Contribution to the study of the mechanism of directed remote-metalation. Evidence for the intermediacy of a geminal dimetallo dialkoxide C(OM)2 (M = Li, K), first doubly charged director of ortho metalation.

The mechanism of the metalation of 2-biphenyl carboxylic acid (1) with the Lochmann-Schlosser superbase was determined by deuteriolysis. Both ortho (C(3)) and remote (C(2')) positions are metalated. The C(2')-metalated species 2 cyclizes instantaneously. Under suitable conditions, the doubly charged geminal dimetallo dialkoxide group C(OM)(2) 4 directs metalation in the adjacent position (C(1)), affording a stable 1-metallo-9H-fluorene-9,9-dimetallo dialkoxide 5 that can be trapped by diverse electrophiles to give 1-substituted 9H-fluoren-9-ones 7 and 9 after acidic workup. [structure: see text]