Formyl group activation of a bromopyrrole ester in Suzuki cross-coupling reactions: application to a formal synthesis of Polycitone AÂ and B and Polycitrin A

A new pyrrole building block is described, which allows for the regiospecific synthesis of 2,3,5-trisubstituted pyrroles and 2,3,4,5-tetrasubstituted pyrroles. Optimization studies are presented for the preparation of the pyrrole building block along with the evaluation of various cross-coupling conditions and cross-coupling agents. A short, formal synthesis of the natural products Polycitone A, Polycitone B, and Polycitrin A from the pyrrole building block is also described.