Asymmetric Formal Total Syntheses of (+)- and (-)-Limaspermidine from Chirally Resolved 2-Pyrone Diels-Alder Cycloadducts via Aromatic C-H Amidation and Imino-Diels-Alder Reaction.

A new asymmetric synthetic route to (+)- and (-)-limaspermidine was devised, starting with chirally resolved enantiomerically pure 2-pyrone Diels-Alder cycloadducts. This route utilizes intramolecular Pd-catalyzed aromatic C-H amidation and imino-Diels-Alder reactions to construct the key indoline and indolizidine subunits onto the central cyclohexane core, allowing the straightforward formal total syntheses of both (+)- and (-)-limaspermidine.