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DOI: 10.1002/cctc.201300774
Oxidative Breakdown of Iodoalkanes to Catalytically
Active Iodine Species: A Case Study in the
a-Tosyloxylation of Ketones
Wusheng Guo,[a] Oriol Vallcorba,[b] Adelina Vallribera,[a] Alexandr Shafir,*[a] Roser Pleixats,*[a]
and Jordi Rius[b]
Catalysis of the oxidative processes by iodoarenes has become
a promising direction in synthesis. The mechanism, involving
the well-known isolable hypervalent iodine species, is generally
limited to aromatic iodides, since the corresponding aliphatic
species are normally highly unstable. Nevertheless, in this work
catalytic amount of several primary, secondary or tertiary io-
doalkanes were found to promotes the a-tosyloxylation of
a range of ketones with RSO3H, including aliphatic sulfonates.
Scheme 1. Hypervalent iodine in the a-tosyloxylation of ketones.
Ox=oxidant.
The process, was found to proceed through the oxidative
breakdown of the iodoalkane to an inorganic catalytic species
ꢀ
(likely IOꢀ or IO2 ), thus falling within the previously described
catalysis using molecular iodine or inorganic iodides. The cata-
lyst eventually becomes deactivated through the precipitation
of an iodine overoxidation product, the structure of which was
solved ab initio from the powder diffraction data as a hitherto
unreported phase of the iodic acid (HIO3).
that, in principle, ArI can be recovered and reused, variants of
such processes have been developed (including asymmetric
versions) following the early reports[4] by the groups of Ochiai
and Kita, whereby ArI was used as a catalyst in the presence of
a cheaper terminal oxidant.[5] In these cases, the catalytic cycle
involves the in situ regeneration of the organoiodine(III) re-
agent (Scheme 1b). The burgeoning field of hypervalent iodine
catalysis was recently the subject of two Minireviews.[5d,e]
In light of the close relationship between hypervalent iodine
catalysis and classical stoichiometric applications, it is not sur-
prising that the field has been limited to iodoarenes. After all,
with the exception of some very bulky or heavily fluorinated
derivatives, hypervalent iodoalkanes are notoriously unsta-
ble,[1b] which makes their use in stoichiometric applications un-
feasible. Indeed, upon generation, the ꢀIX2 moiety in such spe-
cies has a leaving group ability that is orders of magnitude
higher than that of an iodide.[6] During the course of our own
investigations into immobilized organoarenes,[7] we observed
that the products of the oxidative breakdown of certain iodoal-
kanes were still catalytically active. We wondered whether
such activity paralleled the catalysis by simple molecular
iodine and inorganic iodides that was reported recently.[8] We
also became interested in the catalyst deactivation pathways
frequently suffered by such systems.
Iodoarenes are known to undergo oxidation at iodine to give
the corresponding hypervalent iodine reagents. In particular,
partial oxidation of ArI gives rise to highly reactive T-shaped
ArIXX’ species, exemplified by PhI(OAc)2 and PhI(OH)(OTs)
(Koser reagent, Ts=para-toluenesulfonyl).[1] In synthesis, such
a reagent may act as an oxidant capable of delivering one of
the Xꢀ fragments to the product, such as in the oxidative
a-tosyloxylation of aliphatic ketones, which usually proceeds
via an iodonium enolate intermediate (Scheme 1a for a mecha-
nism proceeding through a C-enolate; alternative paths involv-
ing iodonium O-enolates have also been invoked).[2] This kind
of oxidative CꢀH functionalization provides rapid access to val-
uable building blocks for the construction of thiazoles, ox-
azoles, selenazoles, and imidazoles, among others.[3] Given
[a] W. Guo, A. Vallribera, A. Shafir, R. Pleixats
Wusheng Guo, Prof. Adelina Vallribera,
Dr. Alexandr Shafir, Prof. Roser Pleixats
Department of Chemistry
To confirm the catalytic activity of the species obtained
upon the in situ oxidative decomposition of iodoalkanes, the
performance of 2-iodobutane was compared to that of iodo-
benzene in the tosyloxylation of propiophenone by following
a process reported by Togo et al. that involved the employ-
ment of meta-chloroperbenzoic acid (mCPBA) as the terminal
oxidant.[5b] Indeed, the use of a catalytic amount of PhI
(10 mol%) gave, as expected, a 75% yield of the a-tosyloxylat-
ed product after 10 h at 658C. Under the same conditions,
a 10 mol% loading of sBuI also proved active, and it afforded
a respectable 65% yield of the product (Scheme 2), albeit with
Universitat Autꢀnoma de Barcelona
08193-Cerdanyola del Vallꢁs, Barcelona (Spain)
Fax: (+34)93-5812477
[b] O. Vallcorba, J. Rius
Dr. Oriol Vallcorba, Prof. Jordi Rius
Institut de Ciꢁncia de Materials de Barcelona, CSIC
Campus de la UAB, 08193-Bellaterra, Barcelona (Spain)
Supporting information for this article is available on the WWW under
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 468 – 472 468