Azetidin-2-one versus chroman-2-one: Application of ¹H- ¹³C COSY NMR and mass spectroscopy in structure elucidation-class of compounds

Azetidin-2-ones, commonly known as β-lactams, constitute a biologically important class of compound. Treatment of azetidin-2-ones with alkali is known to form diverse types of compounds depending on the stability of the ring. In many cases, the ring is retained in the product at the cost of transformation of substituents. Spectroscopy is the most important tool to characterize the organic compounds. However, in some cases the structures of the products are so closely related that simple IR, 1H NMR, and 13C NMR spectra do not lead to unambiguous structure elucidation. This article reports a novel application of 1H-13C COSY NMR and mass spectroscopy in determining unequivocally an azetidin-2-one ring structure instead of a chroman-2-one ring structure for the product obtained by treatment of 1-benzhydryl-3,3-bis(4- methylphenyl)-4-[2-(o-dip-tolylacyl)hydroxyphenyl]-2-azetidinone with ethanolic sodium hydroxide at room temperature.