Bartoli et al.
into amines, and over the years, the most prominent have
employed triphenylphosphine8 or its excellent alternative with
hydrogen sulfide in pyridine.9 The majority of these reducing
agents have some disadvantages related to their lack of
selectivity and drastic conditions, such as highly basic condi-
tions. In fact, several attempts to chemoselectively reduce the
azides to corresponding amines via a Staudinger reaction were
problematic. Staudinger reduction using triphenylphosphine with
a variety of azides is not able to give a reaction,10 and the use
of the highly reactive trialkylphosphine is necessary to have
complete consumption of the azides and formation of the
phosphazine ylides. These could extrude nitrogen to deliver the
intermediate iminophosphoranes; however, addition of a strong
base to the reaction mixture is required to obtain the hydrolysis
of these stable intermediates.11 As a result, there is always
considerable interest in finding more selective methods.
modern organic synthesis.19 Notably, studies by us and by others
have resulted in the development of methodologies involving
the CeCl3·7H2O/NaI system for providing new means for
promoting organic transformations in a variety of systems.20
As a result of our efforts, we can now report a new CeCl3·
7H2O/NaI-promoted azide-transformation for producing exclu-
sively primary amines.21 Its compatibility with a wide variety
of other sensitive functional groups, and the fact that CeCl3·
7H2O Lewis acid is not deactivated22 or trapped23 by the basic
nitrogen of amine adducts, allow us to believe that our method
represents a valuable alternative to the existing protocols
reported in literature. Another improvement in our CeCl3·7H2O/
NaI-promoted organic transformation of azides to primary
amines is the opportunity to reduce reaction time and to increase
product yield by using microwave technology (eq 1). In fact,
the use of microwave-assisted reaction is an area of increasing
interest in both academic and industrial laboratories.24
Over the past years, it has been shown as NaI in combination
with a Lewis acid such as TiCl4 offers a useful alternative to
existing methods for the reduction of both amine N-oxides and
nitrones.12 These mild reductive properties of the TiCl4/NaI
reagent system prompted Kamal et al. to try the FeCl3/NaI
combination as an efficient complex for the transformation of
azides to the corresponding amines,13 even if some neglected
reaction details need to be considered. The FeCl3, in combination
with different reagents, has also been reported for several other
reductions,14 above all for its Lewis acid ability under mild and
nonbasic conditions.15 The above benefits are, however, ac-
companied by drawbacks. The major drawback associated with
the use of FeCl3 is that it is messy, very acidic, and corrosive,
and the commercial grades also contain varying and often
variable amounts of free hydrochloric acid.16 The current
requirements for green and efficient Lewis acid promoters in
modern organic chemistry have increased attention to several
environmentally friendly17 and atom-economical organic trans-
formations.18 Recent reports have highlighted the applications
of cerium trichloride as a green and efficient Lewis acid in
2. Results and Discussion
Because of the broad range of applications of the CeCl3·7H2O/
NaI system as catalyst in many organic transformations in
solvent-free conditions,20 we decided to apply our Lewis acid
combination impregnated over inorganic support such as SiO2
or Al2O325 to facilitate the azide transformation in amines. Our
initial efforts focused on examining benzyl azide (1a) as the
(17) (a) Blackmond, D. G.; Armostrong, A.; Coombe, V.; Wells, A.
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low toxicity, and high stability toward water, oxygen, and air moisture.
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an ideal “friendly” reagent. Moreover, no particular precautions are necessary
whenhandling it, since it is water and air tolerant, and an absolutely nontoxic
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