Chemistry Reference
In-Depth Information
Computational predictions indicate that extended
-systems could be even more potent
superbases. On the basis of experimental evidence and theoretical results, the set of
general rules for the molecular design of exceedingly strong superbases has been
established by Kova
p
cevi
candMaksi
c [114]: the choice of the appropriate skeleton
subunit (molecular backbone
highly basic functional group); modulation (insertion of
substituents at strategic sites); and inclusion of additional effects (destabilizing in initial
base, stabilizing in the conjugate acid). In addition, application of various physical
phenomena, such as host-mediated basicity shifts [115] may even further increase amine
basicity. Following these premises, novel classes of superbases have been designed:
polyimines, cyclopropeneimines, quinodiimines, polycyclic quinines, carbonyl poly-
enes, [3]carbonylradialenes, iminopolyenes, poly-2,5-dihydropyrrolimines, acenes,
zethrenes, pyrones and pyrone-like structures, N-substituted azacalix[n](2,6) pyridines,
subporphyrins [116], polypyridine macrocycles and bases possessing S
þ
¼
N functional
group (Chapter 11). The success of themolecular designwill be completed by synthesis of
novel bases, preferrably by simple synthetic procedures, possessing chemical stability,
solubility in common organic solvents and, above all, high kinetic activity.
References
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How significant is the influence of
buttressing effect
on their basicity? The Journal of Organic
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