Diastereoselective synthesis of spirocyclopropane-linked pyrazolones from azomethine ylides via C(sp3)-H activation

The cyclopropanation reactions of azomethine ylides are generally stereospecific,with the stereochemistry of the dipole and dipolarophile retained in the cycloadduct.In this work, a method has been developed for the generation of azomethine ylides via C-H activation of unreactive C(sp3)–H bonds of 2-methylazaarenes. Molecular iodine-promoted metal-free C–H activation of alkyl azaarenes has been described [1]. Herein, we represent a novel diastereoselective synthesis of spirocyclopropanelinkedpyrazolones from arylidenepyrazolone derivatives and azomethine ylides, prepared in situ from iodine-catalyzed reaction of 2-methylquinoline or acetophenones with pyridine in the presence of base. These transformations proceeded via the cyclopropanation reaction and followed by anti-elimination of pyridine. These methods offer several advantages, such as being inexpensive, moderate to high yield, short reaction time, with-out ligand or metal, ease of product isolation, which make them attractive processes for the synthesis of spirocyclopropane-linked pyrazolone derivatives. The spirans reported in this work may deserve further attention not only from a synthetic but also from a pharmacological point of view.