| Description |
The occurrence of cyclopentanoid structures in complex polycyclic natural products has nessecitated the investigation into synthetic methods for the annulation of five-membered rings. The cyclization of allylic vinyl ketones under acidic conditions, reported previously by Nazarov, is discussed along with a number of other contributions made by other research groups over the years. An interruption during the Nazarov cyclization, whereby the oxyallyl zwitterion ion is trapped by a pendant olefin, results in the formation of polycyclic hemiketals. The formation of two carbocyclic rings, one heterocyclic ring and the establishment of up to six contiguous stereocenters with complete diastereoselectivity in a single transformation from an achiral precursor is demonstrated. |
