M. Zoghbi et J. Warkentin, SPIRO BETA-LACTAM THIADIAZOLINE AND TRIAZOLINE SYSTEMS - COMPARISON WITH THE CHEMISTRY OF SPIRO BETA-LACTAM OXADIAZOLINES, Tetrahedron, 49(45), 1993, pp. 10229-10238
Triazoline, oxadiazoline, and thiadiazoline ring systems spiro-fused t
o C4 of a beta-lactam ring undergo 1,3-dipolar cycloreversion to form
azomethine-, carbonyl-, and thiocarbonyl ylides, respectively. The ord
er of reactivities is triazoline > thiadiazoline > oxadiazoline.