Alkynyl trifluoroborate

Pd(acac)2 efficiently catalyzes the Suzuki-type reaction of potassium alkynyl trifluoroborates 232 with vinylic tellurides (Scheme 127).303 This reaction presents the advantage of using compounds of the type 232, which can be isolated and manipulated in the air. 

A similar approach has been chosen for the trifluoromethylation of alkynes (Scheme 8). Under copper catalysis, the trifluoromethyl acetylenes are formed from either the free terminal alkyne or from the corresponding alkynyl trifluoroborate [31, 32],... 

Molander has reported the synthesis of functionalized alkynyl trifluoroborates by transmetallation of alkynyllithium compounds with boronates followed by in situ treatment with KHFjIlll]. These alkynyl trifluoroborates are crystalline solids possessing excellent air stability and are shown to undergo facile cross-coupling for example with 4-bromobenzonitrile to give functionalized arylacetylenes in high yields. Thus, the reaction is tolerant to a variety of sensitive functional... 

Non-Sonogashira alkynylation procedures have also been employed with pyrimidines, and selective replacement of the 4- and 6-chlorine atoms of 2,4,6-trichloropyrimidine 258 was able to be achieved using potassium (1-hexyn-l-yl)-trifluoroborate 257 <2002JOC8416>. 

The Suzuki Coupling, which is the palladium-catalysed cross coupling between organoboronic acid and halides. Recent catalyst and methods developments have broadened the possible applications enormously, so that the scope of the reaction partners is not restricted to aryls, but includes alkyls, alkenyls and alkynyls. Potassium trifluoroborates and organoboranes or boronate esters may be used in place of boronic acids. Some pseudohalides (for example triflates) may also be used as coupling partners. 

Molander has published a series of papers demonstrating the utility of potassium alkyl, alkenyl-, alkynyl-, and aryltrifluoroborates in palladium coupling reactions. The crystallinity and air-stability of these trifluoroborate salts make the use of these an interesting alternative to the use of boronic acids or esters. Good yields have been obtained in several related palladium coupling processes, which are most easily classified as Suzuki couplings. The broad applicability of this process is demonstrated by the production of 58 [40], 59 [41], and 60 [42]. 

Alternatives to the Sonogashira reaction involve the use of preformed alkynyl organometallics, such as trifluoroborates, or the reverse coupling of haloalkynes with organometaUics. ... 

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