Pentafluorophenylammonium trifluoromethanesulfonimide: Mild, powerful, and robust catalyst for mukaiyama aldol and mannich reactions between ketene silyl acetals and ketones or oxime ethers

Article abstract of DOI:10.1002/adsc.200900869

Pentafluorophenylammonium trifluoromethanesulfonimide (C₆F ₅N⁺H₃·NTf2^-) promotes Mukaiyama aldol and Mannich reactions using ketene silyl acetals with ketones and oxime ethers, respectively. The prese

Full text of DOI:10.1002/adsc.200900869

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DOI: 10.1002/adsc.200900869
Pentafluorophenylammonium Trifluoromethanesulfonimide:
Mild, Powerful, and Robust Catalyst for Mukaiyama Aldol and
Mannich Reactions between Ketene Silyl Acetals and Ketones or
Oxime Ethers
Ryohei Nagase,a Jun Osada,a Hiroaki Tamagaki,a and Yoo Tanabea,*
a
Department of Chemistry, School of Science and Technology, Kwansei Gakuin University, 2–1 Gakuen, Sanda, Hyogo
669-1337, Japan
Fax : (+81)-79-565-9077; phone: +81-79-565-8394; e-mail: tanabe@kwansei.ac.jp
Received: December 17, 2009; Published online: April 22, 2010
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.200900869.
Abstract: Pentafluorophenylammonium trifluoro-
tiary aldols).[3] There are two related methods for
À
methanesulfonimide (C6F5N+H3·NTf2 ) promotes
direct cross-aldol reaction between different ketones
[4]
Mukaiyama aldol and Mannich reactions using
ketene silyl acetals with ketones and oxime ethers,
respectively. The present robust method is mild, but
powerful enough to utilize less accessible electro-
philes such as enolizable ketones and oxime ethers
to produce a variety of b-hydroxy esters and b-alk-
using stoichiometric Lewis acids, Sn
(OTf)2
and
TiCl4,[5] wherein strong metal chelate formation drives
the aldol addition between different ketones.
In connection with our long-standing interests in
the development of Ti- (or Zr-) Claisen condensa-
tions,[6] relevant aldol[7] and Mannich reactions,[8] we
report herein the pentafluorophenylammonium tri-
fluorÀomethanesulfonimide (triflylimide) (C6F5N+H3·
ACHTUNGTRENNUNG
A
NTf2 ) [true catalyst is Tf2NACTHUNGETRNNU(G TMS), generated in situ]-
1
which was supported by rational H NMR measure-
ments.
catalyzed Mukaiyama aldol reaction between KSAs
and ketones, and Mannich reaction between KSAs
and oxime ethers (Scheme 1).
Keywords: ketene silyl acetals; ketones; Mannich
addition; Mukaiyama aldol addition; oxime ethers;
pentafluorophenylammonium trifluoromethanesul-
fonimide
The initial attempt was guided by the reaction be-
tween KSA 1a and the significantly less reactive 4-
heptanone using several acid catalysts (Table 1). As
expected, the reaction did not proceeded in the ab-
sence of a catalyst (entry 1). Use of CSA (camphor-
sulfonic acid) and PPTS (pyridinium p-toluenesulfo-
nate), as well as TMSOTf and pentafluorophenylam-
monium triflate (PFPAT; C6F5N+H3·OTfÀ),[9] resulted
Catalytic aldol and Mannich additions are well-recog- in almost no reaction (entry 2). Tf2NH and Tf2N-
À
nized as fundamental and pivotal C C bond forming
reactions for the preparation of the ubiquitous b-hy- for their use in aldol and Diels–Alder reactions due
ACHTUNGTREN(NUGN TMS) catalysts have attracted considerable attention
droxy and b-amino carbonyl core building blocks to their super acidity.[10] Indeed, the reaction using the
ACTHNUTRGNEUNG
found in natural products and pharmaceuticals.[1] Due Tf2NH or Tf2N(TMS) catalyst[10h] afforded the desired
to the intrinsic lower reactivity of ketones and reversi- aldol adduct 2a, but this result proved difficult to re-
ble retro-aldol tendency, only a few reports have ap- produce with constant results (entry 3). The difficulty
peared with regard to cross-aldol reactions between is considered to be attributed to the hygroscopic and
different ketones or between ketones and carbonyl sublimation properties of these catalysts for the pres-
equivalents, such as enol silyl ethers and ketene silyl ent case, which requires both high reactivity and ro-
acetals (KSA).[2] Ishiharaꢀs group recently reported a bustness. To overcome this problem, stable and easily
notable Lewis base-catalyzed Mukaiyama aldol addi- handled ammonium salts of Tf2NH were screened.
