Imido transfer of sulfonylimino-λ3-bromane makes possible the synthesis of sulfonylimino-λ3-iodanes

Article abstract of DOI:10.1039/b818489e

Sulfonylimino-λ³-bromane functions as a reactive nitrenoid, because of the hyperleaving group ability of aryl- λ³-bromanyl groups, and undergoes transimidations to iodobenzenes at room temperature under metal-free conditions probably

Full text of DOI:10.1039/b818489e

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Imido transfer of sulfonylimino-k3-bromane makes possible the synthesis
of sulfonylimino-k3-iodanesw
Masahito Ochiai,*a Aiko Nakano,a Akira Yoshimura,a Kazunori Miyamoto,a
Satoko Hayashib and Waro Nakanishi*b
Received (in Cambridge, UK) 20th October 2008, Accepted 10th December 2008
First published as an Advance Article on the web 14th January 2009
DOI: 10.1039/b818489e
Sulfonylimino-k3-bromane functions as a reactive nitrenoid,
because of the hyperleaving group ability of aryl-k3-bromanyl
groups, and undergoes transimidations to iodobenzenes at room
temperature under metal-free conditions probably via an SN2-type
nitrenoid transition state, yielding sulfonylimino-k3-iodanes.
of p-toluenesulfonyl azide in iodobenzene solution at 120 1C
no formation of the desired iminoiodane was detected at all.
They found that under these conditions the tosylimino-
l3-iodane itself decomposes. Transition metal-catalyzed low
temperature decompositions of the sulfonyl azide were also
found to be fruitless. Thus, this type of ingenious approach to
the synthesis of imino-l3-iodanes remains to be established.
We have reported that trifluoromethanesulfonylimino-
l3-bromane 1 functions as an efficient imido group donor and
directly undergoes aziridination of olefins stereospecifically
with retention of original stereochemistry.10 Importantly, the
aziridination proceeds at room temperature using limiting
amounts of alkenes under transition metal-free conditions.
The fact that the observed rate constants for aziridination of
cis-cyclooctene are proportional to concentration of the olefin
suggests the involvement of a bimolecular transition state, in
which an olefin attacks the s* N–Br orbital of the iminobromane
1 in the nitrenoid transfer process. It occurred to us that the
highly active sulfonylimino-l3-bromane 1 probably serves as
an efficient nitrenoid source in the Moriarty’s approach to the
synthesis of imino-l3-iodanes. We report herein the first
example of transimidations yielding imino-l3-iodanes 2, which
involves an imido group transfer from the iminobromane 1 to
the iodine atom of iodobenzenes at room temperature under
metal-free conditions (Scheme 1).
Phenyl(sulfonylimino)-l3-iodanes serve as excellent nitrene
(or nitrenoid) progenitors either in the aziridination of alkenes
or in the C–H amidation of alkanes, arenes, and aldehydes
using Cu, Rh, Ru, or Ag catalysts.1–5 Under thermal or
catalytic conditions, they transfer the imido groups to a range
of heteroatom nucleophiles.6 The hyperleaving group ability
of aryl-l3-iodanyl groups will be responsible for these nitrogen
atom transfer reactions7 and, in most cases, metal imido
species are proposed to be crucial intermediates. These
methods of introducing nitrogen functionalities are highly
reliable, leading to a surge in interest in the research activity
of the areas, especially in the last decade.
The methodology for synthesis of the compounds of this
important class is limited and all of the methods so far reported
rely on ligand exchange on iodine(III) of aryl-l3-iodanes with
sulfonamides in the presence or the absence of a base:1 for
instance, the most widely used phenyl(N-tosylimino)-l3-iodane
was prepared by the reaction of (diacetoxyiodo)benzene
with p-toluenesulfonamide in the presence of KOH.6a
(Dimethoxyiodo)-, (difluoroiodo)-, and iodosylbenzene serve
as reactive l3-iodanes in the ligand exchange reactions.8
However, it has been pointed out by Dauban and Dodd in their
excellent review that preparation of sulfonylimino-l3-iodanes by
the ligand exchange method is often difficult to reproduce and
that conflicting results are found in the literature.1a They also
mentioned that their synthesis of p-MeOC6H4SO2NꢀI+Ph fails
50% of the time even after several years of experience in this field.
