A New Flow Methodology for the Expedient Synthesis of Drug-Like 3-Aminoindolizines

A flow-based synthesis of diversely functionalized indolizines and their aza-analogues is described. These drug-like heterocycles were generated via a tandem Sonogashira/cycloisomerization sequence, starting from widely available 2-bromopyridines and alkynes, employing a simple catalyst system together with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base. The use of flow technology allows a straightforward and rapid access to a variety of novel compounds, and enables linear scale-up from milligram- to gram-scales without a decrease in yield.