Synthesis of 4-alkoxypyridines as intermediates for zwitterionic liquid crystals

Abstract

A series of 4-alkoxypyridines with n = 5-18 was obtained in typical yields of 75-80% by reacting 4-chloropyridine hydrochloride with the appropriate alcohol in DMSO in the presence of powdered NaOH. The reported synthesis is compared to other methods for preparation of 4-alkoxypyridines, and their uses are reviewed. 4-Tridecyloxypyridine is converted into the bis-zwitterionic derivative of [closo-B10H10] 2-, which exhibits liquid crystalline and soft crystalline phases. The solid-state structures of two pyridines and the biszwitterion are established by the single crystal XRD method. The effect of N-atom coordination on the pyridine ring geometry is investigated.

Thermal and Photophysical Properties of Highly Quadrupolar Liquid‐Crystalline Derivatives of the [closo‐B12H12]2− Anion

“…The preparation of 1B[ n ]‐ p , 2B[ n ]‐ p , and 1A[ n ]‐ p series of compounds takes advantage of a recently discovered method for the activation of B−H bonds through aryliodonium zwitterions . Thus, the reaction of anion B with PhI(OAc) 2 in trifluoroacetic acid (TFA; AcOH was ineffective) gave a crude mixture of thermally labile bis‐iodonium zwitterions 3B‐ p and 3B‐ m (Ar=Ph), which without purification reacted with excess appropriate 4‐alkoxypyridine at 60 °C. The initial suspension gradually dissolved and the resulting isomeric pyridinium bis‐zwitterions, 1B[ n ]‐ p and 1B[ n ]‐ m , were separated by means of chromatography to give pure products in overall yields of about 14 and 7 %, respectively (Scheme ).…”

“…General procedure : A mixture of 3A‐ p (200 mg, 0.39 mmol) and appropriate 4‐alkoxypyridine (1.5 mL) was stirred at 80 °C overnight. The mixture was separated by column chromatography (SiO 2 , CH 2 Cl 2 /hexane, 3:2) to give the 1,10‐dipyridinium bis‐zwitterion 1A[ n ]‐ p as the fluorescent fraction in a typical yield of 55–60 %.…”

“…Without further purification, the mixture of isomers of 3B‐ p and 3B‐ m (300 mg, 0.55 mmol) was suspended in 4‐alkoxypyridine (4 mL) and the reaction mixture was stirred at 60 °C overnight. The mixture was separated by means of column chromatography (SiO 2 , CH 2 Cl 2 /hexane, 3:2) to give the 1,12‐bispyridinium bis‐zwitterion 1B[ n ]‐ p as the first fluorescent fraction followed by 1B[ n ]‐ m in typical yields of 14 and 7 %, respectively, based on starting B ‐[Et 3 NH].…”

“…General procedure : A solid mixture of isomeric phenyliodonium zwitterions 7‐ p and 7‐ m (Ar=Ph; 540 mg, 1.05 mmol), which was passed through a SiO 2 plug and washed with pentane, was added to a solution of 4‐alkoxypyridine (1.25 g, ≈5 mmol) in CH 2 Cl 2 (0.4 mL), and the resulting homogenous mixture was stirred overnight at ambient temperature under argon. The reaction progress was monitored by TLC (CH 2 Cl 2 /hexanes, 1:1).…”

Preparation of substituted alkoxypyridines via directed metalation and metal-halogen exchange

“…Various alkoxypyridines are found in pharmaceutical agents, [1][2][3] electronic materials, 4 liquid crystals, 5 organometallic complexes, [6][7][8] and oligomers. 9 They also have been used as synthetic building blocks for natural products and medicinal agents.…”