Stepwise and Concerted Solvolytic Elimination and Substitution Reactions: E1 Reaction via a Primary Carbocation

Solvolysis of 9-(X-methyl)fluorene (1-X, X = I, Br, OBs) in 25 vol % acetonitrile in water gives the elimination product 9-methylidenefluorene and the substitution products 9-(hydroxymethyl)fluorene (1-OH) and 9-(acetamidomethyl)fluorene (1-NHCOMe). Kinetic studies of the corresponding ring-substituted compounds 2-X and 3-X show that the rate of elimination increases with increasing acidity of the substrate, Brønsted α > 0. The small kinetic deuterium isotope effects measured for the elimination reactions of the brosylates 1-OBs and 3-OBs, kH/kD = 2.0 ± 0.1 and 2.8 ± 0.1, respectively, suggest significant amounts of E1 reaction. The bimolecular reactions of the brosylates with added bases may be of irreversible E1cB type in contrast to the reactions of the halides which exhibit E2 reaction with added bases as well as with solvent water.