The reaction of lithium derivatives of aromatic heterocycles with carbon monoxide was studied under several reaction conditions: 2-furyllithium afforded only one product, the tetrahydro-2-furaldehyde (25% yield). On the other hand, 2-thienyllithium and 5-methyl-2-furyllithium gave two and five products, respectively. Although in relatively low yields, formation of highly functionalized compounds takes place in a fast process under mild conditions. For 1,4-dihydroxy-1,4-bis(5-methyl-2-furanyl)butane-2,3-dione, reaction conditions were achieved to obtain this difficult to prepare derivative in 50% yield. To the best of our knowledge, this is the first report on the reaction of lithiated aromatic heterocycles with CO: evidence is given on the involvement of proton transfers in the reactions of 2-furyllithium and 2-thienyllithium, while the reaction of 5-methyl-2-furyllithium seems to proceed through an electron transfer as the first step. Copyright © 2003 John Wiley & Sons, Ltd.