Dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(S)-tert-leucinate]: A new chiral Rh(II) catalyst for enantioselective amidation of C-H bonds

Article abstract of DOI:10.1016/S0040-4039(02)02432-2

Dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(S)-tert-leucinate], characterized by substitution of chlorine atoms for four hydrogen atoms on the phthalimido group in the parent dirhodium(II) complex has been found to be well suited for enantioselective amidation of benzylic C-H bonds with [(4-nitrophenyl)sulfonylimino]phenyliodinane. The observed enantioselectivity of up to 84% ee is the highest reported to date for dirhodium(II) complex-catalyzed C-H amidations.

Full text of DOI:10.1016/S0040-4039(02)02432-2

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 9561–9564
Dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(S)-tert-leucinate]:
a new chiral Rh(II) catalyst for enantioselective amidation
of CꢀH bonds
Minoru Yamawaki, Hideyuki Tsutsui, Shinji Kitagaki, Masahiro Anada and Shunichi Hashimoto*
Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan
Received 25 September 2002; revised 21 October 2002; accepted 25 October 2002
Abstract—Dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(S)-tert-leucinate], characterized by substitution of chlorine atoms for
four hydrogen atoms on the phthalimido group in the parent dirhodium(II) complex has been found to be well suited for
enantioselective amidation of benzylic CꢀH bonds with [(4-nitrophenyl)sulfonylimino]phenyliodinane. The observed enantioselec-
tivity of up to 84% ee is the highest reported to date for dirhodium(II) complex-catalyzed CꢀH amidations. © 2002 Elsevier
Science Ltd. All rights reserved.
1
2
Pioneered by the groups of Breslow and Mansuy in
the early 1980s, transition metal-catalyzed nitrene
transfer reactions with (arenesufonylimino)phenylio-
dinanes have been recognized as potentially powerful
methods for the synthesis of aziridines, amides, or
enantioselectivity (89% ee) known for this type of trans-
11
formations. In recent years we have achieved high
levels of enantiocontrol in a range of catalytic Rh(II)–
carbene transformations by developing dirhodium(II)
carboxylate catalysts, which incorporate N-phthaloyl-
or N-benzene-fused-phthaloyl-(S)-amino acids as
3
amines. Consequently, a great deal of effort has
12
recently been directed toward the development of enan-
tioselective version of these catalytic processes. While
high levels of enantiocontrol in aziridinations have
already been achieved using well-designed chiral cata-
6
bridging ligands. Using the analogy between carbenes
and nitrenes, we now address the issue of enantiocon-
trol in Rh(II)-catalyzed C–H amidation reactions.
4
5
lysts, such as Cu(I)–bis(oxazoline), Cu(I)–diimine,
7
8
Mn(III)–salen or Mn(III)–porphyrin complexes, only
a few examples of enantioselective amidation of CꢀH
bonds have been reported. M u¨ ller and co-workers were
the first to demonstrate asymmetric induction (up to
3
3% ee) in the reaction of [(4-nitrophenyl)sulfonyl-
imino]phenyliodinane, NsNꢁIPh (1, Ns=4-NO C -
2
6
H SO ) and indan (2) employing dirhodium(II) tetra-
4
2
kis[(R)-binaphthylphosphate], Rh (R-BNP) , as a chiral
2
4
9
catalyst. Thereafter, Che and co-workers explored ami-
dation of a series of benzylic hydrocarbons with
TsNꢁIPh in the presence of chiral Ru(III)- or Mn(III)-
porphyrin-catalysts, wherein modest enantioselectivity
9
Following the pioneering work of M u¨ ller, we initially
explored C–H insertion of 1 with 5 equiv. of 2 in the
8b,10
of 54% ee was obtained with 1-ethylnaphthalene.
