[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-tetramethylenecarbamoyl)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)(2,4)pyridinophane (5), 5-(N,N-tetramethylenecarbamoyl)(2,4)pyridinophane (6), and 5-(N-benzylcarbamoyl)(2,4)pyridinophane (7) flipped with ΔG‡ = 11.2 (Tc = 10.3°C), 10.8 (Tc = 0.2°C), and 10.5 kcal/mol (Tc = -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 [E1/2* (half height potential) = -1.65 V (n = 7); -1.63 V (n = 6); -1.29 V va Ag/AgCl (n = 5)] than the reference compound, 2,4-diethyl-5-(N,N-tetramethylenecarbamoyl)pyridinium ion (11) [E1/2* = -1.82 V vs Ag/AgCl]. The reduced species dimerized quickly.
|Number of pages||6|
|Journal||Journal of Organic Chemistry|
|Publication status||Published - 1993|
ASJC Scopus subject areas
- Organic Chemistry