Alkynes trifluoromethanesulfonate

Alkynes react when heated with trifluoroacetic acid to give addition products. Mixtures of syn and anti addition products are obtained. Similar addition reactions occur with trifluoromethanesulfonic acid. These reactions are analogous to acid-catalyzed hydration and proceed through a vinyl cation intermediate. 

The original Sonogashira reaction uses copper(l) iodide as a co-catalyst, which converts the alkyne in situ into a copper acetylide. In a subsequent transmeta-lation reaction, the copper is replaced by the palladium complex. The reaction mechanism, with respect to the catalytic cycle, largely corresponds to the Heck reaction.Besides the usual aryl and vinyl halides, i.e. bromides and iodides, trifluoromethanesulfonates (triflates) may be employed. The Sonogashira reaction is well-suited for the synthesis of unsymmetrical bis-2xy ethynes, e.g. 23, which can be prepared as outlined in the following scheme, in a one-pot reaction by applying the so-called sila-Sonogashira reaction ... 

Trifluoromethylsulfonyl)alkynes such as 4 are easily obtained by sulfonylation of acetylenic anions with trifluoromethanesulfonic anhydride (3). ... 

Benzenetellurinyl trifluoromethanesulfonate (155) reacts with internal alkynes in acetonitrile to afford oxazoles via a spontaneous intramolecular cyclization of the initially formed addition products (156) <92CC1070>. The reactions with aryl alkyl alkynes are regioselective. The addition products from terminal alkynes do not cyclize, but isomerize to stable (Z)-alkenes instead. The pathway shown in Scheme 72 accounts for the products. 

Metal-catalyzed hydroarylation of alkynes catalyzed by electrophilic transition metal complexes has received much attention as a valuable synthetic alternative to the Heck and cross-coupling processes for the synthesis of alkenyl arenes (384). Metal trifluoromethanesulfonates (metal triflates) [M(OTQn M = Sc, Zr, In] catalyze the hydroarylation of alkynes via 71 complexation to give 1,1-diarylalkenes in very good yields (Scheme 32) (385). The reaction likely proceeds by a Friedel-Crafts mechanism via the alkenyl cation intermediate where the aryl starting material also serves as the solvent. 

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