ABSTRACT
A simple and effective organolithium approach to the synthesis of 2-substituted benzo[cd]indoles from peri-dihalonaphthalenes and nitriles has been developed. The reaction proceeds via a surprisingly easy intramolecular aromatic nucleophilic substitution facilitated by the "clothespin effect". The discovered transformation provides good isolated yields, allows usage of an extensive range of nitriles, and demonstrates a good substituents tolerance. UV-absorption and NMR spectra of the obtained benzo[cd]indoles and their protonated forms demonstrated exclusive protonation to the indole nitrogen atom even in the presence of two NMe2 groups in positions 5 and 6 (i. e. "proton sponge" moiety).
ABSTRACT
Non-covalent interactions such as coordination of an organolithium reagent by a directing group and steric repulsion of substituents strongly affect the halogen-lithium exchange process. Here we present the manifestation of the "buttressing effect" - an indirect interaction between two substituents issued by the presence of a third group - and its influence on the ease and selectivity of the bromine-lithium exchange and the reactivity of formed aryllithiums. The increase of the size of the "buttressing" substituent strongly affects the conformation of a NMe2 group, forcing it to hinder ortho-bromine and thus slowing down the exchange. In naphthalene substrates bearing two bromines, this suppresses regioselectivity of the reaction. The "buttressing effect" forces formed aryllithiums to deaggregate, thus boosting their reactivity. This facilitates the decomposition via protolisys by ethereal solvents even at low temperatures and in some cases initiates fast Wurtz-Fittig coupling.
ABSTRACT
A set of novel 1,4-diaryl-1,3-butadiynes terminated by two 7-(arylethynyl)-1,8-bis(dimethylamino)naphthalene fragments was prepared via the Glaser-Hay oxidative dimerization of 2-ethynyl-7-(arylethynyl)-1,8-bis(dimethylamino)naphthalenes. The oligomers synthesized in this way are cross-conjugated systems, in which two conjugation pathways are possible: π-conjugation of 1,8-bis(dimethylamino)naphthalene (DMAN) fragments through a butadiyne linker and a donor-acceptor aryl-C≡C-DMAN conjugation path. The conjugation path can be "switched" simply by protonation of DMAN fragments. X-ray diffraction, UV-vis spectroscopy and cyclic voltammetry are applied to analyze the extent of π-conjugation and the efficiency of particular donor-acceptor conjugation path in these new compounds. X-ray structures and absorption spectra of doubly protonated tetrafluoroborate salts of the oligomers are also discussed.
ABSTRACT
The interaction of peri-dilithionaphthalenes with organic cyanides was studied. Instead of the expected peri-diimines, the reaction leads to the formation of three types of benzo[de]isoquinolines. Treatment of unsubstituted 1,8-dilithionaphthalene with aromatic nitriles results in the formation of 1-amino-1,3-diaryl-1H-benzo[de]isoquinolines. In contrast, 4,5-dilithio-1,8-bis(dimethylamino)naphthalene gives an aromatic isoquinolonium cation via elimination of ammonia under the same condition. Upon treatment with tert-butylcyanide, both dilithionaphthalenes undergo a transformation to 1-amino-3,4-di-tert-butyl-4H-benzo[de]isoquinolines. The observed reactivity was supported by quantum chemical calculations.