In 1985, Moriarty and coworkers evaluated an entirely
different strategy for the synthesis of sulfonylimino-l3-
iodanes, involving the nucleophilic attack of iodobenzenes
on sulfonylnitrenes:9 however, in their attempted thermolysis
To a dichloromethane solution of the bromane 1 was added
a stoichiometric amount of iodobenzene at room temperature
under argon. White precipitates of N-triflylimino(phenyl)-
l3-iodane (2a)8b appeared within a few minutes with reductive
elimination of p-(trifluoromethyl)bromobenzene and the
reaction afforded a high yield of 2a (Table 1, Entry 1). Similarly
to N-tosylimino-l3-iodanes, triflyliminoiodane 2a is sparingly
soluble in unreactive organic media such as dichloromethane,
chloroform, diethyl ether, etc., presumably due to the
aggregated polymeric nature.11 Substituted iodobenzenes with
an electron-donating (Me or MeO) and an electron-withdrawing
group (F, Cl, Br, CF3, CN, CO2Et, or COMe) produced
iminoiodanes 2 efficiently under the conditions (Table 1,
Entries 2–11). The imido transfer reaction of imino-l3-bromane
a Graduate School of Pharmaceutical Sciences, University of
Tokushima, 1-78 Shomachi, Tokushima, 770-8505, Japan.
E-mail: mochiai@ph.tokushima-u.ac.jp; Fax: +81 88-633-9504
b Department of Materials Science and Chemistry, Faculty of Systems
Engineering, Wakayama University, 930 Sakaedani, Wakayama,
640-8510, Japan. E-mail: nakanisi@sys.wakayama-u.ac.jp;
Fax: +8173-457-8253
w Electronic supplementary information (ESI) available: Experimental
details, spectral data and X-ray data. CCDC 692567 and 692568. For
ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/b818489e
Scheme 1 Transylidation between imino-l3-bromane 1 and -iodanes 2.
Chem. Commun., 2009, 959–961 | 959
ꢁc
This journal is The Royal Society of Chemistry 2009

View Article Online
Table 1 Transimidation of imino-l3-bromane 1 with iodobenzenesa
Entry
ArI
2
Yield (%)b
1
2
3
4
5
6
7
8
9
PhI
2a
2b
2c
2d
2e
2f
2g
2h
2i
97
94
90
84
86
96
82
86
100
96
87
o-MeC6H4I
p-MeC6H4I
p-MeOC6H4I
p-FC6H4I
p-ClC6H4I
p-BrC6H4I
p-CF3C6H4I
p-NCC6H4I
p-EtO2CC6H4I
o-MeCOC6H4I
Scheme 2 Bimolecular nitrenoid transition state.
1 (Scheme 2), but not with a mechanism that yields a free
nitrene by a rate-determining unimolecular decomposition of 1.
In order to gain further insight into the mechanism, relative
rates of the imido transfer for a series of substituted
iodobenzenes were measured in dichloromethane by competitive
reactions, in which a mixture of each 10-fold excess of two
competing substrates was used (Table 2). Table 1 shows that
iminoiodanes 2 were formed in high yields irrespective of the
substituents on benzene ring. Ratios of the products 2 were
determined by 1H NMR of the crude reaction mixture.
Electron-releasing p-MeO and p-Me groups remarkably
increase the relative rate krel of the imido group transfer:
Hammett plot showed a good correlation of the relative rate
factors with the sp constants of substituents15 and afforded the
reaction constant r = ꢀ2.79 (r = 0.96). The absolute r value
obtained here is greater than that (r = ꢀ0.54) reported for
free carbene [:C(SO2CF3)2] transfer to iodobenzenes at 140 1C
and that (r = ꢀ0.91) in rhodium carbenoid [Rh = C(SO2CF3)2]
transfer to iodobenzenes at 40 1C.16 This larger negative
r value evaluated in the imido group transfer of l3-bromane
1 indicates greater buildup of positive charge on the iodine
atom of iodobenzenes in the transition state, and probably
suggests a later transition state in the nitrenoid transfer
compared with that in the carbene (or carbenoid) transfer.
