Lanthanide catalysts with tris(perfluorooctanesulfonyl)methide and bis(perfluorooctanesulfonyl)amide ponytails: Recyclable Lewis acid catalysts in fluorous phases or as solids

Article abstract of DOI:10.1016/S0040-4020(02)00313-7

Lanthanide tris(perfluorooctanesulfonyl)methide and bis(perfluorooctanesulfonyl)amide complexes are shown to be immobilized and continuously recycled in fluorous phases or as solids. The lanthanide complexes are thus extremely efficient Lewis acid catalys

Full text of DOI:10.1016/S0040-4020(02)00313-7

TETRAHEDRON
Pergamon
Tetrahedron 58 (2002) 4015±4021
Lanthanide catalysts with tris(per¯uorooctanesulfonyl)methide
and bis(per¯uorooctanesulfonyl)amide ponytails: recyclable
Lewis acid catalysts in ¯uorous phases or as solidsq
Koichi Mikami,a,p Yutaka Mikami,a Hiroshi Matsuzawa,a Yousuke Matsumoto,a Joji Nishikido,b
Fumihiko Yamamotob and Hitoshi Nakajimab
aDepartment of Applied Chemistry, Tokyo Institute of Technology, Tokyo 152-8552, Japan
bThe Noguchi Institute, Tokyo 173-0003, Japan
Accepted 8 March 2002
AbstractÐLanthanide tris(per¯uorooctanesulfonyl)methide and bis(per¯uorooctanesulfonyl)amide complexes are shown to be
immobilized and continuously recycled in ¯uorous phases or as solids. The lanthanide complexes are thus extremely ef®cient Lewis acid
catalysts for carbon±carbon bond forming (CCF) reactions. The CCF reactions such as the Friedel±Crafts acylation, Diels±Alder, and
Mukaiyama aldol reaction are effectively catalyzed by the lanthanide complexes by virtue of the highly electron-withdrawing effect of
tris(per¯uorooctanesulfonyl)methide and bis(per¯uorooctanesulfonyl)amide ponytails without any hydrocarbon spacer. q 2002 Published
by Elsevier Science Ltd.
1. Introduction
spacer for increasing the Lewis acidity of lanthanide
catalysts and for ¯uorous phase immobilization (Fig. 1).
The key to the success is the powerful electron-withdrawing
effect of per¯uoroalkanesulfonyl-methide or -amide group8
without any hydrocarbon spacer. Further to our preliminary
communication, we report the `super' Lewis acidities and
the completely recyclable use of lanthanide(III) tris-
(per¯uorooctanesulfonyl)methide and bis(per¯uorooctane-
sulfonyl)amide complexes in the ¯uorous phases or as
solids.9
A wide variety of Lewis acid catalysts have been developed
for carbon±carbon bond forming (CCF) reactions, on the
basis of the Lewis acid±base complexation in aprotic
polar solvents.1 However, the Lewis acid complexes have
often been employed and then wasted after the reactions in
more than a stoichiometric amount. Therefore, it is desirable
to decrease the amount of a Lewis acid complex in catalytic
reactions by developing a stronger Lewis acid catalyst and
the recycle process thereof. Quite recently, the concept of
¯uorous bi-phasic catalysis (FBC) was introduced as an
environmentally benign recyclable process.2 Phosphine or
phosphite ligands with ¯uorous ponytails and hydrocarbon
spacers have been developed to immobilize late transition
metal catalysts for hydroformylation,3 hydrogenation,4
alkene epoxidation5 and hydroboration6 in the non-polar
¯uorous media. The design and immobilization of strong
Lewis acid catalysts are challenging in this unorthodox
non-polar media for Lewis acid catalysis.7 Numerous
(nine) and long-enough (per¯uorooctyl, C8F17) ¯uorous
ponytails can be attached directly without any hydrocarbon
2. Results and discussion
The solubility of the scandium and ytterbium complexes
with per¯uorooctyl (C8F17) ¯uorous ponytails was ®rst
examined in ¯uorous and/or non-¯uorous solvents.
