Synthesis of Spirofluorenyl‐β‐Lactams through Cycloaddition and Ring Contraction from N‐Aryl Fluorenone Nitrones and Methylenecyclopropanes.

A variety of spirofluorenyl‐β‐lactams have been prepared in moderate yields over three steps from N‐aryl fluorenone nitrones and methylenecyclopropanes through a [3+2] cycloaddition, reduction and subsequent acid‐catalyzed ring contraction cascade strategy under mild reaction conditions. Experimental studies showed that the stereochemistry remained intact after the ring contraction step. Furthermore, the obtained spirofluorenyl‐β‐lactam was easily converted to two novel spiroazetidine and spiroquinolinone scaffolds in good yields. [ABSTRACT FROM AUTHOR]