Aryl triflates alkynylsilane coupling

A catalytic amount of CuCl was found to activate alkynyl(trimethyl)silanes in the palladium-catalyzed coupling reaction with aryl triflates (Eq. 7) [12]. The catalytic cycle is considered to involve the transfer of an alkynyl group from an alkynylsilane to Cu(I) and then to palladium(II). A sequential palladium-catalyzed reaction of trimethylsilylacetylene gives unsymmetrical diarylacet-ylenes (Eq. 8). 

Sonogashira coupling. Stereodefmed enynes including those bearing an alkoxy substituent (i.e., enol and ynol ethers) are readily prepared from alkynes on coupling with alkenyl iodides. Alkynylsilanes can be used instead of 1-alkynes in the coupling with alkenyl and aryl triflates. ... 

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 reaction of optically active allyl(difluoro)phenylsilanes with aryl triflates affords optically active allylarenes with high stereoselectivities, wherein the absolute configuration of the newly generated chiral carbon can be controlled by the choice of a fluoride salt and the solvent polarity (Scheme 29). Aryl and alkenyl triflates are effective coupling partners not only for aUylsilanes but also for alkenyl-, aryl-, alkyl-, and alkynylsilanes as we have been seen in some examples of the preceding sections. 

TMS group is used for protection of terminal alkynes. However, alkynylsilanes themselves can be used for the coupling with aryl and alkenyl triflates using Pd-CuCl as a catalyst [74], Thus the internal alkyne 160 is prepared by stepwise reactions of two different triflates 157 and 159 with trimethylsilylacetylene (134) via 158. 

With the aid of a fluoride ion source, alkynyltrimethylsilanes work as effective alkynyl donors in the Pd-catalyzed cross-coupling with alkenyl iodides.43,43a Recent studies have revealed that the alkynylsilanes react smoothly with aryl iodides and triflates, alkenyl triflates, or alkynyl chlorides under co-catalysis by a Cu or Ag salt.45 46a The use of a Pd/imidazolium chloride system in the presence of Cs2CC>3 and a Cu co-catalyst enables an efficient coupling between alkynyltrimethylsilanes and aryl bromides.47 In some cases, this catalytic system works well under Cu-free conditions. Alkynylsilanols also can be used as alkynyl donors in the coupling with aryl iodides.48 49 When TBAF is employed as activator, the coupling proceeds efficiently without co-catalyst.48... 

A useful alternative under neutral conditions is the coupling reaction of alkynylsilanes with aryl- (or alkenyl-) triflates using a CuCl/Pd cocatalyst system (eq 18). For the mechanistic pathway the authors presume that a transmetalation from silicon to copper takes place as the keystep (Cul being less effective in the transmetalation), allowing the synthesis of symmetrical and un-symmetrical arylalk)mes. 

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