Synthesen mit dem Reagenz Pentamethylcyclopentadienylbromid/Silbertetrafluoroborat: Das Pentamethylcyclopentadienyl‐Kation als reaktive Zwischenstufe

Syntheses with the Reagent Pentamethylcyclopentadienyl Bromide/Silver Tetrafluoroborate: The Pentamethylcyclopentadienyl Cation as Reactive Intermediate Pentamethylcyclopentadienyl bromide 1 reacts with silver tetrafluoroborate with abstraction of the halide ion to form pentamethylcyclopentadienylium tetrafluoroborate ( 2 ). The 4π‐antiaromatic cation in 2 can be trapped with different nucleophiles. Thus, 2 reacts with methanol to give 5‐methoxy‐1,2,3,4,5‐pentamethyl‐1,3‐cyclopentadiene ( 4 ). In the presence of methylamine, dimethylamine, or diethylamine, the corresponding pentamethylcyclopentadienyl‐substituted amines 5 , 6 , and 9 are formed. Trapping of 1 with pyridine or dimethyl sulfide leads to the ionic compounds 7 and 8 , respectively. The reaction of 2 with sterically crowded amines leads to tetramethylfulvene ( 3 ).