presence of 2 mol% of our chiral dirhodium(II) car-
boxylates (Table 1). The use of tetrakis[N-phthaloyl-
More recently, Katsuki and co-worker have disclosed
that a chiral Mn(III)–salen complex modified with an
electron-withdrawing group is an efficient catalyst for
the reaction of TsNꢁIPh with various allylic and ben-
zylic hydrocarbons, and it displays the highest degree of
13
(
S)-phenylalaninate], Rh (S-PTPA) , in dichloro-
2 4
methane at 0°C provided amidation product 3 in 68%
14
yield (entry 1). The enantioselectivity in this reaction
was determined to be 15% ee by HPLC analysis (Daicel
15
Chiralpak AD). The preferred absolute stereochem-
2
4
*
Corresponding author. Tel.: +81-11-706-3236; fax: +81-11-706-4981;
istry of 3 [[h]D +5.67 (c 1.07, CHCl )] was established
3
e-mail: hsmt@pharm.hokudai.ac.jp
as R by comparing the sign of the optical rotation with
0
040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)02432-2

9
562
M. Yamawaki et al. / Tetrahedron Letters 43 (2002) 9561–9564
2
5
(
R)-3 [[h]D +34.5 (c 1.10, CHCl )], which was prepared
plexed sulfonyl nitrene intermediate, leading to further
enhancement of the enantioselectivity. Thus, new
3
16
21
from (R)-1-aminoindan
(p-NO C H SO Cl, aq.
2
6
4
2
NaOH–CH Cl , 0°C, 1 h, 76%). We next screened other
dirhodium(II) carboxylates, Rh (S-TFPTTL) and
2
2
2
4
chiral dirhodium(II) carboxylates, Rh (S-PTA) ,
Rh (S-TCPTTL) were prepared from Rh (OAc) by
2 4 2 4
22
2
4
Rh (S-PTV) , and Rh (S-PTTL) , derived from N-
ligand exchange reaction with N-tetrafluorophthaloyl-
23
2
4
2
4
phthaloyl-(S)-alanine, -valine, and -tert-leucine, respec-
tively (entries 2–4). While uniform sense of
and N-tetrachlorophthaloyl-(S)-tert-leucines, respec-
24,26
a
tively.
Indeed, we were gratified to find that Rh (S-
2
asymmetric induction was observed in all cases, the
highest levels of enantioselectivity were only 27 and
TFPTTL) and Rh (S-TCPTTL) exhibited even higher
enantioselectivities (54% and 66% ee, respectively) than
the unsubstituted parent dirhodium(II) complex,
4
2
4
2
8% ee obtained with Rh (S-PTA) and Rh (S-PTTL) ,
2 4 2 4
17
respectively (entries 2 and 4). Focusing on these two
Rh (S-PTTL)4 (entries 7 and 8). Using Rh (S-
2
2
catalysts, we then evaluated the abilities of Rh (S-
TCPTTL) as a catalyst, we then studied the effects of
2
4
BPTA) and Rh (S-BPTTL) which are characterized
solvent and temperature on enantioselectivity. The sol-
vent survey revealed that dichloromethane was the opti-
mal solvent for this transformation. While benzene and
benzotrifluoride exhibited nearly the same yields and
enantioselectivities as dichloromethane, reaction times
to complete the reaction in these solvents were extended
(entries 9 and 10). Toluene was found to be the least
effective due to the formation of substantial amounts
4
2
4
by an extension of the phthalimido group with one
1
2b
more benzene ring.
Surprisingly, the use of Rh (S-
2
18
BPTA) markedly diminished product yield, although
4
the drop in enantioselectivity was slight (entry 5). The
use of Rh (S-BPTTL)4 resulted in similar levels of
2
product yield and enantioselectivity as found with
Rh (S-PTTL) (entry 6).