The lanthanide(III) tris(per¯uorooctanesulfonyl)methide
complexes were soluble in aromatic and aliphatic ¯uoro-
carbons. However, ¯uoroaromatic solvents were miscible
in non-¯uorous solvents. Therefore, we examined the
aliphatic ¯uorocarbon/non-¯uorous solvent systems with
or without ¯uoroaromatics, in order to check the catalytic
activities of the lanthanide complexes for alcohol acylation
as a probe reaction; in the bi-phases or a homogeneous
phase with ¯uoroaromatics at higher temperature. The
ester formation of cyclohexanol (2 mmol) with acetic
anhydride (2 mmol) in per¯uoromethylcyclohexane
(5 ml), toluene (5 ml) and per¯uorobenzene (3 ml) was
completed within 15 min in the homogeneous phase at
408C, with 1 mol% of scandium and ytterbium complexes
q See Ref. 17.
Keywords: carbon±carbon bond forming reactions; environmental
benignity; ¯uorous phase; lanthanide; Lewis acid catalysis; tris(per¯uoro-
alkanesulfonyl)methide; bis(per¯uorooctanesulfonyl)amide.
p
Corresponding author. Address: Department of Chemical Technology,
Faculty of Engineering, Tokyo Institute of Technology, Meguro-ku,
Tokyo 152-8552, Japan. Tel.: 181-3-5734-2142; fax: 181-3-5734-
2776; e-mail: kmikami@o.cc.titech.ac.jp
0040±4020/02/$ - see front matter q 2002 Published by Elsevier Science Ltd.
PII: S0040-4020(02)00313-7

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K. Mikami et al. / Tetrahedron 58 (2002) 4015±4021
Figure 1. ScL03, L0ˆC(SO2C8F17)3. The core structure of ScL3, LˆC(SO2CF3)3 is optimized at the Hartree±Fock level with 6-31 G basis set for C, F, S, O and
with CEP-31G pseudo potential and basis set for Sc. Then the CF3 group in the core structure is replaced with C8F17 and those chains are optimized using UFF
force ®eld.10
(Scheme 1). Then, the reaction mixture was allowed to stand
at 158C for 3 min, so that the reaction mixture could be
separated into the upper phase (19.9% CF3C6F11, 52.5%
toluene, 27.6% C6F6) and the lower phase (69.9%
CF3C6F11, 13.8% toluene, 16.3% C6F6) (Photo 1). Cyclo-
hexyl acetate was obtained in quantitative yield as
calculated by GC analysis (Table 1). Scandium and
ytterbium complexes were completely (.99%) recovered
in the lower phase as determined by atomic emission
spectrometry.
anhydride (2 mmol) in per¯uoromethylcyclohexane (5 ml)
and toluene (5 ml) was carried out at 308C for 20 min, in the
presence of 1 mol% of lanthanide complexes (Scheme 2).
Then, the heterogeneous two phases were separated within
just 10 s into the upper toluene composition and the lower
Table 1. Esteri®cation in homogeneous phase catalyzed by
Ln[C(SO2C8F17)3]3
Yielda (%)
Yb[C(SO2C8F17)3]3
Sc[C(SO2C8F17)3]3
100 (95)b
We then conducted the reaction and separation in the
bi-phase (FBC) mode of per¯uoromethylcyclohexane/
toluene. The reaction of cyclohexanol (2 mmol) with acetic
100
a
Calculated by GC analysis using n-nonane as an internal standard.
Values in parenthesis refer to the isolated yields.
b
Scheme 1.
Scheme 2.
Photo 1. (1) Before (158C). (2) During (408C). (3) After (3 min, 158C) the
reaction.
Photo 2. (1) Before (258C). (2) After (10 s, 258C) the reaction.

K. Mikami et al. / Tetrahedron 58 (2002) 4015±4021
4017
Table 2. Esteri®cation in two phases catalyzed by Ln[C(SO2C8F17)3]3
Cyclea
Yieldb (%)
Yb[C(SO2C8F17)3]3
Sc[C(SO2C8F17)3]3
1
2
3
4
5
99
99 (98)c
100 (98)c
99
99
100 (98)c
99 (96)c
98
99
Scheme 4.
99 (96)c
a
The catalyst in the lower phase was recycled.
Calculated by GC analysis using n-nonane as an internal standard.
