Fischer Carbene Complexes: A Glance at Two Decades of Research on Higher‐Order Cycloaddition Reactions

Abstract

The structure of Fischer carbene complexes (FCCs) is electron deficient. If bearing an α,β‐unsaturated system, it can generate a wide variety of compounds by undergoing many different transformations, including higher‐order cycloadditions. The latter are described as pericyclic reactions in which more than six electrons participate. These reactions have been employed in various areas of organic synthesis, resulting in highly selective compounds with a broad range of scaffolds. The first studies on higher‐order cycloadditions involving FCCs frequently yielded competing byproducts. Many groups have attempted to increase selectivity by exploring distinct reaction conditions, reagents and co‐catalysts (e. g., metal‐mediated cycloadditions). The present review is the first to focus exclusively on using higher‐order cycloadditions involving FCCs to synthesize carbocycles and heterocycles. Based on two decades of reports, an analysis is made of the main aspects of the mechanisms proposed for higher‐order cycloadditions and the structural diversity obtained by the substituent effect.

Electron‐Rich Oxycarbenes: New Synthetic and Catalytic Applications beyond Group 6 Fischer Carbene Complexes

“…NMR and UV/Vis spectroscopic studies have been performed to investigate the generation of the copper-siloxycarbene intermediate. In particular, the new signal at δ = 304 ppm in the 13 C NMR spectrum strongly suggests the formation of 28.7. Furthermore, when intermediate 28.7 was exposed to air, it readily decomposed to the corresponding silyl benzoate 28.8 and benzil 28.9, which is similar to the oxidation of Group 6 Fischer carbene complexes.…”

“…Group 6 Fischer carbene complexes are organometallic reagents that have been widely used in organic synthesis, thanks to their stability and the electrophilicity at the carbon atom of the carbenes. [10][11][12][13][14] However, new carbene complexes can be obtained through transmetalation processes between Group 6 Fischer metal carbene complexes and late-transition metals (Pd, Pt, Cu, Ni, Rh, Au, etc. ), which result in different reactivity or may involve different reaction pathways than the starting metal carbene complexes.…”

“…[21] Many notable advances in photocatalyzed and transition-metalcatalyzed reactions of acylsilane-derived oxycarbenes have been developed since 2020, but they have not yet been summarized. There are several reviews on the synthesis and transformations of Group 6 Fischer carbene complexes, and the readers are encouraged to read these summaries by Sierra, [10] Dötz, [11] Raubenheimer, [12] Vázquez, [13] and Aguilar. [14] In this Minireview, we will discuss selected examples of late-transition-metal-catalyzed reactions of Group 6 Fischer carbene complexes, and focus on the synthetic and catalytic transformations of free oxycarbenes and late-transition-metal-catalyzed reactions with non-Group 6 Fischer carbenes (Figure 1).…”

“…These complexes are generally stable, and thus various synthetic applications have been developed using them as substrates (Figure 1B). [10][11][12][13][14] Free oxycarbenes and Fischer-type carbene complexes that bear a transition metal other than a Group 6 metal are more reactive. However, the corresponding synthetic and catalytic applications are relatively unexplored, probably because of the difficulty in controlling their reactivity and the need to use a stoichiometric amount of a presynthesized Group 6 metal carbene complex as the starting material.…”

High-order dipolar annulations with metal-containing reactive dipoles

“…Inspired by pioneering work on carbonyl ylides generated from diazo or alkyne groups and carbonyl groups, 88,89 many research groups developed a wide range of HODA reactions using carbene-metal-derived MCRDs. 90 An overview of reaction pathways was shown in Fig. 5: diazo or alkyne precursors react with transition metal catalysts (i.e., Rh, Cu, Au, etc.)…”