Rhodium-catalyzed addition of organo[2-(hydroxymethyl)phenyl] dimethylsilanes to arenesulfonylimines

Article abstract of DOI:10.1246/cl.2008.290

The title reaction is found to proceed in the presence of a rhodium/diene catalyst. Variously substituted diarylmethylamines and allylamines having an N-arenesulfonyl protection are obtained in good yields, which are important building blocks in organic synthesis. Copyright

Full text of DOI:10.1246/cl.2008.290

290
Chemistry Letters Vol.37, No.3 (2008)
Rhodium-catalyzed Addition of Organo[2-(hydroxymethyl)phenyl]dimethylsilanes
to Arenesulfonylimines
Yoshiaki Nakao,Ã1 Masahide Takeda,1 Jinshui Chen,1 Tamejiro Hiyama,Ã1 Yoshitaka Ichikawa,2 Ryo Shintani,2 and Tamio HayashiÃ2
1Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510
2Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502
(Received December 6, 2007; CL-071357; E-mail: nakao@npc05.kuic.kyoto-u.ac.jp,
thiyama@npc05.kuic.kyoto-u.ac.jp, thayashi@kuchem.kyoto-u.ac.jp)
The title reaction is found to proceed in the presence of a
rhodium/diene catalyst. Variously substituted diarylmethyl-
amines and allylamines having an N-arenesulfonyl protection
are obtained in good yields, which are important building blocks
in organic synthesis.
NR3
R2
(diene)Rh–R1
O
A
Si
H
Me2
2
4
(diene)Rh
(diene)Rh
O
NR3
Nucleophilic addition reactions of organometallic reagents
to imines have been studied extensively as versatile protocols
for synthesis of various sec-alkylamines, some of which exhibit
remarkable biological activities.1 Especially, recent studies on
rhodium catalysis have allowed the use of mild nucleophiles
such as organoboron reagents to participate in the transformation
with high chemo- and enantioselectivities.2 Whereas other orga-
nometallic reagents have also been employed in the rhodium-
catalyzed reactions to compensate for the boron-based ones,3 or-
ganosilicon reagents have remained unexplored except for labile
aryl(difluoro)silanes which were employed in the presence of KF
in excess.4 In view of an increasing importance of the silicon-
based protocol with respect to inherent stability, availability,
and non-toxicity associated with organosilicon compounds, we
report herein organo[2-(hydroxymethyl)phenyl]dimethylsilanes
(1) as highly stable and reusable alternative organometallic re-
agents for the rhodium-catalyzed 1,2-addition reaction to imines.
We have recently disclosed that 1 undergoes transmetalation
smoothly to rhodium(I) to give organorhodium species A possi-
bly via rhodium alkoxide C to effect 1,4-addition reactions
across electron-deficient olefins under mild conditions (Scheme
1).5 Thus, it is reasonable to expect that A would react with
imines to afford rhodium amide B, which then acts as a base
to deprotonate 1 and generate C. Overall, the rhodium-catalyzed
1,2-addition reaction using 1 is anticipated to proceed under mild
conditions without any activators.
To prove the viability of our working hypothesis, we first
examined the reaction of [2-(hydroxymethyl)phenyl]phenyldi-
methylsilane (1a: 1.1 mmol) with N-phenylmethylidene-4-nitro-
benzenesulfonamide (2a: 1.0 mmol). The N-sulfonyl protecting
group was chosen simply because it is readily removal after
the addition reaction.6 The reaction proceeded smoothly in the
presence of [Rh(OH)(cod)]2 (1.0 mol % Rh) in THF at 70 ꢀC to
afford N-(diphenylmethyl)-4-nitrobenzenesulfonamide (3aa) in
86% yield (Table 1, Entry 1). Arylsilanes having a labile bromo
group (1b) and sterically demanding 2-methyl group (1c) also
underwent the reaction with 2a in excellent yields (Entries 2
and 3). Silane reagent 1a added to imines derived from elec-
tron-deficient and -rich benzaldehydes as well as alkanals to give
the corresponding adducts in good yields (Entries 4–6). A wide
range of allylic amines were obtained in high yields with excel-
lent regio- and stereospecificities by the addition reactions of
R1 Si
R1 R2
Me2
C
B
HO
R1 Si
NHR3
R1 R2
Me2
1
3
R1
Ph (1a)
4-Br–C6H4 (1b) (E)-PhCH=CH (1g)
2-Me–C6H4 (1c) (Z)-MeCH=CH (1h) 4-MeO–C6H4, Ns (2c)
=
R2, R3
(E)-HexCH=CH (1f) Ph, Ns (2a)
