10-Dimethylamino Derivatives of Benzo[h]quinoline and Benzo[h]quinazolines: Fluorescent Proton Sponge Analogues with Opposed peri-NMe2/-N═ Groups. How to Distinguish between Proton Sponges and Pseudo-Proton Sponges.
For the first time, 10-dimethylamino derivatives of benzo[h]quinoline 6 and benzo[h]quinazoline 7a-e as mixed analogues of archetypal 1,8-bis(dimethylamino)naphthalene ("proton sponge") 1 and quino[7,8-h]quinoline 2a have been examined. Similar to 1 and 2, compounds 6 and 7 display rather high basicity, forming chelated monocations. At the same time, unexpected specifics of the protonated NMe2/-N═ systems consist of a strong shift of the NH proton to the 10-NMe2 group, contrary to the "aniline-pyridine" basicity rule. In case of 4H(+), a rapid migration (in the NMR time scale) of the NH proton between two nitrogen atoms along the N-H···N hydrogen bond was registered at room temperature and frozen below -30 °C with the proton fixed on the NMe2 group. Two different approaches for classification of strong neutral nitrogen organic bases as proton sponges (kinetically inert compounds) or pseudo-proton sponges (kinetically active) are discussed. On this basis, benzoquinoline 6 was identified as staying closer to pseudo-proton sponges while 7a-e to proton sponges due to the presence in their molecules of bulky substituents in the pyrimidine ring. Other remarkable peculiarities of 6 and 7 are their yellow color and luminescence in the visible region distinguishing them from colorless 1 and 2a.
Department of Chemistry, Southern Federal University , Zorge str. 7, 344090 Rostov-on-Don, Russian Federation.
Alexander F
AF
Pozharskii
Department of Chemistry, Southern Federal University , Zorge str. 7, 344090 Rostov-on-Don, Russian Federation.
Valery A
VA
Ozeryanskii
Department of Chemistry, Southern Federal University , Zorge str. 7, 344090 Rostov-on-Don, Russian Federation.
Vladimir Y
VY
Mikshiev
Department of Chemistry, Southern Federal University , Zorge str. 7, 344090 Rostov-on-Don, Russian Federation.
Alexander S
AS
Antonov
Institute of Physical and Organic Chemistry, Southern Federal University , Stachki Ave. 194/2, 344090 Rostov-on-Don, Russian Federation.
Anatoly V
AV
Chernyshev
Institute of Physical and Organic Chemistry, Southern Federal University , Stachki Ave. 194/2, 344090 Rostov-on-Don, Russian Federation.
Anatoly V
AV
Metelitsa
Institute of Physical and Organic Chemistry, Southern Federal University , Stachki Ave. 194/2, 344090 Rostov-on-Don, Russian Federation.
Gennady S
GS
Borodkin
Department of Chemistry, Southern Federal University , Zorge str. 7, 344090 Rostov-on-Don, Russian Federation.
Nikita S
NS
Fedik
Department of Chemistry, Southern Federal University , Zorge str. 7, 344090 Rostov-on-Don, Russian Federation.
Olga V
OV
Dyablo