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Ethyl 3‐ and 5‐Triflyloxy‐1 H ‐pyrazole‐4‐carboxylates in the Synthesis of Condensed Pyrazoles by Pd‐Catalysed Cross‐Coupling Reactions
Author(s) -
Arbačiauskienė Eglė,
Vilkauskaitė Gytė,
Šačkus Algirdas,
Holzer Wolfgang
Publication year - 2011
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201001560
Subject(s) - chemistry , synthon , pyrazole , sonogashira coupling , phenylboronic acid , trifluoromethanesulfonate , medicinal chemistry , coupling reaction , organic chemistry , catalysis , palladium
The easily obtainable title compounds ethyl 5‐ and 3‐triflyloxy‐1 H ‐pyrazole‐4‐carboxylates ( 2 and 5 ) have been used as precursors in Sonogashira‐type cross‐coupling reactions with various alkynes to obtain the corresponding 5‐ and 3‐alkynyl‐4‐(ethoxycarbonyl)pyrazoles 3 and 6 . Cyclization of the latter ortho ‐difunctional synthons afforded different condensed pyrazoles such as pyrano[4,3‐ c ]pyrazol‐4(1 H )‐ones and ‐4(2 H )‐ones 7 and 10 as well as 1,5‐dihydro‐ and 2,5‐dihydro‐4 H ‐pyrazolo[4,3‐ c ]pyridin‐4‐ones 9 and 12 , respectively. Suzuki coupling of triflate 2 with phenylboronic acids gave the corresponding 5‐arylpyrazoles. Heating of 5‐(3‐chlorophenyl)‐1‐phenyl‐1 H ‐pyrazole‐4‐carboxylic acid ( 16 ) with trifluoromethanesulfonic acid led to the formation of the unexpected tetracyclic system 18 . Detailed NMR spectroscopic investigations were undertaken on all obtained products.