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In Search of Oligo(2‐thienyl)‐Substituted Pyridine Derivatives: A Modular Approach to Di‐, Tri‐ and Tetra(2‐thienyl)pyridines
Author(s) -
Bera Mrinal K.,
Hommes Paul,
Reissig HansUlrich
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201101739
Subject(s) - pyridine , thiophene , chemistry , protonation , medicinal chemistry , intramolecular force , tetra , boronic acid , yield (engineering) , photochemistry , combinatorial chemistry , stereochemistry , organic chemistry , materials science , ion , metallurgy
Herein, we describe our attempts to systematically prepare a series of oligo(2‐thienyl)‐substituted pyridine derivatives. The crucial starting material, a β‐alkoxy‐β‐ketoenamide, is easily available on a large scale by the reaction of lithiated methoxyallene with thiophene‐2‐carbonitrile and thiophene‐2‐carboxylic acid. This three‐component reaction is followed by intramolecular cyclization to yield the suitably functionalized 2,6‐di(2‐thienyl)‐substituted pyridine derivates. The two oxygen atoms allow the programmed activation of positions C‐3, C‐4, or C‐5 of the pyridine ring to perform palladium‐catalyzed coupling reactions with thiophene‐2‐boronic acid or 2‐(tributylstannyl)thiophene, and alternatively, reductive removal of groups. With this concept, we were able to prepare five pyridine derivatives with 2‐thienyl substituents in the 2,6‐, 2,3,6‐, 2,4,6‐, 2,3,4,6‐, and 2,3,5,6‐positions. 2,3,4,5,6‐Penta(2‐thienyl)pyridine was not available with our methods. The UV/Vis and fluorescence spectra of all pyridines were recorded and showed a dependence on the substitution pattern and protonation state. For the protonated 2,3,5,6‐tetra(2‐thienyl)‐substituted pyridine, a Stokes shift of about 180 nm with an emission at 515 nm was observed.