Catalytic Methods for the Transfer of Nonstabilized Carbenes

Transition-metal catalysis has fundamentally transformed the way we construct molecules because of the ability of d-block elements to couple two structurally complex molecular fragments. Suzuki and Negishi-type cross-coupling methods are prevalent in catalysis; however, reactions involving metal-carbene alkene couplings (MCAC) are also well-represented in the fragment coupling toolbox because of their ability to construct two bonds simultaneously. Despite this clear utility, it is still challenging to use nonstabilized carbene intermediates (i.e., those with only alkyl groups) in cyclopropanation and C-H insertion reactions, although alkyl cyclopropanes are prevalent in natural products and pharmaceuticals. This perspective article summarizes catalytic methods that have addressed the challenges involved in the transfer of nonstabilized carbene groups to alkenes and other traps.