title: Synthesis of trifluoromethyl-substituted pyrazolo[4,3-c]pyridines - sequential versus multicomponent reaction approach.
abstract: A straightforward synthesis of 6-substituted 1-phenyl-3-trifluoromethyl-1H-pyrazolo[4,3-c]pyridines and the corresponding 5-oxides is presented. Hence, microwave-assisted treatment of 5-chloro-1-phenyl-3-trifluoromethylpyrazole-4-carbaldehyde with various terminal alkynes in the presence of tert-butylamine under Sonogashira-type cross-coupling conditions affords the former title compounds in a one-pot multicomponent procedure. Oximes derived from (intermediate) 5-alkynyl-1-phenyl-3-trifluoromethyl-1H-pyrazole-4-carbaldehydes were transformed into the corresponding 1H-pyrazolo[4,3-c]pyridine 5-oxides by silver triflate-catalyzed cyclization. Detailed NMR spectroscopic investigations ((1)H, (13)C, (15)N and (19)F) were undertaken with all obtained products.
authors.affiliation: Division of Drug Synthesis, Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.
authors.forename: Barbara
authors.initials: B
authors.lastname: Palka
authors.affiliation: Division of Drug Synthesis, Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria ; Department of Biotechnology, Chemistry and Pharmacy, University of Siena, I-53100, Siena, Italy.
authors.forename: Angela
authors.initials: A
authors.lastname: Di Capua
authors.affiliation: Department of Biotechnology, Chemistry and Pharmacy, University of Siena, I-53100, Siena, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Anzini
authors.affiliation: Division of Drug Synthesis, Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria ; Institute of Synthetic Chemistry, Kaunas University of Technology, LT-50254 Kaunas, Lithuania.
authors.forename: Gyté
authors.initials: G
authors.lastname: Vilkauskaité
authors.affiliation: Institute of Synthetic Chemistry, Kaunas University of Technology, LT-50254 Kaunas, Lithuania.
authors.forename: Algirdas
authors.initials: A
authors.lastname: Sačkus
authors.affiliation: Division of Drug Synthesis, Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Holzer
keywords: 13C; 15N; 19F); NMR (1H; Sonogashira coupling; microwave-assisted reactions; multicomponent reactions; trifluoromethylpyrazoles