Addition of organostannanes to isocyanate catalyzed by a rhodium complex

Article abstract of DOI:10.1246/cl.2004.1364

Arylstannanes add to isocyanate in the presence of a rhodium catalyst to afford amides in good to excellent yields. Use of a phenol derivative as an additive is found to play an essential role for the successful reaction.

Full text of DOI:10.1246/cl.2004.1364

1
364
Chemistry Letters Vol.33, No.10 (2004)
Addition of Organostannanes to Isocyanate Catalyzed by a Rhodium Complex
Ã
Tooru Koike, Masabumi Takahashi, Nobumichi Arai, and Atsunori Mori
Chemical Resources Laboratory, Tokyo Institute of Technology, R1-4, 4259 Nagatsuta, Yokohama 226-8503
(Received August 11, 2004; CL-040955)
Arylstannanes add to isocyanate in the presence of a rhodi-
yield of 3a was high when the reaction was carried out with 1:2:1
of 2a, 1, and phenol, while increasing the ratio of phenol toward
isocyanate resulted in lower yields. Several neutral rhodium cat-
alysts, [RhCl(cod)]2 and [Rh(OPh)(cod)]2 similarly effected the
reaction in good to excellent yields. The reaction proceeded in
THF, 1,4-dioxane, cyclopentyl methyl ether, toluene, 1,2-di-
chloroethane, and acetonitrile in good to excellent yields. These
results are summarized in Table 1.
um catalyst to afford amides in good to excellent yields. Use of a
phenol derivative as an additive is found to play an essential role
for the successful reaction.
1
0
A transition metal-catalyzed incorporation of an unsaturated
compound into organic molecules is of considerable interest in
organic and organometallic chemistry directed for the synthesis
of a wide range of biologically and non-biologically important
Table 1. The reaction of PhNCO (1) with aryltributyltin 2a cat-
a
alyzed by a rhodium complex
1
materials. Isocyanate, which is a heterocumulene composed
of C=N and C=O bonds, has been employed as an unsaturated
organic compound with a palladium catalyst using organic elec-
Me
H
N
Ph
N
C
O
+ Me
SnBu3
Ph
2
trophiles. In these reactions, palladium mainly serves as a cata-
O
1
2a
3a
lyst to induce the carbon–nitrogen bond formation. Meanwhile,
formation of a carbon–carbon bond onto the central carbon
atom of isocyanate with a transition metal catalyst has not been
Additive
equiv.b
Yield
/%
Rh Cat
Rh(OH)(cod)]2
Solvent
THF
THF
THF
THF
/
3
studied extensively. Although Grignard reagents have shown
4
[
none
PhOH
PhOH (1)
PhOH (2)
PhOH (3)
PhOH
33
93
68
59
28
0
to react with isocyanate, available reagents and substrates are
limited.
On the other hand, the reaction of main group organometal-
lic compounds such as silicon, boron, and tin with various unsat-
urated organic electrophiles using a rhodium catalyst have been
studied recently.5,6 Subsequently, a wide range of carbon–carbon
THF
THF
none
[
[
[
RhCl(cod)]2
Rh(OPh)(cod)]2
Rh(OH)(cod)]2
THF
THF
toluene
CH3CN
c-C5H9OMe
Cl(CH2)2Cl
PhOH
PhOH
PhOH
PhOH
PhOH
PhOH
99
92
88
55
59
93
bond-forming reactions were achieved with unsaturated organic
compounds. Nevertheless, isocyanate despite being a reactive
unsaturated organic molecule has long been an unexploited fron-
7
tier in this area. The difficulties to achieve the reaction with rho-
dium would be caused by the hydrolysis of isocyanates leading
to the corresponding primary amines whereas the reactions of
such main group reagents favors protic reaction conditions.
Herein, we report that first catalytic nucleophilic arylation and
aUnless noted, the reaction was carried out with (4-methyl-
phenyl)tributyltin (0.3 mmol) and the rhodium catalyst
8
ꢀ
b
alkenylation of isocyanate with organostannanes are achieved
by using phenol derivatives as an additive.
(0.015 mmol) in THF at 70 C for 24 h. The ratio of isocya-
nate 1 (0.6 mmol) and the additive is 2:1 unless specified.
Otherwise, the ratio of additive/1 (0.3 mmol) was shown in
the parenthesis.