tion of KSAs with non-enolizable ketones to give the Although pyridinium and diphenylammonium salts
corresponding b,b-disubstituted b-hydroxy esters (ter- were not effective, the highly acidic but significantly
1128
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Adv. Synth. Catal. 2010, 352, 1128 – 1134

Pentafluorophenylammonium Trifluoromethanesulfonimide: Mild, Powerful, and Robust Catalyst
À
Scheme 1. C6F5N+H3·NTf2 -catalyzed Mukaiyama aldol and Mannich reactions.
Table 1. Screening of acid catalysts.
aldols were provided by the present method. (v) The
syn/anti selectivity was poor or moderate due to the
intrinsic difficulty of ketone-ketone cross-aldol addi-
tions based on the poorer differentiation between
ketone substituents than that of aldehydes.
Next, we applied the present method for the reac-
tion between KSA 1a and four a,b-unsaturated ke-
tones. In clear contrast to the case of using saturated
ketones, Michael-type 1,4-addition predominated over
the aldol addition to give 5-oxo esters 10–13
(Scheme 2).[14]
Entry
Catalyst
Yield [%][a]
Scheme 3 illustrates a plausible mechaÀnism for the
present reaction. Initially, C6F5N+H3·NTf2 reacts with
1
2
3
4
5
none
trace
CSA, PPTS, TMSOTf, PFPAT[b]
trace
a KSA 1 to form the key Tf2N
lease of an intact (much less reactive) methyl ester
and C6F5NH2. Tf2N(TMS) activates a ketone to give
ACHTUNGERTN(NUNG TMS) catalyst with re-
Tf2NH, Tf2ÀN
G
trace–ca. 30[c]
trace
+
À
PyH+·NTf2 , PhNH3 ·NTf2
AHCTUNGTRENNUNG
C6F5N+H3·NTf2
75–77
intermediate A, which couples with 1 giving an aldol
adduct intermediate B. Then B rearranges into a TMS
aldol adduct 2 with reproduction of Tf2NACTHNGUTERNNU(G TMS) possi-
[a]
1
Conversion determined by H NMR.
[b]
[c]
+
C6F5NH3 ·OTfÀ.
Not reproducible.
bly through path b rather than path a, according to
the Yamamoto groupꢀs extensive studies,[10e,f,g,h,i] and
the catalytic cycle is completed. It is worth noting
moisture-insensitive C6F5N+H3·NTf2 produced suc- that Tf2N
ACTHUNTGRENNG(U TMS) is considered to be the true active
À
cessful and reproducible results (entries 4 and 5).[11] catalyst, despite the use Àof the parent simple Brønsted
Thus, we chose C6F5N+H3·NTf2 as a robust catalyst catalyst, C6F5N+H3·NTf2 .
À
for the present study.
1H NMR monitoring studyÀof a mixture of KSA 1a
Table 2 lists the successful results of the present and catalytic C6F5N+H3·NTf2 (20 mol%) in toluene-
À
C6F5N+H3·NTf2 -catalyzed Mukaiyama aldol reaction d8 at À208C, rationally supported the present hypoth-
using a variety of KSAs 1a–1f and ketones under op- esis: the generation not of parent Tf2NH but of NTf2
timized conditions. The salient features are as follows:
(i) The reaction using not only simple KSAs 1a–1c, observed (Figure 1).