Values in parenthesis refer to the isolated yields.
b
c
Table 4. Friedel±Crafts acylation reaction catalyzed by Sc[C(SO2C8F17)3]3
Cyclea
Yieldb (%)
1
2
3
4
94 (87)c
93
93
¯uorous layers (Photo 2). Cyclohexyl acetate was obtained
in good isolated yield. Scandium and ytterbium complexes
were completely (.99%) recovered and reused in the
¯uorous phase without isolation (Table 2).
92
a
The catalyst in the lower phase was recycled.
Calculated by GC analysis using n-decane as an internal standard.
Values in parenthesis refer to the isolated yields.
b
c
Then, the catalytic activities and recyclable use of the
lanthanide complexes were examined for CCF reactions.
The Diels±Alder (D±A) reaction constitutes one of the
most ef®cient construction processes of six-membered
rings.11 The D±A reaction of 2,3-dimethyl-1,3-butadiene
(2 mmol) with methyl vinyl ketone (2 mmol) in per¯uoro-
methylcyclohexane (5 ml) and 1,2-dichloroethane (5 ml)
was carried out at 358C for 8 h, in the presence of a catalytic
amount (5 mol%) of scandium complexes. Then, the hetero-
geneous two phases were separated to give acetylcyclo-
hexene in good isolated yield (Scheme 3). Scandium
methide and amide complexes were completely (.99.9%)
recovered and reused in the recyclable ¯uorous immobilized
phase (Table 3).
dichloroethane (6 ml) at 708C for 6 h. The aromatic ketone
product was obtained in good isolated yields (Scheme 4).
Scandium complex was completely (99.8%) recovered and
reused in the ¯uorous phase (Table 4).
The Mukaiyama aldol reaction is a synthetically and bio-
logically important CCF process.13 The aldol reaction of
benzaldehyde (2 mmol) with trimethylsilyl enol ether
derived from methyl 2-methylpropanoate (2.1 mmol) was
completed within 15 min even in the presence of only
1 mol% of the lanthanide complexes in per¯uoromethyl-
cyclohexane (6 ml) and toluene (6 ml) at 408C (Scheme
5). The aldol product was obtained in good isolated yields.
Lanthanide methide complex was completely (99.8%)
recovered and reused (Table 5).
The Friedel±Crafts (F±C) reaction also constitutes one of
the most useful CCF processes in organic synthesis.12 The
F±C acylation reaction of anisole (2 mmol) with acetic
anhydride (4 mmol) was also carried out in the presence
of a catalytic amount (10 mol%) of the lanthanide
complexes in per¯uoromethylcyclohexane (6 ml) and 1,2-
Scheme 3.
Scheme 5.
Table 3. Diels±Alder reaction catalyzed by Sc[C(SO2C8F17)3]3 and
Sc[N(SO2C8F17)2]3
Table 5. Mukaiyama aldol reaction catalyzed by Ln[C(SO2C8F17)3]3
Cyclea
Yieldb (%)
Cyclea
Yieldb (%)
Sc[C(SO2C8F17)3]3
Sc[N(SO2C8F17)2]3
Yb[C(SO2C8F17)3]3
Sc[C(SO2C8F17)3]3
1
2
3
4
95 (92)c
94 (91)c
95
91 (89)c
92
91
1
2
3
84
85
83
88 (84)c
88
86
95 (92)c
91 (88)c
a
a
The catalyst in the lower phase was recycled.
Calculated by GC analysis using n-nonane as an internal standard.
Values in parenthesis refer to the isolated yields.
The catalyst in the lower phase was recycled.
Calculated by GC analysis using n-nonane as an internal standard.
Values in parenthesis refer to the isolated yields.
b
c
b
c

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K. Mikami et al. / Tetrahedron 58 (2002) 4015±4021
Scheme 6.
Continuous recycling was then conducted in the F±C acyla-
tion reaction (Schemes 4 and 6). p-Acetylanisole was
obtained in good yield (87%) in the organic phase, which
was automatically separated from the ¯uorous phase using a
refractive index (RI) sensor. Substantially, the same
reaction was repeated using the catalyst in the ¯uorous
phase (per¯uoromethylcyclohexane). To the ¯uorous
phase containing the catalyst were added 1,2-dichloro-
ethane, anisole and acetic anhydride, followed by stirring
at 608C for 2 h. The resultant reaction mixture was allowed
to stand still at room temperature (208C) for 15 s, so that the
reaction mixture separated into the organic upper phase and
the lower ¯uorous phase. The Sc C8-methide complex was
recovered and reused in a continuous manner (yields: 1st
run: 87%; 2nd run: 85%; 3rd run: 86%).
