Multigram Scale Total Synthesis of Piperarborenines C-E

We report the development of a multigram scale total synthesis of heterodimeric β-truxinic imides piperarborenines C-E using a catechol-mediated diastereoselective intramolecular [2+2] photocycloaddition. Key innovations lie in the use of (1) catechol as a highly selective auxiliary for the robust and scalable synthesis of homo- and heterodimeric β-truxinates, (2) UV LEDs for direct excitation in the [2+2] cycloaddition step, and (3) a bis pentafluorophenyl ester and LDA for the challenging installation of the syn dihydropyridinone imides. This approach is exceptionally scalable – requiring minimal chromatography, no photocatalysts, and no cryogenic conditions - and will enable thorough evaluation of the biological properties and anticancer profiles of piperaborenines C-E and derivatives thereof.