ORGANIC
LETTERS
2011
Vol. 13, No. 7
1618–1621
Multiple Sonogashira Reactions of
Polychlorinated Molecules. Synthesis and
Photophysical Properties of the First
Pentaalkynylpyridines
Peter Ehlers,†,‡ Antje Neubauer,§ Stefan Lochbrunner,§ Alexander Villinger,† and
Peter Langer*,†,‡
€
Institut fu€r Chemie, Universitat Rostock, Albert-Einstein-Str. 3a, 18059 Rostock,
€
Germany, Leibniz-Institut fu€r Katalyse an der Universitat Rostock e. V., Albert-
€
Einstein-Str. 29a, 18059 Rostock, Germany, and Institut fu€r Physik, Universitat
€
Rostock, Universitatsplatz 3, 18051 Rostock, Germany
Received January 5, 2011
ABSTRACT
Hitherto unknown pentaalkynylpyridines have been prepared in high yields by Sonogashira cross-coupling reactions of pentachloropyridine.
Their photophysical properties were studied and compared to those of penta- and hexaalkynylbenzenes which were efficiently prepared by the
first Sonogashira reactions of pentachlorobenzene and hexachlorobenzene. The pentaalkynylpyridines show promising fluorescence properties
because of their high quantum yields.
In recent years, much attention has been devoted to
polyethynylated carbon-rich molecules, because of their
extended conjugated π-systems.1 Especially polyethynyl-
benzenes (PEBs) have potential as liquid crystals,2 core
structures for dendritic molecules,3 as nonlinear optical
materials,4 or as building blocks for 2D carbon networks,5
which could have a high degree of hardness and thermal
stability. Hexaalkynylbenzenes have been prepared by
Diels-Alder reactions6 and by palladium catalyzed cross-
coupling reactions of hexabromobenzene or hexaiodo-
benzene.7 These syntheses have the drawback of long
†
€
Institut f€ur Chemie, Universitat Rostock.
‡
§
€
Leibniz-Institut f€ur Katalyse an der Universitat Rostock e. V.
€
Institut f€ur Physik, Universitat Rostock.
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10.1021/ol2000183
Published on Web 02/28/2011
2011 American Chemical Society