but also stereocongested TBS-substituted KSAs 1d, With these results in hand, we next investigated the
ACHTUNGTREN(NUNG TMS) with methyl isobutyrate was unambiguously
proceeded smoothly to give the desired b,b-disubsti- C6F5N+H3·NTf2 -catalyzed Mannich reaction between
tuted b-hydroxy esters (tertiary aldols) in good to ex- KSAs 1 and oxime ethers. Oxime ethers are well-
cellent yield. (ii) A striking aspect is that enolizable known superior isosters to imines due to easier prepa-
ketone acceptors were applicable as the substrate ration and inherently higher stability, especially for
with much better performance compared to Ishiharaꢀs reliable aliphatic aldoximes derived from aldehydes
base-catalyzed method.[3] In general, enolizable ke- bearing a hydrogen in the a-position. The Mannich
tones are prone to be transformed to the correspond- reaction using oxime ethers, therefore, has a clear ad-
ing enol silyl ethers by the reaction with KSAs.[12] (iii) vantage over that of imines due to its wide variation.
Acid labile KSAs 1e and 1f underwent the reaction Nonetheless, to the best of our knowledge, there is a
smoothly without loss of the t-Bu group (entries 5, 6, sole report on this topic:[15] the TMSOTf-catalyzed re-
11, and 12).[13] (iv) Benzophenone, methyl pyruvate, action between KSAs and only two oxime ethers.
and phenacyl chloride were applicable as the acceptor However, this method lacks substrate generality due
(entries 22–24). Thus, a variety of inaccessible tertiary to insufficient reactivity. Recently, we reported the
À
Adv. Synth. Catal. 2010, 352, 1128 – 1134
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Ryohei Nagase et al.
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À
Table 2. C6F5N+H3·NTf2 -promoted Mukaiyama aldol reac-
tion between KSAs 1 and ketones.
À
Scheme 2. C6F5N+H3·NTf2 -promoted Michael reaction be-
tween KSAs 1a and a,b-unsaturated ketones.
Entry
Ketone
KSA
Product
de[a]
Yield
[%][b]
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1a
1b
1c
1d
1e
1f
1a
1c
1d
1a
1c
1d
2a
2b
2c
2d
2e
2f
3a
3b
3c
3d
3e
3f
4a
4c
4d
5a
5c
5d
–
–
–
–
–
–
–
1:1
2:1
1:1
1:1
4:1
–
2:1
1:1
–
77
57
91
76[c]
75
59
86
92
91
90
77
59
71
9
10
11
12
13
14
15
16
17
18
89
84[c]
83
–
–
91
88[c]
Scheme 3. Plausible reaction mechanism for the aldol addi-
tion between KSAs 1 and ketones.
19
20
21
1a
1c
1d
6a
6c
6d
–
1:1
1:1
84
78
94[c]
22
1a
1a
1a
7a
8a
9a
98
68
92
Table 3 lists the successful results of a mild and
powerful Mannich reaction between KSAs 1a–1d and
various oxime ethers.
23
The salient features are as follows: (i) In all cases
examined, the present reaction proceeded smoothly
to give the desired b-alkoxyamino esters in good to
excellent yield (NB: all new compounds). (ii) A com-
parable experiment on entry 1 using TMSOTf as cata-
lyst resulted in almost no reaction under identical
conditions. (iii) O-Benzyloximes as well as O-methyl-
oximes were applicable (entries 14–21). (iv) Several
functionalities in the oxime ethers, such as terminal
Br, TBSO, and MeO2C groups, were compatible (en-
24
[a]
1
Determined by H NMR. The syn/anti ratio was not as-
signed.
Isolated yield.
[b]
[c]
Carried out at 0–58C for 3 h. Based on its TMS ether.
TiCl4-(s-Bu)2NH-mediated direct reaction between tries 16–21). (v) The syn/anti selectivity was poor or
esters and oxime ethers,[8] but this method requires a- moderate similar to the aforementioned cross-aldol
brominated ester substrates.
reaction.
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Adv. Synth. Catal. 2010, 352, 1128 – 1134

Pentafluorophenylammonium Trifluoromethanesulfonimide: Mild, Powerful, and Robust Catalyst
À
Figure 1. 1H NMR monitoring study using a mixture of KSA 1a and catalytic C6F5N+H3·NTf2 (20 mol%) in toluene-d8.
