Substitution reactions in the acenaphthene analog of quino[7,8-h]quinoline and an unusual synthesis of the corresponding acenaphthylenes by tele-elimination

The possibility of functionalization of dipyrido[3,2-e:2′,3′-h]acenaphthene containing a quino[7,8-h]quinoline fragment and being a highly basic diazine analog of 1,8-bis(dimethylamino)naphthalene (“proton sponge”) has been studied for the first time. In addition to the pronounced tendency of the title compound to form associates with an intramolecular hydrogen bond of the NHN type (new examples with the participation of pyridine rings, including self-associates are shown) and its inertness to amination reactions of the pyridine rings, the naphthalene core at positions 5(8) and the CH2CH2 bridge (dehydrogenation) undergo chemical modifications under mild conditions, giving the corresponding acenaphthylenes. The latter can also be obtained in an unusual way by tele-elimination from 5,8-dibromodipyridoacenaphthene by reaction with neutral or anionic bases

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

By means of Sonogashira reaction, a series of 2-alkynyl- and 2,7-dialkynyl derivatives of 1,8-bis­(dimethyl­amino)­naphthalene (“proton sponge”) have been obtained from the corresponding iodides. It was disclosed that changing the reaction conditions and isolation protocol or conducting the model experiments with the authentic acetylenes results in several types of palladium- and copper-assisted heterocyclizations with the participation of the CC bond and 1-NMe₂ group. These include: (<i>i</i>) a cyclization into isomeric 1<i>H</i>-benzo­[<i>g</i>]­indoles with [1,3] migration of the <i>N</i>-methyl group into the newly formed pyrrole ring; (<i>ii</i>) a similar cyclization with a loss of the methyl group; (<i>iii</i>) a tandem process of cyclization into benzo­[<i>g</i>]­indoles and their subsequent 3,3′-dimerization; and (<i>iv</i>) a copper-catalyzed oxidative transformation into 3-aroyl­benzo­[<i>g</i>]­indoles. In most cases, the reactions occur in parallel, but under certain conditions, one of the above products becomes predominant or even the only one. Remarkably, in Pd-catalyzed cyclizations <i>i</i>–<i>iii</i>, the acetylenic bond behaves as an electrophile being attacked at the β-position by the amine nitrogen atom. In contrast, in transformation <i>iv</i>, the CC bond attacks by its C_α atom on the aminomethyl radical functionality N­(Me)–CH₂· presumably arising at copper oxidation/deprotonation of the 1-NMe₂ group. Studying rearrangement <i>i</i>, some evidence for the porcelain catalysis was obtained

4,5-Bis(dimethylamino)quinolines: Proton Sponge versus Azine Behavior

Two first representatives, <b>5</b> and <b>6</b>, of the still unknown 4,5-bis(dimethylamino)quinoline have been synthesized and studied. While the former, being protonated either at the peri-NMe₂ groups or at the ring nitrogen, has been shown to display properties of both a proton sponge and azine, its counterpart <b>6</b> behaves exclusively as azine giving only a quinolinium salt

Organometallic Synthesis of 2,3,6,7-Tetrasubstituted 1,8-Bis(dimethylamino)naphthalenes for Investigation of the Double Buttressing Effect in Proton Sponges

The lithiation of 2,7-disubstituted derivatives of 1,8-bis(dimethylamino)naphthalene (DMAN, proton sponge) bearing potentially ortho-directing OMe, NMe2, and SMe groups was studied. It has been shown that OMe groups facilitate selective dual β-lithiation of the naphthalene moiety while the 2(7)-NMe2 groups allow only monolithiation presumably due to the decreased acidity of the ring C–H bonds and conformational immobilization after coordination to the lithium atom. In contrast, the SMe groups provided no ring lithiation and underwent deprotonation of their methyl fragment. The first representatives of previously unknown 2,3,6,7-tetrasubstituted DMANs have been synthesized in good yield after treatment of 2,7-dimethoxy-3,6-dilithio DMAN with the appropriate electrophiles (MeI, Me2S2, Me3SiCl, DMF, etc.). Because the exceedingly high basicity of 2,7-dimethoxy DMAN is commonly attributed to the so-called “buttressing effect” (BE), the availability of 2,3,6,7-tetrasubstituted species provided the first opportunity to study the double BE version. Using X-ray diffraction and basicity measurements, we showed that due to the high conformational mobility of the methoxy groups, the most striking manifestations of double BE are the strong planarization of peri-NMe2 groups and a significant decrease in basicity, while the length and the other properties of the intramolecular NHN hydrogen bond in the corresponding protonated species undergo minor changes