Egon Spengler the city, after the digging of a new subway tunnel resulted in the release of an ancient ghost, Spengler was forced to recruit his only four current students to act as the new Ghostbusters. Although willing to do his share of the legwork, Spengler overestimates his abilities and his aging becomes apparent when he is no longer able to work at the same level as in his younger days, generally working at the firehouse doing research while the team handle the actual 'Ghostbusting', though when the situation calls for it he will help. Melnitz is still carrying a torch for
Pictet–Spengler reaction tetrahydroisoquinoline synthesis. Reaction conditions are generally harsher than the indole variant, and require refluxing conditions with strong acids like hydrochloric acid, trifluoroacetic acid or superacids. Instead of catalyzing the Pictet-Spengler cyclization with strong acid, one can acylate the iminium ion forming the intermediate "N"-acyliminium ion. The "N"-acyliminium ion is a very powerful electrophile and most aromatic ring systems will cyclize under mild conditions with good yields. Tadalafil is synthesized via the "N"-acyliminium Pictet–Spengler reaction. This reaction can also be catalyzed by AuCl and AgOTf. When the Pictet–Spengler reaction is performed with an aldehyde other than formaldehyde, a new chiral center