As was described in the previous report,[8] b-me- give the corresponding b-amino esters 22 and 23
thoxyamino esters, obtained by the present Mannich (Scheme 3).
reaction, can be converted to the corresponding b-
In conclusion, we have developed efficient Mu-
amino esters using Zn-AcOH reagent. In addition, a kaiyama aldol and Mannich reactions between KSAs
mild catalytic hydrogenation of b-O-benzyloxime and ketones or oximeÀethers, respectively, promoted
ester products 18a and 21a proceeded smoothly to by the C6F5N+H3·NTf2 catalyst (total 44 examples).
The present method provides a new avenue for the
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Ryohei Nagase et al.
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+
À
Table 3. C6F5NH3 ·NTf2 -promoted Mannich reaction between
KSAs 1 and oxime ethers.
0.25 mm Silica gel Merck 60 F254 plates. Melting points were
determined on a hot stage microscope apparatus (Asone)
and are uncorrected. NMR spectra were recorded on a
JEOL DELTA 300 spectrometer, operating at 300 MHz for
1H NMR and 75 MHz for 13C NMR. Chemical shifts (d
ppm) in CDCl3 are reported downfield from TMS (=0) or
1
CHCl3 (=7.26) for H NMR. For 13C NMR, chemical shifts
are reported in the scale relative to CDCl3 (77.00 ppm) as
an internal reference. IR spectra were recorded on a
JASCO FT/IR-5300 spectrophotometer. Mass spectra were
measured on a JEOL JMS-T100 LC spectrometer. For the
measurement of HR-MS, the corresponding TMS ethers
were used.
Typical Procedure for Aldol Reaction between KSAs
1a and 4-Heptanone (Table 2, entry 1)
1-Methoxy-1-trimethylsiloxy-2-methyl-1-propene
(1a;
Entry Oxime
ether
KSA Prod- de[a] Yield
261 mg, 1.5 mmol) was added to a stirred solutionÀof 4-hep-
tanone (114 mg, 1.0 mmol) and C6F5N+H3·NTf2 (23 mg,
0.05 mmol) in toluene (0.5 mL) at À50 to À458C under an
argon atmosphere, followed by stirring at the same tempera-
ture for 1 h. The mixture was quenched with water, and
then extracted twice with Et2O. The combined organic
phase was washed with water, brine, dried (Na2SO4) and
concentrated. The obtained crude product was added to a
stirred solution of 6M HCl aqueous solution (2.0 mL) in
MeOH (2.0 mL) at 20–258C, followed by stirring at the
same temperature for 1 h. The mixture was quenched with
water and then extracted twice with Et2O. The combined or-
ganic phase was washed with water, brine, dried (Na2SO4)
and concentrated. The obtained crude product was purified
by SiO2 column chromatography (hexane:Et2O=30:1) to
give the desired product 2a;[16] yield: 167 mg (77%); colour-
less oil; 1H NMR (300 MHz, CDCl3): d=0.89 (6H, t, J=
6.9 Hz), 1.22 (6H, s), 1.27–1.54 (8H, m), 3.70 (1H, s), 3.71
(3H, s); 13C NMR (75 MHz, CDCl3): d=14.8, 17.4, 21.3,
38.6, 50.3, 51.8, 76.0, 179.4; IR (neat): n=3505, 2961, 2874,
1734, 1701, 1273, 1150 cmÀ1.
uct
[%][b]
97
1
1a
14a
–
(<10%)[c]
2
3
4
5
6
7
8
9
10
11
12
13
1b
1c
1d
1a
1b
1c
1d
1a
1c
1d
1a
1c
14b
14c
14d
15a
15b
15c
15d
16a
16c
16d
17a
17c
1:1
1:1
94
98
1.5:1 82[d]
–
83
81
84
1:1
1:1
1.5:1 65[d]
–
1:1
89
86
1.5:1 88[d]
4:1 96
2.3:1 99
14
15
1a
1c
18a
18c
–
99
1.5:1 92
86
1.5:1 86
83
1.5:1 87
87
1.5:1 82
16
17
1a
1c
19a
19c
–
18
19
1a
1c
20a
20c
–
Typical Procedure for Aldol reaction between KSA
1d and Ketones (Table 2, entry 4)
20
21
1a
1c
21a
21c
–
4-Heptanone (114 mg, 1.0 mmol) and 2-tert-butyldimethyl-
AHCTUNGTREGsNNUN iloxy-1-methoxy-1-trimethylsiloxy-1-propene (1d; 436 mg,
[a]
Determined by 1H NMR. The syn/anti ratio was not as- 1.5 mmol) were successively added to a stirred solution of
signed.
