Multiple Transformations of 2-Alkynyl-1,8-bis(dimethylamino)naphthalenes into Benzo[g]indoles. Pd/Cu-Dependent Switching of the Electrophilic and Nucleophilic Sites in Acetylenic Bond and a Puzzle of Porcelain Catalysis

A new family of 1,4-diaryl-1,3-butadiynes based on the “proton sponge”: synthesis, electronic and chemical properties

A new family of 1,4-diaryl-1,3-butadiynes containing two and four fragments of 1,8-bis(dimethylamino)naphthalene (“proton sponge”) were synthesized.

Sterically Facilitated Intramolecular Nucleophilic NMe2 Group Substitution in the Synthesis of Fused Isoxazoles: Theoretical Study

The influence of steric repulsion between the NMe₂ group and a second ortho-(peri-)substituent in the series of 1-dimethylaminonaphthalene and N,N-dimethylanilene ortho-oximes on the ease of the NMe₂ group’s intramolecular nucleophilic substitution is studied. Possible reaction intermediates for three mechanisms are calculated (ωB97xd/def-2-TZVP), and their free Gibbs energies are compared to model reaction profiles. Supporting experiments have proved the absence of studied reactivity in the case of simple 2-dimethylaminobenzaldoxime, which allowed us to establish reactivity limits. The significant facilitation of NMe₂ group displacement in the presence of bulky substituents is demonstrated. The possibility of fused isoxazoles synthesis via the intramolecular nucleophilic substitution of a protonated NMe₂ group in the aniline and naphthalene series is predicted.

N-Methylated 1,8-Diaminonaphthalenes as Bifunctional Nucleo­philes in Reactions with α,ω-Dihalogenoalkanes: A Facile Route to Heterocyclic and Double Proton Sponges

The reaction of 1-dimethylamino-8-(methylamino)naphthalene with 1,3-dibromopropane chemoselectively leads to the product of N,N′-heterocyclization, while in the case of 1,4-dibromobutane and 1,2-bis(bromomethyl)benzene the process results in heterocyclization onto the same nitrogen atom with the formation of previously unknown 1-dimethylamino-8-pyrrolidino- and 1-dimethylamino-8-isoindolino-naphthalenes. The same reactions conducted without adding any auxiliary base lead to the formation of N,N′-linked double proton sponges as a new type of polynitrogen organic receptor. Proceeding as a sequence of quaternization–demethylation–cyclization steps, this heterocyclization process can also be used to construct six-membered rings (piperidino, morpholino), albeit in lower yields. The ability of 1,2-dibromoethane to brominate N-alkylated 1,8-diaminonaphthalenes is also described. It is shown for the first time that a commercially available 1,8-bis(dimethylamino)naphthalene (DMAN) can be used as a starting material in a heterocyclization reaction, which via a one-pot approach and in a short time can be converted into 1,5-dimethylnaphtho[1,8-bc]-1,5-diazacyclooctane or 1-dimethylamino-8-(pyrrolidin-1-yl)naphthalene.

Tuneable access to indole, indolone, and cinnoline derivatives from a common 1,4-diketone Michael acceptor

A convergent strategy is reported for the construction of nitrogen-containing heterocycles from common substrates: 1,4-diketones and primary amines. Indeed, by just varying the substrates, the substituents, or the heating mode, it is possible to selectively synthesize indole, indolone (1,5,6,7-tetrahydroindol-4-one), or cinnoline (5,6,7,8-tetrahydrocinnoline) derivatives in moderate to excellent yields.

Proton-induced fluorescence in modified quino[7,8-h]quinolines: dual sensing for protons and π-donors

The synthesis, as well as spectral, structural and photoluminescence properties of dipyrido[3,2-e:2',3'-h]acenaphthene 5 and quinazolino[7,8-h]quinazolines 6 as representatives of the bidentate -N[double bond, length as m-dash]/-N[double bond, length as m-dash] superbases, are reported. These nitrogen bases being more rigid (5) or π-extended (6) analogs of optically-mute quino[7,8-h]quinoline are both active in terms of fluorescence with quantum yields up to φ = 0.71-0.77. At the same time, their luminescence behavior is opposite to that of peri-NMe₂/NMe₂ naphthalene proton sponges and their hybrid NMe₂/-N[double bond, length as m-dash] analogs. Although 5 and 6 exhibit visible region emission upon protonation, for the hybrid systems the fluorescence is manifested only for bases. The most remarkable observation is that the fluorescence of compound 5 can be switched on not only by means of organic or inorganic acids, but also through the formation of chelate complexes with such weak H-donors as water and primary alcohols. It was disclosed that water is present in the complex as a cluster comprising 8 interconnected H₂O molecules. Overall, the studied compounds demonstrate a previously unobserved type of dual mode optical response, H-sensing (emission enhancement in 5 and 6 on protonation) and π-sensing (emission quenching in 5H⁺ and 6H⁺ on coordination with π-donors). This work seems to be an important contribution to areas such as chemosensorics, the creation of new ligands, hydrogen transfer and some other phenomena representing different types of supramolecular interactions.

Neutral Pyrrole Nitrogen Atom as a π- and Mixed n,π-Donor in Hydrogen Bonding

9-Dimethylaminobenzo[ g]indoles 3-6 and 1-dimethylamino-8-(pyrrolyl-1)naphthalene 7 were examined as possible models for establishing the ability of the pyrrole nitrogen atom to participate in [NHN]⁺ hydrogen bonding as a proton acceptor. Indoles 3-5 (to a lesser extent 6) form rather stable tetrafluoroborates, with the proton mostly located on the NMe₂ group but simultaneously engaged in the formation of a charged intramolecular [NHN]⁺ hydrogen bond (IHB) with the pyrrole N atom. The theoretically estimated energies of IHB in salts 3H⁺BF₄^--6H⁺BF₄^- vary between 7.0-10.7 and 6.2-7.0 kcal mol^-1 in vapor and MeCN, respectively. The pyrrole N atom undergoes a perceptible pyramidalization but still remains involved in the 6π-electron aromatic system, suggesting that the hydrogen bonding in salts 3H⁺BF₄^--6H⁺BF₄^- represents a previously unknown mixed NH···N(n,π) interaction. Despite the favorable orientation of the N-H bond and the pyrrole ring in salt 7H⁺BF₄^-, no signs of NH···N(n) bonding in it were noticed, and the existing interaction was classified as pure NH···N(π). The results obtained may be useful in studies of secondary protein structures, especially those α-helix sections which contain tryptophan residues.

TMSOTf mediated ‘5/6-endo-dig’ reductive hydroamination for the stereoselective synthesis of pyrrolidine and piperidine derivatives

A TMSOTf mediated 5/6-endo-dig reductive hydroamination cascade on internal alkynylamines gave expedient, stereoselective access to pyrrolidine and piperidine derivatives. We also demonstrate that a protecting group on nitrogen has a profound effect on the reactivity as well as diastereoselectivity.

Synthesis of 2,3-dihydro-1H-pyrroles by intramolecular cyclization of N-(3-butynyl)-sulfonamides

Hydroamination of 3-butynamine derivatives to give non-aromatic 2,3-dihydropyrroles was achieved by using PdCl₂ or AuCl as the catalyst.