Trifluoroborates, alkenyl salts

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]. 

The use of trifluoroborate salts in couplings, which are very easily prepared from boronic acids by reaction with KHF2, is a useful variant of the Suzuki reaction. These salts have the advantage of enhanced (often considerably) stabihty compared to boronic acids and this is particularly notable for alkenyl compounds, which can be stored for a considerable time. The coupling conditions are very similar to those for boronates and are apphcable to a wide range of heterocyclic substrates, ... 

Also in the alkenyl group transfer from the trifluoroborate salts to dichloroalkyl aldimines BF3 OFt2 plays an activating role. ... 

Scheme 2.26 Suzuki-Miyaura cross-coupling reactions of alkenyl substrates involving trifluoroborate salts.

Batey and Quach have investigated alkenyl and aryl trifluoroborate salts as coupling agents. Their earlier publication [47], disclosed a C-O cross-coupling protocol... 

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