Protecting Group-Free Synthesis of 1,2-Azaborines: A Simple Approach to the Construction of BN-Benzenoids

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.