Synthesis, structure and aromaticity of carborane-fused carbo- and heterocycles

Abstract

The results of molecular structures, NMR data, and NICS (nucleus-independent chemical shift) and ISE (isomerization stabilization energy) values as well as molecular orbital analyses clearly suggest the presence of considerable aromatic character in the exo five-membered ring of carborane-fused carbo- and heterocycles and considerable conjugation between a 3-D carborane and a fused 2-D π-ring system.

Unpredicted Concentration-Dependent Sensory Properties of Pyrene-Containing NBN-Doped Polycyclic Aromatic Hydrocarbons

“…As shown in Figure 1 , the number of π-electrons of the five-membered NBN ring in Py-NBN-Ph is 6, indicating an aromaticity characteristic. On the other hand, the number of π-electrons in the six-membered NBN ring of Py-NBN-Naphth is 7 and the extra electron occupies the lowest anti-bonding molecular orbitals, which violates the Hückel rule and results in anti-aromaticity [ 46 , 47 , 48 ]. Therefore, the five-membered NBN ring in Py-NBN-Ph and six-membered NBN ring in Py-NBN-Naphth exhibit totally different aromaticity.…”

Palladium‐Catalyzed Oxidative Annulation of 1‐Hydroxy‐o‐Carborane with Internal Alkynes: Facile Synthesis of Carborane‐Fused Oxaboroles†

“…[ 4‐6 ] In view of a wide application of carboranes in optoelectronic materials as functional blocks, [ 2c ] we developed a synthetic method for the preparation of C,C’‐carborane‐fused five‐membered heterocycles for possible applications in organic materials. [ 7 ] They show a considerable σ‐π conjugation between a 3‐D carborane and a fused 2‐D π system. [ 7a ] Such unique phenomenon could be attributed to the π‐donation of the exo ‐heteroatom to the cage carbon p ‐orbitals.…”

“…[ 7 ] They show a considerable σ‐π conjugation between a 3‐D carborane and a fused 2‐D π system. [ 7a ] Such unique phenomenon could be attributed to the π‐donation of the exo ‐heteroatom to the cage carbon p ‐orbitals. Very recently, a convenient method, Pd‐catalyzed intramolecular dehydrogenative BH/OH coupling of 1‐( o’‐ OHC 6 H 3 R 1 )‐ o ‐C 2 B 10 H 10 R 2 was realized for the synthesis of C,B‐carborane‐fused benzoxaboroles.…”

Electronic Effect-Guided, Palladium-Catalyzed Regioselective B–H Activation and Multistep Diarylation of o-Carboranes with Aryl Iodides

“…Thanks to efforts of many researchers, significant achievements have been made in the activation of C–H and B–H units in o -carboranes, including experimental condition optimization, yield enhancement, and chemo-/regioselectivity improvement. − In 2015, Quan and Xie took Pd­(OAc) 2 as catalyst and synthesized a series of B(3)/B(4)-monoarylated o -carboranes through direct activation of B–H bond, with the aid of phosphine ligand and Cs 2 CO 3 . They found out that the regioselectivity of this reaction was influenced by the substituents on the cage carbons in o -carborane substrates.…”