Egon Spengler him, which leaves him a little flustered. He celebrates his 40th birthday during this series, which would put him in his late twenties when "The Real Ghostbusters" began. Age is the largest factor causing Spengler to having transition from active ghost hunting to a mentorship role; in one episode where the original Ghostbusters guest starred on an episode the audience clearly sees middle adulthood has affected the speed and weakened the stamina of the original Ghostbusters. Although Egon Spengler does not appear in the 1990 "The Earth Day Special", his character and status as a Ghostbuster is mentioned, and Harold
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