Optimisation, scope and limitations of the synthesis of 5-aminoindolizines from oxazolo[3,2-a]pyridinium salts

In this letter, we report on our efforts to optimise the reaction conditions and to explore the scope and limitations of the preparation of 5-aminoindolizines starting from oxazolo[3,2-a]pyridinium salts and different amines to evaluate the utility for combinatorial library construction. Thus, we were able to reduce the amount of amine to 1.1 equiv by applying microwave heating, acetonitrile as solvent and DMAP as additional base. Further, we observed that only aliphatic secondary amines with limited steric demand could deliver the desired compounds.