Furan-2,3-diones as masked dipoles: synthesis of isotetronic acids and mechanistic considerations

The formal dipolar behaviour of furan-2,3-diones is illustrated by their reaction with ethyl glyoxylate under Lewis basic activation uniquely, giving access to isotetronic derivatives. The Janus-type nature of the activated species, both nucleophilic and electrophilic is revealed by ring-opening of the starting ketolactone. An unexpected reversible side-reaction was identified by in situ monitoring.