Multigram Scale Synthesis of Piperarborenines C-E

We report the multigram scale synthesis of heterodimeric β-truxinic imides piperarborenines C-E using a catechol-tethered diastereoselective intramolecular [2 + 2] photocycloaddition. Key innovations lie in the use of catechol as a practical auxiliary for the synthesis of homo- and heterodimeric β-truxinates and the use of a UV-LED flow photoreactor in the [2 + 2] step. This approach is highly scalable, requiring a single column purification, no photocatalysts, and no cryogenic conditions.