Mn(salen)-catalyzed enantioselective C-H amination

Article abstract of DOI:10.1016/S0040-4039(01)00427-0

A chiral 3,3′,5,5′-tetrabromosubstituted (salen)manganese(III) complex was found to be an efficient catalyst for asymmetric C-H amination (up to 89% ee). In the reaction of cycloalkenes, allylic amination occurred in preference to aziridination.

Full text of DOI:10.1016/S0040-4039(01)00427-0

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 3339–3342
Mn(salen)-catalyzed enantioselective CꢀH amination
Yoshinori Kohmura and Tsutomu Katsuki*
Department of Chemistry, Faculty of Science, Graduate School, Kyushu University 33, CREST,
JST (Japan Science and Technology), Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
Received 9 February 2001; accepted 9 March 2001
Abstract—A chiral 3,3%,5,5%-tetrabromosubstituted (salen)manganese(III) complex was found to be an efficient catalyst for
asymmetric CꢀH amination (up to 89% ee). In the reaction of cycloalkenes, allylic amination occurred in preference to
aziridination. © 2001 Elsevier Science Ltd. All rights reserved.
(
Salen)manganese(III) complexes [hereafter referred to
cationic Mn(salen)s 1–10 bearing electron-withdrawing
substituents, expecting that such Mn(salen)s would
show higher catalytic activity. We first examined azirid-
1
as Mn(salen)] serve as catalysts for aziridination. We
have disclosed that some optically active Mn(salen)s,
especially second-generation Mn-salen possessing axial
chirality as a chiral element, catalyze highly enantio-
4
ination of cyclohexene using 1 as the catalyst in the
presence of [N-(p-toluenesulfonyl)imino]phenyliod-
inane. Contrary to our expectation, no aziridination
occurred and allylic CꢀH amination proceeded exclu-
sively (Scheme 1).
1b,1c
selective aziridination of styrene derivatives.
On the
other hand, a nitrido (salen)manganese(V) complex was
recently found to undergo nitrene transfer reactions in
the presence of triflic anhydride or trifluoroacetic anhy-
2
dride. Subsequent to this, an optically active nitrido
Thus far, many methodologies for CꢀH amination have
been reported. The first CꢀH amination was reported
(
salen)manganese(V) complex was reported to undergo
5
stoichiometric but highly enantioselective aziridina-
with manganese–porphyrin complexes as catalysts.
3
tion. These aziridination reactions have been consid-
Although CꢀH amination via a nitrenoid species often
6
ered to proceed via nitrenoid intermediates which are
an electrophilic species. In order to expand the scope of
Mn(salen)-catalyzed aziridination, we synthesized
competes with aziridination, electron-deficient man-
7
7b
ganese-,
ruthenium-,
and rhodium porphyrin
7c
complexes were recently reported to catalyze CꢀH
PhI=NTs, 1 (6 mol%)
CH Cl , MS-4A, 5 °C, 3 h
NHTs
2
2
36%
Ph
N
Ph
N
N
O
N
N
N
Mn+
Mn+
Mn
R2
R2 R2
2
O
O
O
R Br
O Cl O
Br
PF -
PF6-
R1
6
R1
R1
R1
Br
Br
1
2
1
2
1
2
1
2
3
4
: R , R = F 7: R , R = H
5: R , R = F
10
1
2
1
2
1
2
:R , R = Cl 8: R = H, R = NO2
6: R , R = Br
1
2
1
2
: R , R = Br 9: R = t-Bu, R = NO2
1
2
: R , R = I
Scheme 1.
Keywords: (salen)manganese(III) complex; asymmetric CꢀH amination; benzylic amination; allylic amination.
*
0
Corresponding author. Fax: +81 92 642 2607; e-mail: katsuscc@mbox.nc.kyushu-u.ac.jp
040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00427-0

