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Sonogashira‐Type Reactions with 5‐Chloro‐1‐phenyl‐1 H ‐pyrazole‐4‐carbaldehydes: A Straightforward Approach to Pyrazolo[4,3‐ c ]pyridines
Author(s) -
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.201100626
Subject(s) - chemistry , sonogashira coupling , pyrazole , pyridine , regioselectivity , trifluoromethanesulfonate , medicinal chemistry , ring (chemistry) , catalysis , combinatorial chemistry , organic chemistry , palladium
Abstract The easily obtainable 5‐chloro‐1‐phenyl‐1 H ‐pyrazole‐4‐carbaldehydes 2 were used as precursors in Sonogashira‐type cross‐coupling reactions with various alkynes to provide the corresponding 5‐alkynyl‐1 H ‐pyrazole‐4‐carbaldehydes 3 . Treatment of these with tert ‐butylamine with microwave assistance afforded the corresponding 1‐phenylpyrazolo[4,3‐ c ]pyridines 4 . The oximes 5 – derived from the aldehydes 3 – were transformed into the corresponding 1‐phenylpyrazolo[4,3‐ c ]pyridine 5‐oxides 6 through silver‐triflate‐catalysed regioselective cyclisation. Ring closure of the oximes 5 in the presence of iodine in ethanol gave the 7‐iodo‐1‐phenylpyrazolo[4,3‐ c ]pyridine 5‐oxides 7 . Detailed NMR spectroscopic investigations were undertaken with all obtained products.