Hydrazone radical promoted vicinal difunctionalization of alkenes and trifunctionalization of allyls: synthesis of pyrazolines and tetrahydropyridazines.

The intramolecular addition of hydrazone radicals to carbon-carbon double bonds was achieved by using TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) or DIAD (diisopropyl azodicarboxylate) as the hydrazone radical initiator as well as the carbon radical scavenger. Consequently, alkenes were difunctionalized to afford pyrazolines and tetrahydropyridazines via C-N forming 5-exo-trig and 6-exo-trig cyclizations, respectively, and allyls were trifunctionalized to afford pyrazolines via C-N forming tandem 1,5-H-shift/5-exo-trig cyclizations under metal-free neutral conditions.