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Fluorous Chemistry and TechnologyЧA Symposium Showcases Ever-Broadening Frontiers.

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Meeting Reviews
Fluorous Chemistry and
Technology—A Symposium
Showcases Ever-Broadening
Frontiers**
John A. Gladysz*
Only an infinitesimal fraction of publications in chemistry directly spawn
new research fields. However, one
good case in point is the report by I.
Horvth and J. Rbai from 1994 that
coined the term “fluorous” and provided the first example of fluorous
biphasic catalysis.[1] Fluorous substances
are simultaneously hydrophobic and lipophobic, and researchers quickly recognized a variety of useful applications for
this phase-orthogonality, which in many
cases has the additional benefit of being
temperature-dependent. Indeed, biological and physical chemists had been
crafting and studying fluorous materials
for some time (cloaked in other nomenclature), and they found eager new partners among synthetic chemists who took
up the quest for novel recyclable catalysts and reagents, tagging strategies
for mixture synthesis and separations,
and other objectives.
Today, there are over 800 papers in
the literature that contain the word fluorous in the title or abstract. Along the
way, a company, “Fluorous Technologies
Incorporated” was founded (2000), and
a “Handbook of Fluorous Chemistry”
[*] Prof. Dr. J. A. Gladysz
Institut f-r Organische Chemie
Friedrich-Alexander-Universit/t
Erlangen-N-rnberg
Henkestraße 42, 91054 Erlangen
(Germany)
Fax: (+ 49) 9131-8526865
E-mail: gladysz@organik.uni-erlangen.de
[**] 1st International Symposium on Fluorous
Technologies in Bordeaux-Talence
(France), July 3–6, 2005
5766
has appeared (2004).[2] Clearly, eleven
years after the seminal paper, the time
for a meeting dedicated to this field
had arrived. Accordingly, over 75 scientists from Europe, Asia, and North
America made the trek to the scenic
venue of Bordeaux in early July. The
co-chairmen J.-M. Vincent (University
of Bordeaux) and R. H. Fish (Lawrence
Berkeley National Laboratory) expertly
handled the organizational details.
Despite the lure of the vineyards and
ch>teaux, science held the center stage
for three exciting days.
The opening talk by I. Horvth
(E?tv?s L@rand University, Budapest)
was both a retrospective and a prospective, and challenged the audience to find
ways of addressing the environmental
persistence associated with most
(CF2)n-based fluorous compounds. A
quest for fluorocarbon-degrading microorganisms was recommended. Subsequent presentations by G. Fontana
(Solvay Solexis, Milan) and J. Rbai
(E?tv?s L@rand University) highlighted
new types of oxygen-containing solvents, ponytails, and tags that are more
promising in terms of biodegradability,
and which have other attractive properties. Nonetheless, a recurrent theme
during the entire conference involved
fluorous-solvent-free protocols for the
recovery of fluorous catalysts and
reagents.
One novel approach was reported by
P. Pollet (Georgia Institute of Technology; collaborators: C. Eckert, C.
Liotta, and P. Jessop). She described
the use of CO2 pressure (sub-supercritical) as a “solubility switch” for fluorous
solutes in organic solvents (Figure 1).
Furthermore, these “gas expanded”
media could desorb fluorous rhodium
catalysts from fluorous silica gel, which
redeposited upon pressure release. M.
Figure 1. Use of CO2 pressure to homogenize
organic (toluene, above) and fluorous (FC-72,
below) liquid phases. A colored solute was
added to the latter. Note the progressive
volume increase. Fluorous solids can be
similarly solubilized in organic solvents.
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Contel (University of Zaragoza; collaborators: J.-M. Vincent and R. H. Fish)
and J. A. Gladysz; detailed new thermomorphic catalysts that could be used
under homogeneous conditions in
alkane, arene, or ether solvents at elevated temperatures, and can be recovered by a simple liquid–solid phase separation at lower temperatures.
New types of fluorous supports were
described, also with the idea of facilitating fluorous-solvent-free procedures.
These included fluorous zirconium
phosphates (E. Hope, University of Leicester), and garden-variety Teflon tape.
Both J. Nishikido (Noguchi Institute,
Tokyo) and A. Biffis (University of
Padua) reported on fluorous catalysts
that had been immobilized on fluorous
silica gel (main group or early transition
metal Lewis acids and dirhodium complexes); the latter presentation also
detailed protocols with fluorous solid
ion exchangers.
The use of fluorous tags in discovery
synthesis and strategic separations continues to undergo remarkable growth.
The state-of-the-art in parallel synthesis
was represented in talks by W. Zhang
(Fluorous Technologies) and D. Curran
(University of Pittsburgh). Attentiongetting developments included the
emergence of fluorous aryl sulfonates
(ArOSO2(CF2)7CF3) as versatile building blocks, and the simultaneous use of
fluorous and polyethylene-glycol-like
tags[3] that allow two-dimensional separations and enable much more complex
libraries to be processed (Figure 2). Fluorous protecting groups can often serve
as phase tags, as demonstrated in elegant syntheses of cyclic peptides by S.
Takeuchi (Niigata University). Heavy
fluorous tags that facilitate oligosaccharide and oligodeoxyribonucleotide syntheses were reported by T. Inazu
(Tokai University) and T. Wada (University of Tokyo).
