Batch and Flow Synthesis of Pyrrolo[1,2‑a]‑quinolines via an Allene-Based Reaction Cascade

An efficient reaction cascade delivering a series of pyrrolo­[1,2-a]­quinolines bearing phosphonate or phosphine oxide moieties is presented. This sequence exploits the in situ transformation of propargylic alcohols into transient allenes by means of a strategic [2,3]-sigmatropic rearrangement followed by trapping of the resulting allenes by an adjacent pyrrole ring. Furthermore, the initial small scale batch process was successfully translated into a continuous flow process allowing efficient preparation of selected pyrrolo­[1,2-a]­quinolines on multigram scale without any safety concerns due to the reaction’s inherent exothermic profile.