Diastereoselective rhodium-catalyzed nitrene transfer starting from chiral sulfonimidamide-derived iminoiodanes

Article abstract of DOI:10.1016/j.tetasy.2005.07.005

The dirhodium-catalyzed aziridination of olefins with chiral sulfonimidamides as iminoiodane precursors has been investigated under stoichiometric conditions. Diastereoisomeric excesses of up to 82% have been achieved using [Rh₂{(S)-nttl}₄

Full text of DOI:10.1016/j.tetasy.2005.07.005

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 16 (2005) 3484–3487
Diastereoselective rhodium-catalyzed nitrene transfer starting
from chiral sulfonimidamide-derived iminoiodanes
b
a
a
Corinne Fruit,a, Fabien Robert-Peillard, Gerard Bernardinelli, Paul Muller,
*
´
¨
Robert H. Doddb,* and Philippe Daubanb,*
aDepartment of Organic Chemistry and Laboratory of X-Ray Crystallography, University of Geneva, 30 quai Ernest Ansermet,
CH-1211 Geneva 4, Switzerland
bInstitut de Chimie des Substances Naturelles, CNRS, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
Received 13June 2005; accepted 8 July 2005
Available online 2 November 2005
Abstract—The dirhodium-catalyzed aziridination of olefins with chiral sulfonimidamides as iminoiodane precursors has been
investigated under stoichiometric conditions. Diastereoisomeric excesses of up to 82% have been achieved using [Rh2{(S)-nttl}4]
as catalyst. Matching and mismatching effects were observed upon use of chiral rhodium(II) carboxylate catalysts.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
R2 = Ts) affording aziridines in very good yields
and with diastereoselectivities up to 60%.6,7 Since
rhodium(II) catalysts are often complementary in scope
to the copper species in various processes1 and given the
recent and increasing interest in the rhodium-catalyzed
aziridination of olefins,8 it therefore appeared to us
interesting to determine and compare the efficiency of
rhodium complexes in analogous diastereoselective
nitrene transfers. Herein, we report the results of our
first investigations with such rhodium(II) catalysts.
The transition metal-catalyzed aziridination of olefins is
a powerful methodology for regioselective C–N bond
formation. The reaction proceeds via intermediate metal
complexed nitrene species, which are generated upon
decomposition of iminoiodanes.1 In conjunction with
chiral copper, rhodium or ruthenium catalysts, these
nitrene precursors may lead to asymmetric nitrene
transfer reactions.1b It has recently been reported that
iminoiodanes can be efficiently generated and decom-
posed to nitrenes in situ,2,3 a process that greatly
enhances the variety of nitrogenous compounds that
can be used for this purpose. Based on this in situ meth-
odology, rhodium- and copper-catalyzed nitrene trans-
fers have been investigated in detail by our groups.4 In
order to broaden the scope of the stereoselective C–N
bond formation, and with the objective of improving
the stereoselectivity, we felt it was interesting to extend
the in situ procedure to chiral iminoiodanes. To this
end, we turned our attention to sulfonimidamides 1
(R1S(@O)(@NR2)NH2)5 as potential chiral hypervalent
iodine(III) reagent precursors. These were initially
found to give highly reactive nitrene species in the
copper-catalyzed reactions, the use of 1a (R1 = p-Tol,
2. Results and discussion
Both enantiomers of sulfonimidamide 1a (Ar = 4-
MePh) were first prepared starting from p-toluenesulfi-
nyl chloride 2 as described in the literature (Scheme
1).9 Thus, after reaction with commercially available
chloramine-T, the enantiomers of the resulting racemic
chloride 3a were separated via reaction with (S)-1-phen-
ylethylamine and fractional recrystallization of the
resulting sulfonimidamide 4a. Cleavage of 4a with triflu-
oroacetic acid afforded (R)- and (S)-1a. The procedure
was adapted for 1b (R = 4-NO2Ph) by use of chlor-
amine-N.10 Single crystals of (À)-1b were obtained
allowing us to determine the absolute configuration to
be (S) by X-ray crystallography (Fig. 1).11 By analogy
and according to the literature,9 the (S)-configuration
was attributed to the (À)-enantiomer of 1a.
*
Corresponding authors. Tel.: +33 (0)1 69 82 45 60; fax: +33 (0)1 69
07 72 47; e-mail: philippe.dauban@icsn.cnrs-gif.fr
0957-4166/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2005.07.005

