Simple inexpensive boron electrophiles for direct arene borylation

Abstract

Electrophilic direct borylation is facilitated, and arene substrate scope enhanced, by using electrophiles derived from inexpensive reagents; specifically an amine, BCl(3) and AlCl(3).

Fundamental and Applied Properties of Borocations

“…Whilst ethers unsurprisingly decompose in the presence of many borocations [22,23], even CH 2 Cl 2 will react with certain borocations [24]. One specific example is from attempts to form [(amine) [25]. Solvent polarity can also significantly effect borocation formation particularly equilibrium positions when using B-Y bond heterolysis effected by neutral Lewis acids as the synthetic route.…”

“…However, due to the complex nature of the equilibrium mixtures derived from BCl 3 /AlCl 3 /amine (Fig. 16), it is not possible to unambiguously attribute enhanced borylation reactivity to greater electrophilicity of the respective borenium cation [25,71]. For example, whilst combination of 2,6-lutidine and BCl 3 followed by addition of AlCl 3 provides solution 11 B NMR spectra consistent with a borenium cation (δ 11B ¼ 46.9 ppm), the use of pyridine or N,N,4-trimethylaniline (DMT) led to broad resonances (δ 11B between 18 and 26 ppm) considerably upfield of that expected for borenium cations.…”

Reactivity of Lewis Acid Activated Diaza- and Dithiaboroles in Electrophilic Arene Borylation

“…18 The Lewis acidities of B(SR) 3 species have been calculated to be significantly greater (toward hydride) than that of BF 3 , 19 suggesting that the arene substrate scope of 1,2-dithiol-ligated boron electrophiles may be comparable to or even broader than that reported for electrophiles derived from BCl 3 . 6 ■ RESULTS AND DISCUSSION (1). Diazaboroles.…”

Lewis Superacidic Ionic Liquids with Tricoordinate Borenium Cations

“…[4,5,7,10] Many borenium complexes have been reported as 'oily materials'. [4] Despite the increasing number of known crystal structures, [5,8,9] they are generally difficult to crystallize, and are typically studied in solution, using 11 B NMR spectroscopy. We hypothesised that these 'oily materials' might be in fact ionic liquids.…”