Syntheses of Isoquinoline and Substituted Quinolines in Charged Microdroplets

A Pomeranz–Fritsch synthesis of isoquinoline and Friedländer and Combes syntheses of substituted quinolines were conducted in charged microdroplets produced by an electrospray process at ambient temperature and atmospheric pressure. In the bulk phase, all of these reactions are known to take a long time ranging from several minutes to a few days and to require very high acid concentrations. In sharp contrast, the present report provides clear evidence that all of these reactions occur on the millisecond timescale in the charged microdroplets without the addition of any external acid. Decreasing the droplet size and increasing the charge of the droplet both strongly contribute to reaction rate acceleration, suggesting that the reaction occurs in a confined environment on the charged surface of the droplet. Microdroplet chemistry: Isoquinolines and quinolines can be synthesized in charged microdroplets during a flight time on the order of a few milliseconds without the addition of external acid as a catalyst. The surface characteristics of the microdroplet are shown to play a critical role in accomplishing these reactions at enhanced rates.