Download full text in PDF Opens in a new window. Article suggestions will be shown in a dialog on return to ScienceDirect. ... Please enable JavaScript to use all the features on this page. ... Triazoline, oxadiazoline, and thiadiazoline ring systems spiro-fused to C4 of a β-lactam ring undergo 1,3-dipolar cycloreversion to form azomethine-, carbonyl-, and thiocarbonyl ylides, respectively. The order of reactivities is triazoline > thiadiazoline > oxadiazoline.