Lithium Carbenoids in Homologation Chemistry

Since their introduction in the synthetic toolbox, lithium carbenoids were considered versatile C-1 donor agents, thus enabling selective insertion processes within preformed X – Y linkages. Their inherent instability – often constituting Achilles' heel of these species – benefited from the use of Barbier-type conditions in order to control and tame decomposition phenomena to unproductive carbenes. Nowadays, the availability of distinct pro-carbenoid sources guarantees straightforward preparation routes and, thus, the applicability in synthetic processes. In this chapter, through a historical perspective, the breakthroughs in homologation processes with these reagents – principally acting in nucleophilic mode – are presented. Not only canonical processes are documented, but also modern sequential transformations triggered by an initial homologative event are thoroughly discussed. In this sense, most of the attention is devoted to – in batch – operations dealing with carbon- and heteroatom-centered electrophiles. The development of – till recently – elusive fluorinated lithium carbenoids for introducing F-containing fragments into organic skeletons complements the significance of logics harnessed on these entities. Finally, a short survey on the most recent (2021–2022) works on boron electrophiles sheds light on the continuous efforts the synthetic community is realizing for assembling complex molecular architectures through intuitive C1 lithium carbenoids-mediated tactics.