Journal
JOURNAL OF ORGANIC CHEMISTRY
Volume 81, Issue 13, Pages 5574-5587Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.joc.6b00917
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Funding
- Russian Foundation for Basic Research [14-03-00010]
- Ministry of Education and Science [4.967.2014/K]
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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 center dot center dot center dot N hydrogen bond was registered at room temperature and frozen below -30 degrees 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.
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