Benzo[1,2‐h:4,3‐h′]diquinoline (“1,14‐Diaza[5]helicene”): Synthesis, Structure, and Properties

The specificity of the [NHN]+ hydrogen bonds in protonated naphthalene proton sponges

“…Examples are such derivatives as 1,8-bis(tetramethylguanidineamino)naphthalene (V) [9] and 1,8-bis(hexamethyltriaminephosphazenyl)naphthalene (VI) [10]. A somewhat individual group of proton sponges are the compounds synthesized by Staab et al with a multi-ring core, such as the phenanthrene type (VII) [11], or with nitrogen atoms incorporated in the aromatic rings, such as benzo[1,2-h:4,3-h 0 ]diquinoline (VIII) [12]. A rich group of sponges was synthesized by Alder et al, namely diamines with nitrogen atoms in the aliphatic rings, for example 1,6-diazabicyclo [4.4.4]tetradecane (IX) [13,14], which is characterized by exceptional features of its NHN + bridges after protonation.…”

Approaches to the Azahelicene System: Synthesis and Spectroscopic Characterization of Some Diazapentahelicenes

“…Two diazapentahelicenes are reported in the literature: the 1,14-diazapentahelicene that was synthesized to be used as proton sponge because the proton is located between the two facing N-atoms [11], and the 6,9-diazapentahelicene (6) prepared as an extension of the synthesis of phenanthridine [12]. Because the 1,14 isomer may accommodate a proton between the N-atoms, we were not interested, at this stage, to repeat its synthesis in view of the subsequent complex formation with larger ions, which would probably not fit in.…”

Heterocyclic superbases: retrospective and current trends

“…Recent experience has shown that a much greater effect is obtained by structural organization of the molecule, in particular, through optimization of the directional alignment of the axes of the lone electron pairs of several heteroatoms together. This was first demonstrated by Staab et al [54][55][56] for diazaarenes 37-39, also termed diaza[n]helicenes (Scheme 14). Even the parent compound of this series, quino [7,8:7',8']quinoline 37 is a superbase with somewhat stronger basicity than proton sponge 11.…”

“…In the case of compound 39, the basicity is lowered virtually to the level of quinoline. It is interesting that the diamagnetic effect of the aromatic -system on the proton in the [N···H−N] + group in cation 38H + is so great that this species still holds the record for the chemical shift of a chelated proton ( N−H ~ 24 ppm) [55]. Recently synthesized pyridine aza-crown ethers 40a-c (azacalix [3](2,6)pyridines) proved to be very strong bases providing trifurcated hydrogen bonding to a proton reaching the interior of the macrocycle [57,58].…”