Nazarov Cyclization/Internal Redox Cyclization Sequence for the Synthesis of N‑Heterocyclic Bridged Ring Systems

A 1,6 conjugate addition/Nazarov electrocyclization/internal redox cyclization sequence was developed. Various 5-hydroxycyclopentenones were made through the 1,6-conjugate addition initiated Nazarov reaction with excellent diastereoselectivities. Under thermal conditions, these underwent a through-space 1,5-hydride-transfer/ring-closure reaction to form bridged bicyclic N-heterocyclic compounds with up to four stereogenic centers. It was also possible to convert simple acyclic dienyl diketones into the bicyclo[3.2.1] products in a one-pot process (with a solvent switch).