The regioselective synthesis of pyrano[3,2-e]indolealkaloid fontanesine B by two different cyclizations is described. The complete regioselectivity is controlled by the C4 Pictet–Spengler cyclization, in which an iminium ion acts as a transient directing (TDG) group. Furthermore, carbolines were constructed by a new Bischler–Napieralski-type cyclization, in which an unprecedented trichloromethyl carbamate
A novel and simple protocol for the synthesis of 1-(2-aminoethyl)pyrano[3,2-e]indole derivatives has been developed using the Pictet-Spengler reaction of N-b-benzylserotonin with alpha,beta-unsaturated aldehydes in the presence of Et3N in 2-propanol or MeOH.