Trisubstituted Boroles by 1,1-Carboboration

A 1,3,4-trisubstituted borole is readily obtained by a 1,1-carboboration sequence starting from a bis(ethynyl)-borane and B(C6F5)(3). Subsequent photolysis converts it to the 1,2,5-trisubstituted borole by means of a di-pi-borane rearrangement.