Oxidation of electron-deficient anilines by HOF. A route to nitro-containing compounds for molecular electronic devices

Article abstract of DOI:10.1021/ol006539j

(matrix presented) Nitroaromatic compounds for molecular electronic devices are prepared by the high-yielding oxidation of electron-deficient anilines using HOF generated in a fluorine-acetonitrile-water system.

Full text of DOI:10.1021/ol006539j

ORGANIC
LETTERS
2000
Vol. 2, No. 21
3405-3406
Oxidation of Electron-Deficient Anilines
by HOF. A Route to Nitro-Containing
Compounds for Molecular Electronic
Devices†
Shawn M. Dirk, Edward T. Mickelson, Jay C. Henderson, and James M. Tour*
Department of Chemistry and Center for Nanoscale Science and Technology, MS 222,
Rice UniVersity, 6100 Main Street, Houston, Texas 77005
tour@rice.edu
Received September 1, 2000
ABSTRACT
Nitroaromatic compounds for molecular electronic devices are prepared by the high-yielding oxidation of electron-deficient anilines using
HOF generated in a fluorine−acetonitrile−water system.
Recent advances in the field of molecular electronics have
shown that oligo(phenylene ethynylene)s containing nitro
groups are good candidates for electronic switching and
storage devices.1 Using functionalized anilines as an ad-
vanced starting point for the synthesis of these molecular
systems, we are relying on the oxidation the amine groups
to generate the types of nitro compounds (1-3) used for
molecular electronics.
transformation,2 oxidations of electron-deficient anilines are
more difficult to carry out, especially when the compounds
also contain alkyne moieties. Efforts to oxidize electron-poor
anilines generally involve extremely harsh conditions, which
may not be suitable for acetylenic groups.3
Our initial target for oxidation was 2,5-dibromo-4-nitro-
aniline (4) (Scheme 1). Attempts to oxidize this compound
Scheme 1
1: X, W ) NO2, Y ) H, Z ) phenylethynyl
2: X, Y ) NO2, W ) H, Z ) phenylethynyl
3: X, W ) NO2, Y ) H, Z ) phenyl
to give 5 using sodium perborate,4 or with an in situ
generation of dimethyldioxirane,5 met with little success.
While oxidation of electron-rich anilines has been studied
extensively and many methods exist to accomplish this
(2) (a) Howe, G. R.; Hiatt, R. R. J. Org. Chem. 1970, 35, 4007. (b)
Emmons, W. D. J. Am Chem. Soc. 1957, 79, 5528. (c) Suresh, S.; Joseph,
R.; Jayachandran, B.; Pol, A. V.; Vinod, M. P. Tetrahedron 1995, 51, 11305.
(3) Nielson, A. T.; Atkins, R. L.; Norris, W. P.; Coon, C. L.; Sitzmann,
M. E. J. Org. Chem. 1980, 45, 2341.
† Dedicated to Fred Wudl (UCLA) on the occasion of his 60th birthday.
(1) (a) Tour, J. M. Acc. Chem Res. In press. (b) Chen, J.; Reed, M. A.;
Rawlett, A. M.; Tour, J. M. Science 1999, 286, 1550. (c) Chen, J.; Wang,
W.; Reed, M. A.; Rawlett, A. M.; Price, D. W.; Tour, J. M. Appl. Phys.
Lett. 2000, 77, 1224.
(4) McKillop, A.; Tarbin, J. A. Tetrahedron 1987, 43, 1753.
10.1021/ol006539j CCC: $19.00 © 2000 American Chemical Society
Published on Web 09/27/2000

