Synthesis of Spiro[2H-1,3-benzoxazine-2,4′-piperidines] from N,N′-Dibenzylidenephenylmethanediamines and 2,6-Diaryl-4-piperidones - Takajo, Tokiharu; Kambe, Satoshi; Ando, Wataru (Synthesis, 1983)