An imido-transfer reaction of aldehydes with N-sulfinylamines using vanadium and molybdenum oxochlorides as catalysts

Article abstract of DOI:10.1016/j.tetlet.2007.11.131

Vanadium and molybdenum oxochlorides were found to be efficient catalysts for imido-transfer between aldehydes and N-sulfinylamines.

Full text of DOI:10.1016/j.tetlet.2007.11.131

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Tetrahedron Letters 49 (2008) 699–702
An imido-transfer reaction of aldehydes with N-sulfinylamines
using vanadium and molybdenum oxochlorides as catalysts
Anton A. Zhizhin, Dmitry N. Zarubin *, Nikolai A. Ustynyuk
A. N. Nesmeyanov Institute of Organoelement Compounds Russian Academy of Sciences, Vavilov Street 28, 119991 Moscow, Russia
Received 23 August 2007; revised 14 November 2007; accepted 21 November 2007
Abstract
Vanadium and molybdenum oxochlorides were found to be efficient catalysts for imido-transfer between aldehydes and
N-sulfinylamines.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Imidation; N-Sulfinylamine; Aldehyde; Azomethine; Vanadium; Molybdenum; Catalysis
The development of transition metal-mediated imido
transfer reactions is an area of considerable interest. The
aziridination and allylic amidation of alkenes,1 transforma-
tion of phosphines into iminophosphoranes,2 condensation
of isocyanates into carbodiimides,3 metathesis of imines4
and carbodiimides5 are well-studied examples. Schiff bases
containing additional n-donor atoms represent one of the
most important types of polydentate ligands in the coordi-
nation chemistry of transition and non-transition metals.
Two synthetic procedures were proposed to prepare azo-
methines via catalytic imido-transfer reaction, (i) MeReO3
catalysed the imidation of aldehydes by isocyanates as
reported by Wang and Espenson,6 and (ii) ruthenium cata-
lysed imido-transfer reaction of Ph3P@NTs7a or PhI@NTs/
as a co-product is necessary. It has been reported that
N-sulfinylamines which are easily prepared by the reaction
of primary amines with thionyl chloride8 can also act as an
imidating reagent in stoichiometric imido-deoxygenation
reactions of aldehydes. However, the scope of N-sulfinyl-
amines concerned is restricted to highly reactive polyfluo-
rinated compounds only.9
Here we report that using cheap and commercially avail-
able vanadium and molybdenum oxochlorides MOCl3
(M = V, Mo) and MoO2Cl2 as catalysts allows the imido-
transfer reaction to be extended to a wide range of both
N-sulfinylamines and aldehydes (Scheme 1, Table 1). We
found that the catalytic reaction proceeds in aliphatic or
aromatic hydrocarbon solvents under an argon atmosphere
and affords aldimines in high yields. Analogous vanadium
and molybdenum imidochlorides demonstrate comparable
catalytic properties. The reaction proceeds at room temper-
ature only for N-sulfinylamines and aldehydes having both
7b
PPh3 with aldehydes as reported by Sain et al. Both are
selective water-free reactions and in comparison with the
classic acid-catalysed condensation of aldehydes with pri-
mary amines, they have the advantage of not requiring
the use of azeotropic distillation or water-absorption for
promoting the process. The former reaction is restricted
by the scope of the starting substrates while the latter is
inconvenient because chromatographic purification of the
target azomethines from triphenylphosphine oxide formed
R
H
R
H
cat. (3-4 mol%)
O
+
ArN=S=O
+
SO2
ArN
heptane or toluene
Δ
1a-l
2a-l
cat.: MOCl3 (M= V, Mo), MoO2Cl2,
(2,4,6-Br3C6H2N)2Mo(OMes)2
*
Corresponding author. Tel.: +7 499 1358861; fax: +7 499 1355085.
Scheme 1.
E-mail address: zaroubine@ineos.ac.ru (D.N. Zarubin).
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.11.131

700
A. A. Zhizhin et al. / Tetrahedron Letters 49 (2008) 699–702
Table 1
The azomethines 2a–l prepared by vanadium or molybdenum-catalysed reaction of N-sulfinylamines with aldehydes
Entry
N-Sulfinylamine
Azomethine
Catalyst (mol %)
Conditions
Yield (%)
100a (84)b
CF3
CF3
Cl
N
a
VOCl3 (3)
Heptane, rt, 0.5 h
N
NSO
Cl
Cl
Cl
b
c
VOCl3 (3)
VOCl3 (3.5)
VOCl3 (3)
Heptane, reflux, 5 h
Heptane, reflux, 4 h
Heptane, reflux, 5 h
100 (98)
91 (69)
83 (75)
Cl
NSO
Cl
NO2
Cl
Cl
Cl
Cl
N
H3C
H3C
NSO
C6F5
N
d
S
S
NSO
NSO
NSO
C6F5
N
Cl
Cl
e
Cl
Br
VOCl3 (3)
Heptane, reflux, 28 h
81 (76)
Cl
Br
N
N
S
Cl
Br
Cl
Br
f
MoO2Cl2 (3)
MoOCl3 (3)
MoOCl3 (3)
Toluene, reflux, 8 h
Toluene, reflux, 24 h
Toluene, reflux, 19 h
98 (77)
75 (73)
85 (72)
NSO
Br
Br
OSN
NSO
g
h
N N
Mes
Mes
H3C
CH3
NSO
CH3
CH3
H3C
N
O
CH3
O
i
j
MoOCl3 (3)
Toluene, reflux, 24 h
77 (74)
O
N
N
NSO
NSO
Mes
Mes
Cl
Cl
Cl
c
(RN)2Mo(OR0)2 (4)
Heptane, reflux, 5 h
93 (89)
Cl
N
Cl
NSO
Cl

