Naphthaleneproton sponges as hydride donors: diverse appearances of the tert-amino-effect

Abstract

It has been shown that the 1-NMe₂ group in the 2-substituted 1,8-bis(dimethylamino)naphthalenes (proton sponges) can intramolecularly donate a hydride ion to an appropriate electron-accepting ortho-substituent such as diarylcarbenium ion, β,β′-dicyanovinyl or methyleneiminium group. This produces the 1-N⁺(Me)CH₂ functionality and triggers a number of further transformations (tert-amino effect) including peri-cyclization, ortho-cyclization or hydrolytic demethylation. In each particular case, the course of the reaction is determined by the nature of the ortho-substituent and the most potent nucleophile presenting in the reaction mixture. For 2,7-disubstituted 1,8-bis(dimethylamino)naphthalenes, two types of tandem tert-amino effect with the involvement of both peri-NMe₂ groups have been registered. The conclusion was made that proton sponges are generally more active in the tert-amino reactions than the corresponding monodimethylaminoarenes. This is ascribed both to higher electron donor ability of proton sponges and markedly shortened distance between electrophilic C_α-atom in the ortho-substituent and hydrogen atoms of the nearest NMe₂ group. Most conversions observed proceed in good to high yields and are useful for the preparation of derivatives of benzo[h]quinoline, quino[7,8:7′,8′]quinoline, 2,3-dihydroperimidine, N,N,N′-trimethyl-1,8-diaminonaphthalene and proton sponge itself.