Diels-Alder Additions as Mechanistic Probes–Interception of Silyl-Isoindenes: Organometallic Derivatives of Polyphenylated Cycloheptatrienes and Related Seven-Membered Rings

Abstract

The intermediacy of short-lived isoindenes, generated in the course of metallotropic or silatropic shifts over the indene skeleton, can be shown by Diels-Alder trapping with tetracyanoethylene, leading to the complete elucidation of the dynamic behaviour of a series of polyindenylsilanes. Cyclopentadienones, bearing ferrocenyl and multiple phenyl or naphthyl substituents undergo [4 + 2] cycloadditions with diaryl acetylenes or triphenylcyclopropene to form the corresponding polyarylbenzenes or cycloheptatrienes. The heptaphenyltropylium cation, [C7Ph7+], was shown to adopt a nonplanar shallow boat conformation. In contrast, the attempted Diels-Alder reaction of tetracyclone and phenethynylfluorene yielded electroluminescent tetracenes. Finally, benzyne addition to 9-(2-indenyl)anthracene, and subsequent incorporation of a range of organometallic fragments, led to development of an organometallic molecular brake.

Cyсlopentadienone and Pyrone Derivatives as Precursors of Electron-Deficient Cycloheptatrienes: Quantum Chemical Investigation and Synthesis

“…Previously it was shown that bulky aryl groups make the transition into axial isomer of heptaarylcycloheptatrienes irreversible and [1,5]-hydride shift takes place only when the initially formed equatorial conformer is long-living. 46,47 In our cases ester groups are less bulky and, moreover, alkyl groups in 9b,c afford simplified conformational flip and, thus, [1,5]-hydride shift 4 to make the more stable unsymmetrical isomer prevalent (in 9b) of equal (in 9c) under This article is protected by copyright. All rights reserved.…”

“…Pyrone derivatives have been used as four-electron components in the synthesis of cycloheptatrienes previously. 47 However, only cyclopropenone ketals gave cycloheptatriene products in the reaction conducted. In some cases, they initially generate a dipole, which in turn undergoes a (4+3)-cycloaddition with pyrones to afford a different arrangement of cyclopropene carbon atoms within the products than in direct reactions.…”

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

“…The ready availability of the mixed benzils 1-ferrocenyl-2-aryl-1,2-dioxoethane, 89 and 92, has been shown to provide a convenient route to ferrocenyl-triaryl-cyclopentadienones, 93 that are versatile precursors to the sterically hindered arenes C 6 R 5 Fc, where R = phenyl or β-naphthyl, and the cycloheptatriene C 7 Ph 6 HFc (Scheme 29) [54,58,59].…”

“…Unsurprisingly, ferrocil does not undergo the benzil-to-benzilic acid rearrangement; once again, such a process would have required the migration of a ferrocenyl unit under electronically unfavorable anionic conditions. The ready availability of the mixed benzils 1-ferrocenyl-2-aryl-1,2-dioxoethane, 89 and 92, has been shown to provide a convenient route to ferrocenyl-triaryl-cyclopentadienones, 93 that are versatile precursors to the sterically hindered arenes C6R5Fc, where R = phenyl or β-naphthyl, and the cycloheptatriene C7Ph6HFc (Scheme 29) [54,58,59].…”