C. Fruit et al. / Tetrahedron: Asymmetry 16 (2005) 3484–3487
3485
O
S
O
NSO2Ar
Cl
ArSO2NNaCl
S
Cl
31-95%, 2 steps
2
3a,b
a Ar = 4-MePh
b Ar = 4-NO2Ph
NH2
49-58%
O
NSO2Ar
NH2
TFA
84%
crystals
35%
S
O
NSO2Ar
(R,S)-4a,b
S
(+)-(R)-1a,b
NH
O
NSO2Ar
Ph
S
(S,S)-4a,b
NH2
TFA
81%
Solution
40%
4a,b
(-)-(S)-1a,b
Scheme 1. Synthesis of sulfonimidamides.
Table 1. Screening of olefins for diastereoselective Rh2(OAc)4-cata-
lyzed aziridination
Entry Olefin
Sulfonimidamide Aziridine Yield de
(%)a (%)b
1
(S)-1a
6a
42
20
2
(R)-1a
(R)-1a
6b
6c
34
<10
<10
4
3
17c
2
4
(R)-1a
(S)-1a
6d
6e
56d
50
<10
—
2
5
6
(S)-1a
(S)-1a
6f
47
—
—
—
CO2Me
7
6g
Figure 1. ORTEP view of the crystal structure of (À)-(S)-1b.
a Isolated yield after flash chromatography. Diastereoisomers could
not be separated on silica gel.
Sulfonimidamide 1a was thus tested as the nitrene pre-
cursor in the rhodium-catalyzed aziridination of olefins
(Scheme 2). A typical procedure involved, at À20 ꢁC
in dichloromethane, the use of alkenes 5 as the limiting
component in the presence of a slight excess of 1a
(1.2 equiv), iodosylbenzene diacetate (1.8 equiv), magne-
sium oxide (3.0 equiv) and a catalytic quantity of
[Rh2(OAc)4] (5 mol %).12 Results are summarized in
Table 1.
b Diastereoisomeric excess (de) was determined by NMR.
c trans-Aziridine.
d cis-Aziridine.
Aziridination of styrene under these conditions was
achieved in 42% yield with 20% de (entry 1). A terminal
olefin such as 1-heptene was also reactive but afforded a
lower yield than styrene (entry 2). More interestingly,
O
NTs
S
NH2
O
NTs
R2
1.2 eq. (R)- or (S)-1a
S
R2
N
R1
R1
1.8 eq. PhI(OAc)2, 3.0 eq. MgO
5 mol% Rh2(OAc)4
R3
R3
4Å molecular sieves
CH2Cl2, -20 °C
1.0 eq. 5
6a-g
Scheme 2.

