Global Aromaticity and Antiaromaticity in Porphyrin Nanoring Anions

Doping, through oxidation or reduction, is often used to modify the properties of π‐conjugated oligomers. In most cases, the resulting charge distribution is difficult to determine. If the oligomer is cyclic and doping establishes global aromaticity or antiaromaticity, then it is certain that the charge is fully delocalized over the entire perimeter of the ring. Herein we show that reduction of a six‐porphyrin nanoring using decamethylcobaltocene results in global aromaticity (in the 6? state; [90 π]) and antiaromaticity (in the 4? state; [88 π]), consistent with the Hückel rules. Aromaticity is assigned by NMR spectroscopy and density‐functional theory calculations.     

Cyclobis(7,8‐(para‐quinodimethane)‐4,4′‐triphenylamine) and Its Cationic Species Showing Annulene‐Like Global (Anti)Aromaticity

π‐Conjugated macrocycles containing all‐benzenoid rings usually show local aromaticity, but reported herein is the macrocycle CBQT , containing alternating para‐quinodimethane and triphenylamine units displaying annulene‐like anti‐aromaticity at low temperatures as a result of structural rigidity and participation of the bridging nitrogen atoms in π‐conjugation. It was easily synthesized by intermolecular Friedel–Crafts alkylation followed by oxidative dehydrogenation. X‐ray crystallographic structures of CBQT , as well as those of its dication, trication, and tetracation were obtained. The dication and tetracation exhibited global aromaticity and antiaromaticity, respectively, as confirmed by NMR measurements and theoretical calculations. Both the dication and tetracation possess open‐shell singlet ground states, with a small singlet–triplet gap.     

Formal [6+3] cycloaddition of fulvenes with 2H-azirine: a facile approach to the [2]pyrindines system

2H-Azirine reacts with fulvenes to give either alkylated fulvene azirines (ultrasound) or the formal [6+3] cycloaddition adducts (Lewis acid). The later constitutes an efficient and novel route to [2]pyrindines.     

HMO-elektronen-Struktur von Annulenen mit Bindungsalternanz

Zusammenfassung Für 4n- und (4n + 2)-Annulene mit Bindungsalternanz werden analytische Ausdrücke für die LCAO-Koeffizienten und die Elemente der Ladungs-/ Bindungsordnungsmatrix hergeleitet. Die auf die Umordnung des Orbital-schemas zurückgehende sprunghafte Änderung der Bindungsordnungen in 4n-Annulenen beim SymmetrieübergangD _(2n)h D _(4n)h wird diskutiert.

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HMO-Electron structure of annulenes with bond alternation

Analytical expressions for the LCAO-coefficients and the elements of the charge-bond order-matrix are derived for 4n and for (4n +2) annulenes with alternant bond lengths. Due to the reorganization of the orbital scheme there is a discontinuity in the bond orders of 4n -annulenes at the symmetry change fromD _(2n)h toD _(4n)h .

     

Aromaticity of Rees-type hydrocarbons—a DFT computational study

The structure and aromatic properties of Rees hydrocarbons 7bH-cyclopent[cd]indene and its benzo-annelated derivative 1a and 2a, respectively, are examined by the B3LYP/6−31+G(d) calculations employing HOMA criterion of Krygowski and coworkers. It is shown that 1a possesses strong π-electron delocalization over the perimeter of the CC bonds, thus forming a quasi-[10]annulene pattern. Its aromatic character is determined to be 83%. In contrast, 2a is less convenient model system for [14]annulene. The reason behind is that the perimeter network of the potentially aromatic 14π-electrons is supplemented by two additional more local aromatic patterns involving 10π and 6π electrons. Consequently, the π-electron delocalization over the molecular rim is incomplete being thus diminished. The aromatic character of the peripheral bonds in both 1a ⁻ and 2a ⁻ anions formed upon deprotonation of the central C–H bond is decreased, since the role of the smaller rings in forming aromatic subsystems is increasing. Finally, polycyano substitution of 1a and 2a decreases aromaticity due to the price paid for the resonance effect taking place between the carbocyclic π-network and the double bonds of the CN groups. The resonance effect is particularly strong in anions derived by heterolytic cleavage of the C–H bond emanating from the central sp ³ carbon atom. Dedicated to Professor T. M. Krygowski for his outstanding scientific achievements on the occasion of his 70th birthday.     

Reaction of Substituted Cyclopentadienyl-magnesium-Chloride with Carbonyl Compound ( Ⅰ )——Reaction of (1, 1-Dialkyl-3-Butenyl) Cyclopentadienyl-magnesium-chloride with Ketones

The substituted cyclopentadienyl-magnesium-chloride, obtained by exocyclic addition of 6,6-dialkylfulvene and allyl-magnesium-chloride, reacted with the ketone 3, the product was hydrolyzed and dehydrated to give the 2-(1 ,1-dialkyl-3-butenyl)-6,6-dialkyl-fulvene 5. The structure of 5 was determined by using the 1H NMR spectra of 5 and the adducts of 5 with tetracyanoethylene.     

Traceless Solid‐Phase Synthesis of Cyclopenta[c]quinolines and Cyclopenta[c]chromenes via Hetero [6+3] Cycloadditions of Fulvene. A Facile Approach to the 11‐Heterosteroids Framework

The hetero [6+3] cycloaddition of fulvenes to benzoquinones and iodoanilines provides an efficient route to the synthesis of cyclopenta[c]‐4H‐chromen‐8‐ol, benzo[d]cyclopenta[e]‐3H‐3‐azin‐8‐ol and other 11‐hetero steroids. The structure of the cyclopenta[c]chromene skeleton was confirmed by the X‐ray structure analysis of thep‐bromobenzoate of 39 . A small library consisting of 110 examples was prepared by reacting benzoquinones or iodoanilines with resin 17 .     

1－芳酰基－3－烷基－6－羟基－6－芳基富烯的合成

１－芳酰基－３－烷基－６－羟基－６－芳基富烯的合成焦纶基,董育斌,马玉道（山东大学应用化学研究所,济南,２５０１００）关键词富烯,二茂铁,芳酰化,合成前文［１］曾报道过甲基锂、苯基锂与６,６－二烷基富烯加成物的芳酰化。为进一步探讨取代环戊二烯负离子的...