Synthesis of five-membered 2-heteroaryl 2-heteroaromatic carboxylates and attempted cyclization to bisheteroaryl[2,3-b:3′,2′-d]pyran-2-one

2-Heteroaryl 2-heteroaromatic carboxylates were prepared by reactions of 2-heteroaromatic carbonyl chlorides and 2(5H)-furanone, 2(5H)-thiophenone, and 1-methyl-2(5H)-pyrrolone in triethylamine. The ¹H nmr spectra of the esters showed that the electronic effect of both heteroaromatic rings did not cause any sizable shift from each other except for 1-methyl-2-pyrrolyl 1-methyl-2-pyrrolecarboxylate ( 5c ). Attempts to cyclize the esters to heteroaryl-fused pyran-2-ones were unsuccessful. The results may be explained by the most stable conformation of the esters in which two heteroatoms are anti along the C? 0 bond of the ester group.