Heterocyclic Compounds from Alloxan and Amines. XIV. Structure of Even-Electron Products Derived from Free-Radical Betaines

Abstract

X-ray crystallographic determination of structure has shown that the even-electron product obtained thermally from 5-(10-phenyl-5,10-dihydro-5-phenazinioyl)-1,3-dimethyl-4-barbiturate (1) (e.g. by heating in benzene) has the structure 1,3-dimethy1-5-(10-phenyl-2,10-dihydrophenazin-2-ylidene)- hexahydropyrimidine-2,4,6-trione (3) instead of the previously supposed dehydro dimer structure (2). Crystals of compound (3) are triclinic, Pī, a 11·014(3), b 9·343(3), c 10·927(3) Å, α 110·47(4), β 64·99(4), γ 101·47(4)º, Z = 2. Full-matrix least-squares refinement gave R 0·09. The rearrangement that occurs in the conversion of the free-radical betaine (1) into the trione (3) is a novel type of N to p-aromatic rearrangement which presumably entails dissociation followed by recombination and oxidation.