Table 2 shows the rhodium-catalyzed addition reaction of
several organostannanes and isocyanates in the presence of sev-
eral phenol derivatives. The reaction was found to occur with
several arylstannanes to afford the corresponding amide deriva-
O
C
N
O C N
R
R
C-N bond formation
Pd catalyst)
C-C bond formation
(Rh catalyst)
(
ꢀ
When PhNCO (1) was treated with 4-CH3C6H4SnBu3 (2a)
in the presence of a rhodium complex [Rh(OH)(cod)]2 (5 mol
), 33% of the addition product 3a was obtained after stirring
in THF at 70 C for 24 h. These results suggest that the catalytic
reaction of isocyanate appears to be difficult probably because
catalytically active rhodium species is hardly regenerated in
the addition reaction. The reaction in the presence of water also
resulted in no reaction and only induced hydrolysis of 1 to afford
aniline by contrast to the remarkable effect of water in the rho-
tives. The reaction proceeded at 70 C for 3–24 h. Phenol deriv-
atives equally effected the reaction irrespective of the electronic
effect by the substituent of the aromatic ring. Among those use
of 4-t-butylphenol was found to result in a slightly higher yield
when the reaction was terminated within a shorter reaction peri-
od. In addition to arylstannanes, alkenylstannanes, which were
%
ꢀ
easily prepared by the reaction of HSnBu with alkynes, similar-
3
ly reacted with isocyanate affording ꢀ,ꢁ-unsaturated amides 3e
and 3f, which allowed further conjugate addition of boronic acid
5
,6
11
dium-catalyzed conjugate addition and several other reactions.
Worthy of note, however, is remarkable improvement of the
yield by the addition of phenol to the reaction mixture of 2. The
in situ without isolation of 3. The reaction of an isocyanate
bearing a nitro group, with which Grignard reagents would not
be tolerable, at the 2- or 3-position of the aromatic ring occurred
9
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.10 (2004)
1365
Table 2. The rhodium-catalyzed reaction of isocyanate 1
1
alternative pathway, which would also be an unprecedented re-
action of the organorhodium reagent i. Nevertheless, we consid-
er that such a substitution pathway is unlikely. The reaction of
isocyanate with phenol proceeded at room temperature to give
a
(
R NCO) with 2 in the presence of Aryl–OH
ArylOH Time Yield
(Aryl)
1
R
Reagent
/h
/%
1
2
iv without catalyst and iv would be under the equilibrium with
isocyanate and phenol at the higher temperature. Thereby, con-
sidering the result to afford a good yield in the reaction with 1:2
of phenol and isocyanate, under which conditions isocyanate
would exist along with iv in the reaction system, insertion of iso-
cyanate to arylrhodium i is plausible. Indeed, the yield of amide
Ph
4-MeC6H4SnBu3 (2a)
PhSnBu3 (2b)
Ph
Ph
Ph
Ph
3
64
81
24
24
24
3
3
3
24
24
24
24
24
24
b
2
4
2
2
2
-MeC6H4SnBu3 (2c)
-MeOC6H4SnBu3 (2d)
d
d
d
56
99
76
92
69
Ph
c
3
gradually lowered with increasing the amount of phenol, by
d
which isocyanate would be completely converted into iv.
In summary, the rhodium-catalyzed reaction of isocyanate
with organostannanes provides a facile synthesis of amides un-
der mild conditions. A variety of secondary amides were synthe-
sized by the combination of isocyanates and tin reagents.
b
H2C=C(Ph)SnBu3 (2e)
PhCH=CHSnBu3 (2f)
2a
Ph
Ph
Ph
Ph
Ph
Ph
76
64
e
4
2
3
-EtC6H4
85
99
86
52
-O2NC6H4 2a
-O2NC6H4 2a
n-C6H13
2a
References and Notes
1
aUnless otherwise specified, the reaction was carried out with 2
‘‘Metal-catalyzed Cross-coupling Reactions,’’ ed. by F.
Diederich and P. J. Stang, Wiley-VCH, Weinheim, Germany
(
(
0.3 mmol), isocyanate (0.6 mmol), and a phenol derivative
0.3 mmol) in the presence of 5 mol % of [Rh(OH)(cod)]2 in
(1999).
ꢀ
b
ꢀ
2
a) S. Kamijo and Y. Yamamoto, J. Org. Chem., 68, 4764
(2003). b) C. Larksarp and H. Alper, J. Org. Chem., 65, 2773
THF at 70 C. The reaction was performed at 120 C in toluene.
c
d
e
4-t-BuC6H4 4-F3CC6H4 The reaction was carried out in
(
2000).
