Rhodium-catalyzed and sonication-accelerated addition of aryltin and aryllead reagents to imines in air and water

Article abstract of DOI:10.1016/j.tetlet.2004.01.160

In the presence of a rhodium catalyst, imines (1a-k) react with phenyltrimethyltin 2a or phenyltrimethyllead 2b in water and air under ultrasonic irradiation at 35°C to give the corresponding diarylmethylamines (3a-k) in good yields.

Full text of DOI:10.1016/j.tetlet.2004.01.160

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 2995–2998
Rhodium-catalyzed and sonication-accelerated addition of aryltin
and aryllead reagents to imines in air and water
Rui Ding,a Cui Huo Zhao,a Yong Jun Chen,a Li Liu,a Dong Wanga,* and Chao Jun Lib,*
aCenter for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China
bDepartment of Chemistry, McGill University, 801 Sherbrooke St. W., Montreal, QC, Canada H3A 2K6
Received 16 September 2003; revised 15 January 2004; accepted 30 January 2004
Abstract—In the presence of a rhodium catalyst, imines (1a–k) react with phenyltrimethyltin 2a or phenyltrimethyllead 2b in water
and air under ultrasonic irradiation at 35 ꢀC to give the corresponding diarylmethylamines (3a–k) in good yields.
ꢁ 2004 Elsevier Ltd. All rights reserved.
In current years, there has been a growing interest in
studying organic reactions in water,1 due to its natural
abundance as well as the inherent advantages of using
water as a solvent. Recently, we have been exploring
transition-metal-catalyzed carbon–carbon bond forma-
tions under the quasi-natural conditions of air and
water.2 Toward such a general goal, a Grignard-type
phenylation of aldehydes with phenyltin reagents in
water was discovered.3 Subsequently, we also found that
in the presence of a rhodium catalyst, a,b-unsaturated
esters, and ketones react with arylbismuth, arylsilicon,
aryltin, and aryllead reagents as well as trialkylvinyltin
reagents in aqueous media to give the corresponding
conjugated addition products under an air atmosphere.4
More recently, Oi et al.5 reported a rhodium-catalyzed
asymmetric 1,4-addition of organosiloxanes to a,b-
unsaturated carbonyl compounds in aqueous media
(dioxane/water 10:1) at 90 ꢀC. On the other hand, the
addition reactions of organometallic reagents to imines6
provide a useful method to synthesize diarylmethyl-
amines, which are structural units of many pharmaco-
logically interesting and biologically important
compounds.7 In general, organolithium and Grignard
reagents are used for this purpose.6b;c;8 Obviously, the
use of anhydrous solvent and inert gas atmosphere are
required for the proceeding of the reaction. Rhodium-
catalyzed arylation reactions of imines with arylstan-
nanes in THF9 and in dioxane10 and with arylboronic
acids in dioxane11 were reported; however, they all
require anhydrous conditions and inert gas atmosphere.
To our knowledge, there has not been any example of
the transition metal-catalyzed addition of arylmetal
reagents to imines in aqueous media reported to date,
probably due to the lower electrophilic reactivity of
C@N bond of imines than that of C@O bond of car-
bonyl compounds and the ready hydrolysis of imines in
water. Herein, we wish to report the results of rhodium-
catalyzed addition reactions of aryltin and aryllead
reagents with imines in water and air under ultrasonic
irradiation or by regular heating.
To start the investigation, the reaction of N-tosylbenz-
ylideneimine (1a, Ar@Ph, R@Ts) with phenyltrimeth-
yltin (2a) in the presence of catalyst Rh2(COD)2Cl2
(5 mol %) was carried out in water at 60 ꢀC (Scheme 1) to
give the addition product, N-tosyldiphenylmethylamine
(3a), in 48% yield (Table 1, entry 1). Meanwhile, it was
observed that the experimental results on the reactions
of imine in water were not easy to repeat, probably due
to hydrolysis of the aldimine 1a during the reaction9b
and the lack of mixing between the solid catalyst and the
solid aldimine compounds in water. The addition of a
R
R
H
HN
N
Rh2(COD)2Cl2, 5 mol%
+
PhMMe3
H2O, 60oC, air or
H2O, 35oC, sonication, air
Ar
Ph
Ar
H
Keywords: Rhodium; Imine addition; Aqueous catalysis; Air atmo-
sphere; Sonication.
2a, M=Sn
2b, M=Pb
3a-h
1a-j
* Corresponding authors. E-mail addresses: dwang210@iccas.ac.cn;
cj.li@mcgill.ca
Scheme 1.
0040-4039/$ - see front matter ꢁ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.01.160