2
4
(
30%) of N-benzyl-4-nitrobenzenesulfonamide arising
It has recently been demonstrated that ligand modifica-
from the CꢀH insertion into a methyl group of toluene
(entry 11). When the reaction in dichloromethane was
conducted at −23°C, the enantioselectivity was
increased to 70% ee without affecting product yield
(entry 12). Although reaction times at −23°C were
extended (6 h) compared to those at 0°C (0.5 h), much
longer reaction times (24 h) were necessary with the
case of Rh (S-PTTL) where product yield was sub-
1
9
tion by incorporating electron-donating or electron-
1
1,20
withdrawing
substituents can have a profound
influence on the rate and enantioselectivity of catalytic
asymmetric reactions. Based on these precedents, we
envisaged that the development of dirhodium(II) car-
boxylates characterized by substitution of electron-
withdrawing groups for four hydrogen atoms on the
phthalimido group could facilitate the formation and
ensuing C–H insertion of the presumed Rh(II)-com-
2
4
stantially reduced (entry 13). These results strongly
suggest that the chlorinated ligand did confer higher
a
Table 1. Enantioselective amidation of indan (2) with NsNꢁIPh (1) catalyzed by chiral dirhodium(II) complexes
Entry
Rh(II) catalyst
Solvent
CH Cl
Temp. (°C)
Time (h)
Yield (%)b
Ee (%)c
R
1
2
3
4
5
6
7
8
9
Rh (S-PTPA)
Bn
0
0
0
0
0
0
0
0
10
0
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
3.5
2.0
3.5
6.0
24.0
12.0
68
75
69
79
23
80
89
87
89
81
15
27
15
28
25
33
54
66
63
59
62
70
27
73
2
4
2
2
2
2
2
2
2
2
2
Rh (S-PTA)
Me
CH Cl
2
4
2
i
Rh (S-PTV)
Pr
Bu
CH Cl
2
4
2
t
Rh (S-PTTL)
CH Cl
2
4
2
Rh (S-BPTA)
Me
CH Cl
2
4
2
t
Rh (S-BPTTL)
Bu
CH Cl
2
4
2
t
Rh (S-TFPTTL)
Bu
(X=F)
(X=Cl)
(X=Cl)
(X=Cl)
(X=Cl)
(X=Cl)
CH Cl
2
4
2
t
Rh (S-TCPTTL)
Bu
CH Cl
2
4
4
4
4
4
2
t
Rh (S-TCPTTL)
Bu
Benzene
CF C H
5
2
t
10
11
12
13
14
Rh (S-TCPTTL)
Bu
2
3
6
t
d
Rh (S-TCPTTL)
Bu
Toluene
CH Cl
0
57
2
t
Rh (S-TCPTTL)
Bu
−23
−23
−40
82
53
51
2
2
2
2
2
t
Rh (S-PTTL)
Bu
CH Cl
2
4
2
t
Rh (S-TCPTTL)
Bu
(X=Cl)
CH Cl
2
4
2
a
Reactions were carried out as follows: 1 (40.4 mg, 0.10 mmol) was added in one portion to a solution of 2 (59 mg, 0.5 mmol, 5 equiv.) and Rh(II)
catalyst (0.002 mmol, 2 mol%) in the indicated solvent (1.0 mL) at the indicated temperature under argon.
Isolated yield based on 1.
b
c
Determined by HPLC [column, Daicel Chiralpak AD; eluent, 3:1 n-hexane:i-PrOH; flow rate, 1.0 mL/min; retention time 11.8 min [(R)-3] and
1
6.7 min [(S)-3]].
d
BnNHNs (ca. 30%) was formed by way of C–H insertion reaction of 1 with a methyl group of toluene.

M. Yamawaki et al. / Tetrahedron Letters 43 (2002) 9561–9564
9563
Table 2. Enantioselective intermolecular CꢀH amidation
with NsNꢁIPh (1) catalyzed by Rh (S-TCPTTL)
tions. In contrast to these results, the present protocol
was found to be less effective for ethylbenzene (7) and
cyclohexene (8).
2
4
In summary, we have demonstrated that Rh (S-
2
TCPTTL) developed through the electronic tuning of
4
Rh (S-PTTL) is effective for enantioselective amida-
2
4
tion of CꢀH bonds, wherein this catalyst has been
found to exhibit even higher reactivity and enantiose-
lectivity (up to 84% ee) than the parent dirhodium(II)
31
complex. Further application of this catalyst to enan-
tioselective aziridinations as well as mechanistic and
stereochemical studies are currently in progress.
Acknowledgements
This research was supported in part by a Grant-in-Aid
for Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology, Japan. We
thank Ms. S. Oka and Ms. M. Kiuchi of Center for
Instrumental Analysis at Hokkaido University for mass
measurements.
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4
reactivity to the associated dirhodium(II) catalyst in
this transformation. While further enhancement of up
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ature to −40°C (entry 14), −23°C was found to be the
temperature limit in terms of both reaction rate and
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5
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6
Having identified the effectiveness of the combinational
use of Rh (S-TCPTTL) as a catalyst and dichloro-
2
4
methane as a solvent, we then investigated the scope
and limitation of this process (Table 2). The amidation
of tetralin (4) under the optimized conditions for indan
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(
2) gave amidation product 9 in high yield with 76% ee
11
(
entry 2). As already demonstrated by Katsuki, 1,1-
2
7
28
dimethylindan(5) and 1,1-dimethyltetralin (6) pro-
vided even higher enantioselectivities than the
unsubstituted parent substrates (entries 1 versus 3 and 2
versus 4). It is worth noting that the enantioselectivity
of 84% ee obtained with 6 is the highest reported to
date for dirhodium(II) complex-catalyzed CꢀH amida-
9. N a¨ geli, I.; Baud, C.; Bernardinelli, G.; Jacquier, Y.;
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with up to 87% ee. Liang, J.-L.; Yuan, S.-X.; Huang,
J.-S.; Yu, W.-Y.; Che, C.-M. Angew. Chem., Int. Ed.
