RSC Adv. 2022 Jun 15;12(28):17701-17705. doi: 10.1039/d2ra02534e. eCollection 2022 Jun 14.
A domino condensation-cyclization method is developed to synthesize indolizidine alkaloids using a P4O10/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 NaBH4 or a saturated NaHCO3 solution provided 12b-H or 12b-OH isoindolo[1,2-a]isoquinolinones, respectively.