PEG-400 assisted Kröhnke synthesis of 2-(2-hydroxyphenyl)-4-arylpyridines annulated by C₅-C₆cycles with substituted benzylidene group

Substituted 2‐(ortho‐hydroxyaryl)cyclopenta[b]pyridines: Synthesis and Fluorescent Properties under Neutral, Acidic Medium and Solid State

“…[a] These results were reported in cited previous work [12] . [b] yield after recrystallization from EtOH‐CHCl 3 mixture (3 : 1) [c] yield after recrystallization from EtOH‐CH 2 Cl 2 mixture (1 : 1).…”

“…There are two possible paths for the reaction, through the formation of mono-enone and cross-conjugated intermediates. [12] To determine the path of the reaction, two four-component transformations were carried out using monobenzylidenecyclopentanones (6 a, b), aromatic aldehydes (2 g, i), pyridinium salt 3 b and ammonium acetate. In both cases, a mixture of two products (7 a + 7 b) was isolated in the same ratio (3 : 1), regardless of the mono-enone used (Scheme 2).…”

“…[15] Consequently, pseudo-five-component reactions and four-component reactions for the synthesis of cyclopenta[b]pyridines by the Kröhnke method proceed through the initial formation of a cross-conjugated intermediate, and not through the initial formation of 2-arylidenecyclopentanone 6 as suggested in previous work. [12] Scheme 1. Pseudo-five-component Krohnke-type reaction in synthesis of 2-(orthohydroxyaryl)cyclopenta[b]pyridines 4, 5.…”

“…[a] These results were reported in cited previous work. [12] [b] yield after recrystallization from EtOH-CHCl 3 mixture (3 : 1) [c] yield after recrystallization from EtOH-CH 2 Cl 2 mixture (1 : 1). The proposed mechanism of pseudo-five-component and four-component reactions: cycloalkanone 1 or mono-enone 6 and aromatic aldehyde 2 undergo aldol condensation with the formation of E-cross-conjugated dienone A with the help of ammonium acetate.…”

“…Here we report on mechanistic details of the synthesis of new derivatives of the series 7-arylidene-4-aryl-2-(ortho-hydroxyaryl)-6,7-dihydro-5H-cyclopenta[b]pyridines, formation of these systems, on their structural features based on twodimensional NOESY spectroscopy and on their luminescent properties in neutral, acidic conditions and in solid state. This work is a development of a previous study, [12] where we obtained a series of 2-(2-hydroxyaryl)pyridines fused with penta-and hexa-carbocycles.…”