Preparation of the title compound (2) by use of Stille couplings and a
Krohnke pyridine synthesis is described. By application of the Stille
coupling reaction, preparation and functionalization of quater- and q
uinquepyridines 26, 27, and 28 were achieved. Elaboration of quinquepy
ridine 27 to the pyridinium salt 30 bearing a protected enal allowed f
or the synthesis of 2 by a one-pot deprotection/Krohnke reaction in ni
ne steps from 4,4'-bipyridine. Use of the Krohnke pyridine synthesis h
as been applied to prepare sexipyridine dibromide 19, but attempts to
induce a macrocyclization via metal-mediated (Pd/Ni/Cu) aryl-aryl coup
ling procedures proved unsuccessful. Acetylene-bridged sexipyridines 3
a and 3b incorporating 2,2'-bipyridine units proved to be inaccessible
via sp-sp(2) or sp-sp coupling protocols.