The hyperleaving group ability of aryl-l3-bromanyl groups
will be responsible for the facile imido group transfer of
l3-bromane 1 to iodobenzenes.16
10
11
2j
2k
a
Reaction conditions: iminobromane 1 (0.075 M), ArI (1.2 equiv.),
b
CH2Cl2, room temperature, 1 h, Ar. Isolated yields.
1 makes it possible to synthesize a hitherto unknown kind
of alkyl(sulfonylimino)-l3-iodane; thus, transimidation to
2,2,2-trifluoroethyl iodide afforded a labile imino(trifluoroethyl)-
iodane 3 (CF3CH2I+NꢀTf) in 76% yield.12
Compared with other iminoiodanes 2, the ortho-acyl
derivative 2k is readily soluble in dichloromethane and
acetonitrile. This is in line with the observation reported by
Protasiewicz et al. that replacement of the intermolecular
Iꢂ ꢂ ꢂN secondary bonding in PhI+NꢀTs with intramolecular
Iꢂ ꢂ ꢂO secondary bonding by introducing a sulfonyl group at
the ortho position impressively increases the solubility in
organic media.14 In fact, the solid state structure of 2k
(Fig. 1) disclosed the formation of intramolecular hypervalent
N(1)–I(1)ꢂ ꢂ ꢂO(1) bonding with a close I(1)ꢂ ꢂ ꢂO(1) contact
(2.527(1) A) and with a near linear triad (165.80(5)1).z This
intramolecular hypervalent bonding will result in a partial
disruption of the polymeric network, and hence enhances
the solubility. Interestingly, ortho-methyl iminoiodane 2b
exhibits an increased solubility in dichloromethane, compared
to the para-isomer 2c. The non-coordinating ortho-methyl
group probably disrupts the formation of the well-arranged
polymeric structure to some extent by its sterically demanding
nature.
Transimidation between ortho-iodobenzoic acid (5) and
bromane 1 directly afforded cyclic l3-iodane 6 with a sulfonamido
ligand on the iodine(III) in high yield (93%, Scheme 3).
The cyclic I-(sulfonamido)benziodoxolone structure was
determined by IR absorption of the carbonyl group at
Rates of the imido group transfer to iodobenzene are
dependent upon the concentration of the iodide. The time-course
of the reaction in acetonitrile-d3 at 23 1C clearly demonstrates
that the rates of disappearance of the bromane 1 increase with
the increasing concentration of iodobenzene (see ESIw). These
results are compatible with a bimolecular nitrenoid transition
state such as 4, involving a rate-limiting nucleophilic attack
of iodobenzene on the negatively charged nitrogen atom of
1666 cmꢀ1 17
Initial formation of the corresponding imino-
.
l3-iodane via the imido group transfer, followed by an
intramolecular coordination of the nearby ortho-carboxy
group to the iodine(III) and a proton transfer, will produce
the benziodoxolone 6.
Table 2 Relative reactivity of ArI evaluated by competitive reactions
Entry
ArI
krel
sp
1
2
3
4
5
6
p-MeOC6H4I
p-MeC6H4I
PhI
p-FC6H4I
p-ClC6H4I
p-CF3C6H4I
9.8
4.9
1.0
0.33
0.18
0.06
ꢀ0.27
ꢀ0.17
0
0.06
0.23
0.54
Fig. 1 ORTEP drawing of the imino-l3-iodane 2k with 50% thermal
ellipsoids.
