Ru(salen)-catalyzed asymmetric sulfimidation using arylsulfonyl azide

Article abstract of DOI:10.1016/S0040-4039(01)01448-4

An (OC)Ru(II)(salen) complex was found to catalyze imidation of alkyl aryl sulfides in the presence of arylsulfonyl azide with high enantioselectivity as well as good chemical yield.

Full text of DOI:10.1016/S0040-4039(01)01448-4

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 7071–7074
Ru(salen)-catalyzed asymmetric sulfimidation using
arylsulfonyl azide
Masakazu Murakami, Tatsuya Uchida 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 16 July 2001; revised 30 July 2001; accepted 3 August 2001
Abstract—An (OC)Ru(II)(salen) complex was found to catalyze imidation of alkyl aryl sulfides in the presence of arylsulfonyl
azide with high enantioselectivity as well as good chemical yield. © 2001 Elsevier Science Ltd. All rights reserved.
Optically active sulfoxides are widely used as chiral
auxiliaries in organic synthesis and many excellent
methodologies for asymmetric sulfoxidation have been
developed.1,2 In contrast, use of sulfimides, nitrogen
equivalents of sulfoxides, in organic synthesis is rather
limited, because of lack of convenient synthetic
method of optically active sulfimides. Optically active
sulfimides were first prepared by conversion from the
corresponding optically active sulfoxides3 and then by
kinetic resolution of racemic sulfimides using an opti-
cally active base.4 Recently, highly diastereoselective
sulfimidations have also been reported by Gaggero et
al. and Uemura et al.5 On the other hand, Uemura et
al. reported that the imidation of alkyl aryl sulfides
using a chiral copper(I)-bis(oxazoline) complex as a
catalyst showed moderate enantioselectivity.6 We also
found that optically active Mn(salen)s 1 and 2 served
as efficient catalysts for enantioselective sulfimida-
tion showing good enantioselectivity (Scheme 1).7
However, there is still room for improvement, espe-
-
+
(R,R)-1 (5 mol %), NMO (50 mol %)
NTs
S
S
Ph
CH2Ph
Ph
CH2Ph
PhI=NTs, PhCl, r.t.
85% ee, 52%
-
NTs
+
S
R
(R,S)-2 (5 mol%)
S
R
PhI=NTs, C6H5CN, rt
NO2
NO2
90% ee, 77%
S
R
N
O
N
N
O
N
Mn+
Mn+
O
O
Ph Ph
Ph Ph
R
R
-
-
PF6
PF6
(R,S)-2
(R,R)-1
Scheme 1.
Keywords: (OC)Ru(salen) complex; asymmetric catalysis; sulfimidation; sulfide; toluenesulfonyl azide.
* Corresponding author.
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01448-4

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M. Murakami et al. / Tetrahedron Letters 42 (2001) 7071–7074
ruthenium equivalent of Mn(salen) 1, showed only
moderate enantioselectivity.
cially in respect of enantioselectivity and the nitrene
precursor.
We next examined sulfimidation with complex 4 as the
catalyst in the presence of various azides (Scheme 3).
All the arylsulfonyl azides used showed a similar high
level of enantioselectivity and no electronic effect on
enantioselectivity was observed, though chemical yields
were moderate. However, we found that the chemical
yield was improved when the amount of the sulfide was
reduced and a slight excess amount of azide was used.
t-Butoxycarbonyl azide (Boc N3) was a poor precursor.
Jacobsen et al. reported that arylsulfonyl azide served
as a nitrene precursor for asymmetric aziridination in
the presence of copper ion under photo-irradiation.8
During our study on asymmetric sulfimidation, we
found that arylsulfonyl azides could be used as a
nitrene precursor in the presence of (OC)Ru(II)(salen)
complexes [hereafter, abbreviated as Ru(salen)]9 with-
out photo-irradiation. Arylsulfonyl azides are readily
prepared from commercially available arylsulfonyl
chlorides in one step. Thus, we examined asymmetric
imidation of methyl phenyl sulfide with toluenesulfonyl
azide by using Ru(salen)s (3–5) as the catalyst (Scheme
2) and found that the reaction with complex 4 as the
catalyst showed high enantioselectivity. Complex 5, the
With these results in hand, we examined imidation of
various sulfides with complex 4 as the catalyst in the
presence of toluenesulfonyl azide (Table 1). Imidation
of alkyl aryl sulfides proceeded smoothly with excellent
-
+
Ph
NTs
catalyst (2 mol %)
MS 4A, CH2Cl2, r.t.
S
+
CH3C6H4SO2N3
(1 eq)
Ph
CH3
S
CH3
(4 eq)
3: 80% ee, 50% (36 h)
4: 97% ee, 48% (24 h)
5: 65% ee, 39% (24 h)
Yields were calculated, based on the amount of the azide.
CO
Ru
CO
N
O
N
O
N
O
N
O
Ru
Ph Ph
3
4
CO
Ru
N
O
N
O
Ph Ph
5
Scheme 2.
-
+
Ph
NTs
4 (2 mol %), MS 4A
S
+
azide
Ph
CH3
S
CH3
CH2Cl2, r.t., 24 h
(1 eq.)
(2 eq)
p-CH3C6H5SO2N3: 97% ee, 74%
p-CH3OC6H5SO2N3: 98% ee, 61%
p-BrC6H5SO2N3: 98% ee, 74%
Boc N3: 71% ee, 22%
Yields and amount of catalyst were calculated, based on the amount of the azide.
p-CH3C6H5SO2N3: 98% ee, 99%
(1 eq)
(1.3 eq.)
(without MS, p-CH3C6H5SO2N3: 96% ee, 56%)
Yields and amount of catalyst were calculated, based on the amount of the sulfide.
Scheme 3.

M. Murakami et al. / Tetrahedron Letters 42 (2001) 7071–7074
7073
Table 1. Asymmetric imidation of various sulfides using Ru(salen) 4 as the catalyst
-
+
NTs
4 (2 mol %), MS 4A
S
R2
R1
+
Ts N3
S
R2
R1
CH2Cl2, r.t., 24 h
(1.3 eq.)
(1eq.)
by HPLC analysis using DAICEL CHIRALCEL OJ
enantioselectivity. On the other hand, the imidation of
dialkyl sulfide, benzyl methyl sulfide, showed moderate
enantioselectivity of 66% ee (entry 7). The low chemical
yield in this reaction may be attributable to strong
coordination of the sulfide to complex 4.
(hexane:i-PrOH=1:1).
In conclusion, we were able to demonstrate that chiral
ruthenium(II)(salen) complex 4 bearing an apical CO
ligand is an excellent catalyst for asymmetric sulfimida-
tion. Study on the mechanism of this reaction is in
progress in our laboratory.
Typical experimental procedure for imidation of
sulfides was exemplified by the reaction of methyl o-
nitrophenyl sulfide with 4 as the catalyst (Table 1, entry
1): (R,R)-complex 4 (1.9 mg, 2.0 mmol) was dissolved in
dry toluene (1 ml), concentrated azeotropically in
vacuo, and re-dissolved in dichloromethane (0.5 ml).
To this solution were added methyl o-nitrophenyl
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