Stable carbocations. Part 13. Intra-ionic cyclisation reactions of ferrocenyl- and phenyl-stabilised vinyl cations

Abstract

Ferrocenylvinyl cations bearing triarylmethyl, ferrocenylmethyl, ferrocenylcarbonyl, or cycloheptafrienyl groups attached to the vinylic p-carbon atom, and the phenylvinyl cation formed by protonation of 3-ferrocenyl-1 -phenylpropyne undergo intra-ionic cyclisation to give a variety of novel mono-, bi-, and tri-cyclic derivatives.

Transannular Addition of Phenols to 1,1′‐Dialkynylferrocenes: Unanticipated Formation of Phenoxy[4]ferrocenophanedienes

“…On the other hand, a protonation of one of the triple bonds would preferentially take place at C b with formation of the ferro- www.chemeurj.org cenyl-stabilized a-vinyl cation. [38,39] This, however, cannot directly undergo the transannular addition at the remaining triple bond with formation of the observed [4]ferrocenophanediene derivatives. Although 1,2-hydride shifts are known in vinyl cations, such a process, which would avoid a re-formation of the triple bond, seems unlikely here, because these shifts usually occur with formation of the more stable vinyl cation.…”

Ferrocenyl Migrations and Molecular Rearrangements: The Significance of Electronic Charge Delocalization

“…This work was elegantly extended to include the addition reactions of trityl cations to alkynylferrocenes to generate ferrocenyl-stabilized vinyl carbocations, 10, that underwent cyclization to form indenes, 11 [15]. The thermodynamic driving force in each case is the positioning of a carbocationic site adjacent to the ferrocenyl moiety, as shown in Scheme 3.…”

“…Inorganics 2020, 8, x FOR PEER REVIEW 3 of 22 to form indenes, 11 [15]. The thermodynamic driving force in each case is the positioning of a carbocationic site adjacent to the ferrocenyl moiety, as shown in Scheme 3.…”

“…The thermodynamic driving force in each case is the positioning of a carbocationic site adjacent to the ferrocenyl moiety, as shown in Scheme 3. In a variant of this concept, the diferrocenyl-alkynes Fc-C≡C-CH2-Fc, 12a, and Fc-C≡C-C(=O)-Fc, 12b, were treated with trifluoroacetic acid to form the ferrocenyl-stabilized vinyl cations, 13a,b [15]. In these systems, cyclization occurred by electrophilic attack on the alkyl-or acyl-linked ferrocenyl substituent to form (η 5 -cyclopentadienyl)(3-ferrocenylpentalenyl)iron, 14a, or (η 5cyclopentadienyl)-(3-ferrocenyl-1-oxo-pentalenyl)iron, 14b, respectively, as depicted in Scheme 4.…”

Cyclisation of diferrocenylbutadiyne dicobalt hexacarbonyl mono-adduct to novel ferrocenotropones

“…Thus, intra-ionic cyclisation of ferrocenylstabilised vinyl cations was observed when a neighbouring p-system was available [5]. As an alkyne dicobalt hexacarbonyl group is known to possess less cationstabilising capacity than a ferrocene group [6], it was anticipated that, in a disubstituted alkyne with competing donors, a-ferrocenyl cationic sites would prevail over Co-complexed propargyl cations [7].…”