Syntheses of macrocyclic oligoesters from 5‐hydroxymethyl‐2‐furancarboxylic acid

New macrocyclic oligoesters 3a – d, containing furan rings, were synthesized by condenzation of 5‐hydroxymethyl‐2‐furancarboxylic acid (1) using 2‐chloro‐1‐methylpyridinium iodide (2) as condensing agent. Water‐insoluble products were separated by GPC and characterized by IR, NMR, MS, and elemental analysis. The product distribution was found to depend remarkably on the reaction conditions. When the mole ratio of 2 to 1 was 1,65 in pyridine was solvent, the cyclic trimer 3a and the tetramer 3b were obtained, both in more than 30% yield. In addition higher cyclic oligoesters (3c – d), linear oligoesters (5b – e), and the polyester (6) were formed. When a large amount of tributylamine was used as a scavenger of hydrogen halides in toluene as solvent, the polyester was the main product. Condensation in hexane in place of toluene, yielded the linear oligoesters as main products. A mechanism is proposed for the formation of the cyclic oligoesters.