Lithiation of 2,4,5,7-Tetrabromo-1,8-bis(dimethylamino)naphthalene: Peculiarities of Directing Groups’ Effects and the Possibility of Polymetalation

"Buttressing Effect" in the Halogen-Lithium Exchange in ortho-Bromo-N,N-dimethylanilines and Related Naphthalenes

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.

The Role of Conjugation in the Halogen-Lithium Exchange Selectivity: Lithiation of 4,6,7,9-Tetrabromo-1,3-dimethyl-2,3-dihydro-1H-perimidine

The first case of successful suppression of the coordination of a lithium atom with a dialkylamino group by the effective conjugation of the latter with the aromatic core has been discovered. This effect controls regioselectivity of the bromine-lithium exchange in 4,6,7,9-tetrabromo-1,3-dimethyl-2,3-dihydro-1H-perimidine, which leads to products with the most effective conjugation. As a result, the product of this quadruple exchange demonstrates no tendency of the coordination of the NMe groups to neighboring lithium atoms despite the absence of steric restrictions. Experimental results are explained by means of quantum chemical calculations: geometry optimization, natural bond analysis and scans using the modredundant scheme.

Spontaneous Cyclization of peri-Diiminonaphthalenes Leading to the Formation of Benzo[de]isoquinolines and Stable Benzo[de]isoquinoliniums

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.