Reactions of Boroles Formed by 1,1-Carboboration

The borole 2, obtained by 1,1-carboboration of phenylbis­(trimethylsilylethynyl)­borane
with B­(C6F5)3, undergoes [4 + 2]
cycloaddition reactions with 1-pentyne and with ethene to give the
7-borabicyclo[2.2.1]­heptadiene and -heptene derivatives, respectively.
The borole 2 reacts with pyridine at room temperature
to give a pyridine-stabilized borolium ion. The reaction proceeds
by phenyl migration and Me3SiF elimination. Carbon monoxide
reacts rapidly with the borole 2 at room temperature
to give the unusual ketene derivative 19 with Me3Si migration across the ring system.