The lanthanide tris(per¯uorooctanesulfonyl)methide and
bis(per¯uorooctanesulfonyl)amide
complexes
were
insoluble in organic solvent such as toluene and 1,2-
dichloroethane at room temperature or below even in the
presence of reaction substrates. However, these complexes
were soluble in organic solvent at high temperature to be a
low melting point. To demonstrate this advantage of the
lanthanide complexes with respect to temperature-
dependent solubility, we examined to reuse these complexes
for the F±C acylation reaction without ¯uorous solvent
Scheme 7. Recovery and reuse of Ln catalyst.

K. Mikami et al. / Tetrahedron 58 (2002) 4015±4021
4019
Table 6. Reuse of Yb[N(SO2C8F17)2]3 as a solid
3.2. Typical procedure for ¯uorous biphase system
3.2.1. Ester formation of cyclohexanol with acetic anhy-
dride. Cyclohexanol (0.21 ml, 0.20 g, 2 mmol) and acetic
anhydride (0.19 ml, 0.20 g, 2 mmol) were added to a
mixture of per¯uoromethylcyclohexane (5 ml) and toluene
(5 ml). To the resultant mixture was added 1 mol% of
scandium tris(per¯uorooctanesulfonyl)methide (89 mg,
0.02 mmol). The solution was stirred at 308C for 20 min.
The resultant mixture was allowed to stand still at room
temperature (208C), so that the reaction mixture separated
into the upper phase of toluene and the lower phase of
per¯uoromethylcyclohexane. Each of the upper phase and
lower phase was individually analyzed by GC. Cyclohexyl
acetate was obtained from the upper phase after evaporation
under reduced pressure and silica gel chromatography
(0.279 g, 98% isolated yield). To the lower phase containing
the catalyst were again added toluene (5 ml), cyclohexanol
(0.21 ml, 0.20 g, 2 mmol) and acetic anhydride (0.19 ml,
0.20 g, 2 mmol), followed by stirring at 308C for 20 min.
The resultant mixture was allowed to stand still at room
temperature (208C), so that the reaction mixture separated
into the upper phase of toluene and the lower phase of
per¯uoromethylcyclohexane. Each of the upper phase and
lower phase was individually analyzed by GC. The overall
yield of cyclohexyl acetate in the upper phase and lower
phase was 100%. Substantially, the same procedure as
mentioned above was repeated further three times. The
overall yields of cyclohexyl acetate were 99, 99, 100% in
Use of catalyst
1
2
3
% Conversiona
.85
.85
.85
a
Determined by GC analysis.
Photo 3. (1) During (808C). (2) After standing at 2208C for 30 min.
(Scheme 7 and Table 6).14 After heating the reaction
mixture at 808C for 6 h, the mixture was allowed to stand
at 2208C for 30 min to precipitate the ytterbium bis-
(per¯uorooctanesulfonyl)amide complex (Photo 3). The
liquid phase was decanted and the residual lanthanide
complex was reused without isolation. No loss of activity
was observed for the catalyst recovered. The total isolated
yield of the product, which was combined from the three
runs, was 78%.
1
the three times repeated reactions, respectively. H NMR
(400 MHz, CDCl3) d 1.20±1.44 (m, 5H), 1.52±1.58 (m,
1H), 1.70±1.74 (m, 2H), 1.84±1.87 (m, 2H), 2.03 (s, 3H),
4.71±4.77 (m, 1H); 13C NMR (100 MHz, CDCl3) d 21.45,
23.81, 25.37, 31.65, 72.61, 170.40; MS (EI, 70 eV): m/z 127
(C6H11CO21), 99 (C6H11O1), 82 (C6H101), 67, 43
(CH3CO1). Elemental analysis (%) calcd for C8H14O2: C
67.57, H 9.92, found: C 67.41, H 9.96.
