Uncommon carbene insertion reactions

Transition-metal-catalysed carbene insertion reaction is a straightforward and efficient protocol for the construction of carbon-carbon or carbon-heteroatom bonds. Compared to the intensively studied and well-established "common" carbene insertion reactions, including carbene insertion into C-H, Si-H, N-H, O-H, and S-H bonds, several "uncommon" carbene insertion reactions, including carbene insertion into B-H, Sn-H, Ge-H, P-H, F-H, C-C, and M-M bonds, have been neglected for a long time. However, more and more studies on uncommon carbene insertion reactions have been disclosed recently, and clearly demonstrate the great synthetic potential of these reactions. The current perspective reviews the history and the newest advances of uncommon carbene insertion reactions, discusses their potential applications and challenges, and also presents an outlook of this promising field.