Stereospecific Copper(II)-Catalyzed Tandem Ring Opening/Oxidative Alkylation of Donor–Acceptor Cyclopropanes with Hydrazones: Synthesis of Tetrahydropyridazines

Aerobic copper­(II)-catalyzed
tandem ring opening and oxidative C–H alkylation of donor–acceptor
cyclopropanes with bisaryl hydrazones is accomplished to produce tetrahydropyridazines,
in which copper­(II) plays dual role as a Lewis acid as well as redox
catalyst. The reaction is stereospecific, and optically active cyclopropanes
can be reacted with high optical purities (89–98% enantiomeric
excess). The substrate scope, functional group tolerance, dual role
of the copper­(II) catalyst, and the use of air as an oxidant are the
important practical features. A product bearing a 3-bromoaryl group
can be subjected to Pd-catalyzed Suzuki coupling with boronic acid
in high yield.