Convenient access to readily soluble symmetrical dialkyl-substituted α-oligofurans

An expedient approach to the synthesis of well soluble symmetrical dialkyl-substituted α-oligofurans containing up to 8 π-conjugated furan heterocycles is reported. An ultimate symmetry and high solubility of these α-oligofurans were guaranteed using the 3,3'-diheptyl-2,2'-bifuran core and its symmetrical elongation through Suzuki-Miyaura or Stille cross-couplings. 3,3'-Diheptyl-2,2'-bifuran was prepared from 2,2'-bifuran-3,3'-dicarbaldehyde by the Wittig olefination and subsequent Pd/C-catalyzed transfer hydrogenation. The most appropriate access to 2,2'-bifuran-3,3'-dicarbaldehyde was achieved through a regioselective lithiation of 3-furanaldehyde acetal followed by CuCl2-induced homocoupling and deprotection. Single crystal X-ray analysis of 2,2'-bifuran-3,3'-dicarbaldehyde revealed anti-arrangement of the furan rings in planar molecules and an unexpected tight herringbone-type packing in crystals.