How is 9,9'-Spirobi[fluorene]-2,2'-diamine (CAS: 67665-45-6) typically synthesized?

9,9'-Spirobi[fluorene]-2,2'-diamine (CAS: 67665-45-6) is synthesized via a multistep process involving the fluorene core and a diamine. The reaction typically requires conditions that promote the spirocyclization of the fluorene moiety, followed by the coupling of the diamine. Common solvents include DMF, and the use of catalysts such as bis(triphenylphosphine)palladium(0) can enhance the selectivity and yield of the product. This method ensures high purity and a high degree of molecular weight control.