Rapid Generation and Safe Use of Carbenes Enabled by a Novel Flow Protocol with In-line IR spectroscopy

A powerful new continuous process for the formation and use of donor/acceptor‐substituted carbenes is described. The safety profile of diazo group transfer on methyl phenylacetate was determined including kinetic studies in batch and in flow using in‐line IR analysis. Batch work‐up and liquid chromatography were circumvented by developing an optimized liquid/liquid flow separation method providing aryl diazoacetates in high purity. Fast screening of reaction conditions in flow with in‐line IR analysis allowed rapid reaction optimization. Finally, a multistep process of diazo group transfer, extraction, separation and subsequent diazo decomposition combined with multiple XH insertion reactions was established. Safe flow: The generation, purification and reaction of diazo derivatives in flow allows CH, NH, and OH insertions as well as cyclopropanations in a non‐hazardous way. Decomposition data and kinetic studies using in‐line IR spectroscopy enabled the development of a high‐yielding multistep flow chemistry protocol.