ꢁc
This journal is The Royal Society of Chemistry 2009
960 | Chem. Commun., 2009, 959–961

View Article Online
OTs, OTf, etc. It seems reasonable to assume that the NHTf
group with a relatively large trans influence prefers to bind to
benziodoxolyl units, but not to benziodazolyl units, on the basis
of a preferred combination of trans influences.18
Notes and references
z Crystal data. For 2k. C9H7F3INO3S: M = 393.12, orthorhombic,
space group Pna21 (No. 33), a = 10.1845(3), b = 19.9169(5),
,
c = 5.9157(2) A, V = 1199.96(6) A3, Z = 4, m(Mo Ka) = 28.814 cmꢀ1
T = 93 K, 10 881 reflections measured, 10 360 unique; R(int) = 0.023,
final R1 = 0.0154 (I 4 2s), Rw = 0.0379. CCDC 692568. For 8a:
C8H6F3IN2O3S: M = 394.11, orthorhombic, space group P212121
(No. 19), a = 11.1853(4), b = 14.2294(4), c = 14.5837(4) A,
V = 2321.14(12) A3, Z = 8, m(Mo Ka) = 29.818 cmꢀ1, T = 93 K,
22 608 reflections measured, 22 562 unique; R(int) = 0.030, final
R1 = 0.0215 (I 4 2s), Rw = 0.052. CCDC 692567.
Scheme 3 Transimidation of benzoic acid 5 and benzamides 7.
1 Reviews: (a) P. Dauban and R. H. Dodd, Synlett, 2003, 1571;
(b) P. Muller and C. Fruit, Chem. Rev., 2003, 103, 2905;
(c) V. V. Zhdankin and P. J. Stang, Chem. Rev., 2002, 102, 2523.
2 For aziridination of alkenes, see: (a) D. A. Evans, M. M. Faul and
M. T. Bilodeau, J. Am. Chem. Soc., 1994, 116, 2742;
(b) S. K.-Y. Leung, W.-M. Tsui, J.-S. Huang, C.-M. Che,
J.-L. Liang and N. Zhu, J. Am. Chem. Soc., 2005, 127, 16629;
(c) P. Dauban, L. Saniere, A. Tarrade and R. H. Dodd, J. Am.
Chem. Soc., 2001, 123, 7707; (d) S.-M. Au, J.-S. Huang, W.-Y. Yu,
W.-H. Fung and C.-M. Che, J. Am. Chem. Soc., 1999, 121, 9120.
3 For amination of alkanes, see: (a) K. W. Fiori and J. Du Bois,
J. Am. Chem. Soc., 2007, 129, 562; (b) C. Liang, F. Collet,
F. Robert-Peillard, P. Muller, R. H. Dodd and P. Dauban,
J. Am. Chem. Soc., 2008, 130, 343.
4 For amination of arenes, see: (a) Z. Li, D. A. Capretto,
R. O. Rahaman and C. He, J. Am. Chem. Soc., 2007, 129,
12058; (b) M. R. Fructos, S. Trofimenko, M. M. Diaz-Requejo
and P. J. Perez, J. Am. Chem. Soc., 2006, 128, 11784.
5 For amidation of aldehydes, see J. W. W. Chang and P. W.
H. Chan, Angew. Chem., Int. Ed., 2008, 47, 1138.
6 (a) Y. Yamada, T. Yamamoto and M. Okawara, Chem. Lett.,
1975, 361; (b) H. Okamura and C. Bolm, Org. Lett., 2004, 6, 1305.
7 (a) M. Ochiai, in Chemistry of Hypervalent Compounds, ed. K.-y.
Akiba, Wiley-VCH, New York, 1999, p. 359; (b) T. Okuyama,
T. Takino, T. Sueda and M. Ochiai, J. Am. Chem. Soc., 1995, 117,
3360.
8 (a) G. Besenyei, S. Nemeth and L. Simandi, Tetrahedron Lett.,
1993, 34, 6105; (b) L. M. Yagupolskii, V. I. Popov, N. V. Pavlenko,
I. I. Maletina, A. A. Mironova, R. Yu. Gavrilova and V. V. Orda,
Zh. Org. Khim. USSR, 1986, 22, 2169.