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R. Ding et al. / Tetrahedron Letters 45 (2004) 2995–2998
Table 1. Rh-catalyzed reaction of imine 1a with PhSnMe3 (2a)
preference of addition reaction over hydrolysis. Inter-
estingly, if THF was used as solvent instead of water, the
reaction of 1a with 2a at 35 ꢀC for 1.5 h gave only a trace
amount of 3a either with or without sonication (entries
4–5). The acceleration of sonication to the reaction was
only observed in water solution, even though a homo-
geneous THF solution of the reagents and the Rh cat-
alyst was formed during the reaction.
Entry
Conditions
Yielda of 3a (%)
1
2
3
4
5
H2O/60 ꢀC/14 h
H2O/35 ꢀC/1.5 h
H2O/35 ꢀC/sonication/1.5 h
THF/35 ꢀC/1.5 h
THF/35 ꢀC/sonication/1.5 h
48
Trace
80
Trace
Trace
a Isolated yield after column chromatography on silica gel.
Based on these experimental results, various arylimines
were selected as substrates in the rhodium-catalyzed
reaction of imines with phenyltrimethyltin (2a) and
phenyltrimethyllead (2b) in water and air at 35 ꢀC under
sonication. When N-(p-methoxyphenyl)-benzylidene-
imine(1i) and N-phenyl-benzylideneimine (1j) were used
under the same conditions, no or only a small amount of
the corresponding addition products were detected in
the reaction mixture (Table 2, entries 11–12). On the
other hand, the reactions of N-tosylarylimines 1a–g with
2a or 2b in the presence of rhodium catalyst (5 mol %)
proceeded smoothly under the same conditions to give
phenylarylmethylamines 3a–g in good yields (entries
surfactant (SDS) did not improve reproducibility of the
experimental results. However, when the mixture of 1a,
2a and the catalyst in water was sonicated at 35 ꢀC for
1.5 h, the reaction proceeded smoothly to afford product
3a in 80% yield (Scheme 1, Table 1, entry 3) with high
reproducibility.12 In contrast, only a trace of 3a was
observed on TLC, if the reaction was carried out under
the same conditions without sonication (entry 2). Soni-
cation turned the reaction mixture into an emulsion and
accelerated the Rh-catalyzed addition of aryltin reagent
to imine in water dramatically,13 resulting in a great
Table 2. Rh-catalyzed reactions of imines with PhMMe3 in water under sonication
Entry
Imine
PhMMe3
Product
Yielda
81
Ts
NHTs
N
1
2a
(3a)
(3a)
(1a)
Ph
Ph
Ph
Ph
H
Ts
(1a)
H
NHTs
Ph
N
2
2b
78
Ph
Ts
NHTs
N
N
N
N
(3b)
(3c)
(3d)
(3d)
3
4
2a
2a
77
75
(1b)
p-ClPh
o-ClPh
2-furyl
2-furyl
Ph
NHTs
Ph
p-ClPh
o-ClPh
2-furyl
2-furyl
H
Ts
(1c)
H
Ts
(1d)
H
NHTs
Ph
5
2a
84
Ts
(1d)
H
NHTs
Ph
6
7
2a
2a
85
76
Ts
(1e)
H
NHTs
Ph
N
(3e)
PhCH=CH
NHTs
Ph
PhCH=CH
Ts
N
(3f)
(1f)
8
9
2a
2a
63
p-MePh
p-MePh
p-MeOPh
p-O2NPh
H
Ts
(1g)
NHTs
Ph
N
60b
(3g)
(3h)
p-MeOPh
p-O2NPh
H
NHTs
Ph
Ts
N
10
2a
30b;c
(1h)
H
PMP
N
(1i)
11
12
2a
2a
None
Ph
Ph
H
Ph
(1j)
H
NHPh
N
(3i)
Trace
Ph
Ph

R. Ding et al. / Tetrahedron Letters 45 (2004) 2995–2998
2997
Table 2 (continued)
Entry
Imine
PhMMe3
Product
Yielda
Me
Me
Me
(3j)
O
N
O
S
H
S
HN
13
14
2a
58
(1k)
(1k)
Ph
Ph
Ph
Me
O
O
N
S
S
H
HN
2c
76d
(3k)
Ph
PhCl-(o)
Ph
2a ¼ PhSnMe3, 2b ¼ PhPbMe3, 2c ¼ o-ClPhPbMe3.
a Isolated yields, 35 ꢀC, sonication for 1.5 h.
b Sonicated for 2 h.
c 45% yield of p-O2NPhCH(OH)Ph (4) was obtained.
d de ¼ 34%.
1–9). The latter was attributed to the activation of the
C@N bond by an electron-withdrawing tosyl group.
Phenyllead reagent exhibited the same reactivity as
phenyltin reagent (entries 2 vs 1 and 6 vs 5). It was found
that the use of arylimines with electron-donating group
in the phenyl ring (1f–g) gave products 3f–g in lower
yields (entries 8–9). An exception is the case of N-tosyl-
p-nitrobenzylideneimine 1h, from which only 30% yield
of the product 3h was obtained and, in addition, (p-
nitrophenyl)phenylmethanol (4) was detected (3h:4 ¼
1:1.5). The results suggested that addition reaction and
hydrolysis of imines competed in water. For most imines
used, the addition reaction surpassed the hydrolysis of
imine to give the desired products in good yields.
However, in the case of 1h, the hydrolysis of imine is
faster than the addition reaction. Subsequently, the
hydrolysis product p-nitrobenzaldehyde reacted with 2a
to afford 4. The p-toluenesulfinylimine (1k) exhibited a
relatively lower reactivity (58% yield) than p-toluene-
sulfonylimine (80% yield, entries 13 vs 1). However,
when a chiral imine, (+)-N-(S)-p-toluenesulfinylbenzyl-
ideneimine[(+)-1k], was allowed to react with o-chloro-
phenyltrimethyllead (2c) in water under sonication, a
mixture of two diastereomers of 3k was obtained in 76%
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We thank the financial support for this study provided
by the National Natural Science Foundation of China
(No. 20332030, 20232010) and The Chinese Academy of
Sciences.

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