Heterocycles from Heterocycles. 1,3-Diaryl-4,5-imidazolidinediones from 1,3,5-Triarylhexahydro-1,3,5-triazines and Oxalyl Chloride

1,3-Diaryl-4,5-imidazolidinediones (6) are easily synthesized from 1,3,5-triarylhexahydro-1,3,5-triazines (1) and oxalyl chloride (5) in a reaction not likely to involve the zwitterionic intermediate (3) of the N-methylenearylamine dimer, but viewing the sequential pick up of two units of the monomer (2) by oxalyl chloride (5). The essential role of ethyl alcohol added to the reaction mixture is recognized. Reaction conditions have been optimized and some ten imidazolidinediones (6) were prepared in good to excellent yields. Geometric parameters of 6 were obtained by X-ray diffraction analysis: all the nuclei are found almost in one plane except for a small twist of the phenyl rings about the C-N bond.