A Novel Ring Transformation of Pyridinium Salts as a Route to 4-Arylpyridines

Abstract

Regiospecific phenylation of pyridine derivatives at the 4‐position takes place in the reaction of 4‐methylpyridinium salts 1 with other pyridinium salts 2 by intermolecular transformation of the pyridine ring in 1 and participation of the methyl group of 2. The method developed makes it possible to carry out ring transformation not only for pyridinium salts 1 but even for pyridine itself. 4‐Phenylpyridine (3) was produced in 29−57% yields. The new reaction proceeds in an aqueous medium on heating and on treatment with methylammonium sulfite. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2002)

2-Alkylidene-4-oxothiazolidine Vinyl Bromides: Versatile Precursors for C(5) Functionalization via Pyridine-Assisted Bromine Transfer

“…Spectroscopic data and elemental analyses were consistent with the structures 9-11. 29 Despite the fact that pyridine is a poor leaving group and that the pyridinium ring is susceptible to nucleophilic attack at the 2-, 4-and 6-positions, 30 in some cases followed by ring cleavage, 31,32 we did not observe a decrease in effectiveness of these substitution reactions affording new 5-amino and 5-alkoxy-2-alkylidene-4oxothiazolidines.…”

Advances in the synthesis of 4-aryl- and 4-hetarylpyridines

“…Thus the long-term heating of pyridine and 4-methylpyridinium salt 153 (R 2 = Pr i ) with an aqueous solution of methylammonium sulfite made it possible to obtain 4-phenylpyridine (65a) in yields approaching 20%. 162…”

Reactivity of 4-Methylpyridinium Salts in a New Reaction of Ring Transformation of Pyridine and Isoquinoline Derivatives

“…In keeping with the previously suggested mechanism of this type reactions [15,17] apparently the sulfite-ion addition to salt IIa and IIb occurs thus distorting the aromaticity of the pyridine ring followed by its opening. The non-cyclic intermediate thus formed underwent condensation promoted by a base with the active methyl group of salt Ia and Ib which in the form of anhydro base acts as a C-nucleophile in the process of the pyridine ring transformation.…”