8.1.37 Lithium Halocarbenoids in Modern Synthesis

Mono- and dihalo lithium carbenoids have been extensively used in synthesis as homologating agents for introducing C1-units into organic arrays. Although in principle they exhibit both nucleophilic and electrophilic behavior, the former is predominantly observed. Herein, an overview of their reactivity toward carbon electrophiles is presented together with some recent advancements on modified versions of the (aza- and oxa-) Matteson homologation. Detailed information on the preparation of these agents, as well as the use of emergent technologies (microfluidic techniques) is also discussed. Particular emphasis is given to hitherto elusive fluorinated methyllithiums as a consequence of the impact they could have for introducing CH2F groups in medicinally relevant structures.