Generation of 3- and 5-lithiothiophene-2-carboxylates via metal-halogen exchange and their addition reactions to chalcogenoxanthones

The synthesis of chalcogenorhodamines by using dianions generated from 5-bromothiophene-2-carboxylic acid and 3-bromothiophene-2-carboxylic acid through metal-halogen exchange with tert-butyllithium (t-BuLi) are reported. The analysis has shown that the deprotonation is faster than metal-halogen exchange with the bromothiophene-2-carboxylic acids using t-BuLi.