
Oxa-Pictet–Spengler reaction as key step in the synthesis of novel σ receptor ligands with 2-benzopyran structure
Keywords: σ ligands; Oxa-Pictet–Spengler reaction; Intramolecular Oxa-Pictet–Spengler reaction; 2-Benzopyrans; Spirocyclic piperidines; Tricyclic systems; Aryl-N-distance