these mechanistic aspects, in order to better under-
stand this quite unique and novel catalytic reaction. Further-
more, the extension of this convenient and expeditious
fluorination process to other enolizable substrates, as well as
to the corresponding asymmetric chlorination reaction[
using N-chlorosuccinimide =NCS) are the object of current
[1] ªSelective Fluorination in Organic and Bioorganic Chemistryº: J. T.
Welch, ACS Symp. Ser. 1991, 456.
[
2] V. A. Soloshonok, Enantiocontrolled Synthesis of Fluoro-Organic
Compounds. Stereochemical Challenges and Biomedicinal Targets,
Wiley, New York, 1999.
[
3] ªAsymmetric Fluoroorganic Chemistry. Synthesis, Applications, and
Future Directionsº: P. V. Ramachandran, ACS Symp. Ser. 2000, 746.
4] M. Hudlicky, A. E. Pavlath, Chemistry of Organic Fluorine Com-
[
poundsII
, ACS Monograph 187, American Chemical Society,
Washington, 1995.
[
5] G. Sankar Lal, G. P. Pez, R. G. Syvret, Chem. Rev. 1996, 96, 1737± 1755.
26]
[6] G. G. Furin, Methoden Org. Chem. ꢀHouben-Weyl) 4th ed. 1952 ± , Vol.
E10a, 1999, pp. 432 ± 499.
[7] E. Differding, R. W. Lang, Tetrahedron Lett. 1988, 29, 6087 ± 6090.
[27]
and future work.
[
8] S. D. Taylor, C. C. Kotoris, G. Hum, Tetrahedron 1999, 55, 12431 ±
Received: July 17, 2000 [Z15459]
12477.
Angew. Chem. Int. Ed. 2000, 39, No. 23
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1433-7851/00/3923-4361 $ 17.50+.50/0
4361

COMMUNICATIONS
[
9] F. A. Davis, P. V. N. Kasu, Org. Prep. Proced. Int. 1999, 31, 125 ± 143.
6À
Octahedral SeO and Square-Pyramidal
6
[
10] F. A. Davis, P. Zhou, C. K. Murphy, G. Sundarababu, H. Qi, W. Han,
4
À
SeO , Two New Oxoselenate Anions**
R. M. Przeslawski, B.-C. Chen, P. J. Carrall, J. Org. Chem. 1998, 63,
5
2
273 ± 2280.
Helmut Haas and Martin Jansen*
[
[
[
[
11] Y. Takeuchi, T. Suzuki, A. Satoh, T. Shiragami, N. Shibata, J. Org.
Chem. 1999, 64, 5708 ± 5711.
12] S. P. Vincent, M. D. Burkart, C.-Y. Tsai, Z. Zhang, C.-H. Wong, J. Org.
Chem. 1999, 64, 5264 ± 5279.
For kinetic as well as thermodynamic reasons cations in
tetrahedral and octahedral complexes usually show a lower
Lewis acidity than in three- or fivefold coordination. We have
therefore considered the main driving force for the surpris-
ingly smooth acid ± base reaction of the addition of O to
SeO4 inthe sy nt hesis of Li 4SeO5 to be the formationof a
13] J. J. McAtee, R. F. Schinazi, D. C. Liotta, J. Org. Chem. 1998, 63,
2
161 ± 2167.
14] R. E. Banks, S. N. Mohialdin-Khaffaf, G. S. Lal, I. Sharif, R. G. Syvret,
J. Chem. Soc. Chem. Commun. 1992, 595 ± 597.
15] R. E. Banks, US-A 5,086,178, 1992.
2
À
2À
[1]
[
[
16] a) T. Umemoto, S. Fukami, G. Tomizawa, K. Harasawa, K. Kawada,
K. Tomita, J. Am. Chem. Soc. 1990, 112, 8563 ± 8575; b) R. E. Banks,
N. J. Lawrence, A. L. Popplewell, J. Chem. Soc. Chem. Commun. 1994,
collective solid-state structure A A'B , thus the order variant
of anAB structure type, and the associated gain in lattice
4
5
[2]
energy. Also the unexpected coordination polyhedron =CN ˆ
3
3
43 ± 344. c) S. Stavber, M. Zupan, Tetrahedron Lett. 1996, 37, 3591 ±
594.
5
, trigonal-bipyramidal) was attributed to this overriding
[
[
17] D. A. Evans, S. G. Nelson, J. Am. Chem. Soc. 1997, 119, 6452 ± 6453.
18] H. Yamamoto, LewisAcid Reagent .s A Practical Approach , Oxford
University Press, Oxford, 1999.
structure-chemical argument. That such explanations are not
applicable, is confirmed by the preparation of two other
oxoselenates, for which at first glance there are no structural
features apparent that stabilize a hexaoxo- or pentaoxo anion.
