Anionic Thia-Fries Rearrangements of Electron-Rich Ferrocenes and the Unanticipated Formation of Diferrocenyl Sulfate from 2-(Trimethylsilyl)ferrocenyl Imidazolylsulfonate

Abstract

Upon ortho lithiation ferrocenyl triflate and 1,1′-ferrocenediyl ditriflate undergo anionic thia-Fries rearrangements instead of triflate elimination. To differentiate between an ortho metalation and an ortho deprotonation, 2-(trimethylsilyl)ferrocenyl triflate was shown to undergo an anionic thia-Fries rearrangement to 2-((trifluoromethyl)sulfonyl)ferrocenol (5) in 84% yield upon treatment with tetrabutylammonium fluoride. Metalation of the respective tributylstannyl derivative with butyllithium also led to 5 in 99% yield as the result of the anionic thia-Fries rearrangement. 2-Methoxyferrocenyl triflate also underwent the rearrangement upon ortho deprotonation with lithium diisopropylamide in practically quantitative yield at low temperature. The electron-rich 2-(((trifluoromethyl)sulfonyl)oxy)ferrocenolate was generated from 2-(((trifluoromethyl)sulfonyl)oxy)ferrocenyl acetate. However, ortho deprotonation again afforded the anionic thia-Fries rearrangement product. These results clearly show that even very electron rich ferrocene derivatives undergo an anionic thia-Fries rearrangement instead of a triflate elimination. In an attempt to induce an elimination supported by steric crowding, 2,3,4-trimethylferrocenyl triflate was deprotonated, giving 3,4,5-trimethyl-2-((trifluoromethyl)sulfonyl)ferrocenol in quantitative yield as the result of an anionic thia-Fries rearrangement. As an alternative to the triflates ferrocenyl imidazolylsulfonate was tested as the starting material. While this compound could not be deprotonated, the corresponding 2-trimethylsilyl derivative reacted with tetrabutylammonium fluoride in a very unusual reaction to give diferrocenyl sulfate in almost quantitative yield.

Cobalt‐Catalyzed ortho‐Methylation of Ferrocenes Bearing ortho‐Directing Groups by Catalytic Directed C–H Bond Activation

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Ferrocene is an aromatic organometallic compound, which easily undergoes electrophilic substitution. [26,27] Such an ortholithiation may give rise to rearrangement reactions, for example an anionic thia-Fries rearrangement [28,29] or a closely related anionic phospha-Fries rearrangement. [26,27] Such an ortholithiation may give rise to rearrangement reactions, for example an anionic thia-Fries rearrangement [28,29] or a closely related anionic phospha-Fries rearrangement.…”

“…[24] Lithiation and 1,1′-dilithiation are well established, [25] and an ortho-lithiation in the presence of an ODG is also possible. [26,27] Such an ortholithiation may give rise to rearrangement reactions, for example an anionic thia-Fries rearrangement [28,29] or a closely related anionic phospha-Fries rearrangement. [30,31] We recently reported that the double anionic thia-Fries rearrangement at either one of the cyclopentadienyl ligands takes place in high yield under mild reaction conditions with an unprecedented interannular stereoinduction leading to the exclusive formation of the meso product.…”

Improved Syntheses of 1,2‐Disubstituted Ferrocenes

“…and 1,2,1′,2′-tetradehydroferrocene ("ferrocenediyne") we recently reported the formation of 2-(trifluoromethylsulfonyl)ferrocenols by unprecedented anionic thia-Fries rearrangements of ferrocenyl triflates under mild reaction conditions in high yields instead of the desired elimination products. [34,35] An osmium complex with 1,2-dehydroferrocene as a ligand has been reported by Cullen et al as early as in 1992. [36] Herein, we report new or significantly improved syntheses of 1,2-dihaloferrocenes as well as ferrocenecarboxylic acid derivatives obtained by ortho-lithiation.…”

Asymmetric synthesis of hetero-1,2,3,4,5-pentasubstituted ferrocenes

“…Achiral 1,2,3,4,5-pentahalogenoferrocenes (Cl, Br, F) are accessible in a few steps, [15][16][17][18][19][20] while iterative metalation-functional group manipulation allows the tedious syntheses of pentasubstituted ferrocenes bearing up to three different substituents (Scheme 1). [21][22][23] Here, we report how the wise choice of substituents can enable hetero-1,2,3,4,5-pentasubstituted ferrocenes to be delivered, either as racemates or enantioenriched products, marking a milestone in metallocene science (Scheme 1).…”