Rapid construction of the aza-propellane core of acutumine via a photochemical [2 + 2] cycloaddition reaction

Synthetic efforts toward the chlorinated aza-propellane alkaloid acutumine (1) are described. The key vicinal quaternary centers were constructed by a photochemical [2 + 2] cycloaddition reaction of a furanyl-tetrahydroindolone. Dihydroxylation of the [2 + 2] product enabled a tandem retro-aldol/intramolecular ketalization reaction, which revealed the aza-propellane core of 1 while generating an unusual, caged, pentacyclic hemiketal product.