Taming the beast: fluoromesityl groups induce a dramatic stability enhancement in boroles

Abstract

Boroles with a fluoromesityl group on the B atom have greatly improved air stability compared to their mesityl analogues.

Electronic Push–Pull Modulation by Peripheral Substituents in Pentaaryl Boroles

“…We choose Xyl F because its remote substitution positions rule out potential intramolecular donation from fluorine atoms into the LUMO. Such LUMO‐raising interactions may cause the blueshifted absorptions observed for Marder's (PhC) 4 BMes F ( λ max =549 nm), which were otherwise not in line with the qualitative model …”

“…Yamaguchi reported on electron‐rich thienyl groups in the butadiene backbone, which led to markedly altered HOMO–LUMO gaps . Marder's group prepared a bicyclic cycloalkyl‐diphenyl borole with a fluoromesityl residue on the boron atom . Erker found an access to unsymmetrically substituted boroles by 1,1‐carboboration of dialkynyl boranes .…”

Ring expansion reactions of anti-aromatic boroles: a promising synthetic avenue to unsaturated boracycles

“…Two outcomes were observed, both giving rise to 1,1--insertion products. 49 Attempts to isolate this species by the reaction of boroles with O 2 only led to the isolation of species lacking boron. A less hindered variant featuring H and TMS on the α--carbon, eliminated dinitrogen resulting in the 1,1--insertion of the carbene moiety (26 and 27).…”

“…The bulkier di-tolyl--substituted derivative resulted in insertion of the terminal nitrogen to form 1,2--azaborines 24 and 25 akin to the conversion of Int15 to 23 in the azide mechanism. 23,49,58 Alternatively, N--methylmorpholine--N--oxide (NMMO) proved to be an effective oxygen atom source. Despite the flourishing field of 1,2--azaborine chemistry, an analogous unsaturated 1,2--PBC 4 heterocycle has been elusive.…”

“…59 The mechanism to form these species was rationalized via oxygen coordination (Int20), followed by the formation of bicyclic intermediate Int21 via intramolecular attack of the butadiene to the carbon of the nitrone and a subsequent B--C bond cleavage. 67 An imine with two phenyl groups on the α--carbon and a benzyl group on nitrogen formed a stable adduct (49). Such eight--membered cyclic compounds are difficult to prepare and are unusual examples of BNOC 5 rings.…”