Recyclization of available 5-hydroxypyrrolines with semicarbazide and its analogues has been studied. As a result, rare 1,4-dihydropyridazines with carboxamide function at the N-1 atom have been synthesized in up to 88% isolated yields.

Expedient protocols for the synthesis of three types of highly functionalized azaheterocyclic scaffolds (dihydropyridazines, tetrahydropyridazines, and partially saturated tricyclic systems) from readily available hydroxypyrrolines and hydrazides are described. The directions of the transformation of a common initial intermediate, namely a Brønsted acid-activated hydroxypyrroline, depend on the reaction conditions and the structure of the hydrazides.

Tetrahydropyrrolo[1,2-d]oxadiazoles have been synthesized in good-to-excellent yields via the cycloaddition of nitrile oxides (in situ generated from aldoximes) to readily accessible functionalized Δ1-pyrrolines. The reaction smoothly proceeds at room temperature...