Scalable, Chromatography-Free Synthesis of Alkyl-Tethered Pyrene-Based Materials. Application to First-Generation “Archipelago Model” Asphaltene Compounds

In
this paper, we report a highly efficient, scalable approach
to the total synthesis of conformationally unrestricted, electronically
isolated arrays of alkyl-tethered polycyclic aromatic chromophores.
This new class of modular molecules consists of polycyclic aromatic
“islands” comprising significant structural fragments
present in unrefined heavy petroleum, tethered together by short saturated
alkyl chains, as represented in the “archipelago model”
of asphaltene structure. The most highly branched archipelago compounds
reported here share an architecture with first-generation dendrimeric
constructs, making the convergent, chromatography-free synthesis described
herein particularly attractive for further extensions in scope and
applications to materials chemistry. The syntheses are efficient,
selective, and readily adaptable to a multigram scale, requiring only
inexpensive, “earth-abundant” transition-metal catalysts
for cross-coupling reactions and extraction and fractional crystallization
for purification. This approach avoids typical limitations in cost,
scale, and operational practicality. All of the archipelago compounds
and synthetic intermediates have been fully characterized spectroscopically
and analytically. The solid-state structure of one archipelago model
compound has been determined by X-ray crystallography.