An intramolecular azomethine ylide–alkene cycloaddition approach to pyrrolo[3,2-c]quinolines-synthesis of a C2-truncated martinelline model

Microwave-Assisted Synthesis of Substituted Hexahydro-pyrrolo[3,2-c]quinolines

“…This led to ethyl 2-(N-tosyl-N-allylamino)benzoate. In the following step the ester group was reduced with LiAlH 4 and the alcohol thus prepared was finally oxidized with MnO 2 to give the required aldehyde 4 (Scheme 3) [6].…”

“…Secondary amines were prepared by the method published in [11]. Ethyl 2-(4-toluenesulfonylamino)benzoate was prepared according to [6] General Method for the Synthesis of Secondary Amines 5 [11].…”

“…The pure product was obtained by distillation under vacuum. [6] (1.0 g, 3.2 mmol) was dissolved in dry dichloromethane (30 mL) and to this solution MnO 2 (7.64 g, 87.9 mmol) was added. The mixture was stirred at room temperature for 12 h, then it was filtered and the filtrate evaporated to dryness.…”

“…Crystallization from ethyl acetate gave white crystals (0.7 g, 70%) mp 110 °C (lit. [6] mp 109 -110 115. 86, 117.74, 120.71, 120.96 (2xC), 121.95, 122.24 (2xC), 122.30 (2xC), 123.6 (2xC), 125.2, 123.4 Aldehyde 4 (0.51 g, 1.6 mmol) was dissolved in dry toluene (30 mL) and then amine 5a (0.30 g, 1.9 mmol), triethylamine (0.25 g, 2.5 mmol) and dried LiBr (0.17 g, 2 mmol) were added.…”

“…The cycloaddition was accompanied with decarboxylation, which was very important for the subsequent synthetic steps. These attempts were further developed into a total synthesis of the martinelline skeleton [5,6].…”