3
340
Y. Kohmura, T. Katsuki / Tetrahedron Letters 42 (2001) 3339–3342
amination exclusively. Besides metalloporphyrin com-
plexes, ruthenium cyclic amine and bipyridine
complexes have been disclosed to be efficient catalysts
3%-positions had adverse effect on enantioselectivity
(entry 10).
8
for CꢀH amination, and copper salts have also been
reported to promote CꢀH amination selectively under
modified Kharash–Sosnovsky conditions using peroxy-
It should be noted that a neutral Mn(salen) such as 10
was inferior to cationic Mn(salen) 3 as the catalyst for
the present reaction in terms of enantioselectivity and
9,10
13
carbamate as an oxidant.
Efforts have been directed
chemical yield (entry 11).
toward asymmetrization of some of these methodolo-
6d,9,11
gies; however, success has been limited.
On the
We next examined the effect of the solvent and reaction
temperature on enantioselectivity by using 3 as the
catalyst (Table 2). The reactions in acetonitrile, ethyl
acetate, acetone, and toluene were slow (entries 2–5). In
general, the reaction proceeded smoothly in halocar-
bons (entries 1 and 6–9) and the best result, in terms of
enantioselectivity and chemical yield, was obtained
when 1,1,2,2-tetrachloroethane was used as the solvent
other hand, our new result seemed to be compatible
with the results observed with electron-deficient metal-
loporphyrin complexes. Therefore, we examined asym-
metric CꢀH amination with chiral Mn(salen) complexes
bearing electron-withdrawing groups as the catalysts.
We first examined benzylic amination of indan with
various Mn(salen)s as catalysts (Table 1). Non-substi-
tuted Mn(salen) ent-7 showed poor catalytic activity
(
entry 9). As reaction temperature was lowered, enan-
tioselectivity was improved without depressing chemical
(
entry 8). Mn(salen) 1 bearing electron-withdrawing
yield (entries 9–11) and the highest enantioselectivity of
fluoro groups exhibited higher catalytic activity as
expected, especially when chloro and bromo groups
were the electron-withdrawing group (entries 1–5).
Complex 3 and its enantiomer ent-3 showed the same
level but opposite sense of enantioselectivity, suggesting
that CꢀH amination occurred in the coordination
sphere of Mn(salen) (entries 3 and 4). Based on the
6
6% ee was achieved at −40°C (entry 11).
Under the optimized conditions, we also examined the
reaction of cyclohexene, cycloheptene, tetralin, 1,1-
14
14
dimethyltetralin, and 1,1-dimethylindan (Table 3).
The reaction of cyclohexene gave 1-[N-(p-toluenesul-
fonyl)amino]cyclohex-2-ene of 67% ee selectively and
no aziridination product was detected, while the reac-
tion of cycloheptene gave 1-[N-(p-toluenesulfonyl)-
amino]cyclohept-2-ene of 41% ee together with a small
amount of the aziridination product (amination
1
2
reactivity–selectivity principle, we expected that enan-
tioselectivity would be improved in the order of the
reactions with 1, 2, 3, and 4. Differing from the expec-
tation, complex 3 showed the best enantioselectivity
(
entry 3). We also synthesized Mn(salen)s, 5 and 6,
15
product: aziridination product=4.8:1). The benzylic
amination of tetralin and 1,1-dimethyltetralin pro-
ceeded with good enantioselectivity of 77% ee and 82%
ee, respectively. High enantioselectivity of 89% ee was
obtained in the reaction of 1,1-dimethylindan.
bearing a diphenylethylenediamine moiety and exam-
ined CꢀH amination. However, they showed lower
enantioselectivity than the corresponding Mn(salen)s, 1
and 3, bearing a cyclohexanediamine moiety (entries 6
and 7). Mn(salen)s, 8 and 9, bearing nitro groups at the
5- and 5%-positions also showed catalytic activity but
enantioselectivities were only modest (entries 9 and 10).
Introduction of a bulky tert-butyl group at the 3- and
Typical experimental procedure was exemplified by the
benzylic amination of indan with 3 as the catalyst at
Table 1. Asymmetric amination of indan with various Mn(salen)s as catalysts
Entry
Complex
Time (h)
Yield (%)a
ee (%)b
Config.c
1
2
3
4
5
6
7
8
9
1
2
3
3
3
3
3
3
3
3
3
3
3
3
37
59
63
70
44
54
58
18
32
25
12
5
41
44
43
26
5
3
6
16
4
23
S
S
S
R
S
S
S
R
S
S
S
ent-3
4
5
6
ent-7
8
9
10
1
0
1
1
a
b
c
Isolated yield. Yield was calculated based on the amount of [N-(p-toluenesulfonyl)imino]phenyliodinane used.
Determined by HPLC analysis (DAICEL CHIRALPAK AD, hexane/2-propanol=9:1).
Determined by comparing the elution order of the present product and the p-toluenesulfonylated commercial (R)-(−)-1-aminoindan (Aldrich
Chemical Co., Inc.) in HPLC analysis (see footnote b).

