SummaryThe enantioselective carbenoid insertion into C(sp3)–H bonds is an important tool for the synthesis of complex molecules due to the high control of enantioselectivity in the formation of stereogenic centers. This paper presents a brief review of the early issues, related mechanistic studies and recent applications on this chemistry area.

A method for the synthesis of bicyclic N‐heterocyclic cores from N‐terminal α,β‐unsaturated diazoketones has been developed. The transformation involves three sequential steps that include N‐deprotection, an intramolecular aza‐Michael, and a photochemical Wolff rearrangement as a one‐pot protocol. By using this strategy, a series of substituted bicyclic N‐heterocycles, particularly, indolizidines and pyrrolizidines, were synthesize in good yields.

Carbenes play a key role in a plethora of organic transformations. Although stabilized diazo carbonyl compounds predominate as a source of electrophilic carbenes, the hazardous nature of nonstabilized analogues calls for their in situ generation from stable precursors. Among these, 1,3,4-oxadiazolines serve as diazoalkane surrogates under UV light irradiation. In view of their high stability, diverse reactivities, and straightforward synthesis, milder methodologies for the activation of these compounds that permit the use of UV-light-sensitive substrates are highly valued. Herein, we report the visible-light-induced activation of oxadiazolines by triplet energy transfer catalysis that, in contrast to UVinduced processes, alters their reactivity and enables the generation of carbenes. The formed reactive species react with electron-poor olefins, thereby giving valuable spirocyclopropanes. Mechanistic investigations, both theoretical and experimental, uncover plausible pathways and highlight the importance of the triplet energy transfer steps.