Tandem photocycloaddition - Retro-Mannich fragmentation of enaminones. A route to spiropyrrolines and the tetracyclic core of koumine
Intramolecular [2 + 2] photocycloaddition of β-aminoalkylidene malonates gives transiently a cyclobutane which undergoes retro-Mannich fragmentation to a Δ1-pyrroline. The tandem sequence, exemplified in two series based on tryptamine and aminoethyl-1,4-c