Y. Kohmura, T. Katsuki / Tetrahedron Letters 42 (2001) 3339–3342
3341
Table 2. Asymmetric amination of indan with 3 as the catalyst in various solvents
Entry
Solvent
Temp. (°C)
Time (h)
Yield (%)a
ee (%)b
Config.c
1
2
3
4
5
6
7
8
9
CH Cl
5
5
5
5
5
5
5
5
5
3
3
3
3
3
3
3
3
3
63
0
19
17
9
62
62
57
74
72
63
44
–
S
–
2
2
CH CN
3
CH CO C H
32
36
42
47
47
44
54
61
66
S
S
S
S
S
S
S
S
S
3
2
2
5
CH COCH
3
3
C H CH
6
5
3
C H Cl
6
5
CHCl3
(CH Cl)
2
2
(CHCl2)2
(CHCl2)2
(CHCl2)2
1
1
0
1
−20
−40
12
24
a
b
c
Isolated yield. Yield was calculated based on the amount of [N-(p-toluenesulfonyl)imino]phenyliodinane used.
Determined by HPLC analysis (DAICEL CHIRALPAK AD, hexane/2-propanol=9:1).
Determined by comparing the elution order of the present product and the p-toluenesulfonylated commercial (R)-(−)-1-aminoindan (Aldrich
Chemical Co., Inc.) in HPLC analysis (see footnote b).
a)
Table 3. Asymmetric CꢀH amination of various substrates with 3 as the catalyst
a)
Reaction was carried out in 1,1,2,2-tetrachloroethane at −40°C for 24 h.
Isolated yield. Yield was calculated based on the amount of [N-(p-toluenesulfonyl)imino]phenyliodinane used.
Determined by HPLC analysis (DAICEL CHIRALPAK AD, hexane/ethanol=9:1).
b)
c)
d)
25
Determined by comparison of the specific rotation of tert-butyl cyclohex-2-ene-1-carbamate derived from the product {[h] −69.6° (c 0.48,
D
2
3
CHCl )} with the reported value {(R)-isomer; [h] +101° (c 2.80, CHCl , 95% ee)} (Ref. 16).
3
D
3
e)
f)
1
Formation of a small amount of aziridine derivative was detected by H NMR analysis (see text).
23
Determined by comparison of the specific rotation of cyclohept-2-en-1-ylamine hydrochloride derived from the product {[h]D −6.0° (c 0.095,
CH OH)} with the reported value {(S)-isomer; [h]D −14.5° (c 1.04, CH OH, 96% ee)} (Ref. 17).
3
3
g)
h)
Determined by HPLC analysis (DAICEL CHIRALPAK AD, hexane/2-propanol=9:1).
Determined by comparison of the specific rotation of 1-amino-1,2,3,4-tetrahydronaphthalene derived from the product {[h] +33.1° (c 1.48,
25
D
2
2
C H )} with the reported value {(R)-isomer; [h] −46° (c 5, C H )} (Ref. 18).
6
6
D
6
6
i)
Determined by HPLC analysis (DAICEL CHIRALPAK AD, hexane/ethanol=19:1).
Configuration was not determined.
Determined by HPLC analysis (DAICEL CHIRALPAK AD, hexane/2-propanol=40:1).
j)
k)
−
40°C: To a mixture of molecular sieves 4 A
8.4 mg, 10 mmol), and 1,1,2,2-tetrachloroethane (4.0
,
(50 mg), 3
the reaction mixture was stirred at −40°C for a further
24 h. The mixture was directly subjected to a pad of
silica gel (hexane/AcOEt=7:3) and the filtrate was
concentrated in vacuo. The residue was further purified
by column chromatography on silica gel (hexane/
AcOEt=9:1 to 7:3) to give (S)-1-[N-(p-toluenesulfonyl)-
(
mL) was added indan (49 mL, 0.4 mmol) under nitrogen
and the whole mixture was stirred for 10 min at −40°C.
To the mixture was added [N-(p-toluenesul-
fonyl)imino]phenyliodinane (61.8 mg, 0.17 mmol) and

