Iterative Synthesis of Fused Oligofurans

Significance

The authors present an elegant three-step sequence to append fused furan rings onto the olefin of unsaturated furan systems. The sequence can then be repeated, eventually arriving at highly symmetric oligomeric polyfurans. The sequence of reactions, which is performed on both sides of the symmetric molecule concurrently, consists of a copper-catalyzed cyclopropanation using ethyl diazoacetate, followed by reduction of the resultant ester to the primary alcohol which is then oxidized using IBX. The oxidation presumably results in the formation of an aldehyde which then undergoes an immediate rearrangement to the furan system. The authors describe the intermediate as having a ”push-pull" substitution pattern on the cyclopropane, with the electrons of the furan forcing to open the cyclopropane followed by back-attack via the oxygen atom of the enolate providing the furan product.