Isolated yield.
Use of TMSOTf.
Carried out at 0–58C for 3 h.
À
C6F5N+H3·NTf2 (23 mg, 0.05 mmol) in toluene (0.5 mL) at
0–58C under an argon atmosphere, followed by stirring at
the same temperature for 3 h. A similar work-up procedure
as for preparing 2a gave the desired product 2d; yield:
[b]
[c]
[d]
1
306 mg (76%); colourless oil; H NMR (300 MHz, CDCl3):
d=0.01 (3H, s), 0.076 (9H, s), 0.082 (3H, s), 0.82–0.93 (6H,
m), 0.89 (9H, s), 1.15–1.49 (4H, m), 1.44 (3H, s), 1.50–1.79
(4H, m), 3.65 (3H, s); 13C NMR (75 MHz, CDCl3): d=À3.7,
À2.9, 2.9, 15.0, 17.7, 17.8, 18.5, 22.4, 25.9, 37.4, 37.9, 51.3,
82.8, 83.9, 175.0; IR (neat): n=2959, 1742, 1458, 1250, 1146,
1115, 1086, 1005, 839, 777 cmÀ1; HR-MS (ESI): m/z=
427.2677, calcd. for C20H44O4Si2 (M+Na+): 427.2676.
synthesis of a variety of quite less accessible b-hy-
droxy esters and b-alkoxyamino esters of interest, es-
pecially, in the context of natural product synthesis
and process chemistry.
Experimental Section
All reactions were carried out in oven-dried glassware
under an argon atmosphere. TLC analysis was performed on
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Pentafluorophenylammonium Trifluoromethanesulfonimide: Mild, Powerful, and Robust Catalyst
Typical Procedure for Michael Reaction between
KSA 1a and Benzalacetophenone (Scheme 2)
KSA 1a (261 mg, 1.5 mmol) was added to a stirred solution
of
benzalacetophenone
(208 mg,
1.0 mmol)
and
À
C6F5N+H3·NTf2 (23 mg, 0.05 mmol) in toluene (0.5 mL) at
À50 to À458C under an argon atmosphere, followed by stir-
ring at the same temperature for 1 h. A similar work-up pro-
cedure as for the aldol reaction gave the desired product
10;[17] yield: 267 mg (86%).
Scheme 4. Deprotection of the benzyloxy group of Mannich-
type adducts.
MeOH (3.0 mL), and the mixture was stirred equipped with
an H2 balloon for 16 h at 20–258C. The mixture was filtered
thorough the Celite using a glass filter, and the filtrate was
concentrated under reduced pressure. The obtained crude
product was purified by SiO2 column chromatography (hex-
ane:AcOEt=10:1) to give the desired product 22 or 23.
Typical Procedure for Mannich Reaction between
KSAs 1a and O-(Methyl)octanaldoxime (Table 3,
entry 1)
O-(Methyl)octanaldoxime (157 mg, 1.0 mmol) and KSA 1a
(261 mg, 1.5 mmol) were successively added to a stirred so-
À
lution of C6F5N+H3·NTf2 (23 mg, 0.05 mmol) in toluene
(0.5 mL) at À50 to À458C under an argon atmosphere, fol-
lowed by stirring at the same temperature for 1 h. The mix-
ture was quenched with water, which was extracted twice
with Et2O. The combined organic phase was washed with
water, brine, dried (Na2SO4) and concentrated. The obtained
crude product was purified by SiO2 column chromatography
(hexane:Et2O=15:1) to give the desired product 14a; yield:
Supporting Information
Characterization data for all known products 3a,[17] 3c,[18]
3e,[16] 5a,[19] 5c,[20] 7a,[20] 8a,[21] 10,[17] 11,[22] 12,[23] 13,[24] and all
new products 2b–2f, 3f, 4a, 4c, 4d, 5d, 6a, 6b, 6d, 9a, 14a–
14d, 15a–15d, 16a, 16c, 16d, 17a, 17c, 18a, 18c, 19c, 20a, 20c,
21a, 21c are available in the Supporting Information.
