Activation of alkanes upon reaction with PhI(OAc)2-I2

Article abstract of DOI:10.1002/1521-3773(20020715)41:14<2556::AID-ANIE2556>3.0.CO;2-C

You can also choose from alkanes! Either mono- or bifunctional iodo derivatives can be prepared from alkanes (see scheme) in an efficient and selective manner by using PhI(OAc)₂, I₂, and an alcohol.

Full text of DOI:10.1002/1521-3773(20020715)41:14<2556::AID-ANIE2556>3.0.CO;2-C

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[3] V. Balzani, A. Credi, F. M. Raymo, J. F. Stoddart, Angew. Chem. 2000,
112, 3484 3530; Angew. Chem. Int. Ed. 2000, 39, 3348 3391.
[4] J.-P. Sauvage, Acc. Chem. Res. 1998, 31, 611 619.
I
OAc
I
PhI(OAc)2, I2
PhI(OAc)2, I2
tBuOH, 40°C
tBuOH, RT, hν
n
n
n
[5] L. Zelikovich, J. Libman, A. Shanzer, Nature 1995, 374, 790 792.
¬
[6] T. R. Ward, A. Lutz, S. P. Parel, J. Ensling, P. G¸tlich, P. Buglyo, C.
3
1
2
Orvig, Inorg. Chem. 1999, 38, 5007 5017.
Scheme 1. Photochemical and thermal reactivity of hydrocarbons with
PhI(OAc)2 I2.
[7] V. Amendola, L. Fabbrizzi, C. Mangano, P. Pallavicini, A. Perotti, A.
Taglietti, J. Chem. Soc. Dalton Trans. 2000, 185 189.
[8] P. Gans, A. Sabatini, A. Vacca, Talanta 1996, 43, 1739 1753.
[9] V. Amendola, C. Brusoni, L. Fabbrizzi, C. Mangano, H. Miller, P.
Pallavicini, A. Perotti, A. Taglietti, J. Chem. Soc. Dalton Trans. 2001,
3528 3533.
[10] E. V. Anslyn, Acc. Chem. Res. 2001, 34, 963 972.
[11] L. Fabbrizzi, A. Leone, A. Taglietti, Angew. Chem. 2001, 113, 3156
3159; Angew. Chem. Int. Ed. 2001, 40, 3066 3069.
into the corresponding iodinated derivatives, under irradi-
ation conditions (2 Â 100 W lamps), in high yield, under
relatively mild conditions, and in rather short reaction times.
In addition, toluene (1e) also gives benzyliodide (2e) as the
sole reaction product.[8] Linear alkanes react affording
mixtures of monoiodinated derivatives in good combined
yield, showing high selectivity for secondary positions (Ta-
ble 1).
[12] V. Balzani, V. Polin, E. Schmohel, Synthesis 1998, 3, 321 324.
An outstanding feature of this iodine(iii)-induced activation
of alkanes was observed when carrying out the reactions
under thermal instead of photochemical conditions.[9] In this
case, bifunctional compounds 3 were obtained as major, or
even single, reaction products (Scheme 1, Table 2). The global
Activation of Alkanes upon Reaction with
PhI(OAc)2 I2**
¬
¬
Jose Barluenga,* Francisco Gonzalez-Bobes, and
¬
¬
Jose M. Gonzalez
Table 1. Synthesis of iodoalkanes 2 from alkanes 1.[a]
Entry Alkane (1)
Concentra- Reaction Product (2)
Yield
[%][c]
Carbon hydrogen-bond-activation reactions are challeng-
ing processes in organic synthesis.[1] Halogenation reactions
have been thoroughly studied and widely practiced and
provide a simple and classic way to functionalize hydro-
carbons.[2] However, the iodination of alkanes has been a
particularly elusive reaction and still remains as an active
research area.[3] The endothermic nature of the overall
process has been invoked to explain the failure of a radical-
chain approach to accomplish this reaction.[4, 5] While per-
forming b-scission reactions of cycloalkanols,[6] we noticed
that (diacetoxyiodo)benzene [PhI(OAc)2][7] gave rise to a
mixture of compounds, where iodocyclohexane (2b) was
found as the major product, resulting from an activation of the
cyclohexane used as solvent.
tion [m][b]
time [h]
I
1
0.04
1.5
98
97
92
1a
2a
2b
I
2
0.04
0.02
4
6
1b
I
3
1c
2c
I
Herein we report new approaches to selectively produce
either iodoalkanes 2 or 1-acetoxy-2-iodocycloalkanes 3 from
readily available hydrocarbons 1. The products 2 and 3 arise
4
0.02
0.02
8
1
85[d]
À
from single and double formal C H-bond-activation reac-
1d
2d
tions, respectively. This unique reaction manifold can be
tuned by treating alkanes 1 with PhI(OAc)2, iodine (I2), and
tert-butylalcohol (tBuOH) simply by using photochemical or
thermal conditions (Scheme 1).