In summary, we have disclosed lanthanide tris(per¯uoro-
octanesulfonyl)methide and bis(per¯uorooctanesulfonyl)-
amide complexes15 as ef®cient immobilized Lewis acid
catalysts with or without ¯uorous media by virtue of the
powerful electron-withdrawing effect of the tris(per¯uoro-
octanesulfonyl)methide and bis(per¯uorooctanesulfonyl)-
amide ponytails without any hydrocarbon spacer.16
3.2.2. The Diels±Alder reaction of 2,3-dimethyl-1,3-
butadiene with methyl vinyl ketone. 2,3-Dimethyl-1,3-
butadiene (0.23 ml, 0.16 g, 2 mmol) and methyl vinyl
ketone (0.17 ml, 0.14 g, 2 mmol) were added to a mixture
of per¯uoromethylcyclohexane (5 ml) and 1,2-dichloro-
ethane (5 ml). To the resultant mixture was added 5 mol%
of scandium tris(per¯uorooctanesulfonyl)methide (0.44 g,
0.1 mmol). The solution was stirred at 358C for 8 h. The
resultant mixture was allowed to stand still at room tempera-
ture (208C), so that the reaction mixture separated into the
upper phase of 1,2-dichloroethane and the lower phase of
per¯uoromethylcyclohexane. Each of the upper phase and
lower phase was individually analyzed by GC. Acetylcyclo-
hexene was obtained from the upper phase after evaporation
under reduced pressure and silica gel chromatography
(0.280 g, 92% isolated yield). To the lower phase containing
the catalyst were again added 1,2-dichloroethane (5 ml),
2,3-dimethyl-1,3-butadiene (0.23 ml, 0.16 g, 2 mmol) and
methyl vinyl ketone (0.17 ml, 0.14 g, 2 mmol), followed
by stirring at 358C for 8 h. The resultant mixture was
allowed to stand still at room temperature (208C), so that
the reaction mixture separated into the upper phase of 1,2-
dichloroethane and the lower phase of per¯uoro-
methylcyclohexane. Each of the upper phase and lower
phase was individually analyzed by GC. The overall yield
3. Experimental
3.1. General
1H and 13C NMR spectra were measured on a JEOL JNM-
EX400 (400 MHz) spectrometers. Chemical shifts of H
1
NMR were expressed in parts per million relative to chloro-
form (d 7.26) or tetramethylsilane (d 0.00) as an internal
standard in chloroform-d. Chemical shifts of 13C NMR were
expressed in parts per million relative to chloroform-d (d
77.0) as an internal standard. GC analysis was carried out on
SHIMADZU GC-1700AF and GC±MS analysis was taken
by Hewlett±Packard G1800A GLS. Atomic emission spec-
trometer is of IRIS/AP Nippon Jarrell Ash Co. 1,2-Dichoro-
ethane and toluene were freshly distilled from calcium
hydride. Per¯uoromethylcyclohexane and per¯uorobenzene
were distilled from phosphorous pentaoxide.

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K. Mikami et al. / Tetrahedron 58 (2002) 4015±4021
of acetylcyclohexene in the upper phase and lower phase
was 94%. Substantially, the same procedure as mentioned
above was repeated further two times. The overall yields of
acetylcyclohexene were 95, 95% in the two times repeated
reactions, respectively. 1H NMR (400 MHz, CDCl3) d
1.18±1.58 (m, 1H), 1.61 (s, 3H), 1.63 (s, 3H), 1.90±2.14
(m, 5H), 2.17 (s, 3H), 2.52±2.60 (m, 1H); 13C NMR
(100 MHz, CDCl3) d 18.82, 19.02, 25.32, 27.93, 31.22,
33.08, 48.25, 123.81, 125.25, 211.60; MS (EI, 70 eV): m/z
152 (M1), 137 (C8H13CO1), 119, 109 (C8H131), 91, 79, 67,
43 (CH3CO1). Elemental analysis (%) calcd for C10H16O: C
78.90, H 10.59, found: C 78.99, H 10.51.
phase was individually analyzed by GC. The aldol product
from the upper phase was obtained (0.391 g, 84% isolated
yield). To the lower phase containing the catalyst were
again added toluene (6 ml), benzaldehyde (0.20 ml,
0.21 g, 2 mmol) and trimethylsilyl enol ether derived from
methyl 2-methylpropanoate (0.37 g, 2.1 mmol) followed by
stirring at 408C for15 min. The resultant mixture was
allowed to stand still at room temperature (208C), so that
the reaction mixture separated into the upper phase of
toluene and the lower phase of per¯uoromethylcyclo-
hexane. Each of the upper phase and lower phase was indi-
vidually analyzed by GC. The overall yield of the aldol
product in the upper phase and lower phase was 88%.
