Tropo(thio)ne-embedded homoHPHACs: does the tropylium cation induce global antiaromaticity in expanded hexapyrrolohexaazacoronene?

Abstract

Tropo(thio)ne-embedded homoHPHACs and their dications were synthesised by an electrophilic annulation of secoHPHAC and successive oxidation. 13C NMR spectra of the dications represented global 22π homoaromaticity via homoconjugation, while alkylation...

Troponoid Compounds as Therapeutic Agents and as Targets and Templates for Chemical Synthesis

“…Highlighting such potential are demonstrations that troponoid thiocrown ethers display useful metallophilic properties 37 while tropone-fused porphyrinoids show greatly altered electronic properties 38 as do somewhat related systems with embedded tropo(thio)ne residues. 39 Simple metal complexes of thujaplicin (13) 40 have been touted for use as emission materials in agricultural films while the parent compound (viz. 11) has been shown to react with fingermark residues and may form the basis for newgeneration visualization techniques.…”

“…deficient nature of troponoids would appear to render such systems resistant to certain cycloaddition reactions, notably normal electron demand Diels-Alder reactions, these can still take place although forcing conditions may be required. For example, Ito and co-workers have shown that tropolone-O-methyl ether (39) engages in thermally promoted Diels-Alder reactions with acrylonitrile (40) to give a mixture of the regio-and stereoisomeric adducts 41-44 in a combined yield of 85% (Scheme 1). 49 High-pressure-promoted Diels-Alder reactions of certain simple troponoids with 2-cyclopentenone have also been reported and these proceed in the anticipated manner.…”

“…Troponoids can also participate in [6+3]-cycloaddition reactions. So, for example, inspired by the work of Trost, 55 we reacted 56 -tropolone O-methyl ether (39) with the trimethylenemethane precursor 50 in the presence of a palladium catalyst and obtained the previously reported adduct 51 together with variable quantities of a derivative arising from the addition of trimethylenemethane to the carbonyl group of the primary product (Scheme 3). Adduct 51 can be engaged in a range of reactions, one of which is a modestly selective and DMDO-mediated mono-epoxidation to give oxide 52 that engages in an acid-catalyzed and deepseated rearrangement to give the tricyclic ketal 53.…”

Liquid Crystalline Magneto-Optically Active Peralkylated Azacoronene

“…A subsequent study by Takase et al demonstrated that alkyl substitution at the periphery increased solubility, prevented intermolecular couplings, and allowed for the isolation and characterization of both the neutral and dication species. Chemical modification of the peripheral substituents, the inner core, and via π-extension have since led to many other analogs. ,,,− These studies highlighted the aromaticity of HPHAC derivatives and their ability to display multiple stable oxidation states.…”

Substituent effects on paratropicity and diatropicity in π-extended hexapyrrolohexaazacoronene

“…Several research groups, including ours, have studied the synthesis and characterisation of hexapyrrolohexaazacoronene (HPHAC), a nitrogen-containing polycyclic aromatic compound, using pyrroles. 7–10 Composed of electron-rich pyrroles, HPHACs are easily oxidised, and their dications exhibit aromaticity based on macrocyclic conjugation, although their antiaromatic tetracations have not yet been successfully isolated and characterized (Fig. 1a).…”