Fluorosulfonylferrocene, (Trifluoromethylsulfonyl)ferrocene and New Ferrocenyl Sulfonates: Directed ortho Lithiation and New Anionic Thia‐Fries Rearrangements at Ferrocene

Abstract

Dedicated to the 70th anniversary of the discovery of ferroceneFerrocenyl triflates are known to undergo anionic thia-Fries rearrangements at low temperature in high yields. In order to expand the scope of this reaction, ferrocenyl sulfonates and sulfonylferrocenes were prepared and their reactivity investigated. Treatment of ferrocenyl fluorosulfonate with lithium 2,2,6,6-tetramethylpiperidide gave rise to a new anionic thia-Fries rearrangement at ferrocene. The formation of a rare oxathiine was observed with ferrocenyl (pentafluorophenyl) sulfonate as a result of an ortho lithiation and a subsequent intramolecular nucleophilic aromatic substitution. In contrast to fluorinated ferrocenyl sulfonates, fluorosulfonylferrocene as well as (trifluoromethylsulfonyl)ferrocene underwent ortho lithiation under comparable reaction conditions.

The First Anionic Thia‐Fries Rearrangement at the Cobaltocenium Cation

“…So far, (aryl triflate)tricarbonylchromium and ferrocenyl triflates were the only organometallic complexes, at which it had been observed. [22][23][24][25]32,33] The first step of the anionic thia-Fries rearrangement is the deprotonation at the ortho position next to the triflate substituent. In view of the positive charge of the cobaltocenium ion anticipating an increased CÀ H acidity we saw the chance to realize the rearrangement with a weaker base than LDA.…”

“…[48] In the course of our investigations with ferrocene systems it was shown that the anionic thia-Fries rearrangement does not take place with ferrocenyl mesylate or tosylate. [23] This gave rise to check, if the corresponding cobaltocenium salts behave accordingly, or if the rearrangement took place with them. When cyclopentadienone complex 6 was treated with methanesulfonic anhydride, the required reaction temperature was higher than with triflic anhydride, presumably due to the decreased electrophilicity of the anhydride.…”

“…[9,10] We have investigated the chemistry of ferrocene under a variety of aspects for a longer period of time. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Among these, the first anionic thia-Fries rearrangements at ferrocene were reported, which start from ferrocenyl triflate (1) or from 1,1'ferrocenediyl ditriflate (3) and gave rearranged products 2 or 4, respectively in high yields under very mild reaction conditions (Scheme 1). [24] Remarkably, 4 was exclusively formed as the meso diastereomer, an unprecedented interannular stereoinduction, which was recently investigated by theoretical calculations.…”

“…[22] A number of electron rich derivatives of 1 were shown to undergo this reaction, [25] and most recently, ferrocenyl fluorosulfonate was shown to react accordingly. [23] The first step of the reaction is a deprotonation by the strong non-nucleophilic lithium base at the ortho position next to the sulfonate group, which acts as an ortho directing group. Important reviews covering this chemistry have recently been published.…”

Exploring the boundaries of ferrocenesulfonyl fluoride chemistry

“…1, top right). 46 Further functionalization was demonstrated by a deprotolithiation-electrophilic trapping sequence using lithium 2,2,6,6-tetramethylpiperidide (LiTMP) as the base and Fig. 1 Ferrocenesulfonyl fluorides already reported.…”