Experimental and computational evidence for KOt-Bu-promoted synthesis of oxopyrazino[1,2-a] indoles

A novel series of oxopyrazino[1,2-a]indole derivatives were prepared via a two-step synthetic procedure including a Ugi-four-component reaction followed by the transition metal-free intramolecular hydroamination of Ugi adducts in the presence of KOt-Bu in DMF at room temperature. Density functional theory (DFT) calculations were also performed to elucidate the mechanistic aspects of the reaction.