Carbenes generated from visible light irradiation are readily accessible, highly reactive intermediates that have been recently applied in several organic reactions. An overview of the field including key features and examples is provided herein.

Carbenes are very important reactive intermediates to access a variety of complex molecules and are applied widely in organic synthesis and drug discovery. Typically, their chemistry is accessed by the use of transition metal catalysts. Herein, we describe the application of low‐energy blue light for the photochemical generation of carbenes from donor–acceptor diazoalkanes. This catalyst‐free and operationally simple approach enables highly efficient cyclopropenation reactions with alkynes and the rearrangement of sulfides under mild reaction conditions, which can be utilized for both batch and continuous‐flow processes.

A dual catalytic system combining photoredox and Lewis base catalysis has been developed. By the appropriate choice of light source and catalyst, the photoredox cycle can be optimally modulated to match the base catalyzed reaction cycle to provide the corresponding products under mild reaction conditions.

Controlling the reactivity of carbene intermediates is ak ey parameter in the development of selective carbene transfer reactions and is usually achieved by metal complexes via singlet metal-carbene intermediates.I nt his combined experimental and computational studies,w es how that the reactivity of free diaryl carbenes can be controlled by the electronic properties of the substituents without the need of external additives.T he introduction of electron-donating and -withdrawing groups results in as ignificant perturbation of singlet triplet energy splitting of the diaryl carbene intermediate and of activation energies of consecutive carbene transfer reactions.T his strategy nowo vercomes al ong-standing paradigm in the reactivity of diaryl carbenes and allows the realization of highly chemoselective carbene transfer reactions with alkynes.W ec ould show that free diaryl carbenes can be readily accessed via photolysis of the corresponding diazo compounds and that these carbenes can undergo highly chemoselective cyclopropenation, cascade,o rC ÀHf unctionalization reactions.E xperimental and theoretical mechanistic analyses confirm the participation of different carbene spin states and rationalizef or the observed reactivity.

Let there be light: A heterogeneous photocatalytic system based on easily recyclable TiO(2) or ZnO allows cross dehydrogenative coupling reactions of tertiary amines. The newly developed protocols have successfully been applied to various C-C and C-P bond-forming reactions to provide nitro amines as well as amino ketones, nitriles and phosphonates.