Synthesis of Five-membered 2-Heteroaryl 2-Heteroaromatic Carboxylates and Attempted Cyclization to Bisheteroaryl[2,3-b:3',2'-d]pyran-2-one

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 Hnmr 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-pyrroly] 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-O bond of the ester group.