Sonogashira reaction aryl/vinyl triflates

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 ... 

Csp-Csp Cross-coupling. The palladium and copper cocatalyzed cross-coupling between vinyl/aryl halides or triflates and terminal acetylenes, known as the Sonogashira reaction, is the most straightforward and powerful method for the construction of Csp -Csp bonds with retention of the vinyl stereochemistry and has been widely reviewed (eq 26). ... 

Unlike other cross-coupling reactions, for which the scope has rapidly expanded in recent years, the range of electrophilic substrates that can be used successfully in the Sonogashira protocol is still rather limited. Vinylic substrates (iodides, bromides, chlorides, triflates, and more recently tosylates) typically yield the best results. For aromatic substrates, iodides and triflates are preferred over bromides, which in turn give far better yields than aryl chlorides. This latter aspect of the reaction is particularly frustrating when one considers the recent advances in the activation of aryl chloride substrates for reactivity in other cross-coupling protocols. ... 

Alkynyltrimethylsilanes act as effective alkynyl donors in the presence of a fluoride ion source [15]. Recent studies on the Sonogashira-type reaction of alkynylsilanes have revealed that the use of a Cu(I) [554] or Ag(I) [555] salt leads to highly efficient coupling with vinyl and aryl triflates (Scheme 10.213). 

The last Pd(0) catalyzed cross-coupling reaction covered in this chapter is the Sonogashira coupling. It involves transmetallation of an alkynyl-Cufl) species to Pd followed by coupling to an aryl or vinyl iodide or triflate. The Cu(I) alkynyl complex is created in situ by the reaction of a terminal alkyne with Cul in the presence of trieth-ylamine. The reaction is most commonly used to create diaryl alkynyl products. 

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