Using a Johnson‐Claisen Rearrangement Strategy to Construct Azaindoles – A Streamlined and Concise Route for the Commercial Process of Fevipiprant

A novel and concise synthesis of the DP2 receptor antagonist Fevipiprant (NVP‐QAW039) was developed. The initial research route was suffering from a long reaction sequence to the functionalized 7‐aza‐indole core followed by a poorly selective N(1)‐alkylation with the benzyl side chain. These limitations were overcome by introducing the side chain early by reductive amination between the functionalized aldehyde and 2‐amino‐3‐bromopyridine. The Sonogashira coupling with prop‐2‐yn‐1‐ol introduces the 3 missing carbon atoms to build the 7‐aza‐indole core and sets the stage for the innovative Johnson‐Claisen key step. The reaction of the advanced propargylic alcohol derivative with trimethyl orthoacetate led to a reactive allene intermediate which spontaneously and selectively cyclizes to the 7‐aza‐indole QAW039‐methyl ester. QAW039 was isolated after ester saponification. Selectivity, yield, and ecological footprint of the new synthesis were significantly improved, and scalability was demonstrated. A novel and concise synthesis of the DP2 receptor antagonist Fevipiprant (NVP‐QAW039) was developed. The key step – a Johnson Claisen reaction followed by an intramolecular hydroamination of the formed reactive allene moiety allowed to build the 7‐aza‐indole framework, while overcoming the low selectivity and low yield of the initial research route, and give access to a commercially viable process with a reduced ecological footprint.