The MgBr2-catalyzed formal [3+2] cycloaddition of donor-acceptor activated cyclopropanes with nitrosoarenes offers a novel approach to various structurally diverse isoxazolidines. The reactions, which are experimentally easy to conduct, occur with complete stereospecificity and perfect control of regioselectivity. Product isoxazolidines can be readily transformed into α-amino lactones by reductive or decarboxylative N-O cleavage and subsequent lactonisation, and the N-aryl bond cleavage is also possible under oxidative conditions.

No transition metals are necessary in the reaction of in situ generated arynes with nitrosoarenes to give substituted carbazoles. Depending on the fluoride source and the solvent, either N‐arylated carbazoles or NH‐carbazoles are obtained (see scheme; DME=dimethoxyethane, OTf=trifluoromethanesulfonate). In these cascades a CC and one or two CN bonds are formed. The reactions are easy to conduct and proceed under mild conditions.

Dearomative [3 + 2] annulation of N-heterocycles with donor–acceptor aminocyclopropanes: fast access to indolizidine building blocks.