Electrophilic chemistry (protonation, nitration, bromination) of crowded (Z)-2,2,5,5-tetramethyl-3,4-diphenylhex-3-ene; formation of phenanthrenium ions by facial ring protonation/transannular cyclization in superacid media; p,p-dinitration and p,p-dibromination with NO 2 + BF 4 – and Br 2 –SO 2