Ra p id Sm I2-Med ia ted Red u ction s of Alk yl Ha lid es a n d
Electr och em ica l P r op er ties of Sm I2/H2O/Am in e
Anders Dahle´n,† Go¨ran Hilmersson,*,† Brian W. Knettle,‡ and Robert A. Flowers, II*,‡
Organic Chemistry, Department of Chemistry, Go¨teborg University, SE-412 96 Go¨teborg, Sweden, and
Department of Chemistry and Biochemistry, Texas Tech University, Box 41061,
Lubbock, Texas 79409-1061
hilmers@organic.gu.se; robert.flowers@ttu.edu
Received February 7, 2003
Mixtures of SmI2/H2O/amine have been found to reduce alkyl halides more efficiently than SmI2/
HMPA/alcohol mixtures at room temperature. Alkyl and aryl iodides were quantitatively reduced
in <1 min and alkyl bromides in 10 min, while alkyl and aryl chlorides required more than 5 h for
completion. Determination of the reaction order of Et3N in the reduction of 1-chlorodecane showed
that the reaction order is one. Water was shown not to participate in the rate-determining step of
this reduction. There was a significant change of the UV-vis spectrum and color of SmI2 upon
addition of either PMDTA or water, while no effect was observed with the addition of Et3N or
TMEDA. Although the combination of SmI2, water, and amines produces a very efficient reducing
system, cyclic voltammetric experiments showed that the redox potential is nearly identical with
that of SmI2 alone. These results are consistent with precipitation providing the driving force for
reduction. Taken together, the results of these experiments show that the combination of SmI2/
H2O/amine provides a fundamentally novel and useful approach to enhance the reactivity of SmI2.
In tr od u ction
cosolvents have been used in SmI2-based reactions none
have the general utility of HMPA.6,7 Although countless
reactions require SmI2-HMPA for success, the major
negative aspect of this reducing system is the high
carcinogenicity of HMPA.
Samarium(II) diiodide was introduced as a reducing
agent by Kagan and co-workers in 1980.1 Since then a
number of SmI2-based reactions including reductions,2
reductive couplings,3 and sequenced reactions4have been
developed, and new applications for this selective single
electron transfer reagent are steadily being discovered.
Samarium diiodide is a rather mild reducing agent and
strongly coordinating cosolvents are necessary to enhance
the rate of some SmI2-mediated reactions. In particular,
HMPA has been found to drastically increase both the
reactivity and selectivity of many reactions.5 While other
Recently two of us (A.D. and G.H.) have discovered that
the combination of SmI2/amine/water is superior to
SmI2-HMPA in some reactions.8,9 During our study of
SmI2/H2O/amine mixtures we have previously reported
that ketones, imines, and R,â-unsaturated esters are
reduced instantaneously, i.e. completed in less than 10
s.9 Furthermore, it has been shown that the combination
of amine and water has a remarkably strong effect on
the reactivity of SmI2 for the reduction of olefins as well.8b
In particular, alkyl chlorides are known to be somewhat
more difficult to reduce compared to other functional
groups, e.g. ketones, imines, and R,â-unsaturated es-
ters,1,10 and we wanted to examine the utility of this
protocol in the reduction of this more recalcitrant case.
† Go¨teborg University.
‡ Texas Tech University.
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10.1021/jo034173t CCC: $25.00 © 2003 American Chemical Society
Published on Web 05/15/2003
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J . Org. Chem. 2003, 68, 4870-4875