21. The synthesis of the fluorinated analogues of chiral
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C. J.; Pepper, A. G.; Slawin, A. M. Z. Adv. Synth. Catal.
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2
002, 41, 3465.
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25
24. According to the procedure of Bose, N-tetrafluoro-
20
phthaloyl-(S)-tert-leucine [[h]D −40.8 (c 1.58, EtOH)] and
20
N-tetrachlorophthaloyl-(S)-tert-leucine [[h]D −34.7 (c
1.69, EtOH)] were prepared from (S)-tert-leucine and
tetrafluoro- or tetrachlorophthalic anhydride without any
racemization.
2
83; (f) For enantioselective intermolecular cyclopropa-
nation using dirhodium(II) carboxamidate catalyst,
25. Bose, A. K. Organic Syntheses, Collect. Vol. V; Wiley:
New York, 1973; p. 973.
Rh (S-PTPI) , see: Kitagaki, S.; Matsuda, H.; Watanabe,
2
4
N.; Hashimoto, S. Synlett 1997, 1171.
3. NsNꢁIPh (1) was prepared from NsNH and PhI(OAc)
26. The new dirhodium(II) carboxylates exhibited satisfac-
1
13
1
1
1
tory spectral (IR, 270 MHz H NMR and 67.8 MHz
C
2
2
as described: Yamada, Y.; Yamamoto, T.; Okawara, M.
Chem. Lett. 1975, 361.
NMR), analytical, and mass spectral characteristics.
27. Eisenbraun, E. J.; Harms, W. M.; Burnham, J. W.;
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4. The CꢀH amidation of indan (2) with 1.5 equiv. of 1 in
the presence of 2 mol% of Rh (S-PTPA) afforded the
2
4
amidation product 3 in 18% yield with 19% ee.
5. Previously, M u¨ ller reported that Rh (S-PTPA) -catalyzed
2
4
amidation of 2 with 1 in CH Cl afforded 3 in 77% yield
with 7% ee.
29. (a) Weidmann, R.; Guette, J. P. C.R. Seances Acad. Sci.,
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2
2
9
16. R-1-Aminoindan was purchased from Aldrich Chemical
Company, Inc.
30. (R)-1-Phenylethylamine was purchased from Wako
1
7. We also examined Rh (S-PTTL) -catalyzed CꢀH amida-
Chemical Industries, Ltd.
2
4
tion of TsNꢁIPh with 2, which gave the amidation
product in 16% yield with 38% ee. On the other hand, a
similar reaction of [[(4-methoxyphenyl)sulfonyl]imino]-
phenyliodinane gave a complex mixture of products.
8. The reason cannot be given at present.
31. Representative procedure (Table 2, entry 1): 1 (80.8 mg,
0.20 mmol) was added in one portion to a solution of 2
(118 mg, 1.00 mmol, 5.0 equiv.) and bis(ethyl acetate)
adduct of Rh
mol%) in CH
(S-TCPTTL)
Cl (2.0 mL) at −23°C. After 6.0 h of
2
(7.9 mg, 0.004 mmol, 2
2
4
1
1
2
9. (a) Jacobsen, E. N.; Zhang, W.; G u¨ ler, M. L. J. Am.
Chem. Soc. 1991, 113, 6703; (b) RajanBabu, T. V.; Ayers,
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A. Org. Lett. 2000, 2, 4137.
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stirring at this temperature, the whole mixture was con-
centrated in vacuo and purified by column chromatogra-
phy (silica gel, 5:1 n-hexane:ethyl acetate) to provide
9
25
(R)-3 (52.4 mg, 82%); [h]
+22.7 (c 1.30, CHCl ). Enan-
D 3
tiomeric excess was determined to be 70% by HPLC
analysis [column, Daicel Chiralpak AD; eluent, 3:1 n-
hexane:i-PrOH; flow rate, 1.0 mL/min; retention time,
11.8 min [major (R)-isomer] and 16.7 min [minor (S)-iso-
mer].
2