The Borole Route to Reactive Pentafluorophenyl-Substituted Diboranes(4).

The β-borylborole 3 adds phenylacetylene in a [4+2]-cycloaddition to give the boryl-substituted 7-boranorbornadiene derivative 4 b. Thermolysis (60 °C) results in a rearrangement with B-B coupling to give the tetraaryldiborane(4) 6 b. It splits dihydrogen with cleavage of the B-B bond. With the terminal acetylene 1-pentyne the diborane(4) compound 6 b undergoes a rare 1,1-diboration reaction to yield the respective geminal diborylalkene product 14.