Development of a Continuous Flow Synthesis of Lorazepam

Lorazepam, a widely used sedative that appears on the World Health Organization list of essential medicines, experiences periodic shortages. Using a workflow involving route scouting, high-throughput experimentation, and impurity profiling to develop an optimal sequence, we report a novel 5-step route for synthesis of lorazepam in flow. The five steps comprise N-acylation, diazepine ring closure, imine N-oxidation, Polonovski-type rearrangement, and ester hydrolysis to give lorazepam. Each step was optimized and translated to continuous flow. The mean residence times for each of the individual flow reactions summed to a total of 72.5 min for the 5-step sequence. We also report a comprehensive analysis of the purity and byproduct profile to maximize the desired product purity in each step, leading to over 99% pure lorazepam.