T. Muraoka, I. Matsuda, and K. Ito, Organometallics, 20, 4676
2000).
Addition of Grignard reagents to isocyanate: a) Y. Zhang,
J. Jiang, and Y. Chen, Tetrahedron Lett., 28, 3815 (1987).
b) H. M. Singleton and W. R. Edwards, Jr., J. Am. Chem.
Soc., 60, 540 (1938). c) H. Gilman and M. Furry, J. Am. Chem.
Soc., 50, 1214 (1928).
toluene.
3
4
(
to afford the corresponding amide in a reasonable yield. Hexyl-
isocyanate was also found to effect the reaction efficiently.
We consider that the reaction proceeds as depicted in
Scheme 1. Arylrhodium i is formed by migration of the aryl
group of the tin reagent 2 to rhodium via transmetalation. The
intermediate i of thus formed allows the addition to isocyanate
forming N- or O-bound rhodium species ii. Since these species
hardly reacted with the tin reagent to regenerate i, the catalytic
reaction did not take place efficiently in the absence of phenol.
By contrast, protonation of ii takes place with phenol to give
amide 3 accompanied by phenoxyrhodium species iii, which is
the active species for the transmetalation to allow the further cat-
alytic reaction smoothly.
5
a) Y. Takaya, M. Ogasawara, T. Hayashi, M. Sakai, and
N. Miyaura, J. Am. Chem. Soc., 120, 5579 (1998). b) S. Oi,
M. Moro, S. Ono, and Y. Inoue, Chem. Lett., 1998, 83. c) A.
Mori, Y. Danda, T. Fujii, K. Hirabayashi, and K. Osakada,
J. Am. Chem. Soc., 123, 10774 (2001). d) T. Koike, X. Du, T.
Sanada, Y. Danda, and A. Mori, Angew. Chem., Int. Ed., 42,
8
2
9 (2003). e) T.-S. Huang and C.-J. Li, Chem. Commun.,
002, 2348. f) M. Yamane, K. Uera, and K. Narasaka, Chem.
Lett., 33, 424 (2004) and references cited therein.
Formation of carbamate iv by the reaction of isocyanate
with phenol and following substitution of iv with i might be an
6
7
For reviews: a) K. Fagnou and M. Lautens, Chem. Rev., 103,
1
69 (2003). b) A. Mori, in ‘‘Latest Frontiers of Organic
Synthesis,’’ ed. by Y. Kobayashi, Research Signpost, India
2002), pp 83–102.
Ph
N C O
(
1
Friedel–Crafts reaction of isocyanates with arylstannanes in the
presence of stoichiometric Lewis acid: a) M. Arnswald and
W. P. Neumann, J. Org. Chem., 58, 7022 (1993). See also: b)
J. W. McFarland, and L. C. Yao, J. Org. Chem., 35, 123 (1970).
a) M. Kosugi, K. Sasazawa, Y. Shimizu, and T. Migita, Chem.
Lett., 1977, 301. b) J. K. Stille, Angew. Chem., Int. Ed. Engl.,
Aryl SnBu3
Aryl Rh
(i)
2
3
8
9
+
2
O
ORh
2
5, 508 (1986).
Rh OR (iii)
R = H or Ph)
Ph
Ph
Similar effect of a phenol derivative as an additive was also
observed in the rhodium-catalyzed reactions: a) L. Navarre,
S. Darses, and J.-P. Genet, Angew. Chem., Int. Ed., 43, 719
Aryl
N
Aryl
N
(
Rh
(ii)
(
2
2004). b) T. Fujii, T. Koike, A. Mori, and K. Osakada, Synlett,
002, 295.
3
10 Cyclopentyl methyl ether was kindly donated by Nippon Zeon
Co. Ltd.
i
+
1
1 For example, 3e that was formed in situ further reacted
ꢀ
O
H
with PhB(OH)2 and 4-CF3C6H4B(OH)2 at 120 C for 24 h to
Ph
N
OPh
PhOH + 1
Ph
Aryl
N
afford the conjugate addition products in 52 and 67% yields,
respectively.
2 The reaction of 1 with phenol at room temperature for 2 h
afforded the corresponding carbamate in a quantitative yield.
H
O
iv)
3
(
1
Scheme 1. Plausible mechanism of the reaction of isocyanate.
Published on the web (Advance View) September 18, 2004; DOI 10.1246/cl.2004.1364