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Pyridine‐substituted hydroxythiophenes. V . Preparation of 5‐(2‐, 3‐and 4‐pyridyl)‐2‐hydroxythiophenes
Author(s) -
Zhang Yihua,
Hömfeldt AnnaBritta,
Gronowitz Salo
Publication year - 1995
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570320313
Subject(s) - chemistry , boron trifluoride , tautomer , dichloromethane , alkylation , pyridine , medicinal chemistry , boron , catalysis , organic chemistry , solvent
5‐(2‐, 3‐ and 4‐Pyridyl)‐2‐ t ‐butoxythiophenes have been prepared in very good yields by Pd(0) catalyzed cross‐coupling of the three isomeric bromopyridines with 5‐trimethylstannyl‐2‐ t ‐butoxythiophene derived from 2‐bromothiophene via 2‐ t ‐butoxythiophene. Dealkylation of 5‐(2‐, 3‐ and 4‐pyridyl)‐2‐ t ‐but‐oxythiophenes with boron trifluoride etherate in dichloromethane at room temperature led to predominant formation of rearranged products, 5‐(2‐ and 3‐pyridyl)‐3‐ t ‐butyl‐3‐thiolene‐2‐ones, together with a small amount of 5‐(2‐ and 3‐pyridyl)‐2‐hydroxythiophenes as a mixture of two tautomeric keto forms in the case of the 2‐pyridyl and the 3‐pyridyl isomers, and exclusive formation of rearranged product in the case of the 4‐pyridyl isomer. However, dealkylation of 2‐methoxy‐5‐(2‐, 3‐ and 4‐pyridyl)thiophenes, prepared similarly to the 5‐(2‐, 3‐ and 4‐pyridyl)‐2‐ t ‐butoxythiophenes, with boron tribromide under the same reaction conditions as above resulted exclusively in the tautomeric mixture of 5‐(2‐ and 3‐pyridyl)‐3‐thiolene‐2‐ones and 5‐(2‐ and 3‐pyridyl)‐4‐thiolene‐2‐ones in the case of the 2‐pyridyl and 3‐pyridyl isomers. In the case of the 4‐pyridyl isomer polymerization took place.