1
251 mg (97%); colourless oil; H NMR (300 MHz, CDCl3):
d=0.88 (3H, t, J=6.5 Hz), 1.06–1.62 (12H, m), 1.155 (3H,
s), 1.157 (3H, s), 3.11 (), 3.41 (3H, s), 3.65 (3H, s), 5.56
(1H, br s); 13C NMR (75 MHz, CDCl3): d=14.1, 20.2, 22.6,
23.2, 27.6, 28.1, 29.2, 29.7, 31.8, 45.6, 51.6, 61.3, 66.2, 178.1;
IR (neat): n=2928, 2857, 1736, 1466, 1435, 1263, 1192,
Acknowledgements
This research was partially supported by Grant-in-Aids for
Scientific Research on Basic Areas (B) “18350056”, Priority
Areas (A) “17035087” and “18037068”, and Exploratory Re-
search “17655045” from the Ministry of Education, Culture,
Sports, Science and Technology (MEXT).
1142 cmÀ1
;
HR-MS (ESI): m/z=282.2040, calcd. for
C14H29NO3 (M+Na+): 282.2045.
Typical Procedure for Mannich reaction between
KSA 1d and O-(Methyl)octanaldoxime (Table 3,
entry 4)
References
O-Methyloctanaldoxime (157 mg, 1.0 mmol) and KSA 1d
(436 mg, 1.5 mmol) were successively added to a stirred so-
À
lution of C6F5N+H3·NTf2 (23 mg, 0.05 mmol) in toluene
[1] a) C. H. Heathcock, in: Comprehensive Organic Synthe-
sis, (Eds.: B. M. Trost, I. Fleming), Pergamon, Oxford,
1991, Vol. 2, p 181; b) J. Clayden, N. Greeves, S.
Warren, P. Wothers, in: Organic Chemistry, Oxford,
New York, 2001, p 689.
(0.5 mL) at 0–58C under an argon atmosphere, followed by
stirring at the same temperature for 3 h. A similar work-up
as for preparing 14a [SiO2 column chromatography (hex-
ACHTUNGTRENNUNGane:Et2O=80:1)] gave the desired product 14d; yield:
1
[2] a) M. B. Smith, J. March, in: Marchꢀs Advanced Organ-
ic Chemistry, 6th edn., Wiley, New York, 2006, p 1351;
for recent examples, see: b) S. E. Denmark, Y. Fan, J.
Am. Chem. Soc. 2002, 124, 4233; c) K. Oisaki, Y. Suto,
M. Kanai, M. Shibasaki, J. Am. Chem. Soc. 2003, 125,
5644; d) S. E. Denmark, Y. Fan, M. D. Eastgate, J. Org.
Chem. 2005, 70, 5235; e) K. Oisaki, D. Zhao, M. Kanai,
M. Shibasaki, J. Am. Chem. Soc. 2006, 128, 7164.
[3] M. Hatano, E. Takagi, K. Ishihara, Org. Lett. 2007, 9,
4527.