Substantially, the same procedure as mentioned above was
repeated. The overall yield of the aldol product was 86%.
MS (EI, 70 eV): m/z 281 (M111), 265, 179
(Me3SiOPhCH1), 163, 115, 89, 73 (Me3Si1). Elemental
analysis (%) calcd for C15H24O3Si: C 64.25, H 8.62,
found: C 64.45, H 8.67.
3.2.3. The Friedel±Crafts acylation of anisole with acetic
anhydride. Anisol (0.22 ml, 0.22 g, 2 mmol) and acetic
anhydride (0.38 ml, 0.41 g, 4 mmol) were added to a
mixture of per¯uoromethylcyclohexane (6 ml) and 1,2-
dichloroethane (6 ml). To the resultant mixture was added
10 mol% of scandium tris(per¯uorooctanesulfonyl)methide
(0.89 g, 0.2 mmol). The solution was stirred at 708C for 6 h.
The resultant mixture was allowed to stand still at room
temperature (208C), so that the reaction mixture separated
into the upper phase of 1,2-dichloroethane and the lower
phase of per¯uoromethylcyclohexane. Each of the upper
and lower phases was individually analyzed by GC.
p-Methoxyacetophenone was obtained from the upper
phase after evaporation under reduced pressure and silica
gel chromatography (0.261 g, 87% isolated yield). To the
lower phase containing the catalyst were again added 1,2-
dichloroethane (6 ml), anisol (0.22 ml, 0.22 g, 2 mmol) and
acetic anhydride (0.38 ml, 0.41 g, 4 mmol) followed by stir-
ring at 708C for 6 h. The resultant mixture was allowed to
stand still at room temperature (208C), so that the reaction
mixture separated into the upper phase of 1,2-dichloro-
ethane and the lower phase of per¯uoromethylcyclohexane.
Each of the upper phase and lower phase was individually
analyzed by GC. The overall yield of p-methoxyaceto-
phenone in the upper phase and lower phase was 93%.
Substantially the same procedure as mentioned above was
repeated further two times. The overall yields of p-methoxy-
acetophenone were 93, 92% in the two times repeated
reactions, respectively. 1H NMR (400 MHz, CDCl3) d
2.55 (s, 3H), 3.87 (s, 3H), 6.93 (d, 2H, Jˆ9.8 Hz), 7.94 (d,
2H, Jˆ9.8 Hz); 13C NMR (100 MHz, CDCl3) d 26.36,
55.44, 113.57, 130.22, 130.46, 163.31, 196.55; MS (EI,
70 eV): m/z 150 (M1), 135 (MeOPhCO1), 107 (MeOPh1),
92, 77, 64, 63, 43 (CH3CO1). Elemental analysis (%)
calcd for C9H10O2: C 71.98, H 6.71, found: C 72.10,
H 6.69.
3.3. Continuous recyclingvia automatic separation using
a refractive index sensor
The same F±C reaction was repeated using the catalyst
contained in the lower phase. Anisol (0.22 ml, 0.22 g,
2 mmol) and acetic anhydride (0.38 ml, 0.41 g, 4 mmol)
were added to a mixture of per¯uoromethylcyclohexane
(6 ml) and 1,2-dichloroethane (6 ml). To the resultant
mixture was added 10 mol% of scandium tris(per¯uoro-
octanesulfonyl)methide (0.89 g, 0.2 mmol). The solution
was stirred at 608C for 2 h. The resultant mixture was
allowed to stand still at room temperature (208C), so that
the reaction mixture was separated into the upper phase of
1,2-dichloroethane and the lower phase of per¯uoromethyl-
cyclohexane. The upper phase containing p-methoxyaceto-
phenone was separated from the lower phase containing the
catalyst. p-Methoxyacetophenone was obtained from the
upper phase after evaporation under reduced pressure and
silica gel chromatography (0.260 g, 87% isolated yield). To
the lower phase containing the catalyst were again added
1,2-dichloroethane (6 ml), anisole (0.22 ml, 0.22 g, 2 mmol)
and acetic anhydride (0.38 ml, 0.41 g, 4 mmol), followed by
stirring at 608C for 2 h.
