Modular Synthesis of Lamellarins via Regioselective Assembly of 3,4,5-Differentially Arylated Pyrrole-2-carboxylates

A modular synthesis of lamellarins via 3,4,5-differentially arylated pyrrole-2-carboxylate intermediates has been developed. The key reactions employed are Br-Li exchange-methoxycarbonylation of 2,5-dibromo-1-(tert-butoxycarbonyl)-1H-pyrrole (1) followed by palladium-catalyzed iterative Suzuki-Miyaura coupling of the pyrrole core. The 3,4,5-triarylpyrrole 4 thus synthesized was readily converted to 5,6-saturated lamellarin L (2) and 5,6-unsaturated lamellarin N (3) via lactonization followed by annulation of the pyrrole nitrogen and lateral aromatic ring at C5 using 2-bromoethyl phenyl sulfide or bromoacetaldehyde dimethyl acetal as two-carbon homologation agents. In principle, this strategy allows the production of diverse lamellarins in short steps with high yields using readily accessible arylboronic acids as aromatic modules.