3486
C. Fruit et al. / Tetrahedron: Asymmetry 16 (2005) 3484–3487
as shown for the reaction with trans- and cis-hex-2-ene,
the aziridination was stereospecific with respect to the
olefin geometry (entries 3and 4). However, as often
observed in Rh(II)-catalyzed cyclopropanations and
aziridinations, the trans-isomer afforded a significantly
lower yield than the cis-olefin.13 It is noteworthy that
in the case of cyclopentene and cyclohexene (entries
5 and 6), no insertion into an allylic C–H bond was
observed. In both cases, only aziridines 6e and 6f were
isolated in 50% and 47% yield, respectively. These
results differ sharply from previous Rh(II)-catalyzed nit-
rene transfers with sulfonamide-derived iminoiodanes,
for which allylic C–H insertion was the major path-
way.14 Finally, no reaction took place in the case of
methyl acrylate (entry 7). This is in distinct contrast to
the Cu-catalyzed aziridination with sulfonimidamides
where acrylates gave very high yields.6 This observation
highlights the complementary role of rhodium and cop-
per catalysts in nitrene transfers.
Chiral Rh(II) carboxylate and carboxamidate catalysts
were then screened in conjunction with sulfonimid-
amides 1a–b for the asymmetric aziridination of styrene
and its para- or meta-substituted derivatives (Scheme 3).
Yields and diastereoselectivities were generally im-
proved when the aziridination was carried out with the
chiral rhodium carboxylate catalysts [Rh2{(S)-nttl}4]15
or [Rh2{(R)-ntv}4]16 (Table 2, entries 1, 3and 4) while
the chiral Rh(II) carboxamidate [Rh2{(4S)-meox}4]17
gave the same low induction and modest yields (entry
5). More interestingly, matching and mismatching
effects could be observed with the [Rh2{(R)-ntv}4] cata-
lyst (entries 3and 4): a matched pair for double induc-
tion is formed with the sulfonimidamide (R)-1a.
However, contrary to our expectations,18 use of the p-ni-
tro analogue 1b did not give satisfactory results since
both yields and diastereoselectivities were lower (entry
6 vs entry 1).
The effect of a substituent on the aromatic moiety of styr-
ene was then studied using the preceding chiral dirho-
dium(II) carboxylate catalysts in combination with the
matched sulfonamidamides. The best results in terms
of yield and selectivity were obtained with para-haloge-
nated styr- enes in the presence of sulfonimidamide 1a
(entries 7 and 9), p-bromostyrene, for example, affording
aziridine 6h in 59% yield and with 82% de. Once more,
sulfonimidamide 1b proved to be a less efficient nitrene
precursor (entries 8 and 10). Electron-donor substitu-
ents, such as methoxy or methyl, resulted in lower yields
and diastereo- selectivities (entries 12 and 13) while
acceptor substituents, that is, p-trifluoromethyl- and
m-nitrostyrene, afforded aziridines 6j and 6m with 60%
and 55% de, respectively (entries 11 and 14).
O
NSO2Ar
NH2
O
NSO2Ar
S
S
N
PhI(OAc)2, MgO
3 mol% [Rh2L*4],
X
X
1.0 eq. 5
6a, h-m : Ar = 4-MePh
7a-c :
Ar = 4-NO2Ph
X
L* :
O
O
N
O
O
N
O
OMe
O
N
H
CO2H
CO2H
O
3. Conclusion
X = H : {(S)-nttl}
{(R)-ntv}
{(4S)-meox}
In conclusion, we have shown that sulfonimidamide-
derived iminoiodanes are efficient nitrene donors for
the rhodium-catalyzed aziridinations of olefins. Under
X = Br : {(S)-4-Br-nttl}
Scheme 3.
Table 2. Aziridination of styrene and substituted styrenes with chiral Rh(II) catalysts
Entry
Sulfonimidamide
Chiral rhodium catalyst [Rh2L
]
X
Aziridine
Yield (%)a
de (%)b
4
*
1
2
3
4
5
6
7
8
(S)-1a
(S)-1a
(S)-1a
(R)-1a
(S)-1a
(S)-1b
(S)-1a
(S)-1b
(R)-1a
(S)-1b
(S)-1a
(S)-1a
R)-1a
(R)-1a
[Rh2{(S)-nttl}4]
[Rh2{(S)-4-Br-nttl}4]c
[Rh2{(R)-ntv}4]
[Rh2{(R)-ntv}4]
[Rh2{(S)-meox}4]
[Rh2{(S)-nttl}4]
[Rh2{(S)-nttl}4]
[Rh2{(S)-nttl}4]
[Rh2{(R)-ntv}4]
[Rh2{(S)-nttl}4]
[Rh2{(S)-nttl}4]
[Rh2{(S)-nttl}4]
[Rh2{(R)-ntv}4]
[Rh2{(R)-ntv}4]
H
H
H
H
H
H
4-Br
4-Br
4-Cl
4-Cl
4-CF3
4-OMe
4-Me
3-NO2
6a
6a
6a
6a
6a
7a
6h
7b
6i
6380
66
54
55
42
29
59
3
52
25
55
17
33
18
43
20
74
20
61
82
0
54
9
70
54
60
49
36
55
10
11
12
13(
14
7c
6j
6k
6l
6m
a Isolated yield after flash chromatography. Diastereoisomers could not be separated on silica gel.
b Diastereoisomeric excess (de) was determined by NMR.
c With 2.3mol % of catalyst.