3.4. The Friedel±Crafts acylation catalyzed by
ytterbium bis(per¯uorooctanesulfonyl)amide as a solid
10 mol% of ytterbium bis(per¯uorooctanesulfonyl)amide
(0.31 g, 0.1 mmol), anisol (0.11 ml, 0.11 g, 1 mmol) and
acetic anhydride (0.19 ml, 0.20 g, 2 mmol) were added to
1,2-dichloroethane (5 ml). The solution was stirred at 808C
for 6 h. The resultant mixture was allowed to stand still in a
convenient freezer (2208C) to precipitate the ytterbium
complex. After 30 min, the liquid phase of the resultant
mixture was decanted and the residual solid catalyst
was reused without isolation. Catalyst remained in the
vessel in the third reaction. Liquid phases, which were
obtained in each reaction, were combined, concentrated
under reduced pressure. p-Methoxyacetophenone was
puri®ed by silica gel chromatography (0.354 g, 78%
isolated yield).
3.2.4. The Mukaiyama aldol reaction of benzaldehyde
with trimethylsilyl enol ether of methyl 2-methyl-
propanoate. Benzaldehyde (0.20 ml, 0.21 g, 2 mmol) and
trimethylsilyl enol ether derived from methyl 2-methyl-
propanoate (0.37 g, 2.1 mmol) were added to a mixture of
per¯uoromethylcyclohexane (6 ml) and toluene (6 ml). To
the resultant mixture was added 1 mol% of scandium tris-
(per¯uorooctanesulfonyl)methide (89 mg, 0.02 mmol). The
solution was stirred at 408C for 15 min. The resultant
mixture was allowed to stand still at room temperature
(208C), so that the reaction mixture separated into the
upper phase of toluene and the lower phase of per¯uoro-
methylcyclohexane. Each of the upper phase and lower

K. Mikami et al. / Tetrahedron 58 (2002) 4015±4021
4021
Tetrahedron Lett. 2000, 41, 57. (b) Tian, Y.; Chan, K. S.
Tetrahedron Lett. 2000, 41, 8813.
References
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of super acids: bis(tri¯uoromethanesulfonyl)amine is stronger
than tri¯uofomethanesulfonic acid by DGˆ7.7 kcal/mol and
tris(tri¯uoromethanesulfonyl)methane is stronger than bis-
(tri¯uoromethanesulfonyl)amine by DGˆ2.8 kcal/mol. They
have also reported that bis(per¯uorobutanesulfonyl)amine is
stronger than bis(tri¯uoromethanesulfonyl)amine by DGˆ
7.7 kcal/mol: J. Am. Chem. Soc. 1994, 116, 3047.
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(b) Santelli, M.; Pons, J.-M. Lewis Acid and Selectivity in
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Zoukan, Kagaku Dojin: Tokyo, 1995; p 177. (d) Oh, T.;
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Lewis Acid Promoted Reactions, Schinzer, D., Ed.; Kluwer
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Organotitanium Reagents in Organic Synthesis; Springer:
Berlin, 1986.
9. Mikami, K.; Mikami, Y.; Matsumoto, Y.; Nishikido, J.;
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10. Rappe, A. K.; Casewit, C. J.; Colwell, K. S.; Goddard, W. A.;
Skiff, W. M. J. Am. Chem. Soc. 1992, 114, 10024.
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Â
1174. (e) Horvath, I. T. Acc. Chem. Res. 1998, 31, 641.
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357. (a) Bach, T. Angew. Chem., Int. Ed. Engl. 1994, 33,
417. (c) Gennari Comprehensive Organic Synthesis; Trost,
B. M., Fleming, I., Eds.; Pergamon: Oxford, 1991; Vol. 2,
p 629.
