Synthesis of 6-methyl-3,4-dihydropyrazinones using an Ugi 4-CR/allenamide cycloisomerization protocol.

A synthetic approach to the 6-methyl-3,4-dihydropyrazinone core from Ugi adducts is described. This methodology relies on the regioselective C-N bond formation between an allenamide moiety at C-ß and an amide anion formed under base-mediated conditions. This protocol allows easy access to tricyclic systems such as pyrazino[2,1-a]isoindole and pyrazino[2,1-a]isoquinoline nuclei.