309 mg (82%); colourless oil; H NMR (300 MHz, CDCl3):
d=0.075 (3Hꢂ3/5, s), 0.083 (3Hꢂ2/5, s), 0.11 (3Hꢂ3/5, s),
0.17 (3Hꢂ2/5, s), 0.84–0.91 (12H, m), 1.16–1.56 (12H, m),
1.38 (3Hꢂ2/5, s), 1.46 (3Hꢂ3/5, s), 3.05 (1Hꢂ3/5, dd, J=
2.1, 9.6 Hz), 3.14 (1Hꢂ2/5, dd, J=2.4, 9.3 Hz), 3.37 (3Hꢂ2/
5, s), 3.43 (3Hꢂ3/5, s), 3.67 (3Hꢂ2/5, s), 3.69 (3Hꢂ3/5, s),
5.99 (1H, br s); 13C NMR (75 MHz, CDCl3): d=À3.4, À3.1,
À2.81, À2.77, 14.1, 18.4, 18.6, 22.6, 23.2, 24.2, 25.8, 25.9, 26.8,
27.2, 27.4, 28.0, 29.2, 29.6, 29.7, 31.8, 51.7, 60.7, 61.4, 66.6,
67.7, 77.8, 79.3, 175.2, 176.0; IR (neat): n=2930, 1754, 1464,
1254, 1192, 1130, 1005, 837, 779 cmÀ1; HR-MS (ESI): m/z=
398.2707, calcd. for C19H41NO4Si (M+Na+): 398.2703.
[4] T. Mukaiyama, N. Iwasawa, R. W. Stevens, T. Haga,
Tetrahedron 1984, 40, 1381.
[5] Y. Tanabe, N. Matsumoto, T. Higashi, T. Misaki, T.
Itoh, M. Yamamoto, K. Mitarai, Y. Nishii, Tetrahedron
(Symposium in Print) 2002, 58, 8269.
[6] a) Y. Tanabe, Bull. Chem. Soc. Jpn. 1989, 62, 1917;
b) Y. Tanabe, R. Hamasaki, S. Funakoshi, Chem.
Commun. 2001, 1674; c) Y. Tanabe, A. Makita, S. Funa-
General Procedure of Catalytic Hydrogenation of b-
(Benzyloxyamino) Esters (Scheme 4)
10% Pd-C (106 mg, 0.1 mmol) was added to a stirred solu-
tion of 3-(benzyloxyamino) ester 18a or 21a (1.0 mmol) in
Adv. Synth. Catal. 2010, 352, 1128 – 1134
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1133

Ryohei Nagase et al.
COMMUNICATIONS
koshi, R. Hamasaki, T. Kawakusu, Adv. Synth. Catal.
2002, 344, 507; d) T. Misaki, R. Nagase, K. Matsumoto,
Y. Tanabe, J. Am. Chem. Soc. 2005, 127, 2854; e) A.
Iida, S. Nakazawa, T. Okabayashi, A. Horii, T. Misaki,
Y. Tanabe, Org. Lett. 2006, 8, 5215.
perature for 0.5 h. Evaporation of the solvent gave a
crude solids which was washed with hexane (10 mLꢂ5)
to give the desired pure product as colourless moisture-
insensitive, and easily handled crystals; yield: 1.34 g
(96%); mp 105–1078C; 1H NMR (acetone-d6,
300 MHz): d=9.14 (3H, br s); 13C NMR (75 MHz): d=
[7] a) Ref.[5]; b) Y. Tanabe, K. Mitarai, T. Higashi, T.
Misaki, Y. Nishii, Chem. Commun. 2002, 2542; c) R.
Nagase, N. Matsumoto, K. Hosomi, T. Higashi, S. Funa-
koshi, T. Misaki, Y. Tanabe, Org. Biomol. Chem. 2007,
5, 151; d) R. Nagase, M. Katayama, H. Mura, N.
Matsuo, Y. Tanabe, Tetrahedron Lett. 2008, 49, 4509.
[8] T. Funatomi, S. Nakazawa, K. Matsumoto, R. Nagase,
Y. Tanabe, Chem. Commun. 2008, 771.
ACTHNUTRGNEUNG
111.0, 120.9 [1J(13C,19F)=321 Hz], 137.8, 141.6, 142.6,
145.0, 146.0; IR (KBr): n=3403, 1352, 1333, 1197,
1144 cmÀ1.
[12] a) E. Nakamura, T. Murofushi, M. Shimizu, I. Kuwaji-
ma, J. Am. Chem. Soc. 1976, 98, 2346; b) J. J. Song, Z.
Tan, J. T. Reeves, D. R. Fandrick, N. K. Yee, C. H. Sen-
anayake, Org. Lett. 2008, 10, 877.
[9] Commercially available; TCI-P1626: a) T. Funatomi, K.
