Recent Advances in Halogen Bond-assisted Organic Synthesis

Abstract

: Halogen bond interactions, which take place between an electrophilic halogen and the electron-pair of a Lewis base and exhibit high directionality (approximately 180°), are non-covalent bond interactions similar to the hydrogen bond interaction. Many reports on halogen bond interactions have been published thus far, but many of them discuss halogen bond in the context of crystal engineering or supramolecular architecture. Since a seminal report by Bolm in 2008, halogen bond-assisted or -promoted organic synthesis has received significant attention. This review aims to introduce the molecular design of suitable halogen bond donors and organic transformations involving halogen bond interactions to afford a variety of organic compounds.

“Anti‐electrostatic” Halogen Bonding between Ions of Like Charge

“…The population of the antibonding orbital of the XB donors as a result of a partial charge transfer weakens the C−X bond and facilitates thermal and photochemical reactions with participation of the halogenated species. [ 91 , 92 ] While polarization implies that partially deformed reactants remain essentially isolated species, charge transfer leads to a joint entity with a common molecular orbital system showing diagnostic UV‐Vis bands. [ 10 , 93 ] Their irradiation results in complete electron transfer which could be fruitfully utilized in synthesis.…”

“…[ 10 , 93 ] Their irradiation results in complete electron transfer which could be fruitfully utilized in synthesis. [ 91 , 92 , 94 ] The intensity of the absorption band is determined by the magnitude of the electronic coupling of the reactants. The latter attenuate the barrier for the thermal electron transfer (and follow‐up reactions) and the rate of such processes can be predicted from the spectral and structural characteristics of the complex using Marcus‐Hush theory.…”

Ligand Steric Hindrances Switch Bridging (μ2-I)···O,O to Two-Center I···O Halogen-Bonding Mode in the Assembly of Diketonate Copper(II) Species

“…The supramolecular assembly of metal diketonates is commonly associated with π–π, , M−π, M···M metallophilic interactions, − intermolecular hydrogen bonding, and also with M···O semicoordination. ,, Some recent reports have been focused on the application of (acac)­M (Hacac = acetylacetone) complexes as synthons for crystal engineering studies that utilize halogen bonding (abbreviated as HaB; for recent reviews on HaB, see refs − ) as a structure-directing interaction.…”

Visible Light-Assisted Ring-Opening of Cyclic Ethers with Carboxylic Acids Mediated by Triphenylphosphine and N-Halosuccinimides

“…Most recently, our group discovered the formation of halogen bond complexes , between N -halosuccinimides and enamines or polycyclic aromatic hydrocarbons, which can be used for the direct acyloxylation of ketones or arenes using carboxylic acids under visible light irradiation . While it is well-known that N -halosuccinimides form halogen bond complexes with various nitrogen-containing compounds, , formation of halogen bond complexes between N -halosuccinimides and phosphines have not been documented, probably because the combination of N -halosuccinimides and phosphines is believed to form only polar reagents .…”