9 R. M. Moriarty, B. R. Bailey, O. Prakash and I. Prakash, J. Am.
Chem. Soc., 1985, 107, 1375.
10 M. Ochiai, T. Kaneaki, N. Tada, K. Miyamoto, H. Chuman,
M. Shiro, S. Hayashi and W. Nakanishi, J. Am. Chem. Soc., 2007,
129, 12938.
Imido group transfer to ortho-iodobenzamides 7 does take
place efficiently under our conditions; very interestingly,
however, no formation of the cyclic l3-iodane 9 was detected.
Thus, transimidation with iodobenzamide 7a afforded imino-
l3-iodane 8a quantitatively. Similarly, p-methyl imino-l3-iodane
8b was prepared in 97% yield. These results are in marked
contrast to the reaction with iodobenzoic acid 5. Fig. 2
illustrates the solid-state structure of imino-l3-iodane 8a, in
which two independent but closely related molecules 8aa and
8ab that are almost in a mirror image relationship exist.z Both
imino-l3-iodanes 8aa and 8ab are stabilized by more powerful
intramolecular hypervalent bonding between iodine(III) and
oxygen atoms compared to 2k, which was suggested by their
shorter distances (Fig. 2b). These stronger close contacts in 8a
will result in a greater weakening of the trans N–I bonds by
structural trans influence of the ligands and, therefore, N–I
bond distances in 8a are appreciably longer than that in 2k.18
Why does imino-l3-iodane 8a not adopt the cyclic
benziodazolone structure 9? Mutual ligand influence on
hypervalent bonding of aryl-l3-iodanes will probably determine
these structural preferences. The benziodoxolyl unit in 6,
associated with a moderate trans influence, accommodates a trans
ligand with various degrees of trans influence, such as Ph, OH,
OMe, OAc, Cl, OTs, OTf, etc., whereas the benziodazolyl unit in
9, with a significantly greater trans influence, is applicable only to
trans ligands with weak or moderate influence, such as OAc, Cl,
11 A. K. Mishra, M. M. Olmstead, J. J. Ellison and P. P. Power,
Inorg. Chem., 1995, 34, 3210.
12 1H NMR spectra (acetone-d6) of the iminoiodane 3 are always
contaminated with
a small amount of CF3CH2I, probably
produced by the decomposition during measurements. A large
downfield shift of the methylene group (d 5.06 ppm) of 3 compared
to that (d 3.99 ppm) of CF3CH2I and the ESI-MS clearly indicate
the formation of 313
.
13 For perfluoroalkyl-l3-iodanes, see T. Umemoto, Chem. Rev., 1996,
96, 1757.
14 D. Macikenas, E. Skrzypczak-Jankun and J. D. Protasiewicz,
J.Am. Chem. Soc., 1999, 121, 7164.
15 C. Hansch, A. Leo and R. W. Taft, Chem. Rev., 1991, 91, 165.
16 M. Ochiai, N. Tada, T. Okada, A. Sota and K. Miyamoto, J. Am.
Chem. Soc., 2008, 130, 2118.
17 Synthesis of 1-(tosylamido)-1,2-benziodoxol-3(1H)-one with
a
similar cyclic structure has been reported. See V. V. Zhdankin,
M. McSherry, B. Mismash, J. T. Bolz, J. K. Woodward,
R. M. Arbit and S. Erickson, Tetrahedron Lett., 1997, 38, 21.
18 M. Ochiai, T. Sueda, K. Miyamoto, P. Kiprof and V. V. Zhdankin,
Angew. Chem., Int. Ed., 2006, 45, 8203.
Fig. 2 (a) ORTEP structures of imino-l3-iodanes 8aa and 8ab with
50% thermal ellipsoids. (b) Distances [A] of hypervalent N–Iꢂ ꢂ ꢂO
bonding interactions.
ꢁc
This journal is The Royal Society of Chemistry 2009
Chem. Commun., 2009, 959–961 | 961