A Camouflagednido-Carborane Anion: Facile Synthesis of Octa-B-methyl-1,2-dicarba-closo-dodecaborane(12) and Its Deboration Reaction

Abstract

The exhaustive methylation of the three isomers of the icosahedral carboranes 1,2-, 1,7-, and 1,12-dicarbadodecaborane(12) (ortho-(1), meta-(2), and para-carborane (3)) under Friedel ± Crafts conditions using MeI/AlCl 3 is described. Regioselectively ortho-and meta-carborane are octamethylated providing 4,5,7,8,9,10,11,12-octamethyl-1,2-dicarba-closo-dodecaborane(12) (6) and 4,5,6,8,9,10,11,12-octamethyl-1,7-dicarba-closo-dodecaborane(12) (8) in high yield. Their BH vertices adjacent to both CH vertices remain unmethylated. Paracarborane can be quantitatively converted to its deca-B-methyl derivative 4.

Synthesis and evaluation of transthyretin amyloidosis inhibitors containing carborane pharmacophores

“…The corresponding methyl ester of 2 produced from 4,5,7,8,9,10,11,12-octamethyl-1,2-dicarba-closo-dodecaborane, was similarly subjected to basemediated saponification to give 2 in good yield (44) (45). Lithiation of the free C-H vertex followed by reaction with methyl chloroformate yielded the methyl esters of 6 and 8 (compound 7), which were saponified to provide the acids in good yield.…”

Magnesium Reagents Featuring a 1,1′‐Bis(o‐carborane) Ligand Platform

“…These methods, which include transition‐metal‐catalyzed cross‐coupling and electrophilic substitution, enable site‐selective substitution from simple precursors that provide derivatized carboranes with tailored steric and electronic profiles. Taking advantage of such functionalization avenues, we synthesized H 2 ‐Mebc from H 2 ‐bc using Hawthorne's method with the intent of evaluating the potential role of such B ‐vertex substitution on the behavior of Mg‐based bis( o ‐carboranyl) transfer reagents.…”

“…These chemical shifts are consistent with other o ‐caboranes containing B ‐bound alkyl substituents reported in the literature. [15j], [15k], [15l], , In contrast to 1a , only one set of methyl and methylene peaks are observed in [D 8 ]THF solvent, and they correspond to the bound DME ligands. According to 13 C NMR spectroscopy, the carbon resonances corresponding to the cage‐bound methyl groups in 1b are severely broadened due to coupling with quadrupolar 11 B and 10 B nuclei ( S = 3/2, 80 % natural abundance; S = 3, 20 % natural abundance, respectively) but can be observed between about 0.5 and –3.0 ppm.…”

“…Importantly, the electronic influence of methyl substituents in 2b relative to 2a highlights the possibility of employing functionalized bis(carboranyl) ligands to modulate the ligand fields of chelated main group or transition metals while holding the steric environment in the immediate vicinity of the chelated atom constant. Given recent advances in the development of methods toward selectively functionalizing specific boron vertices of ortho ‐ and meta ‐carborane, other functionalized derivatives of this bis(carboranyl) ligand class may prove useful for clearly identifying and strategically leveraging electronic effects when employed as supporting ligands.…”

Carborane — Wenn Kohlenstoff und Bor sich treffen

“…Beim ortho-Carboran gelingt die C-Lithiierung (ebenso sind auch Mono-und Di-lithio-Zwischenstufen von meta-und para-Carboran erhältlich) und eröffnet zahlreiche Anwendungen, wie sie für Organolithiumverbindungen hinreichend bekannt sind (Abbildung 8). Aufgrund ihrer Beständigkeit lassen sich ortho-und meta-Carboran an acht Positionen und das para-Carboran sogar an allen zehn Boratomen methylieren (Friedel/Crafts-Bedingungen) [16]. Aufgrund ihrer Beständigkeit lassen sich ortho-und meta-Carboran an acht Positionen und das para-Carboran sogar an allen zehn Boratomen methylieren (Friedel/Crafts-Bedingungen) [16].…”