Total Synthesis of Racemic Thieno[3,2-]thiochromene Tricarboxylate, a Luciferin from Marine Polychaeta .

We report the first total synthesis of racemic luciferin, a thieno[3,2-]thiochromene tricarboxylate comprising a 6-6-5-fused tricyclic skeleton with three sulfur atoms in different electronic states. The key transformation is based on tandem condensation of bifunctional thiol-phosphonate, obtained from dimethyl acetylene dicarboxylate, with benzothiophene-6,7-quinone. The presented convergent approach provides the synthesis of the target compound with a previously unreported fused heterocyclic core in 11 steps, thus allowing for unambiguous confirmation of the chemical structure of luciferin by 2D-NMR spectroscopy.