Comparing Gas-Liquid Segmented and Tube-in-Tube Setups for the Aerobic Dimerization of Desmethoxycarpacine with an Automated Flow Platform

The hazardous nature of molecular oxygen can be mitigated with the use of flow reactors of small size which, in turn, accelerate the gas to liquid mass transfer rate. In this contribution, we describe a reconfigurable automated flow platform integrating an online HPLC monitoring for the cobalt-catalyzed aerobic oxidative dimerization of desmethoxycarpacine 1 to carpanone 2. The flow platform was configured for aerobic oxidation under either a gas-liquid segmented or tube-in-tube strategy. An extensive optimization study concluded that the tube-in-tube device was penalized by the use of expensive and fragile Teflon AF-2400 tubing while the gas-liquid segmented setup featured higher yields (62% vs. 48%), faster reaction rates (5 min vs. 20 minutes) and better robustness.