I
5
92[e]
2e
1e
Our initial studies with cyclohexane (1b) showed that the
presence of an alcohol is necessary for an efficient alkane
activation. tBuOH was found to be the most effective of all
the alkanols tested. Thus, cycloalkanes were cleanly converted
I
2f
6
0.04
4
85[f]
2g
I
1f
I
¬
¬
[*] Prof. Dr. J. Barluenga, F. Gonzalez-Bobes, Dr. J. M. Gonzalez
¬
Instituto de QuÌmica Organometalica ™Enrique Moles∫
Unidad Asociada al C.S.I.C.
Universidad de Oviedo
33071 Oviedo (Spain)
Fax : (‡34)98-510-3450
2h
[a] All reactions performed with the following stoichiometry: PhI(OAc)2
(1 equiv), I2 (1.1 equiv), tBuOH (1 equiv). The alkane was used as solvent.
[b] Referred to iodine. [c] GC yield unless otherwise specified. [d] Compound 2d
was isolated in 80% yield upon column chromatography with n-hexane as eluant.
E-mail: barluenga@sauron.quimica.uniovi.es
[**] This research was supported by DGES (Grant PB97-1271). F.G.-B. [e] Determined by 1H NMR spectroscopy. [f] Proportions of isomers (determined
thanks FICYT for a fellowship.
by GC): 2g:2h ˆ 1:1.5, 2 f:2g ‡ 2h ˆ 1:15.
2556
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Angew. Chem. Int. Ed. 2002, 41, No. 14

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Table 2. Synthesis of 1-acetoxy-2-iodocycloalkanes 3 from cycloalkanes
1.[a]
acetylhypoiodite formed ™in situ∫ would account for the
observed trans diastereoselectivity in which 1-acetoxy-2-
iodocycloalkanes 3 are obtained (Scheme 2).
[b]
Entry Cycloalkane (1) PhI(OAc)2
Product (3)
Yield [%][c]
In conclusion, a new method amenable for the selective
mono- and bifunctionalization of alkanes has been described,
under mild, simple and efficient conditions. The reported
examples leading to the synthesis of bifunctional derivatives
constitute the first diastereoselective vicinal activation reac-
tion of a hydrocarbon. Further investigations concerning the
interaction of iodine(iii) species with alkanes are in progress.
I
1
2
3.5
2
71
OAc
1a
1b
3a
I
92
47
OAc
3b
OAc
ExperimentalSection
I
3
4
2
3
All reactions were carried out under a positive pressure of nitrogen.
Alkanes 1 were dried under reflux over sodium, distilled under nitrogen,
and purged with argon to remove oxygen traces prior to their use.
1c
3c
3b: Iodine (1.1 mmol, 280 mg) and tBuOH (2 mmol, 0.2 mL) were
sequentially added to a suspension of PhI(OAc)2 (2 mmol, 644 mg) in 1b
(25 mL). The resulting mixture was stirred at 408C (bath temperature) for
14 h. The mixture was allowed to cool and then quenched with sodium
thiosulfate (5% solution in water, 25 mL). The mixture was transferred to a
separating funnel, the aqueous layer was reserved and the organic one
distilled under reduced pressure to recover excess 1b. The distillation
residue was diluted with diethyl ether (20 mL), mixed with the previously
reserved aqueous layer and extracted. The aqueous phase was further
extracted with diethyl ether (3 Â 20 mL). The combined organic layers were
washed with NaOH (5% solution in water, 2 Â 40 mL), brine (2 Â 40 mL),
and dried over sodium sulfate. The solvent was removed at reduced
pressure. The resulting liquid was further purified by column chromatog-
raphy (hexane/ethyl acetate 25/1) to give 3b as a pale yellow liquid (245 mg,
92%).
I
65
OAc
1d
3d
[a] All reactions performed with 1.1 equivalent of I2. The alkane was used
as solvent. Reaction time 14 h. [b] Molar ratio [PhI(OAc)2]:tBuOH ˆ 1:1.
[c] Isolated yield referred to I2.
transformation formally represents a direct and unprecedent-
ed diastereoselective 1,2-functionalization of an alkane. All
the reactions were performed under ambient light at 408C
(bath temperature) and different amounts of PhI(OAc)2 were
required to obtain fair to excellent yields of compounds 3.
When cycloheptane (1c) was employed as substrate in the
reaction, a ring contraction was observed, affording the
unexpected methylcyclohexane derivative 3c in 47% yield
(Table 2).
