The condensation of 2,6-dichloroimidazo[1,2-a]pyridine with ribonolactone gives a novel imidazo[1,2-a]pyridine C-nucleoside with an unexpected site of ribosylation.

A novel ribosylated imidazo[1,2-a]pyridine C-nucleoside was synthesized by condensing a lithiated 2,6-dichloroimidazo[1,2-a]pyridine (1) with a protected ribonolactone (2), followed by acetylation to give the intermediate nucleoside 4. This intermediate was reductively deacetoxylated and deprotected to give what was determined to be the novel and unexpected 2,6-dichloro-5-(beta-D-ribofuranosyl)imidazo[1,2-a]pyridine (7) and the corresponding alpha-product (8). The site of ribosylation was established with long range proton-carbon decoupling experiments. This ribosylation at C5 was. entirely unexpected in view of previously reported condensations with lithiated imidazo[1,2-a]pyridines which occurred only at the C3 position. Copyright (C) 1996 Elsevier Science Ltd