(f) Cornils, B. Angew. Chem., Int. Ed. Engl. 1997, 36, 2057.
Â
3. (a) Horvath, I. T.; Kiss, G.; Cook, R. A.; Bond, J. E.; Stevens,
Â
P. A.; Rabai, J.; Mozeleski, E. J. J. Am. Chem. Soc. 1998, 120,
3133. (b) Kainz, S.; Koch, D.; Baumann, W.; Leitner, W.
Â
Angew. Chem., Int. Ed. Engl. 1997, 36, 1628. (c) Horvath, I.
 Â
T.; Rabai, J. U.S. Patent 5463082, 1995. (d) Horvath, I. T.;
Â
Rabai, J. Science 1994, 266, 72.
14. (a) Wende, M.; Meier, R.; Gladysz, J. A. J. Am. Chem. Soc.
2001, 123, 11490. (b) Ishihara, K.; Kondo, S.; Yamamoto, H.
Synlett 2001, 1371.
4. (a) Richter, B.; Spek, A. L.; van Koten, G.; Deelman, B.-J.
J. Am. Chem. Soc. 2000, 122, 3945. (b) Chechik, V.; Crooks,
R. M. J. Am. Chem. Soc. 2000, 122, 1243. (c) Haar, C. M.;
Huang, J.; Nolan, S. P.; Peterson, J. Organometallics 1998, 17,
5018. (d) Rutherford, D.; Juliette, J. J. J.; Rocaboy, C.;
15. Recently, catalytic F±C acylation was reported to give 82%
conversion at 1108C for 2 h using ytterbium bis(per¯uoro-
hexanesulfonyl)per¯uorooctanesulfonylmethide (10 mol%),
anisole (1 mmol), and acetic anhydride (2 mmol) in per¯uoro-
methyldecaline (1 ml). The homogeneous mixture was diluted
with CH2Cl2 (5 ml) and then the layers were separated. The
organics were extraced three times with hot (858C) per¯uoro-
methyldecaline (3£5 ml) to give the combined ¯uorous
extracts with 96% recovery of the complex:Barrett, A. G. M.;
Braddock, D. C.; Catterick, D.; Chadwick, D.; Henschke, J. P.;
McKinnell, P. M. Synlett 2000, 847.
Â
Horvath, I. T.; Gladysz, J. A. Catal. Today 1998, 42, 381.
5. (a) Cavazzini, M.; Manfredi, A.; Montanari, F.; Quici, S.;
Pozzi, G. Chem. Commun. 2000, 2171. (b) Betzemeier, B.;
Lhermitte, F.; Knochel, P. Synlett 1999, 489. (c) Quici, S.;
Cavazzini, M.; Ceragioli, S.; Montanari, F.; Pozzi, G.
Tetrahedron Lett. 1999, 40, 3647. (d) Pozzi, G.; Cinato, F.;
Montanari, F.; Quici, S. Chem. Commun. 1998, 877. (e) Pozzi,
G.; Ban®, S.; Manfrdi, A.; Montanari, F.; Quici, S.
Tetrahedron 1996, 52, 11879.
16. Unfortunately,
lanthanide
(scandium,
ytterbium)
tris(per¯uorobutanesulfonyl)methide and bis(per¯uorobutane-
sulfonyl)amide is too short ¯uorous ponytail to render the
complexes in ¯uorous media.
Â
6. (a) Juliette, J. J. J.; Rutherford, D.; Horvath, I. T.; Gladysz,
J. A. J. Am. Chem. Soc. 1999, 121, 2696. (b) Juliette, J. J. J.;
17. A part of this work has been presented at the Ann. Meeting of
Chem. Soc. of Jpn, Chiba, March 28, 2000, Mikami, K.;
Mikami, Y.; Matsumoto, Y.; Yamamoto, F.; Nishikido; J.,
Nakajima, H. Abstr. No. 1F415.
Â
Horvath, I. T.; Gladysz, J. A. Angew. Chem., Int. Ed. Engl.
1997, 36, 1610.
7. Recent example of
a ¯uorous BINOL±Ti catalyst:
(a) Nakamura, Y.; Takeuchi, S.; Ohgo, Y.; Curran, D. P.