3
342
Y. Kohmura, T. Katsuki / Tetrahedron Letters 42 (2001) 3339–3342
amino]-indan as a colorless solid (29.8 mg, 63%, 66%
ee).
Weinberg, R.; Breslow, R. Tetrahedron Lett. 2000, 41,
8063–8067.
. Au, S.-M.; Huang, J.-S.; Che, C.-M.; Yu, W.-Y. J. Org.
8
In conclusion, we were able to achieve good to high
enantioselectivity in CꢀH amination for the first time
by using the (salen)manganese complex appropriately
modified with an electron-withdrawing group as the
catalyst.
Chem. 2000, 65, 7858–7864.
9. Kohmura, Y.; Kawasaki, K.; Katsuki, T. Synlett 1997,
1456–1458.
0. For other CꢀH aminations, see: (a) Tsushima, S.;
Yamada, Y.; Onami, T.; Oshima, K.; Chaney, M. O.;
Jones, N. D.; Swartzendruber, J. K. Bull. Chem. Soc. Jpn.
1
1
989, 62, 1167–1178; (b) Johannsen, M.; Jørgensen, K. A.
References
J. Org. Chem. 1994, 59, 214–216; (c) Bruncko, M.;
Khuong, T.-A. V.; Sharpless, K. B. Angew. Chem., Int.
Ed. Engl. 1996, 35, 454–456 and references cited therein;
1
. (a) O’Connor, K. J.; Wey, S. J.; Burrows, C. J. Tetra-
hedron Lett. 1992, 33, 1001–1004; (b) Noda, K.; Hosoya,
N.; Irie, R.; Ito, Y.; Katsuki, T. Synlett 1993, 469–471;
(
d) Herron, B. F.; Bagby, M. O.; Isbell, T. A.; Byrdwell,
W. C.; Plattner, R.; Weisleder, D. J. Am. Oil Chem. Soc.
997, 74, 229–234; (e) Srivastava, R. S.; Nicholas, K. M.
(
9
c) Nishikori, H.; Katsuki, T. Tetrahedron Lett. 1996, 37,
1
245–9248.
J. Am. Chem. Soc. 1997, 119, 3302–3310.
2
3
. Du Bois, J.; Hong, J.; Carreira, E. M.; Day, M. W. J.
Am. Chem. Soc. 1996, 118, 915–916.
. Minakata, S.; Ando, T.; Nishimura, M.; Ryu, I.;
1
1. Modest enantioselectivities of 31 and 28% ees have been
achieved in amination of indan with Rh [(R)-bnp] and
2
4
Cu[tris(oxazoline)] complexes, respectively, as the cata-
lysts (see Refs. 6d and 9). More recently, moderate
enantioselectivity of 54% ee has been achieved in amina-
tion of 1-ethylnaphthalene with a chiral Ru–porphyrin
complex as the catalyst: Zhou, X.-G.; Yu, X.-Q.; Huang,
J.-S.; Che, C.-M. Chem. Commun. 1999, 2377–2378.
2. Morrison, R. T.; Boyd, R. N. Organic Chemistry, 6th ed.;
Prentice-Hall: New Jersey, 1992; p. 115.
Komatsu, M. Angew. Chem., Int. Ed. Engl. 1998, 37,
3
392–3994.
4
. Cr(salen) bearing a 3,3%,5,5%-tetrafluorosubstituted ligand
has been reported to be an efficient catalyst for asymmet-
ric epoxidation of trans-b-methylstyrene: Ryan, K. M.;
Bousquet, C.; Gilheany, D. G. Tetrahedron Lett. 1999,
1
1
4
0, 3613–3616.
5
. (a) Breslow, R.; Gellman, S. H. J. Chem. Soc., Chem.
Commun. 1982, 1400–1401; (b) Mahy, J. P.; Bedi, G.;
Battioni, P.; Mansuy, D. Tetrahedron Lett. 1988, 29,
3. Complex 10 has been reported to serve as a catalyst for
epoxidation: Robert, A.; Tsapara, A.; Meunier, B. J.
Mol. Catal. 1993, 85, 13–19.
1
927–1930.
1
1
1
4. Reez, M. T.; Westermann, J.; Kyung, S.-H. Chem. Ber.
6
. (a) Mahy, J. P.; Bedi, G.; Battioni, P.; Mansuy, D.
Tetrahedron Lett. 1988, 29, 1927–1930; (b) Evans, D. A.;
Faul, M. M.; Bilodeau, M. T. J. Am. Chem. Soc. 1994,
1
985, 118, 1050–1057.
1
5. The ratio was determined by H NMR analysis (270
MHz).
1
16, 2742–2753; (c) M u¨ ller, P.; Baud, C.; Jacquier, Y.
6. da Zhang, Z.; Scheffold, R. Helv. Chim. Acta 1993, 76,
2602–2615.
17. Braun, H.; Felber, H.; Kreße, G.; Ritter, A.;
Schmidtchen, F. P.; Schneider, A. Tetrahedron 1991, 47,
3313–3328.
Tetrahedron 1996, 52, 1543–1548; (d) N a¨ geli, I.; Baud, C.;
Bernardineli, G.; Jacquier, Y.; Moran, M.; M u¨ ler, P.
Helv. Chim. Acta 1997, 80, 1087–1105 and references
cited therein.
7
. (a) Yang, J.; Weinberg, R.; Breslow, R. Chem. Commun.
2
000, 531–532; (b) Yu, X.-Q.; Huang, J.-S.; Zhou, X.-G.;
18. Weidmann, R.; Guette, J. P. C. R. Acad. Sci., Paris, Ser.
C 1969, 268, 2225–2227; Chem. Abstr. 1969, 71, 61037e.
Che, C.-M. Org. Lett. 2000, 2, 2233–2236; (c) Yang, J.;
.