The Fiesselmann thiophene synthesis is a name reaction in organic chemistry that allows for the generation of 3-hydroxy-2-thiophenecarboxylic acid derivatives from α,β-acetylenic esters with thioglycolic acid and its derivatives under the presence of a base.
After deprotonation the thioglycolic acid ester attacks the tripel bond of the alkyne.
Elimination of a thioglycolic acid ester results in an α,β-unsaturated ketone.
A variation of the Fiesselmann synthesis by Lissavetzky starts from a cyclic β-ketoester and thioglycolic acid.
Fry used this variation for the synthesis of tyrosinkinase inhibitors, starting from a substituted pyridine.