A lecture by W. Bannwarth (University of Freiburg) showed how fluorous
tags can be used to immobilize DNA
fragments on fluorous silica gel, allowing the facile purification of synthetic
oligonucleotides. His data indicated a
high potential for the fixation of biomolecules on surfaces by fluorous–fluorous
interactions, and applications in molecular biology and proteomics are believed
to be just around the corner. Taking the
Angew. Chem. Int. Ed. 2005, 44, 5766 – 5768
Angewandte
Chemie
Figure 2. Double demixing of a sample with both fluorous and oligomeric ethylene glycol (OEG)
tags on a FluoroFlash PF-C8 HPLC column.
biological interface one step further, K.
Hatanaka (University of Tokyo) described fluorous-tagged glycoside primers
in which the saccharide chains can be
elongated by cellular enzymes. This
demonstrates for the first time that fluorous-tagged compounds can be taken up
in the cell to participate in the biosynthetic machinery without the need for
protection and deprotection steps usually required for chemical oligosaccharide synthesis.
J. Riess (UC San Diego and Alliance
Pharmaceutical) then shifted the theme
into the clinic—by no means a new
venue for fluorous chemistry—and
described the search for fluorous ultrasound contrast agents that optimize
microbubble lifetime. The physical–biochemical interface was also represented
in presentations by M. P. Krafft (Institut
Charles Sadron, Strasbourg) and V.
Percec (University of Pennsylvania).
The former detailed the unique properties associated with phospholipids that
contain
fluorocarbon–hydrocarbon
diblocks, and applications in lung surfactant therapy for neonatal respiratory
distress syndrome. The latter featured
wedge-shaped building blocks for supramolecular chemistry that contain fluorous domains, and self-assembly processes leading to channels that conduct
water and ions.
Additional self-assembly phenomena that involve “halogen bonding”
and lead to fluorous solid-state networks were described by P. Metrangolo
(Milan Polytechnic; collaborator: G.
Resnati). Many other types of phase
phenomena received attention, such as
design strategies for fluorous gelators,
Angew. Chem. Int. Ed. 2005, 44, 5766 – 5768
in the lecture of J.-L. Pozzo (University
of Bordeaux; collaborator: J.-M. Vincent). B.-J. Deelman (ARKEMA, The
Netherlands) reported new theoretical
approaches to optimizing fluorophilicities. M. F. Costa Gomes (University of
Clermont-Ferrand) explained how thermodynamicists rigorously measure and
model phase equilibria, particularly
with respect to gas solubilities in fluorous liquids. Differences between nonpolar, polar, and quadrupolar solutes
were emphasized. Unusually selective
brominations were effected by J. Iskra
(Jozef Stefan Institute, Ljubljana) by
layering reacting species (substrate and
Br2) on the opposite sides of a fluorocarbon interface, the so-called “phase vanishing” technique. Applications of reversible “phase switching” (Scheme 1)
were featured in posters from the J.-M.
Vincent research group.
Oxidations with molecular oxygen
were also well-represented. K. Pamin
(Polish Academy of Sciences, Krakow;
collaborator: J. Haber) disclosed new
families of fluorous porphyrin catalysts
for the oxidation of alkenes, and E.
Magnier (University of Versailles),
R. H. Fish and M. Contel detailed manganese, cobalt, and copper complexes of
cyclic polyamine ligands for the oxidation of alkanes, alkenes, alcohols, and
other functional groups. Another
approach, relayed by O. Holczknecht
(CNR Institute, Milan; collaborator: G.
Pozzi), used fluorous derivatives of
TEMPO in conjunction with NaOCl or
ArI(OAc)2.
Many additional advances in catalysis were reported. One new direction
involved the use of fluorous crown
ethers and phosphonium salts as phasetransfer catalysts, as recounted by A.
Stuart (Leicester). G. Pozzi described
highly enantioselective transition metal
catalysts based on heavy fluorous
chiral nitrogen donor ligands. The lecture of J. Otera (Okayama University)
featured fluorous organotin catalysts
that are unparalleled for transesterifications and that have a variety of unusual
phase properties. G. Vld (E?tv?s
L@rand University; collaborator: I.
Horvth) detailed improved routes to a
variety of fluorous phosphines that see
extensive use in catalysis.
At the banquet, I. Horvth and J.
Rbai were presented with the first
International Award for Fluorous Technologies, in recognition of their groundbreaking contributions noted above.
The program concluded with a free-spirited panel discussion. There was unanimous sentiment that fluorous chemistry
is a wide-open field that will continue
to rapidly grow and expand into new
applications. An important message for
readers is that there are abundant
Scheme 1. Reversible phase switching: a fluorous dicopper complex that binds pyridines and
extracts them into fluorous phases; applications in histamine detection were described.
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5767
Meeting Reviews
opportunities for newcomers. The
natives are friendly (not to mention hospitable), cooperation abounds, and
there is a conspicuous lack of turf battles. For those interested in climbing on
board, one opportunity will be the
second Symposium, which is scheduled
5768
www.angewandte.org
to be held in Kamakura, Japan in July
of 2007.
[2] Handbook of Fluorous Chemistry (Eds.:
J. A. Gladysz, D. P. Curran, I. T.
Horvth), Wiley-VCH, New York, 2004.
[3] C. S. Wilcox, S. Turkyilmaz, Tetrahedron
Lett. 2005, 46, 1827.
[1] I. T. Horvth, J. Rbai, Science 1994, 266,
72.
DOI: 10.1002/anie.200502639
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2005, 44, 5766 – 5768
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