A. A. Zhizhin et al. / Tetrahedron Letters 49 (2008) 699–702
701
Yield (%)
64 (50)
Table 1 (continued)
Entry
N-Sulfinylamine
Azomethine
Cl
Catalyst (mol %)
Conditions
Cl
c
CH3
CH3
N
k
(RN)2Mo(OR0)2 (3)
Heptane, reflux, 5 h
Cl
NSO
Cl
Cl
Cl
OCH3
OCH3
NSO
c
l
(RN)2Mo(OR0)2 (3)
Toluene, reflux, 2.5 h
90 (86)
N
But
a
Spectroscopically estimated.
Isolated.
R = 2,4,6-Br3C6H2, R0 = 2,4,6-Me3C6H2.
b
c
good solubility in hydrocarbons and electron-withdrawing
substituents (Table 1, entry a). In all the other cases stud-
ied, refluxing was necessary. Vanadium oxotrichloride
works very well in aliphatic solvents with sterically unhin-
dered substrates (Table 1, entries a–e). Molybdenum oxo-
chlorides in toluene were preferred as catalysts for
sterically hindered reagents, for example those containing
mesityl or 2,4,6-tribromophenyl groups (Table 1, entries
f–i). Neither vanadium nor molybdenum oxochlorides
catalysed the reaction of N-sulfinylamines with aliphatic
aldehydes. We also found that molybdenum imidoaroxide
of the oxochloride by N-sulfinylamine initially proceeds
to afford the imido complex and sulfur dioxide as a co-
product. Then the complex undergoes the imido ligand
exchange with the aldehyde to regenerate the starting oxo-
chloride and release the target aldimine. The stoichiometric
variants of the first10 and the second stages6,11 of this cata-
lytic cycle are well documented in the literature. The same
catalytic cycle is realised if imides are used as catalysts
instead of oxides. In this case the catalytic cycle starts from
the opposite position. The details of the mechanism are
currently under investigation.
(2,4,6-Br3C6H2N)2Mo(OMes)2
(Mes = 2,4,6-Me3C6H2)
In summary, a novel water-free method for the synthesis
of azomethines is presented. It is based on the imido-trans-
fer reaction of aldehydes with N-sulfinylamines catalysed
by vanadium or molybdenum oxochlorides. The advanta-
ges of this method are the easy availability of different N-
sulfinyl derivatives of primary amines, cheap catalysts, high
selectivity, simple operations and good yields. This method
can be conveniently used for the preparation of a wide
range of azomethines.
catalysed the imidation of branched aliphatic aldehydes
to give aldimines (Table 1, entries k and l). It should be
noted that (2,4,6-Br3C6H2N)2Mo(OMes)2 is effective with
both aliphatic and aromatic aldehydes. This method is
especially useful for the synthesis of azomethines from
poorly-nucleophilic primary amines which are difficult to
access by classic acid-catalysed condensation of primary
amines with aldehydes. To evaluate the effect of the
catalyst, blank experiments were carried out under the
same reaction conditions. 1-Sulfinylamino-2-(trifluoro-
methyl)benzene and 2,4-dichlorobenzaldehyde, 1,3,5-tri-
methyl-2-(sulfinylamino)benzene and 2-furaldehyde, and
1,3,5-trichloro-2-(sulfinylamino)benzene and 2-methyl-
propanal were mixed in pairs in the absence of catalysts.
No aldimines were detected in all cases even after pro-
longed heating of the reaction mixtures.
Acknowledgement
The research described in this publication was supported
by the Russian Foundation for Basic Research (Grant 07-
03-00939a).
Supplementary data
The proposed catalytic cycle of the imido transfer pro-
cess is shown in Scheme 2. For the reaction catalysed by
metal oxochlorides the metathetical imido-deoxygenation
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.
2007.11.131.
References and notes
R'
ClnM O
RN
RN SO
SO2
H
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R'
ClnM NR
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Scheme 2.

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