Cascade Reaction of Donor–Acceptor Cyclopropanes: Mechanistic Studies on Cycloadditions with Nitrosoarenes and <i>cis</i>-Diazenes

Tandem ring opening, elimination, and cycloaddition of donor–acceptor cyclopropanes were observed in Yb­(OTf)₃-catalyzed cycloaddition with nitrosoarenes. The reaction results in formation of tetrahydro-1,2-oxazine instead of the normal cycloadduct isoxazolidine via in situ nitrone formation. A similar cascade sequence was observed with <i>cis</i>-diazines. Mechanistic studies on this unique transformation offer an entirely new approach for reaction design with donor–acceptor cyclopropanes