Selective synthesis of tetrahydroimidazo[1,2-a]pyridine and pyrrolidine derivatives via a one-pot two-step reaction

In the presence of triethylamine, the addition reaction of substituted α-amino acid alkyl esters including ethyl hyperphenylalaninate, phenylalaninate, isoleucinate, and alaninate with dialkyl but-2-ynedioate afforded active β-enamino esters, which in turn reacted with aromatic aldehydes and malononitrile to give tetrahydroimidazo[1,2-a]pyridine derivatives in moderate yields. Under similar reaction conditions, the reaction of ethyl glycinate with dialkyl but-2-ynedioate resulted in a 1,3-dipolar azomethine ylide, which reacted further with in situ-generated arylidene malononitrile, alkyl cyanoacetate, and cyanoacetamide to give polysubstituted pyrrolidine derivatives in good yields.