For the Na O/Na SeO system the solid-state reactionat a
[
19] M. Santelli, J.-M. Pons, LewisAcidsand Selectivity in Organic
Synthesis, CRC, New York, 1996.
[
[
20] R. O. Duthaler, A. Hafner, Chem. Rev. 1992, 92, 807 ± 832.
21] K. Narasaka, N. Iwasawa, M. Inoue, T. Yamada, M. Nakashima, J.
Sugimori, J. Am. Chem. Soc. 1989, 111, 5340 ± 5345.
2
2
4
molar ratio of the starting materials of 1:2[ under standard
3]
pressure gave Na Se O , which contains hexaoxoselenate=vi)
6
2
9
[
[
[
22] For a comprehensive review on TADDOLs and their use in
and tetraoxoselenate=vi) anions, whereas at a ratio of 1:1
asymmetric synthesis, see: D. Seebach, A. K. Beck, A. Heckel, Angew.
Chem. 2001, 113, inpress; Angew. Chem. Int. Ed. 2001, 40, inpress. We
thank Professor Seebach for a copy of the manuscript prior to
publication.
under hydrostatic pressure Na SeO was formed. The single-
4
5
crystal structure analysis[ confirmed in the first case that
4]
according to the formulation Na =SeO )=SeO ) anoctahe-
1
2
6
4 3
23] =R)-3a ˆ dichloro[4R, 5R-2,2-dimethyl-a,a,a',a'-tetraphenyl-1,3-dioxo-
dral orthoselenate anion had been obtained for the first time
Figure 1). This displays the point symmetry O withinthe
lane-4,5-dimethanolato=2-)-O,O']titanium. =R)-3b ˆ dichloro[4R,5R-
=
h
2
,2-dimethyl-a,a,a',a'-tetra=1-naphthyl)-1,3-dioxolane-4,5-dimethan-
olato=2-)-O,O']titanium. The two corresponding TADDOL ligands are
commercially available.
24] Crystallographic data =excluding structure factors) for the structures
reported inthis paper have beendeposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-145414 =[=R)-3a=DME)]) and CCDC-145415 =[=R)-3b-
=
NCMe)
applicationto CCDC, 12 UnionRoad, Cambridge CB21EZ, UK =fax:
‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
25] A representative experimental procedure is as follows: Complex 3b
10.3 mg, 0.0125 mmol) was added to a solutionof b-ketoester 1d in
2
]). Copies of the data canbe obtai ne d free of charge on
=
[
=
acetonitrile =0.25 mmol in 1 mL), and the mixture was stirred until a
clear yellow solution was obtained =5 min). To this was added a
À1
saturated F-TEDA solution=2.0 mL; 0.145 molL ; 0.29 mmol) in
MeCN. After 7 min, TLC =TBME/hexane 1/5, R
.36, R
f
=starting material) ˆ
0
f
=product) ˆ 0.50; detectionby UV a nd /or phosphomolybdic
acid; TBME ˆ tert-butyl methyl ether) indicated complete conversion.
The reactionmixture was extracted with water =50 mL) a nd TBME
=
30 mL), the organic phase was filtered through Al
2 3
O =1 g; washed
with additional TBME) and evaporated. Liquid chromatography
=
=
TBME/hexane 1/20) gave 2d =49 mg; 82%) of as colorless oil
70.8% ee by HPLC).
6 2 9
Figure 1. Crystal structure of Na Se O =perspective representation).
[
[
26] L. Hintermann, A. Togni, Helv. Chim. Acta 2000, 83, 2425 ± 2435.
27] Note added inproof =27. October 2000): After this work was
submitted the first Lewis acid catalyzed asymmetric ring opening of
epoxides by fluoride was reported. See: S. Bruns, G. Haufe, J. Fluorine
Chem. 2000, 104, 247 ± 254.
margins of error of the structure determination. The dimen-
2
À
Å
sions of the tetrahedral SeO4 ions =d
Se-O
ˆ 163.6 pm, O-Se-
O ˆ 109.538) are comparable with those of already known
[6]
oxoselenates=vi) with tetrahedral anions =cf. Na SeO with
2
4
Å
À
d
Se-O
ˆ 164.8 pm). The increase of the average Se O bond
[
*] Prof. Dr. M. Jansen, Dipl.-Chem. H. Haas
Max-Planck-Institut für Festkörperforschung
Heisenbergstrasse 1, 70569 Stuttgart =Germany)
Fax : =‡49)711-689-1502
E-mail: martin@jansen.mpi-stuttgart.mpg.de
[
**] This work was supported by the Fonds der Chemischen Industrie.
4362
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1433-7851/00/3923-4362 $ 17.50+.50/0 Angew. Chem. Int. Ed. 2000, 39, No. 23