As af irst example of metal-free and catalytic fluorinative transformationsofalkynes, we developed acycloisomerization-fluorination sequence of N-propargyl amides catalyzed by an iodine(III) species. The iodine(III) catalyst is in situ generated from iodoarene as aprecatalyst with Selectfluor as af luorinating oxidant in the presence of HF·pyridine.Fluorines ubstituents show am arked improvemento fp roperties, such as solubility,b ioavailability, and metabolic stability, in many examples of introducing fluorine into pharmaceuticals and bioactive substances. [1] Accordingly,e fficient introduction methods of fluorine into organic compounds have received much attention recently. [2] Amongt hem,t he combination of cyclization and fluorination reaction in as ingle operation provides highly efficient approaches to give fluorinated heterocycles from unsaturated compounds bearing ah eteroatom nucleophile. For the synthesis of fluorinated aliphatic heterocycles, variousm etal-catalyzed intramolecular aminofluorination [3] and oxyfluorinationr eactions [4] of alkenes [5] or their metal-free methods [6,7] have been developed. In contrastt ot he reactions of alkenes, the cycloisomerization-fluorination sequence of alkynes has been less studied. [8,9] Althoughg old catalysts with Selectfluor have been well employed for this sequence, the catalytic systemsw ere not effective on that of N-propargyl amides (see the Supporting Information). Also, to the best of our knowledge, metal-free methods for such sequence have not been achievedy et. Moreover,b ecause halocyclization reactions of N-propargyl amides by general halogenating reagents hardly bring about aromatization to halogenated oxazoles, [10] one-pot two-step methods, including metal catalysis for the synthesis of halogenated oxazoles, have been developed by Hashmi's and other groups(Scheme 1a). [10b,c, 11] One the other hand, as part of our studies on the metal-free synthesis of aromatic heterocyclest hrough the activation of alkynes by hypervalent iodine(III) reagents, [12] we have recently found the cycloisomerization-acetoxylation sequence of Npropargyl amides with PhI(OAc) 2 (PIDA) (Scheme 1b). [12a] This reaction, which can afford oxazoles bearing the acetoxyg roup in as ingleo peration, inspired us to examine the formation of fluorinated oxazoles. Herein, ametal-free and catalytic cycloisomerization-fluorinations equence of N-propargyl amides mediated by iodine(III) is described (Scheme 1c).In recent years, there has been ac onsiderable growth in the application of hypervalent iodine reagents to organic syntheses due to their low toxicity and transition-metal-like reactivities, such as an activation of unsaturated bonds, reductive elimination, and ligand exchange. [13] Particularly,( difluoroiodo)arenes (ArIF 2 )c an be used in fluorinative transformations of unsaturated compounds withouta ny metal catalysts. [14] These procedures have been extended to some metal-free cycloisomerization-fluorinationr eactions of alkenes. [15] For example, Hara et al. repo...
