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.