Homologation Reactions in Organic Synthetic Chemistry

Dear Colleagues,

Homologation reactions—defined as synthetic operations that transform a given reactant into the next member of a homologue series—constitute powerful and versatile tools for preparative chemistry. Usually, the methylene group (CH₂) represents the constant unit differentiating the members of the series. From a synthetic perspective, the prototypical homologation reaction is the Arndt–Eistert reaction between a carboxylic acid derivative and diazomethane, resulting in the formation of a versatile α-diazoketone susceptible for further elaboration. The well-known safety drawbacks related to the use of diazomethane have stimulated the search for effective and risk-limited reagents to perform homologations and, today, chemists can rely on a wide portfolio of versatile alternatives ranging from the Wittig to the Corey–Chaykovsky, the Morita–Baylis–Hillman or the Köbrich reactions.

In recent years, carbenoids have emerged as suitable reagents for accomplishing homologations. They are organometallic compounds containing a metal atom (e.g., Li, Mg, Zn) and at least one heteroatom-containing element (e.g., halogen, N, O) linked to the same carbon. This feature makes them unique entities in the synthetic panorama, in primis for their constitutive ambiphilicity, enabling them to manifest nucleophilic or electrophilic behaviour, depending on the reaction conditions.

This Special Issue aims to cover the general field of homologations, focusing on the development and synthetic uses of these techniques in synthesis. Researchers active in the fields are, therefore, warmly invited to propose original research articles, as well as relevant state-of-the-art reviews or perspectives, to be published in this Special Issue of Molecules.

Prof. Dr. Vittorio Pace
Dr. Laura Castoldi
Guest Editors

Dr. Margherita Miele
Guest Editor Assistant

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• homologation
• methylene insertion
• diazo compounds
• halocarbenoids
• C1-equivalents