C. Fruit et al. / Tetrahedron: Asymmetry 16 (2005) 3484–3487
3487
9. Tsushima, S.; Yamada, Y.; Onami, T.; Oshima, K.;
Chaney, M. O.; Jones, N. D.; Swartzendruber, J. K. Bull.
Chem. Soc. Jpn. 1989, 62, 1167–1178.
10. Ando, T.; Kano, D.; Minakata, S.; Ryu, I.; Komatsu, M.
Tetrahedron 1998, 54, 13485.
stoichiometric conditions, aziridines could be obtained
in modest to good yields (17–66%) with diastereoselec-
tivities up to 82%. Matching and mismatching effects
were also observed, indicating that selectivities could
be optimized by carefully choosing the rhodium(II) car-
boxylate catalyst and the sulfonimidamide. A notewor-
thy feature is the complementarity between rhodium
and copper complexes in terms of substrate: while cop-
per salts give the best results with a,b-unsaturated car-
bonyl compounds,6 rhodium catalysts are more
suitable for styrene derivatives. Finally, the ability of
rhodium(II) complexes to catalyze nitrene insertions
into a C–H bond encourages us to evaluate the potential
of sulfonimidamides in such diastereoselective processes
since recent papers reflect the growing interest in devel-
oping efficient intermolecular C–H amination.19 Work is
currently in progress in this direction as is the prepara-
tion and the screening of a series of substituted
sulfonimidamides.
11. X-ray crystallographic data for (C13H13N3O5S2), (À)-(S)-
1b: Mw = 355.4, l = 0.384 mmÀ1, Dx = 1.574 g Æ cmÀ3
,
monoclinic, P21, Z = 2, a = 7.3572(6), b = 6.9268(À43),
˚
˚
c = 14.7339(13) A, b = 93.095(10)ꢁ, V = 749.77 (11) A
;
pale yellow prism 0.40 · 0.19 · 0.0740 mm. Crystallo-
graphic data (excluding structure factors) for the struc-
tures in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplemen-
tary publication numbers CCDC 273222. Copies of the
data can be obtained, free of charge, on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax:
+44(0) 1223 336033 or e-mail: deposit@ccdc.cam.ac.uk].
12. General procedure for aziridination of olefins: CH2Cl2 (0.5–
0.6 mL) (c = 0.5 M) was added by syringe to a flask
containing the olefin (0.25–0.30 mmol), sulfonimidamide
1a or 1b (1.2 equiv), PhI(OAc)2 (1.8 equiv), MgO
˚
(3equiv), activated 4 A molecular sieves and Rh(II)
catalyst (2.3–5.0 mol %) under argon at À20 ꢁC. The
suspension was then stirred at À20 ꢁC for 24 h. It was
then diluted with CH2Cl2 (5 mL) and filtered through a
pad of Celite. The filter cake was washed with CH2Cl2 and
the filtrate was concentrated under reduced pressure. The
residue was purified by chromatography (SiO2, pentane/
EtOAc 7:3) to afford the desired aziridine. Selected data
for 6a (values in italics refer to the minor diastereomer,
Acknowledgements
This work was supported by the Swiss National Science
Foundation (Projects No. 20-52581.97 and 2027-
048156) and by the Institut de Chimie des Substances
Naturelles (fellowship to F.R.-P.). Support and sponsor-
ship concerted by COST Action D24 ꢀSustainable
Chemical Processes: Stereoselective Transition Metal-
Catalyzed Reactionsꢁ are kindly acknowledged.
1
where applicable): H NMR (300 MHz, CDCl3) d 2.38 (s,
3H), 2.39 (s, 3H), 2.42 (s, 6H), 2.44 (d, J = 4.8 Hz, 1H),
2.58 (d, J = 4.8 Hz, 1H), 3.12 (d, J = 7.6 Hz, 1H), 3.24 (d,
J = 7.6 Hz, 1H), 3.84 (dd, J = 7.6 and 4.8 Hz, 1H), 3.98
(dd, J = 7.6 and 4.8 Hz, 1H), 7.20 (m, 18H), 7.82 (m, 8H);
13C NMR (62.5 MHz, CDCl3) d 21.3, 21.5, 36.0, 37.6,
42.0, 43.4, 126.4, 126.5, 126.6, 127.7, 128.5, 129.0, 129.1,
129.8, 133.7, 134.1, 134.2, 140.4, 142.5, 142.6, 145.5; mass
spectrum (ES) m/z 426 (M)+. Anal. Calcd for
C22H22N2O3S2: C, 61.95; H, 5.20; N, 6.57; S, 15.03.
Found: C, 61.74; H, 5.21; N, 6.36; S, 15.01.
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