P(4)O(10)/TfOH mediated domino condensation–cyclization of amines with diacids: a route to indolizidine alkaloids under catalyst- and solvent-free conditions

A domino condensation–cyclization method is developed to synthesize indolizidine alkaloids using a P(4)O(10)/TfOH reagent system without the employment of either a catalyst or solvent. The use of a few aliphatic and aromatic dicarboxylic acids is shown along with various primary amines. This method is suitable for synthesizing pyrrolo[2,1-a]isoquinolines, pyrido[2,1-a]isoquinolines, and isoindolo[1,2-a]isoquinolinones in excellent yields. When phthalic acid is used, a workup with either NaBH(4) or a saturated NaHCO(3) solution provided 12b-H or 12b-OH isoindolo[1,2-a]isoquinolinones, respectively.