Synthesis of 3-substituted 2,3-dihydropyrazino[1,2- a ]indol-4(1 H )-ones by sequential reactions of 2-indolylmethyl acetates with α-amino acids.

The synthesis of 2,3-dihydropyrazino[1,2- a ]indol-4(1 H )-ones from the sequential reaction of amino acid methyl esters with readily available indole-2-ylmethyl acetates is described. The reaction proceeds in situ under basic conditions of highly unstable and reactive 2-alkylideneindolenines followed by Michael-type addition of α-amino acid methyl esters/intramolecular cyclization.