Generation of Gold(I) Carbenes by Retro‐Buchner Reaction: From Cyclopropanes to Natural Products Synthesis

Abstract

The gold(I)‐catalyzed retro‐Buchner (decarbenation, retrocyclopropanation) reaction of 7‐substituted cycloheptatrienes has emerged as a safe and powerful alternative for the generation of gold(I) carbenes. These carbenes can cyclopropanate alkenes, take part in intramolecular reactions, or engage in higher cycloadditions with different partners, giving rise to a wide range of relevant structures. This review covers the developments made on the generation of gold(I) carbenes via decarbenation reactions, and the applications of these reactions in organic synthesis.

Buchwald‐Type Ligands on Gold(I) Catalysis

“…Hence, our group implemented the use of 7substituted-1,3,5-cycloheptatrienes 56 for the generation of gold(I)-carbenes 58 (Scheme 12). [75] Cycloheptatrienes 56 are in equilibrium with their norcaradiene tautomers 57, [76,77] which react with electrophilic gold(I) complexes by a stepwise retro-cyclopropanation [78] to generate gold(I)-carbene 58 together with one molecule of benzene resulting in an overall retro-Buchner process. Gold(I)-carbene 58 can then be trapped inter-and intramolecularly with different alkenes giving rise to a number of synthetically useful transformations.…”

“…Gold(I)-carbene 58 can then be trapped inter-and intramolecularly with different alkenes giving rise to a number of synthetically useful transformations. [75] The use of cycloheptatrienes as carbene precursors represents a much safer alternative compared to the more conventional generation of metal carbenes from diazo compounds due to their thermal stability. Furthermore, the starting materials are easily accessible in multigram scale by addition of the corresponding organolithium or Grignard reagent to commercially available tropylium tetrafluoroborate or via Julia-Kocienski olefination.…”

“…However, the preparation of derivatives 54 is not straightforward. Hence, our group implemented the use of 7‐substituted‐1,3,5‐cycloheptatrienes 56 for the generation of gold(I)‐carbenes 58 (Scheme ) . Cycloheptatrienes 56 are in equilibrium with their norcaradiene tautomers 57 , which react with electrophilic gold(I) complexes by a stepwise retro‐cyclopropanation to generate gold(I)‐carbene 58 together with one molecule of benzene resulting in an overall retro‐Buchner process.…”

“…Cycloheptatrienes 56 are in equilibrium with their norcaradiene tautomers 57 , which react with electrophilic gold(I) complexes by a stepwise retro‐cyclopropanation to generate gold(I)‐carbene 58 together with one molecule of benzene resulting in an overall retro‐Buchner process. Gold(I)‐carbene 58 can then be trapped inter‐ and intramolecularly with different alkenes giving rise to a number of synthetically useful transformations . The use of cycloheptatrienes as carbene precursors represents a much safer alternative compared to the more conventional generation of metal carbenes from diazo compounds due to their thermal stability.…”

α‐Imino Gold Carbene Intermediates from Readily Accessible Sulfilimines: Intermolecular Access to Structural Diversity

“…[6] Functionalized gold carbenes have been frequently proposed as highly reactive intermediates in such reactions. Generally, gold carbenei ntermediates areg enerated by decomposition of diazo compounds, [7] 1,2-acyloxy migration of propargylic esters, [8] cycloisomerization of 1,n-enynes or [9] enynones, [10] ring-opening reaction of cyclopropenes, [11] dual activation of 1,5-diynes, [12] retro-Buchnerr eaction of cycloheptatrienes, [13] and gold-catalyzed oxygen, [14] nitrene [15] as well as carbene [16] transfer reactions. Among these modes, the generation of highly reactive gold carbene intermediates through gold-catalyzed group-transfer to CCt ripleb onds and subsequent diverse evolutions has experienced significant attention in the last decade.…”