Job/Unit: O43539
/KAP1
Date: 19-01-15 17:22:24
Pages: 6
FULL PAPER
DOI: 10.1002/ejoc.201403539
One-Pot Preparation of Alkyl Iodides from Esters by Indium-Catalyzed
Reductive Cleavage of a Carbon–Oxygen Bond
[a]
[a]
[a]
[a]
Norio Sakai,* Yohei Matsushita, Takeo Konakahara, Yohei Ogiwara, and
Keisuke Hirano[
b]
Keywords: Indium / Iodine / Esters / Nucleophilic substitution / Reduction / Polymers
We describe the indium-catalyzed reductive iodination of ali-
phatic and aromatic esters with iodine and 1,1,3,3-
alkyl groups, halogens, a hydroxy group, a thioether, and an
alkene moiety. Also, this procedure was applied to the cleav-
tetramethyldisiloxane (TMDS). This reducing procedure ac- age of carbon–oxygen bonds in acrylate polymers.
commodates a variety of esters, including esters containing
ing system did not give any reaction with an ester.[6] In a
breakthrough for catalytic conversion, Baba et al. achieved
the catalytic reductive chlorination of ketones or aldehydes
Introduction
The synthesis of alkyl halides has been widely investi-
gated in organic chemistry, because they are important and
central intermediates for a variety of further molecular
with Me SiHCl (chlorodimethylsilane) and a catalytic
2
[7]
amount of In(OH)3. We also reported the indium-cata-
[
1]
transformations. In particular, in the past two decades,
the reductive halogenation of a carbonyl compound with
an appropriate halide source in the presence of a relatively
mild reducing reagent, a hydrosilane, has been one of the
most straightforward approaches to the preparation of alkyl
halides. As an example of a reductive halogenation of carb-
onyl compounds with superstoichiometric amounts of a
catalyst in the presence of a hydrosilane, Palomo et al. re-
ported the TMSCl-promoted (TMS = trimethylsilyl) re-
ductive iodination of aldehydes with sodium iodide in the
lyzed reductive bromination and iodination of carboxylic
acids with TMDS and halogen sources, such as trimethyl-
silyl bromide (TMSBr) or I , to give alkyl bromides or iod-
2
[8–10]
ides.
However, reductive halogenation, and in particu-
lar the direct iodination of esters with a hydrosilane, has
not been extensively examined before now.
Previously, we have shown that the desired reductive io-
dination of esters could be accomplished simply by the ad-
dition of iodine to a reducing catalytic system that con-
[8a]
verted esters into ethers.
However, the substrates exam-
[
2]
presence of TMDS (1,1,3,3-tetramethyldisiloxane). Also,
a reductive iodination of aldehydes and ketones with excess
amounts of diiodosilane (SiH I ) leading to the correspond-
ined there were limited to only two examples. Because esters
are commonly used as protecting groups for carboxylic
acids in natural product synthesis, their synthetic utility is
extremely high. Thus, we systematically investigated the in-
dium-catalyzed reductive iodination of a variety of esters
2
2
ing alkyl iodides has been disclosed by Keinan and cowork-
ers.[ Moreover, Das and coworkers reported a reductive
bromination of aldehydes using a combination of PMHS
3]
with TMDS and I . In this paper, we report the full details
2
(
(
polymethylhydrosiloxane) and bromide sources, such as
of this study, along with the results of the application of
this reducing reagent system to an effective cleavage of ester
moieties in a polymer chain.
bromodimethyl)sulfonium bromide or NBS (N-bromosuc-
[4]
cinimide), without a metal catalyst. In this context,
Kabalka reported a reductive preparation of benzyl brom-
ides from aldehydes and alkylboron dibromides, but this
method was limited to aromatic aldehydes.[ Periasamy et
al. found that a BH /I /diethylaniline system produced a re-
5]
Results and Discussion
3
2
ductive iodination of carbonyl compounds, but this reduc-
On the basis of our previous work, we examined the opti-
mal conditions for the direct iodination of methyl phenyl-
acetate as a model substrate (Table 1). Initially, the effect of
a hydrosilane was investigated. For instance, when an ester
and molecular iodine were treated with 6 equiv. (Si–H) of
[
[
a] Department of Pure and Applied Chemistry, Faculty of Science
and Technology, Tokyo University of Science (RIKADAI),
Noda, Chiba 278-8510, Japan
E-mail: sakachem@rs.noda.tus.ac.jp
b] Functional Base Products Sector, Nitto Denko Corporation,
Toyohashi, Aichi 441-3194, Japan
TMDS in CHCl
3
at 60 °C, the reaction was complete within
1
h to give the corresponding alkyl iodide (i.e., 1a) in quan-
titative yield (Table 1, Entry 1). When the amount of hydro-
silane in the reaction was decreased to 4 equiv. (Si–H) per
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201403539.
Eur. J. Org. Chem. 0000, 0–0
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