957 Pyrazolo[1,5-a]pyridines, due to being isosteric to indole and purine, as well as increased metabolic stability, are widely used in drug design. For example, they were used to obtain anti-tuberculosis drugs, 1 EP1 receptor antagonists, 2 kinase p38 inhibitors. 3 Developed in Japan drug ibudilast, 2-methyl-1-[2-(propan-2-yl)pyrazolo-[1,5-a]- pyridin-3-yl]propan-1-one, is an inhibitor of PDE4 phosphodiesterases and is used in the treatment of asthma and post-stroke conditions. 4 Recently, ibudilast was consi- dered as a promising agent for the treatment of multiple sclerosis. 5 In modern medicinal chemistry, much attention is paid to the introduction of fluorine atoms into organic molecules. 6 Indeed, about a quarter of new small molecule drugs approved by the FDA in 2015–2018 contain fluorine atoms. Examples of the use of fluoropyrazolo[1,5-a]- pyridine scaffold in the design of drugs for the treatment of autoimmune diseases 7 and PI3K-γ kinase inhibitors were reported. 8 The main methods for the preparation of fluoropyrazolo[1,5-a]pyridine structures are annulation of the pyrazole ring to the derivatives of N-aminopyridinium salts 2,9,10 or direct fluorination of the pyrazole ring with N–F reagents. 11 It is notably that the recently proposed method for the fluorination of heterocyclic compounds by fluoro- decarboxylation of the corresponding carboxylic acids by the action of Selectfluor reagent 12 was successfully applied to pyrazolo[1,5-a]pyridines. 7,8 The aim of this work was to study the process of fluorination of 2,3-disubstituted pyrazolo[1,5-a]pyridines with N–F reagents. Pyrazolopyridines 1a,b (Scheme 1), which are easily synthesized by the reaction of dimethyl acetylenedicarboxylate or methyl 3-phenylpropiolate with pyridinium N-imine, were chosen as model compounds. 13 After adding 1.2 equiv of Selectfluor reagent to pyrazolo- pyridine 1a,b in anhydrous MeCN, complete consumption of the fluorinating reagent was observed. Further evapo- ration of the reaction mixture in the presence of silica gel and subsequent purification of the resulting product by column chromatography on SiO 2 led to 3-fluoropyrazolo- pyridines 2a,b (Scheme 1). Chemistry of Heterocyclic Compounds 2020, 56(7), 957–960 Synthesis of 3-fluoropyrazolo[1,5-a]pyridines by fluorination of methyl pyrazolo[1,5-a]pyridine-3-carboxylates Sabina V. Alieva 1,2 , Aleksey Yu. Vorob'ev 1 * 1 N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, 9 Akademika Lavrentieva Ave., Novosibirsk 630090, Russia; e-mail: vor@nioch.nsc.ru 2 Novosibirsk State University, 1 Pirogova St., Novosibirsk 630090, Russia Submitted March 23, 2020 Accepted April 24, 2020 The reaction of methyl esters of pyrazolo[1,5-a]pyridine-2,3-dicarboxylic and 2-phenylpyrazolo[1,5-a]pyridine-3-carboxylic acids with the fluorinating reagent Selectfluor gave 3-fluoropyrazolo[1,5-a]pyridine-2-carboxylic acid methyl ester and 3-fluoro-2-phenylpyrazolo- [1,5-a]pyridine. Monitoring the progress of the reaction by 1 H NMR spectroscopy showed the formation of an intermediate fluorine- containing σ-complex. Keywords: pyrazolo[1,5-a]pyridines, Selectfluor, electrophilic fluorination. Scheme 1 Translated from Khimiya Geterotsiklicheskikh Soedinenii, 2020, 56(7), 957–960 0009-3122/20/56(7)-0957©2020 Springer Science+Business Media, LLC DOI 10.1007/s10593-020-02757-7