Triphenylcyclopropenium bromide

Triphenylcyclopropenium bromide is prepared from triphenylcyclopropen-^tbutylether by the addition of dry hydrogenbromide. triphenylcyclopropen-^tbutylether is in turn obtained from the addition of a carbenoid to tolan. The cyclopropenium ion is the simplest Hückel aromatic system ((4n+2)=2 for n=0). Due to its great ring strain the compound shows a variety of rearrangements.