Ring Expansion of Diazo-Functionalized 4-Hydroxycyclobutenone: Catalytic Ring Opening and Recyclization to 2(5<i>H</i>)-Furanone/Cyclopentenedione and Thermal 4π−8π Electrocyclic Ring Opening−Closure to Diazepinedione
cyclopentene-1,3-dione via an alpha-carbocation intermediate and a carbenoid (carbene) intermediate, respectively. Thermal rearrangement of some of these compounds led to the formation of diazepinediones without the extrusion of nitrogen through tandem 4pi electrocyclicringopening and 8pi electrocyclicring closure processes.