How is 9-Benzyl-2,9-diazaspiro[5.5]undecane dihydrochloride (CAS: 1198286-24-6) typically synthesized?

9-Benzyl-2,9-diazaspiro[5.5]undecane dihydrochloride is typically synthesized through multistep synthesis involving the formation of a diazaspiro intermediate followed by benzyl protection and hydrochloride salt formation. The reaction is often catalyzed by a phase transfer catalyst and proceeds with good yield and high selectivity.