Trifluoroborate stability

Potassium aryl- and 1-alkenyltrifluoroborates (ArBFsK and RBF3K) are easily prepared from organoboronic acids or esters. In general, the trifluoroborates have greater air stability and greater nucleophilicity " when compared to the... 

A formal total synthesis of oximidine II was achieved by G.A. Molander et al., using an intramoiecuiar Suzuki-type cross-coupiing between an alkenyl potassium trifluoroborate and an alkenyl bromide to construct the highly strained, polyunsaturated 12-membered macrolactone core of the natural product. " The stability of potassium trifluoroborates was exploited in order to establish the best conditions for the macrocyclization. 

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]. 

Organo-SOMO catalysis has been successfully exploited to achieve the first asymmetric a-vinylation of aldehydes using vinyl trifluoroborate salts and the commercial Kim and MacMillan catalyst 191. " ° Vinyl potassium trifluoroborate salts participate in enantioselective and regioselec-tive carbon-carbon bond formation with the aldehyde-derived radical cation 192 to form a (3-borato-stabilized radical 193 (Scheme 25.90), which in the presence of a suitable oxidant will undergo rapid electron transfer to render the (3-cation (not shown). Subsequent Peterson elimination of the trifluoroborate group with tran.s-selectivity followed by iminium hydrolysis of 194 would then reveal an optically enriched R-( )-vinyl aldehyde (e.g., 195). 

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... 

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