Cyclization of Dialkyl(3‐phenylpropen‐2‐yl)‐(3‐phenylpropyn‐2‐yl)ammonium Bromides by the Action of an Aqueous Alkali Solution. Aqueous‐Alkaline Cleavage of the Cyclization Products — N,N‐Dialkyl‐4(9)‐phenyl‐3a,4‐dihydrobenzo[f]isoindolinium Bromides.