„cis‐Diaza‐bis‐σ‐homobenzole”︁ ([_π2_s + _σ2_s + _σ2_s]‐Cycloreversion) – 1,4‐Dihydro‐1,4‐diazocine („Aromatizität”︁)

Abstract

Ausgehend von ,,cis-Benzoltriimin" (3) werden mit 90 -40% Ausbeute die N,N'-disubstituierten Derivate 8 b -f hergestellt. Nitrosierung zu den unterhalb -30 "C 'H-NMR-spektroskopisch identifizierten N-Nitrosoverbindungen 10b -f und N20-Eliminierung fuhren zu den cis-Diazabis-a-homobenzolen (,,cis-Benzoldiiminen") 11 b -f. Deren [,2, + .2, + a2,]-Cycloreversion zu den 1,4-disubstituierten 1,4-Dihydro-1,4-diazocinen 14b -e (11 f liefert -uber 14f? -nur Polymere) ist je nach Art der N-Substitution derart schnell, da8 unter den milden Herstellungsbedin- ( l l f yieldsonly -via 14f? -polymers). With& = 97 + 2 kJ . mol-' (logA = 11.7; AH* = 92 f 2 kJ . mol-'; AS* = -31 f 6 J . K-' . mol-') the most stable cis-benzene diimine l l b is clearly more labile than cis-benzene dioxide. From 14d the diazocine dianion 16 is obtainable by conventional means. The 1,4-dihydro-1 ,4-diazocine parent molecule 5 obtained by protonation of 16 is stable towards acid and base. From this and from systematic 'H-and 13C NMR studies it is concluded, that 5 and its donor-substituted derivatives 14e,g as well as its dianion 16 have a planar structure with strong 10-electron delocalisation (,,aromatic" diaza[8]annulenes) whilst the acceptor-substituted derivatives 14 b -d prefer the twist-boat-chair conformation and are therefore not diatropic.

Aromaticity as a Cornerstone of Heterocyclic Chemistry

“…NMR data for anion 216 are in agreement with an aromatic stabilization. , 1,4-Dioxocines 218 are in turn paratropic and exist in equilibrium with their 2σ → 2π valence isomers: syn -benzene dioxides 217 (Scheme ) . Their chemistry and behavior in magnetic fields have been evaluated. , …”

In Pursuit ofcis,cis,cis‐Cyclonona‐2,5,8‐triene‐1,4,7‐trione – An Adventure in Medium‐Sized Ring Chemistry

“…[45] The experimental work launched high-level calculations [46] that confirmed early estimates [33,47] as to the "aromaticity" of the [σ2s + σ2s + σ2s]-trishomobenzenoid transition states B and related the much higher kinetic stabilities of the triscyclobuta analogues to the "antiaromaticity" of the corresponding transition states. A very rewarding extension of our synthetic activities centered on cis-(bis)hetero-bis-σ-homobenzenes (X,Y = NR,NR; [48] O,NR; [49] CHR,NR [50] ) and the derived 1,4-(hydro)diheterocines and hydroheterocine anions, another novel class of medium-ring heterocycles. [45] Conflicting theoretical predictions [51] as to the latter's potential "aromaticity" were clarified when N-electron donor/acceptor substitution allowed the isolation of nonplanar, "localized" as well as of planar, "delocalized" rings.…”

2D Semiconducting Polymers Based on Aromatic 1,5‐Diheterocines with Oxygen and Nitrogen

“…Thereof, 1,4diheterocines and their isomers are well-known. [2][3][4][5][6][7][8][9][10][11][12] The unsubstituted 1,5-diheterocines, however, are standalone. To the best of our knowledge there is only one (theoretical) account [13] describing their molecular and electronic structures available so far.…”