Syntheses and Properties of 5-Substituted [n](2,4)Pyridinophanes, Model Compounds of NAD(P)

[n](2,4)Pyridinophane derivatives 5–8 having an ester or an amide group at the 5-position were synthesized by aza-Wittig reactions between β-substituted vinyliminophosphoranes and cyclic α,β-unsaturated ketones. [β-(Methoxycarbonyl)vinyl]- (1), [β-(N,N-tetrametnylenecarbamoyl)vinyl]-(2), [β-(N-benzylcarbamoyl)vinyl]- (3), and (β-carbamoylvinyl)iminophosphorane (4) were synthesized from the corresponding vinyl azides and triphenylphosphine. The heptamethylene chains of 5-(methoxycarbonyl) [7] (2,4)pyridinophane (5), 5-(N,N-tetramethylenecarbamoyl) [7] (2,4) pyridinophane (6), and 5-(N-benzylcarbamoyl)[7](2,4)pyridinophane (7) flipped with ΔG^‡ = 11.2 (T_c = 10.3°C), 10.8 (T_c = 0.2°C), and 10.5 kcal/mol (T_c = −5.2°C), respectively. At lower temperatures, the three conformations of the heptamethylene bridge were frozen. Methylpyridinium iodides 10 (n = 7, 6, and 5) derived from 6 were reduced more easily [E_1/2* (half height potential) = −1.65 V (n = 7); −1.63 V (n = 6); −1.29 V vs Ag/AgCl (n = 5)] than the reference compound, 2,4-diethyl-5-(N,N-tetramethylenecarbamoyl)pyridinium ion (11) [E_1/2* = −1.82 V vs Ag/AgCl]. The reduced species dimerized quickly.