highly regio- and diastereoselective synthesis of oxo-1,2,3,4-tetrahydropyrazino[1,2-a]indoles, based on a post-ugi condensation: joint experimental and computational study

A novel series of oxo-1,2,3,4-tetrahydropyrazino[1,2-a]indoles were synthesized via a two-step pathway. in the first step, ugi-four-component condensation of 2-formylindole, amines, (e)-4-alkoxy-4-oxobut-2-enoic acids, and isocyanides gave the corresponding ugi-adducts. this adduct underwent intramolecular hydroamination in the presence of k2co3 in ch3cn at room temperature to afford diastereoselective synthesis of a range of oxo-1,2,3,4-tetrahydropyrazino[1,2-a]indoles. a comparison of experimentally observed cd and uv–visible spectra with the theoretical dft calculated ecd spectra was used to predict the major diastereomer.