boron and 1-2-azaborine

Upon reaction with either molecular oxygen or di-tert-butylperoxide in the presence of a simple copper(I) salt and an alcohol, a range of 1,2-azaborines readily exchange B-alkyl or B-aryl moieties for B-alkoxide fragments. This transformation allows alkyl and aryl groups to serve for the first time as removable protecting groups for the boron position of 1,2-azaborines during reactions that are not compatible with the easily modifiable B-alkoxide moiety. This reaction can be applied to synthesize a previously inaccessible BN isostere of ethylbenzene, a compound of interest in biomedical research. A sequence of epoxide ring opening using N-deprotonated 1,2-azaborines followed by an intramolecular version of the boron deprotection reaction can be applied to access the first examples of BN isosteres of dihydrobenzofurans and benzofurans, classes of compounds that are important to medicinal chemistry and natural product synthesis.

Topics: Benzene Derivatives; Benzofurans; Boron; Boron Compounds

The BN analogue of ortho-benzyne, 1,2-azaborine, is generated by flash vacuum pyrolysis, trapped under cryogenic conditions, and studied by direct spectroscopic techniques. The parent BN aryne spontaneously binds N2 and CO2, thus demonstrating its highly reactive nature. The interaction with N2 is photochemically reversible. The CO2 adduct of 1,2-azaborine is a cyclic carbamate which undergoes photocleavage, thus resulting in overall CO2 splitting.

Topics: Benzene Derivatives; Boron; Boron Compounds; Carbamates; Carbon Dioxide; Models, Molecular; Nitrogen

The protecting group-free synthesis of a versatile 1,2-azaborine synthon 5 is described. Previously inaccessible 1,2-azaborine derivatives, including the BN isostere of phenyl phenylacetate and BN1 triphenylmethane were prepared from 5 and characterized. The structural investigation of BN phenyl phenylacetate revealed the presence of a unique NH-carbonyl hydrogen bond that is not present in the corresponding carbonaceous analogue. The methyne CH in BN triphenylmethane was found to be less acidic than the corresponding proton in triphenylmethane. The gram-quantity synthesis of the parent 1,2-azaborine 4 was demonstrated, which enabled the characterization of its boiling point, density, refractive index, and its polarity on the ET(30) scale.

Topics: Benzene Derivatives; Boron; Boron Compounds; Models, Molecular; Molecular Structure; Nitrogen