Divergent Reactivity of Nitrocyclopropanes with Huisgen Zwitterions and Facile Syntheses of 3‑Alkoxy Pyrazolines and Pyrazoles

A novel annulation reaction of trans-2-substituted-3-nitrocyclopropane-1,1-carboxylates with in situ generated Huisgen zwitterions is reported, providing facile synthesis of 3-alkoxy pyrazolines in good yields and high diastereoselectivities. This reaction unveils the divergent reactivity of the nitrocyclopropanes as a kind of versatile donor–acceptor cyclopropanes. It is also demonstrated that the prepared 3-alkoxy pyrazolines from di-tert-butyl azodicarboxylate can be readily transformed into the corresponding 3-alkoxy 1H-pyrazoles in moderate yields.