Modeling Biologically Important NH···π Interactions Using peri-Disubstituted Naphthalenes

Directed Ortho and Remote Metalation of Naphthalene 1,8-Diamide: Complementing SEAr Reactivity for the Synthesis of Substituted Naphthalenes

Mono- and dianion species of 1,8-naphthalene diamide 2 were generated under sec-BuLi/TMEDA conditions and trapped with a variety of electrophiles to give 2- and 2,7- substituted products 3 and 4. Using Suzuki-Miyaura cross-coupling, mono- and di-iodinated products were converted into the corresponding 2-aryl (5) and 2,7-diaryl (6) products, respectively. The amide-amide rotation barrier of 2 was established by VT NMR, and the structure of fluorenone structure 9, obtained by remote metalation, was secured.

Combination of "Buttressing" and "Clothespin" Effects for Reaching the Shortest NHN Hydrogen Bond in Proton Sponge Cations

A series of previously unknown 2,4,5-tri- and 2,4,5,7-tetrasubstituted 1,8-bis(dimethylamino)naphthalenes and their salts with HBF₄ containing bulky spherically shaped substituents (Me, Br, and SiMe₃) in the naphthalene ring has been synthesized. Using XRD analysis of 11 samples, the influence of the so-called "buttressing" and "clothespin" effects on their molecular structure and the NHN hydrogen bond geometry in the solid cations were investigated. The combined action of both effects has been shown to significantly increase the compression of the hydrogen bond. As a result, the previous record of the hydrogen bond shortness (N···N = 2.524 Å) has been surpassed in favor of 2.502 Å found for the tetrafluoroborate of 2,4,5,7-tetramethyl-1,8-bis(dimethylamino)naphthalene. The molecular structure of the latter differs by perfect symmetry and practically barrier-free proton transfer in the [NHN]⁺ bond. On the basis of the results of quantum-chemical calculations, it is suggested that the value of 2.502 Å likely represents or lies very close to the theoretical limit for the short hydrogen bonds between the amine-type nitrogen atoms.

Interaction, bond formation or reaction between a dimethylamino group and an adjacent alkene or aldehyde group in aromatic systems controlled by remote molecular constraints

Control of the spacing between a dimethylamino group and a polarised alkene by remote constraints determines if the groups make a n–π* interaction, form a Me₂N–C bond or a (MeN)CH₂–C bond initiated by the tertiary amino effect.

Direct enantioseparation of axially chiral 1,1′-biaryl-2,2′-diols using amidine-based resolving agents

Amidine-based optically active resolving agents for enantiomer separation of axially chiral 1,1′-biaryl-2,2′-diols have been developed. A strongly basic amidine bearing no substituents on its nitrogen atoms enables the formation of their diastereomeric salts upon being mixed with weakly acidic phenol derivatives. Enantiopure 1,1′-biaryl-2,2′-diols can be obtained in high yields after only one crystallization of their salts with the chiral amidine derived from dehydroabietic acid. X-ray crystallography revealed that the amidine moiety forms a salt with the phenol group and additional intermolecular NH/π interactions contribute to the efficient chiral recognition process.

Enantioseparation of atropisomeric biphenols using a chiral amidine derived from dehydroabietic acid was reported. Only one crystallization of their mixture gave pure diastereomeric salts of biphenols from racemate.