To
synthesize meso-ethynylene-conjugated porphyrin
arrays, the Sonogashira cross-coupling reaction is straightforward
to construct the C(sp)–C(sp2) bonds, but the reaction
is often accompanied by side reactions such as the Glaser homocoupling.
The rate-determining oxidative addition step results in the unexpected
kinetic competition with the Glaser homocoupling, which is desired
to be circumvented. We here propose two sets of improved strategies
for the synthesis of arylene–ethynylene-linked porphyrin arrays
from the meso-brominated porphyrin and alkynes. First,
we explored the solvent-modulated approach employing dichloromethane
as the reaction solvent to minimize the formation of the copper acetylide
dimer as the intermediate for the Glaser homocoupling, while the scope
of the approach is limited. Subsequently, we have developed the trimethylsilanolate-promoted
Hiyama-type approach that activates alkynyl trimethylsilanes (TMSs)
by use of potassium trimethylsilanolate under amine-free conditions.
The latter approach is advantageous not only in skipping the preprotodesilylation
of the TMS group but also in achieving an excellent isolated yield.
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