4-Cl–C6H4, Ns (2b)
=
vinyl (1d)
H2C=CMe (1e) Me2CH=CH (1j)
(E)-PrCH=CPr (1i)
c-C6H11, Ts (2d)
(Ns = 4-O2N–C6H4–SO2,
Ts = 4-Me–C6H4–SO2)
Scheme 1.
variously substituted alkenylsilanes carried out at 35–50 ꢀC
(Entries 7–16). Successful addition of vinylsilane 1d and prop-
en-2-ylsilane 1e is worth noting, because the corresponding
vinylboronic acids have rarely been employed in the rhodium-
catalyzed transformations due mainly to thermal instability.7
In all the addition reactions demonstrated herein, formation of
silicon residue 4 in >80% yield, which is reusable for regener-
ation of the tetraorganosilicon reagents, were confirmed by
1H NMR analyses of crude products.
In the presence of chiral diene ligand (S,S)-Ph-bndÃ,2e,2f the
reaction of 1e with 2a proceeded in an enantioselective manner
to give substituted chiral allylamine (R)-3ea of 91% ee in 68%
yield (eq 1).8 This result represents, though preliminary, the
first example of the enantioselective addition of an alkenyl
nucleophile to imines by rhodium catalysis. Further efforts for
the enantioselective 1,2-addition reaction of the silicon reagents
to sulfonylimines are being made in our laboratories.
In summary, we have demonstrated that organo[2-(hydroxy-
methyl)phenyl]dimethylsilanes undergo the 1,2-addition reac-
tion to arenesulfonylimines. Compared with the reported silicon-
based reaction,4 the present one allows use of readily accessible,
highly stable, and reproducible tetraorganosilicon compounds in
a stoichiometric amount in most cases under mild conditions
without any activator. The present protocol provides us with
Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.3 (2008)
291
[Rh(OH)((S,S )-Ph-bnd*)]2
(8 mol % Rh)
Table 1. Addition of organo[2-(hydroxymethyl)phenyl]dimethyl-
silanes (1) to arenesulfonylimines 2
NHNs
Ph
(1)
+
2a
1e
(1.2 equiv.)
THF, 60 °C, 6 h
[Rh(OH)(cod)]2
(1 mol % Rh)
Me
(R)-3ea, 68% yield, 91% ee
1 (1.2 mmol)
NHSO2Ar
O
+
+
Si
R1 R2
THF, 35–70 °C
Ph
2 (1.0 mmol)
Me2
3
4
Ph
(S,S)-Ph-bnd*
Entry
1
1
2
Temp/°C Time/h
Product
NHNs
Yield/%a
1ab 2a
70
1
86 (3aa)
We thank Mr. Hidekazu Imanaka for initial experiments
on this work. This work has been supported financially by a
Grant-in-Aid for Creative Scientific and Priority Areas ‘‘Synergy
of Elements’’ from MEXT.
Ph
Ph
NHNs
1bb 2a
70
2
92 (3ba)
98 (3ca)
90 (3ab)
2
3
Ph
Br
Me NHNs
Ph
References and Notes
1cb 2a
70
2
1
2
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NHNs
4
5
1ab 2b
1ab 2c
70
70
1
0.5
R = Cl
Ph
OMe 91 (3ac)
R
NHTs
6
7
8
9
1ab 2d
1dc 2a
1e 2a
1fd 2a
70
50
35
1.5
94 (3ad)
64 (3da)
96 (3ea)
Ph
NHNs
48
Ph
NHNs
3
Ph
Me
NHNs
35
35
35
3
1
3
93 (3fa)
95 (3ga)
89 (3ha)f
Hex
Ph
Ph
3
NHNs
10 1g 2a
11 1he 2a
Ph
Me NHNs
Ph
NHNs
Ph
12
13
1i 2a
1j 2a
35
35
2
98 (3ia)
98 (3ja)
Pr
4
5
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0.5
Me
Me NHNs
Ph
14
15
1j 2b
1j 2c
35
35
1
0.5
R = Cl
93 (3jb)
OMe 96 (3jc)
Me
R
6
7
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16
1j 2d
35
4
95 (3jd)
Me
8
9
The absolute configuration was determined by X-ray
crystallography. See Supporting Information for details.10
For reviews, see: a) T. Hiyama, T. Kusumoto, in Comprehen-
sive Organic Synthesis, ed. by B. M. Trost and I. Fleming,
Pergamon, Oxford, 1991, Vol. 8, pp. 763–792. b) B. M.
Trost, Z. T. Ball, Synthesis 2005, 853. For hydrosilylation to
synthesize 1, see: c) Y. Nakao, H. Imanaka, J. Chen, A. Yada,
T. Hiyama, J. Organomet. Chem. 2007, 692, 585.
b
aIsolated yields based on 2. Reaction run with 1.1 mmol of 1.
cReaction run with 2.0 mmol of 1d. dReaction run with 1.0 mmol
of 1f. E/Z = 12:88 (1H NMR). fE/Z = 13:87 (1H NMR).
e
an alternative to the boron-based one to synthesize variously
substituted sec-alkylamines, especially in view that a wide
variety of stable alkenyl(triorgano)silanes with various substitu-
tion patterns are available in a predictable manner by rich hydro-
silylation chemistry.9
10 Supporting Information is available electronically on the
CSJ-Journal Web site; http://www.csj.jp/journals/chem-lett/.
Published on the web (Advance View) February 9, 2008; doi:10.1246/cl.2008.290