Synthesis, bridgehead functionalization, and photoisomerization of 9,10-diboratatriptycene dianions.

9,10-Diboratatriptycene salts M[RB(μ-CH)BR] (R = H, Me; M = Li, K, [-BuN]) have been synthesized [4 + 2] cycloaddition between doubly reduced 9,10-dihydro-9,10-diboraanthracenes M[DBA] and benzyne, generated from CHF and CHLi or LiN(-Pr). [HB(μ-CH)BH] reacts with CHCl to form quantitatively the bridgehead-derivatized [ClB(μ-CH)BCl], while twofold H abstraction with B(CF) in the presence of SMe leads cleanly to the diadduct (MeS)B(μ-CH)B(SMe). Photoisomerization of K[HB(μ-CH)BH] (THF, medium-pressure Hg lamp) provides facile access to diborabenzo[]fluoranthenes, a little explored form of boron-doped polycyclic aromatic hydrocarbons.