The Charge‐Reverse Analogy as an Inspiration for the Preparation of Polydentate Lewis Acidic Boranes

Abstract

Reversing the charge: The recent preparation of a masked version of a 2,2′‐diborabiphenyl (the radical anion of its adduct with benzo[c]cinnoline is shown) constitutes a noticeable achievement on the way to bidentate Lewis acidic boranes with optimized properties as ligands and opens up the chemistry of this unique class of bidentate Lewis acids.

Substitution of hydroxide by fluoride at the boron center of a BODIPY dye

“…Slow evaporation of the toluene produced a crop of dark red crystals of 2 (75 mg, 56% yield, not optimized). 1 …”

“…The resulting red-orange microcrystalline solid was collected by filtration and dried in vacuo to give 3 (69 mg, 97% yield). 1 …”

“…The solvent was removed under reduced pressure and the residue was recrystallized at À40 8C from EtOAc (5 mL) to afford 4 as a bright orange crystalline solid (46 mg, 91% yield). 1 …”

“…The coordination of fluoride anions to boron compounds has attracted a great deal of interest because of its implication in the field of anion sensing [1][2][3][4][5] and molecular imaging by [ 18 F]-positron emission tomography [6][7][8]. As part of our contribution to the general area of fluoride ion coordination to boron compounds, we have recently reported that cationic BODIPY compounds [9,10] such as A + react with fluoride anions in CHCl 3 to afford the corresponding BODIPY difluoride species [11].…”

Allylation of Ketones with a Ferrocene‐Based Planar Chiral Lewis Acid

“…However, most of the planar chiral ferrocene derivatives reported to date relate to the Lewis basic phosphine and amine ligands, which have found widespread use as nucleophilic catalysts [1] and as ligands in transition-metal-catalyzed chiral synthesis. [2] Surprisingly, the use of the charge-reverse complementary Lewis acids, [3] the planar chiral ferrocenylboranes, in asymmetric synthesis has not been demonstrated, although chiral organoboranes are well known to serve as highly versatile reagents and catalysts. [4] In fact, the only prior example of a planar chiral organoborane in stereoselective synthesis is the use of (h 5 -1,2-azaborolyl)iron complexes in stereoselective aldol reactions and imine additions by Fu and co-workers.…”