Wakasugi, T. Misaki, Y. Tanabe, Green Chem. 2006, 8,
1022; b) A. Iida, J. Osada, R. Nagase, T. Misaki, Y.
Tanabe, Org. Lett. 2007, 9, 1859.
[13] Practical and robust method for the preparation of 1e
and 1f and related KSAs: T. Okabayashi, A. Iida, K.
Takai, Y. Nawate, T. Misaki, Y. Tanabe, J. Org. Chem.
2007, 72, 8142.
[14] It is a usual behaviour that Michael addition predomi-
nates over 1,2-type aldol addition; for an example, see
Ref.[2a], p. 1110.
[10] a) B. Mathieu, L. Ghosez, Tetrahedron Lett. 1997, 38,
5497; b) A. Ishii, T. Kotera, T. Saeki, K. Mikami, Syn-
lett 1997, 1145; c) K. Ishihara, Y. Hiraiwa, H. Yamamo-
to, Synlett 2001, 1851; d) J. Cossy, F. Lutz, V. Alauze, C.
Meyer, Synlett 2002, 45; e) K. Ishihara, Y. Hiraiwa, H.
Yamamoto, Chem. Commun. 2002, 1564; f) D. Nakashi-
ma, H. Yamamoto, Org. Lett. 2005, 7, 1251; g) K. Ina-
naga, K. Takasu, M. Ihara, J. Am. Chem. Soc. 2005,
127, 3668; h) M. B. Boxer, H. Yamamoto, J. Am. Chem.
Soc. 2006, 128, 48; i) Y. Hiraiwa, K. Ishihara, H. Yama-
moto, Eur. J. Org. Chem. 2006, 1837; j) K. Takasu, N.
Shindoh, H. Tokuyama, M. Ihara, Tetrahedron 2006, 62,
11900; k) M. E. Jung, D. G. Ho, Org. Lett. 2007, 9, 375.
[11] pKb values of counter amines: ca. 9.4 (PhNH2), 13.8
(pyridine), 14.2 (C6F5NH2), calculated by SciFinder
Scholarꢃ. Advanced Chemistry Development (ACD/
Labs) Software V8.14 for Solaris ꢁ 1994–2006 ACD/
Labs. Preparation of C6F5N+H3·NTf2À: A solution of
2,3,4,5,6-pentafluoroaniline (549 mg, 3.0 mmol) in tolu-
ene (3.0 mL) was added to a stirred solution of
(CF3SO2)2NH (843 mg, 3.0 mmol) in toluene (6.0 mL)
at 0–58C, and the mixture was stirred at the same tem-
[15] K. Ikeda, K. Achiwa, M. Sekiya, Tetrahedron Lett.
1983, 24, 4707.
[16] G. Wenke, E. N. Jacobsen, G. E. Totten, A. C. Karydas,
Y. E. Rhodes, Synth. Commun. 1983, 13, 449.
[17] S. Kobayashi, S. Nagayama, J. Am. Chem. Soc. 1998,
120, 2985.
[18] K. Oisaki, D. Zhao, M. Kanai, M. Shibasaki, J. Am.
Chem. Soc. 2006, 128, 7164.
[19] G. Bartoli, L. Lunazzi, M. Massaccesi, A. Mazzanti, J.
Org. Chem. 2004, 69, 821.
[20] K. Takai, T. Ueda, N. Ikeda, T. Ishiyama, H. Matsushi-
ta, Bull. Chem. Soc. Jpn. 2003, 76, 347.
[21] H. Doucet, J.-L. Parrain, M. Santelli, Synlett 2000, 871.
[22] T. Mukaiyama, S. Kobayashi, M. Tamura, Y. Sagawa,
Chem. Lett. 1987, 491.
[23] T. Nakagawa, H. Fujisawa, Y. Nagata, T. Mukaiyama,
Bull. Chem. Soc. Jpn. 2005, 78, 236.
[24] K. Ishihara, N. Hanaki, M. Funahashi, M. Miyata, H.
Yamamoto, Bull. Chem. Soc. Jpn. 1995, 68, 1721.
1134
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ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2010, 352, 1128 – 1134