What is it about?
Homologation reactions extend the carbon framework of organic molecules by one or more carbon atoms and are among the most important transformations in synthetic chemistry. This chapter reviews the chemistry of magnesium carbenoids, a unique class of organomagnesium intermediates that have carbene-like reactivity. We describe methods for generating magnesium carbenoids from α-chloro-substituted sulfoxides and summarize their applications in the homologation of carbonyl compounds, phenolates, naphtholates, alkynes, and Grignard reagents. Particular attention is given to key reaction pathways, including β-oxido carbenoid rearrangements, Fritsch–Buttenberg–Wiechell (FBW) rearrangements, and nucleophilic substitution processes that enable efficient carbon-chain extension.
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Why is it important?
Magnesium carbenoids are α-halo-substituted organomagnesium compounds that contain both a halogen atom and a magnesium substituent on the same carbon center. Their characteristic electrophilic and carbene-like reactivity has enabled the development of a variety of homologation reactions for carbonyl compounds, alkynes, phenolates, and Grignard reagents. This chapter brings together more than two decades of developments in the field and provides a unified view of how magnesium carbenoids can be used to extend carbon skeletons, synthesize homologated carbonyl compounds and alkynes, perform ring-expansion reactions, and even homologate Grignard reagents. By highlighting both mechanistic insights and synthetic applications, this review serves as a practical guide for researchers interested in developing new homologation strategies and reactive organometallic chemistry.
Perspectives
Writing this chapter provided an opportunity to look back on the development of magnesium carbenoid chemistry from its early stages to its current applications in synthetic methodology. What continues to fascinate me is the unusual dual nature of these intermediates: despite being organomagnesium species, they often display electrophilic and carbene-like behavior that challenges conventional concepts of reactivity. Bringing together diverse examples of carbonyl homologation, alkyne synthesis, ring expansion, and Grignard reagent homologation helped reveal common mechanistic themes that may not be obvious when individual reactions are viewed separately. I hope this chapter helps researchers appreciate the versatility of magnesium carbenoids and encourages the discovery of new transformations based on their unique reactivity.
Associate Professor Tsutomu Kimura
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This page is a summary of: Magnesium Carbenoids in Homologation Chemistry, May 2023, Wiley,
DOI: 10.1002/9783527830237.ch4.
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