New Alkaloid Derivatives by the Reaction of 3,4-Dihydro-β-Carbolines with 1,3- Dipoles; Synthesis and a Theoretical Study[1]

The reaction of 3,4-dihydro-β-carboline derivatives with 1,3-dipoles, such as a nitrile imine and a nitrile oxide led to triazolopyridoindole and oxadiazolo-pyridoindole derivatives, respectively, that are novel synthetic alkaloids. Stereostructure, stability and further reactions of the pyridoindoles were also investigated. The oxadiazolo-pyridoindoles underwent reaction with a second unit of nitrile oxide to afford the corresponding trisubstituted 1,2,4-triazole 2-oxides. The mechanisms of the above reactions were studied in detail by high level quantum chemical calculations. It was found that the reaction of the 1,3-dipoles is not an expected 1,3-cycloaddition, but rather a stepwise addition reaction. The exact mechanism was found to be dependent on the substitution pattern.