For the basis of a mechanistic proposal, an initial formation
of intermediate species of hypoiodite nature, which result
from the interaction of the PhI(OAc)2 I2 system and an
alcohol, is widely accepted.[10] Thus, generation of tert-
butylhypoiodite (tBuOI) could be reasonably invoked to
promote the synthesis of the observed iodoalkanes 2 by a
radical-chain mechanism.[4] The formation of the bifunctional
derivatives 3 could be explained assuming a ligand transfer
from PhI(OAc)2 to the iodoalkane 2 previously formed,[11, 12]
which gives rise to (diacetoxyiodo)alkane species (A;
Scheme 2), which are in general unstable. An elimination
reaction to generate an olefin (B), followed by addition of the
Received: February 18, 2002
Revised: March 27, 2002 [Z18726]
[1] For leading references: a) Activation of unreactive bonds and organic
synthesis (Ed.: S. Murai), Springer, Berlin, 1999; b) C. Jia, T.
Kitamura, Y. Fujiwara, Acc. Chem. Res. 2001, 34, 633 639; c) W. D.
Jones, Science 2000, 287, 1942 1943; d) G. Dyker, Angew. Chem.
1999, 111, 1808 1822; Angew. Chem. Int. Ed. 1999, 38, 1698 1712;
e) S. S. Stahl, J. A. Labinger, J. E. Bercaw, Angew. Chem. 1998, 110,
2298 2311; Angew. Chem. Int. Ed. 1998, 37, 2180 2192.
[2] a) For a review: E. S. Huyser in The Chemistry of the Carbon-Halogen
Bond, Part 1 (Ed.: S. Patai), Wiley, New York, 1973, pp. 549 607;
b) For a list of reagents, with references, see: R. C. Larock in
Comprenhensive Organic Transformations, VCH, New York, 1989,
pp. 311 313.
[3] a) P. R. Schreiner, O. Lauenstein, E. D. Butova, A. A. Fokin, Angew.
Chem. 1999, 111, 2956 2958; Angew. Chem. Int. Ed. 1999, 38, 2786
2788; b) O. Lauenstein, A. A. Fokin, P. R. Schreiner, Org. Lett. 2000,
2, 2201 2204; c) A. A. Fokin, O. Lauenstein, P. A. Gunchenko, P. R.
Schreiner, J. Am. Chem. Soc. 2001, 123, 1842 1847.
[4] D. D. Tanner, G. C. Gidley, J. Am. Chem. Soc. 1968,
90, 808 809.
[5] L. Liguori, H.-R. Bj˘rsvik, A. Bravo, R. Fontana, F.
Minisci, Chem. Commun. 1997, 1501 1502.
I
PhI(OAc)2, I2
(via tBuOI)
tBuOH
¬
[6] J. Barluenga, F. Gonzalez-Bobes, S. R. Ananthoju,
1b
2b
¬
M. A. GarcÌa-MartÌn, J. M. Gonzalez, Angew. Chem.
2001, 113, 3491 3494; Angew. Chem. Int. Ed. 2001,
40, 3389 3392.
[7] For reviews on (diacetoxyiodo)benzene, see: a) H.
Togo, M. Katohgi, Synlett 2001, 565 581; b) P. J.
Stang, V. V. Zhdankin, Chem. Rev. 1996, 96, 1123
1178; c) A. Varvoglis, Chem. Soc. Rev. 1981, 10, 37 7
407.
OAc
I
I
I
PhI(OAc)2
- PhI
OAc
+ AcOI
- AcOH
OAc
H
2b
A
B
3b
[8] To our knowledge a direct and efficient iodination of
toluene is almost without precedent. Previously, a
Scheme 2. Proposed reaction mechanism.
Angew. Chem. Int. Ed. 2002, 41, No. 14
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1433-7851/02/4114-2557 $ 20.00+.50/0
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NMR spectroscopy[16] and in situ SAXS measurements.[9, 10]
These studies suggest that the aggregation of the primary units
is an important step in the nucleation process, and that it
depends on many factors, such as the alkalinity of the
precursor solution, the type of silica source, and aging time.
However, structural information regarding the initial frame-
work species assembled from molecular precursors is still very
limited.
34% yield was reported in the preparation of 2e from 1e and tBuOCl/
HgI2, see reference [4].
[9] None of the bifunctional derivatives 3 were observed when perform-
ing the reaction under photochemical conditions, even using an excess
of PhI(OAc)2. For instance, when 1a was treated with PhI(OAc)2
(2 equiv), I2 (1.1 equiv), and tBuOH (2 equiv) under the influence of
light at room temperature, only the formation of 2a was observed
after 8 h, the excess PhI(OAc)2 was recovered.
