The crystal structure of tert-butyl 7,9-dibenzyl-2-oxo-1,7,9-triazaspiro[4.
5]dec-3-ene-1-carboxylate, C26H31N3O3, is reported. The molecule has impose
d mirror symmetry and the hexahydropyrimidine ring adopts a chair conformat
ion with two benzyl substituents bonded equatorially to the ring N atoms. T
he 3-pyrrolin-2-one is attached as a spiro-skeleton to the hexahydropyrimid
ine ring by one axial C-C and one equatorial C-N bond.