ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Synthesis and reactions of 2-[3-(trifluoromethyl)phenyl]furo[3,2- c ]pyridine

Ivana Bradiaková, Naďa Prónayová, Anton Gatial, and Alžbeta Krutošíková

Department of Chemistry, Faculty of Natural Sciences, University of St. Cyril and Methodius, SK-917 01 Trnava, Slovakia

E-mail: alzbeta.krutosikova@ucm.sk

Received: 12 December 2007

Abstract: (E)-3-{5-[3-(Trifluoromethyl)phenyl]furan-2-yl}propenoic acid (I) was prepared from 5-[3-(tri-fluoromethyl)phenyl]furan-2-carbaldehyde under the Doebner’s conditions. The obtained acid was converted to the corresponding azide II, which was cyclized by heating in diphenyl ether to 2-[3-(trifluoromethyl)phenyl]-4,5-dihydrofuro[3,2-c]pyridin-4-one (III). This compound was aromatized with phosphorus oxychloride to chloroderivative IV which was reduced with H₂NNH₂-Pd/C to the title compound V. 2-[3-(Trifluoromethyl)phenyl]furo[3,2-c]pyridin-5-oxide (VI) was synthesized by reaction of V with 3-chloroperoxybenzoic acid in dichloromethane. On treatment of VI with benzoyl chloride and potassium cyanide (Reissert-Henze reaction), corresponding 2-[3-(trifluoromethyl)phenyl]furo[3,2-c]pyridine-1-carbonitrile (VII) resulted. 5-Amino-2-[3-(trifluoromethyl)phenyl]furo[3,2-c]pyridin-5-ium-4-methylbenzene sulfonate (VIII) was prepared by direct N-amination of the title compound V with 1-[(aminooxy)sulfonyl]-4-methylbenzene in dichloromethane. Then, VIII was transformed to a non-isolated zwitterionic N-imid IX which afforded the corresponding furo[3,2-c]pyrazolo[1,5-a]pyridine carboxylic acid esters X, XI by 1,3-dipolar cycloaddition reactions with dimethyl but-2-ynedionate (DBD) or ethyl propiolate. The structures of all compounds were confirmed by their IR and NMR spectra.

Keywords: fused heterocycles - furo[3,2-c]pyridines - furo[3,2-c]pyridin-5-oxide - 1,3-dipolar cycloaddition - furo[3,2-c]pyrazolo[1,5-a]pyridines

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-008-0039-6

Chemical Papers 62 (4) 428–434 (2008)