[10] For recent evidence: a) J. Madsen, C. Viuf, M. Bols, Chem. Eur. J.
¬
2000, 6, 1140 1146; b) J. L. Courtneidge, J. Lusztyk, D. Page,
In previous studies we have investigated the nucleation and
growth processes of zeolites A (LTA) and Y (FAU) (using the
tetramethylammonium (TMA) ion) by HRTEM.[11] It was
observed that the crystalline structures nucleate in amorphous
gel aggregates existing in the colloidal aqueous solutions, and
that these gel aggregates are completely converted into
crystalline products after extended reaction times.
Tetrahedron Lett. 1994, 35, 1003 1006.
[11] J. Gallos, A. Varvoglis, J. Chem. Soc. Perkin Trans. 1 1983, 1999 2002.
[12] We have observed that 2b was cleanly converted into 3b under
comparable thermal conditions, thus providing additional evidence for
the proposed mechanism.
Herein, we examine the formation of the colloidal pre-
cursor solution and the crystal growth of Si-MFI by in situ
DLS combined with 29Si solid-state NMR spectroscopy,
HRTEM, and other techniques.
A clear precursor solution, prepared for the synthesis of Si-
MFI zeolite, was aged at room temperature on an orbital
shaker for 24 h (A24h) to 30 days (A30d). Samples were
heated to 908C and then examined by in situ DLS measure-
ments. A major advantage of the in situ study is the
elimination of invasive procedures that may modify the
crystallization process of the Si-MFI zeolite. Figure 1 shows
Mechanism of the Transformation of Silica
Precursor Solutions into Si-MFI Zeolite
Svetlana Mintova,* Norman H. Olson, J¸rgen Senker,
and Thomas Bein*
Dedicated to Professor Jens Weitkamp
on the occasion of his 60th birthday
The mechanisms governing the transformation of precursor
solutions or gels into zeolitic materials are still not fully
understood.[1 5] The scientific challenge is to understand these
mechanisms to enhance synthetic control for the design of
new zeolite structures, and for the preparation of novel
assemblies such as films, monoliths, and functional nano-
structures.
The crystal growth of silicalite-1–a microporous poly-
morph with MFI topology–has received considerable atten-
tion because it can serve as model system for a fundamental
understanding of the mechanism of zeolite formation.[6 9] The
nanoscale organosilicate clusters in the precursor solutions
used for the synthesis of nanosized MFI-type zeolite have
been observed with techniques such as dynamic light scatter-
ing (DLS),[6] nuclear magnetic resonance (NMR),[7, 8] small-
angle X-ray scattering (SAXS),[9, 10] and high-resolution trans-
Figure 1. DLS data of TPA-silica precursor solutions: a) aged for 24 h
(A24h) at room temperature, and after heating for b) 4 min (A24hH4m)
and c) 6 h (A24hH6) at 908C. The distribution function analysis (DFA) is
displayed as scattering intensity per unweighted particle size classes (I ˆ
scattering intensity).
13]
mission electron microscopy (HRTEM).[11 It appears that
nanoscale species with a size of about 3 4 nm are formed in
the precursor solutions before long-range order is establish-
ed.[14, 15] Additional information about the structure, particle
size, and shape of the silicate species in the MFI-precursor
solutions containing organic additives was obtained by using
the particle size (r) distribution of the precursor solution aged
for 24 h (A24h), and for samples heated to 908C for 4 min
(A24hH4m) and 6 h (A24hH6). Prior to heating, the presence
of sub-colloidal particles with sizes in the range of about 1
10 nm is observed in the A24h sample. These particles are
shown to be amorphous by X-ray diffraction. After hydro-
thermal treatment of solution A24h for only 4 min (Fig-
ure 1b), an increase of the scattering intensity is observed,
due to the presence of a second generation of particles with
mean radius of about 15 nm (sample A24hH4m; Figure 1b).
The two particle populations present in these samples are
quite diverse, the first having a mean radius of about 2.3 nm
and the second having a radius of about 15 nm. By increasing
the heating time from 4 min to 6 h (sample A24hH6; Fig-
ure 1c), the peak indicative for the presence of sub-colloidal
[*] Dr. S. Mintova, Prof. T. Bein, Dr. J. Senker
Department of Chemistry
University of Munich
Butenandtstrasse 5 11, 81377 Munich (Germany)
Fax : (‡49)89-2180-7622
E-mail: svetlana.mintova@cup.uni-muenchen.de
tbein@cup.uni-muenchen.de
Dr. N. H. Olson
Department of Biology
Purdue University
West Lafayette, IN 47907 (USA)
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Angew. Chem. Int. Ed. 2002, 41, No. 14