While 90% H2O2 in CF3COOH6 has been used to accomplish
similar oxidations, we elected to pursue other avenues before
attempting this route.
Table 1. Comparison of HOF to NaBO3‚H2O Oxidations
The formation of HOF from F2 + H2O has been studied
extensively by Appelman.7 Furthermore, the use of HOF/
CH3CN mixtures for the oxidation of organic species, and
aromatic amines in particular, has been reported previously.8,9
Thus, as an alternative to highly concentrated H2O2 oxida-
tions, we chose to use HOF as an oxidizer of our electron-
deficient aniline systems.
HOF was generated in situ by bubbling a 20% F2 in He
mixture10 through 62 mL of a 3% water in acetonitrile
mixture maintained at -20 °C. This in situ generation is
necessary due to the instability of HOF, even at these low
temperatures.7 After bubbling the F2/He mixture through the
water/acetonitrile mixture for 2 h at 50 sccm,11 the resulting
HOF/acetonitrile mixture was purged with He for several
minutes to eliminate any unreacted F2 (CAUTION).12 The
species to be oxidized (0.8-1.5 mmol) was then added to
the HOF/acetonitrile as a solution in either acetone (10 mL)
or ethyl acetate (10 mL). The oxidation reaction was allowed
to proceed for 5 min at -20 °C before being neutralized by
pouring it into saturated aqueous sodium bicarbonate (100-
200 mL). Standard workup and characterization followed.
Table 1 shows a comparison of yields for HOF and sodium
perborate4 reactions. In all cases, the HOF oxidations led to
higher yields in much shorter time periods than with the
sodium perborate oxidations. Note that the oxidation with
sodium perborate typically required 3 days to achieve the
yields shown in Table 1. Repeated attempts to oxidize 4 with
dimethyldioxirane5 were all unsuccessful.
strategies. Additionally, since acetate groups have been
shown to be inert toward HOF,8 we thought it possible that
1-3 could be made by directly oxidizing their aniline
counterparts, greatly simplifying our syntheses. Attempts to
carry out this oxidation remain elusive, perhaps due to the
ease by which the thiol is deprotected. Furthermore, sulfur
has been shown to be oxidized by HOF.13 HOF oxidations
also appear to be incompatible with aryl iodides, as evidenced
by our failed attempts to oxidize 4-iodoaniline.
In summary, we have found HOF to be an excellent
oxidizer for electron-deficient anilines. Furthermore, this is
the first reported example using HOF to oxidize electron-
deficient aniline systems containing alkynes. The high yields
of oxidized product, coupled with the extremely rapid
oxidation rates (relative to other methods in use), make HOF
a useful reagent for this purpose.
As HOF has turned out to be an excellent oxidizer for
these types of electron-deficient aniline systems, we are in
the process of trying modified oxidations of related com-
pounds in an effort to streamline our subsequent coupling
(5) Zabrowski, D. L.; Moormann, A. E.; Beck, K. R., Jr. Tetrahedron
Lett. 1988, 29, 4501.
(6) Emmons, W. D. J. Am. Chem. Soc. 1954, 76, 3470.
(7) (a) Appelman, E. H.; Thompson, R. C. J. Am. Chem. Soc. 1984, 106,
4167. (b) Poll, W.; Pawelke, G.; Mootz, D.; Appelman, E. H. Angew. Chem.,
Int. Ed. Engl. 1988, 27, 392. (c) Dunkelberg, O.; Haas, A.; Klapdor, M. F.;
Mootz, D.; Poll, W.; Appelman, E. H. Chem. Ber. 1994, 127, 1871.
(8) Kol, M.; Rozen, S. J. Chem. Soc., Chem. Commun. 1991, 8, 567.
(9) Appelman, E. H.; Dunkelberg, O.; Kol, M. J. Fluorine Chem. 1992,
56, 199.
(10) F2 is an extremely hazardous gas. Utmost care must be taken when
working with this chemical. For safety protocols, we suggest consulting
the Matheson Gas Data Book. We have both generated the F2/He mixtures
and purchased them as the mixture from Matheson. The latter procedure is
simpler.
Acknowledgment. We thank the Defense Advanced
Research Project Agency, the Office of Naval Research, the
Robert A. Welch Foundation (E.T.M.), and the NSF REU
summer program (J.C.H.).
1
Supporting Information Available: H NMR, 13C NMR,
IR, and mass spectroscopy data for all compounds. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(11) Standard cubic centimeter per minute (sccm).
(12) We did experience some explosions early on in our study which
we attributed to insufficient purging times. Presumably, unreacted F2 was
reacting violently with our material to be oxidized upon adding the aniline
to the HOF/acetonitrile mixture. By purging the reaction vessel for 15 min
with 100 sccm of He after the F2 + H2O f HOF + HF reaction was
complete, our explosion problem ceased.
OL006539J
(13) Dunkelberg, O.; Haas, A.; Klapdor, M. F.; Mootz, D.; Poll, W.;
Appelman, E. H. Chem. Ber. 1994, 127, 1871.
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Org. Lett., Vol. 2, No. 21, 2000