Preparation of Optically Pure 3'-Methylspiro<imidazolidine-4,4'(1'H)-quinazoline-2,2',5(3'H)-trione by Combination of Optical Resolution and Racemization

Article abstract of DOI:10.1021/jo00031a043

Optically pure 3'-methylspiro-2,2',5(3'H)-trione was prepared by optical resolution using brucine as a resolving agent.The resulting optically pure spirohydantoin was racemized by refluxing 1n 1,2-dichlorobenzene for 17 h, or more effectively upon heating in 10percent HCl at 90 deg C for 2 h.In the acid-catalyzed racemization, the introduction of difluoromethyl group at the 3-nitrogen of hydantoin ring increased the racemization rate, while the introduction of methyl group at the 3-nitrogen reduced it.Theses results suggest that the acid- catalyzed racemization proceeds via the N-acyliminium ion generated by the cleavage of the N₃ - C₄ bond of the spirohydantoin ring.