Heteroaryl trifluoroborate

The key step of this synthetic route is an iminium organocatalyzed Friedel-Crafts reaction of an in situ generated activated boronate 20 intermediate and crotonaldehyde (21), forming a non-traditional Friedel-Crafts adduct 22, as the result of an unexplored regjoselectivity (C2 versus C3). Additionally, the feasible structural variations on the starting heteroaryl trifluoroborate salt could allow straightforward access to various natural product analogues. 

PCy3 also proved to be the ligand of choice for a wide-ranging study of Suzuki couplings of heteroaryl chlorides and heteroarylboronic acids (Equation 2.18) where aryl boronate esters and aryl trifluoroborates could also be employed [33]. 

Lee J-K, Gwinner MC, Berger R, Newby C, Zentel R, Friend RH, Sirringhaus H, Ober CK (2011) High-performance electron-transporting polymers derived from a heteroaryl bis (trifluoroborate). J Am Chem Soc 133 9949-9951... 

Tertiary aminotrifluoroborates couple equally well with aryl and heteroaryl bromides with 1.3 equivalents of the aminotrifluoroborate at higher concentration using the XPhos ligand and long reaction times (45 h). This represented optimised conditions from an early report wherein the true identity of the trifluoroborate species was incompletely understood and the salt had been contaminated with KBr (Scheme 16.17). 

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