On the reaction of (vinylimino)phosphoranes and related compounds.: Novel synthesis and properties of [n](2,4)pyridinophanes and [n](2,4)quinolinophanes (n=9-7)

A short, new synthesis of [n](2,4)pyridinophanes 13a-c (n = 9-7) and 14a-c (n = 9-7), as well as 15a (n = 9) and 16a (n = 9) consists of the reaction of 3-aminocyclohex-2-enone and several beta-amino enones with cycloalk-2-enones in an enamine-alkylation process, subsequent condensation of the amino group with a carbonyl function, and dehydrogenation of the product in the presence of a dehydrogenating agent (10% Pd/C). Cyclohexenone-annulated [n](2,4)pyridinophanes 13a-c, which have a quinoline skeleton, were converted conveniently to a series of [n](2,4)quinolinophanes 26a-c (n = 9-7), including the known [8](2,4)quinolinophane 26b. H-1 NMR spectroscopy at various temperatures clarified the dynamic behavior of the heptamethylene chain of [7](2,4)pyridinophanes 13c, 14c, and [7](2,4)quinolinophane 26c. The energy barriers (Delta G(c)(double dagger)) for bridge flipping are 11.3 kcal mol(-1) (T-c -10 degrees C) for 13c, 11.7 kcal mol(-1) (T-c 0 degrees C) for 14c, and 12.2 kcal mol(-1) (T-c -5 degrees C) for 26c. The heptamethylene chain of 26c does not flex easily as compared with that of 13c and 14c. The deformation of the pyridine ring of 13a-c and 26a-c is also suggested by the red shifts of the UV spectra and by the H-1 NMR spectra. The base strength of 26a-c seems to be almost independent of the size of the methylene bridge, although pK(a)-values of the protonated form of 26a-c become slightly larger when the methylene bridge becomes shorter.